Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | |
| 2 | Debugging on Linux for s/390 & z/Architecture |
| 3 | by |
| 4 | Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com) |
| 5 | Copyright (C) 2000-2001 IBM Deutschland Entwicklung GmbH, IBM Corporation |
| 6 | Best viewed with fixed width fonts |
| 7 | |
| 8 | Overview of Document: |
| 9 | ===================== |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 10 | This document is intended to give a good overview of how to debug |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 11 | Linux for s/390 & z/Architecture. It isn't intended as a complete reference & not a |
| 12 | tutorial on the fundamentals of C & assembly. It doesn't go into |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 13 | 390 IO in any detail. It is intended to complement the documents in the |
| 14 | reference section below & any other worthwhile references you get. |
| 15 | |
| 16 | It is intended like the Enterprise Systems Architecture/390 Reference Summary |
| 17 | to be printed out & used as a quick cheat sheet self help style reference when |
| 18 | problems occur. |
| 19 | |
| 20 | Contents |
| 21 | ======== |
| 22 | Register Set |
| 23 | Address Spaces on Intel Linux |
| 24 | Address Spaces on Linux for s/390 & z/Architecture |
| 25 | The Linux for s/390 & z/Architecture Kernel Task Structure |
| 26 | Register Usage & Stackframes on Linux for s/390 & z/Architecture |
| 27 | A sample program with comments |
| 28 | Compiling programs for debugging on Linux for s/390 & z/Architecture |
| 29 | Figuring out gcc compile errors |
| 30 | Debugging Tools |
| 31 | objdump |
| 32 | strace |
| 33 | Performance Debugging |
| 34 | Debugging under VM |
| 35 | s/390 & z/Architecture IO Overview |
| 36 | Debugging IO on s/390 & z/Architecture under VM |
| 37 | GDB on s/390 & z/Architecture |
| 38 | Stack chaining in gdb by hand |
| 39 | Examining core dumps |
| 40 | ldd |
| 41 | Debugging modules |
| 42 | The proc file system |
| 43 | Starting points for debugging scripting languages etc. |
| 44 | Dumptool & Lcrash |
| 45 | SysRq |
| 46 | References |
| 47 | Special Thanks |
| 48 | |
| 49 | Register Set |
| 50 | ============ |
| 51 | The current architectures have the following registers. |
| 52 | |
| 53 | 16 General propose registers, 32 bit on s/390 64 bit on z/Architecture, r0-r15 or gpr0-gpr15 used for arithmetic & addressing. |
| 54 | |
| 55 | 16 Control registers, 32 bit on s/390 64 bit on z/Architecture, ( cr0-cr15 kernel usage only ) used for memory management, |
| 56 | interrupt control,debugging control etc. |
| 57 | |
| 58 | 16 Access registers ( ar0-ar15 ) 32 bit on s/390 & z/Architecture |
| 59 | not used by normal programs but potentially could |
| 60 | be used as temporary storage. Their main purpose is their 1 to 1 |
| 61 | association with general purpose registers and are used in |
| 62 | the kernel for copying data between kernel & user address spaces. |
| 63 | Access register 0 ( & access register 1 on z/Architecture ( needs 64 bit |
| 64 | pointer ) ) is currently used by the pthread library as a pointer to |
| 65 | the current running threads private area. |
| 66 | |
| 67 | 16 64 bit floating point registers (fp0-fp15 ) IEEE & HFP floating |
| 68 | point format compliant on G5 upwards & a Floating point control reg (FPC) |
| 69 | 4 64 bit registers (fp0,fp2,fp4 & fp6) HFP only on older machines. |
| 70 | Note: |
| 71 | Linux (currently) always uses IEEE & emulates G5 IEEE format on older machines, |
| 72 | ( provided the kernel is configured for this ). |
| 73 | |
| 74 | |
| 75 | The PSW is the most important register on the machine it |
| 76 | is 64 bit on s/390 & 128 bit on z/Architecture & serves the roles of |
| 77 | a program counter (pc), condition code register,memory space designator. |
| 78 | In IBM standard notation I am counting bit 0 as the MSB. |
| 79 | It has several advantages over a normal program counter |
| 80 | in that you can change address translation & program counter |
| 81 | in a single instruction. To change address translation, |
| 82 | e.g. switching address translation off requires that you |
| 83 | have a logical=physical mapping for the address you are |
| 84 | currently running at. |
| 85 | |
| 86 | Bit Value |
| 87 | s/390 z/Architecture |
| 88 | 0 0 Reserved ( must be 0 ) otherwise specification exception occurs. |
| 89 | |
| 90 | 1 1 Program Event Recording 1 PER enabled, |
Matt LaPlante | a2ffd27 | 2006-10-03 22:49:15 +0200 | [diff] [blame] | 91 | PER is used to facilitate debugging e.g. single stepping. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 92 | |
| 93 | 2-4 2-4 Reserved ( must be 0 ). |
| 94 | |
| 95 | 5 5 Dynamic address translation 1=DAT on. |
| 96 | |
| 97 | 6 6 Input/Output interrupt Mask |
| 98 | |
| 99 | 7 7 External interrupt Mask used primarily for interprocessor signalling & |
| 100 | clock interrupts. |
| 101 | |
| 102 | 8-11 8-11 PSW Key used for complex memory protection mechanism not used under linux |
| 103 | |
| 104 | 12 12 1 on s/390 0 on z/Architecture |
| 105 | |
| 106 | 13 13 Machine Check Mask 1=enable machine check interrupts |
| 107 | |
| 108 | 14 14 Wait State set this to 1 to stop the processor except for interrupts & give |
| 109 | time to other LPARS used in CPU idle in the kernel to increase overall |
| 110 | usage of processor resources. |
| 111 | |
| 112 | 15 15 Problem state ( if set to 1 certain instructions are disabled ) |
| 113 | all linux user programs run with this bit 1 |
| 114 | ( useful info for debugging under VM ). |
| 115 | |
| 116 | 16-17 16-17 Address Space Control |
| 117 | |
| 118 | 00 Primary Space Mode when DAT on |
| 119 | The linux kernel currently runs in this mode, CR1 is affiliated with |
| 120 | this mode & points to the primary segment table origin etc. |
| 121 | |
| 122 | 01 Access register mode this mode is used in functions to |
| 123 | copy data between kernel & user space. |
| 124 | |
| 125 | 10 Secondary space mode not used in linux however CR7 the |
| 126 | register affiliated with this mode is & this & normally |
| 127 | CR13=CR7 to allow us to copy data between kernel & user space. |
| 128 | We do this as follows: |
| 129 | We set ar2 to 0 to designate its |
| 130 | affiliated gpr ( gpr2 )to point to primary=kernel space. |
| 131 | We set ar4 to 1 to designate its |
| 132 | affiliated gpr ( gpr4 ) to point to secondary=home=user space |
| 133 | & then essentially do a memcopy(gpr2,gpr4,size) to |
| 134 | copy data between the address spaces, the reason we use home space for the |
| 135 | kernel & don't keep secondary space free is that code will not run in |
| 136 | secondary space. |
| 137 | |
| 138 | 11 Home Space Mode all user programs run in this mode. |
| 139 | it is affiliated with CR13. |
| 140 | |
| 141 | 18-19 18-19 Condition codes (CC) |
| 142 | |
| 143 | 20 20 Fixed point overflow mask if 1=FPU exceptions for this event |
| 144 | occur ( normally 0 ) |
| 145 | |
| 146 | 21 21 Decimal overflow mask if 1=FPU exceptions for this event occur |
| 147 | ( normally 0 ) |
| 148 | |
| 149 | 22 22 Exponent underflow mask if 1=FPU exceptions for this event occur |
| 150 | ( normally 0 ) |
| 151 | |
| 152 | 23 23 Significance Mask if 1=FPU exceptions for this event occur |
| 153 | ( normally 0 ) |
| 154 | |
| 155 | 24-31 24-30 Reserved Must be 0. |
| 156 | |
| 157 | 31 Extended Addressing Mode |
| 158 | 32 Basic Addressing Mode |
| 159 | Used to set addressing mode |
| 160 | PSW 31 PSW 32 |
| 161 | 0 0 24 bit |
| 162 | 0 1 31 bit |
| 163 | 1 1 64 bit |
| 164 | |
| 165 | 32 1=31 bit addressing mode 0=24 bit addressing mode (for backward |
Matt LaPlante | 6c28f2c | 2006-10-03 22:46:31 +0200 | [diff] [blame] | 166 | compatibility), linux always runs with this bit set to 1 |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 167 | |
| 168 | 33-64 Instruction address. |
| 169 | 33-63 Reserved must be 0 |
| 170 | 64-127 Address |
| 171 | In 24 bits mode bits 64-103=0 bits 104-127 Address |
| 172 | In 31 bits mode bits 64-96=0 bits 97-127 Address |
| 173 | Note: unlike 31 bit mode on s/390 bit 96 must be zero |
| 174 | when loading the address with LPSWE otherwise a |
| 175 | specification exception occurs, LPSW is fully backward |
| 176 | compatible. |
| 177 | |
| 178 | |
| 179 | Prefix Page(s) |
| 180 | -------------- |
| 181 | This per cpu memory area is too intimately tied to the processor not to mention. |
| 182 | It exists between the real addresses 0-4096 on s/390 & 0-8192 z/Architecture & is exchanged |
| 183 | with a 1 page on s/390 or 2 pages on z/Architecture in absolute storage by the set |
| 184 | prefix instruction in linux'es startup. |
| 185 | This page is mapped to a different prefix for each processor in an SMP configuration |
| 186 | ( assuming the os designer is sane of course :-) ). |
| 187 | Bytes 0-512 ( 200 hex ) on s/390 & 0-512,4096-4544,4604-5119 currently on z/Architecture |
| 188 | are used by the processor itself for holding such information as exception indications & |
| 189 | entry points for exceptions. |
| 190 | Bytes after 0xc00 hex are used by linux for per processor globals on s/390 & z/Architecture |
Matt LaPlante | 3f6dee9 | 2006-10-03 22:45:33 +0200 | [diff] [blame] | 191 | ( there is a gap on z/Architecture too currently between 0xc00 & 1000 which linux uses ). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 192 | The closest thing to this on traditional architectures is the interrupt |
| 193 | vector table. This is a good thing & does simplify some of the kernel coding |
| 194 | however it means that we now cannot catch stray NULL pointers in the |
| 195 | kernel without hard coded checks. |
| 196 | |
| 197 | |
| 198 | |
| 199 | Address Spaces on Intel Linux |
| 200 | ============================= |
| 201 | |
| 202 | The traditional Intel Linux is approximately mapped as follows forgive |
| 203 | the ascii art. |
| 204 | 0xFFFFFFFF 4GB Himem ***************** |
| 205 | * * |
| 206 | * Kernel Space * |
| 207 | * * |
| 208 | ***************** **************** |
| 209 | User Space Himem (typically 0xC0000000 3GB )* User Stack * * * |
| 210 | ***************** * * |
| 211 | * Shared Libs * * Next Process * |
| 212 | ***************** * to * |
| 213 | * * <== * Run * <== |
| 214 | * User Program * * * |
| 215 | * Data BSS * * * |
| 216 | * Text * * * |
| 217 | * Sections * * * |
| 218 | 0x00000000 ***************** **************** |
| 219 | |
| 220 | Now it is easy to see that on Intel it is quite easy to recognise a kernel address |
| 221 | as being one greater than user space himem ( in this case 0xC0000000). |
| 222 | & addresses of less than this are the ones in the current running program on this |
| 223 | processor ( if an smp box ). |
| 224 | If using the virtual machine ( VM ) as a debugger it is quite difficult to |
| 225 | know which user process is running as the address space you are looking at |
| 226 | could be from any process in the run queue. |
| 227 | |
| 228 | The limitation of Intels addressing technique is that the linux |
| 229 | kernel uses a very simple real address to virtual addressing technique |
| 230 | of Real Address=Virtual Address-User Space Himem. |
| 231 | This means that on Intel the kernel linux can typically only address |
| 232 | Himem=0xFFFFFFFF-0xC0000000=1GB & this is all the RAM these machines |
| 233 | can typically use. |
| 234 | They can lower User Himem to 2GB or lower & thus be |
| 235 | able to use 2GB of RAM however this shrinks the maximum size |
| 236 | of User Space from 3GB to 2GB they have a no win limit of 4GB unless |
| 237 | they go to 64 Bit. |
| 238 | |
| 239 | |
| 240 | On 390 our limitations & strengths make us slightly different. |
| 241 | For backward compatibility we are only allowed use 31 bits (2GB) |
Matt LaPlante | 6c28f2c | 2006-10-03 22:46:31 +0200 | [diff] [blame] | 242 | of our 32 bit addresses, however, we use entirely separate address |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 243 | spaces for the user & kernel. |
| 244 | |
| 245 | This means we can support 2GB of non Extended RAM on s/390, & more |
| 246 | with the Extended memory management swap device & |
| 247 | currently 4TB of physical memory currently on z/Architecture. |
| 248 | |
| 249 | |
| 250 | Address Spaces on Linux for s/390 & z/Architecture |
| 251 | ================================================== |
| 252 | |
| 253 | Our addressing scheme is as follows |
| 254 | |
| 255 | |
| 256 | Himem 0x7fffffff 2GB on s/390 ***************** **************** |
| 257 | currently 0x3ffffffffff (2^42)-1 * User Stack * * * |
| 258 | on z/Architecture. ***************** * * |
| 259 | * Shared Libs * * * |
| 260 | ***************** * * |
| 261 | * * * Kernel * |
| 262 | * User Program * * * |
| 263 | * Data BSS * * * |
| 264 | * Text * * * |
| 265 | * Sections * * * |
| 266 | 0x00000000 ***************** **************** |
| 267 | |
| 268 | This also means that we need to look at the PSW problem state bit |
| 269 | or the addressing mode to decide whether we are looking at |
| 270 | user or kernel space. |
| 271 | |
| 272 | Virtual Addresses on s/390 & z/Architecture |
| 273 | =========================================== |
| 274 | |
| 275 | A virtual address on s/390 is made up of 3 parts |
| 276 | The SX ( segment index, roughly corresponding to the PGD & PMD in linux terminology ) |
| 277 | being bits 1-11. |
| 278 | The PX ( page index, corresponding to the page table entry (pte) in linux terminology ) |
| 279 | being bits 12-19. |
| 280 | The remaining bits BX (the byte index are the offset in the page ) |
| 281 | i.e. bits 20 to 31. |
| 282 | |
| 283 | On z/Architecture in linux we currently make up an address from 4 parts. |
| 284 | The region index bits (RX) 0-32 we currently use bits 22-32 |
| 285 | The segment index (SX) being bits 33-43 |
| 286 | The page index (PX) being bits 44-51 |
| 287 | The byte index (BX) being bits 52-63 |
| 288 | |
| 289 | Notes: |
| 290 | 1) s/390 has no PMD so the PMD is really the PGD also. |
| 291 | A lot of this stuff is defined in pgtable.h. |
| 292 | |
| 293 | 2) Also seeing as s/390's page indexes are only 1k in size |
| 294 | (bits 12-19 x 4 bytes per pte ) we use 1 ( page 4k ) |
| 295 | to make the best use of memory by updating 4 segment indices |
| 296 | entries each time we mess with a PMD & use offsets |
| 297 | 0,1024,2048 & 3072 in this page as for our segment indexes. |
| 298 | On z/Architecture our page indexes are now 2k in size |
| 299 | ( bits 12-19 x 8 bytes per pte ) we do a similar trick |
| 300 | but only mess with 2 segment indices each time we mess with |
| 301 | a PMD. |
| 302 | |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 303 | 3) As z/Architecture supports up to a massive 5-level page table lookup we |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 304 | can only use 3 currently on Linux ( as this is all the generic kernel |
| 305 | currently supports ) however this may change in future |
| 306 | this allows us to access ( according to my sums ) |
| 307 | 4TB of virtual storage per process i.e. |
| 308 | 4096*512(PTES)*1024(PMDS)*2048(PGD) = 4398046511104 bytes, |
| 309 | enough for another 2 or 3 of years I think :-). |
| 310 | to do this we use a region-third-table designation type in |
| 311 | our address space control registers. |
| 312 | |
| 313 | |
| 314 | The Linux for s/390 & z/Architecture Kernel Task Structure |
| 315 | ========================================================== |
| 316 | Each process/thread under Linux for S390 has its own kernel task_struct |
| 317 | defined in linux/include/linux/sched.h |
| 318 | The S390 on initialisation & resuming of a process on a cpu sets |
| 319 | the __LC_KERNEL_STACK variable in the spare prefix area for this cpu |
Matt LaPlante | 53cb472 | 2006-10-03 22:55:17 +0200 | [diff] [blame] | 320 | (which we use for per-processor globals). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 321 | |
Matt LaPlante | 53cb472 | 2006-10-03 22:55:17 +0200 | [diff] [blame] | 322 | The kernel stack pointer is intimately tied with the task structure for |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 323 | each processor as follows. |
| 324 | |
| 325 | s/390 |
| 326 | ************************ |
| 327 | * 1 page kernel stack * |
| 328 | * ( 4K ) * |
| 329 | ************************ |
| 330 | * 1 page task_struct * |
| 331 | * ( 4K ) * |
| 332 | 8K aligned ************************ |
| 333 | |
| 334 | z/Architecture |
| 335 | ************************ |
| 336 | * 2 page kernel stack * |
| 337 | * ( 8K ) * |
| 338 | ************************ |
| 339 | * 2 page task_struct * |
| 340 | * ( 8K ) * |
| 341 | 16K aligned ************************ |
| 342 | |
| 343 | What this means is that we don't need to dedicate any register or global variable |
| 344 | to point to the current running process & can retrieve it with the following |
| 345 | very simple construct for s/390 & one very similar for z/Architecture. |
| 346 | |
| 347 | static inline struct task_struct * get_current(void) |
| 348 | { |
| 349 | struct task_struct *current; |
| 350 | __asm__("lhi %0,-8192\n\t" |
| 351 | "nr %0,15" |
| 352 | : "=r" (current) ); |
| 353 | return current; |
| 354 | } |
| 355 | |
| 356 | i.e. just anding the current kernel stack pointer with the mask -8192. |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 357 | Thankfully because Linux doesn't have support for nested IO interrupts |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 358 | & our devices have large buffers can survive interrupts being shut for |
| 359 | short amounts of time we don't need a separate stack for interrupts. |
| 360 | |
| 361 | |
| 362 | |
| 363 | |
| 364 | Register Usage & Stackframes on Linux for s/390 & z/Architecture |
| 365 | ================================================================= |
| 366 | Overview: |
| 367 | --------- |
| 368 | This is the code that gcc produces at the top & the bottom of |
Matt LaPlante | 992caac | 2006-10-03 22:52:05 +0200 | [diff] [blame] | 369 | each function. It usually is fairly consistent & similar from |
| 370 | function to function & if you know its layout you can probably |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 371 | make some headway in finding the ultimate cause of a problem |
| 372 | after a crash without a source level debugger. |
| 373 | |
| 374 | Note: To follow stackframes requires a knowledge of C or Pascal & |
| 375 | limited knowledge of one assembly language. |
| 376 | |
| 377 | It should be noted that there are some differences between the |
| 378 | s/390 & z/Architecture stack layouts as the z/Architecture stack layout didn't have |
| 379 | to maintain compatibility with older linkage formats. |
| 380 | |
| 381 | Glossary: |
| 382 | --------- |
| 383 | alloca: |
| 384 | This is a built in compiler function for runtime allocation |
| 385 | of extra space on the callers stack which is obviously freed |
| 386 | up on function exit ( e.g. the caller may choose to allocate nothing |
| 387 | of a buffer of 4k if required for temporary purposes ), it generates |
| 388 | very efficient code ( a few cycles ) when compared to alternatives |
| 389 | like malloc. |
| 390 | |
| 391 | automatics: These are local variables on the stack, |
| 392 | i.e they aren't in registers & they aren't static. |
| 393 | |
| 394 | back-chain: |
| 395 | This is a pointer to the stack pointer before entering a |
| 396 | framed functions ( see frameless function ) prologue got by |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 397 | dereferencing the address of the current stack pointer, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 398 | i.e. got by accessing the 32 bit value at the stack pointers |
| 399 | current location. |
| 400 | |
| 401 | base-pointer: |
| 402 | This is a pointer to the back of the literal pool which |
| 403 | is an area just behind each procedure used to store constants |
| 404 | in each function. |
| 405 | |
| 406 | call-clobbered: The caller probably needs to save these registers if there |
| 407 | is something of value in them, on the stack or elsewhere before making a |
| 408 | call to another procedure so that it can restore it later. |
| 409 | |
| 410 | epilogue: |
| 411 | The code generated by the compiler to return to the caller. |
| 412 | |
| 413 | frameless-function |
| 414 | A frameless function in Linux for s390 & z/Architecture is one which doesn't |
| 415 | need more than the register save area ( 96 bytes on s/390, 160 on z/Architecture ) |
| 416 | given to it by the caller. |
| 417 | A frameless function never: |
| 418 | 1) Sets up a back chain. |
| 419 | 2) Calls alloca. |
| 420 | 3) Calls other normal functions |
| 421 | 4) Has automatics. |
| 422 | |
| 423 | GOT-pointer: |
| 424 | This is a pointer to the global-offset-table in ELF |
| 425 | ( Executable Linkable Format, Linux'es most common executable format ), |
| 426 | all globals & shared library objects are found using this pointer. |
| 427 | |
| 428 | lazy-binding |
| 429 | ELF shared libraries are typically only loaded when routines in the shared |
| 430 | library are actually first called at runtime. This is lazy binding. |
| 431 | |
| 432 | procedure-linkage-table |
| 433 | This is a table found from the GOT which contains pointers to routines |
| 434 | in other shared libraries which can't be called to by easier means. |
| 435 | |
| 436 | prologue: |
| 437 | The code generated by the compiler to set up the stack frame. |
| 438 | |
| 439 | outgoing-args: |
| 440 | This is extra area allocated on the stack of the calling function if the |
| 441 | parameters for the callee's cannot all be put in registers, the same |
| 442 | area can be reused by each function the caller calls. |
| 443 | |
| 444 | routine-descriptor: |
| 445 | A COFF executable format based concept of a procedure reference |
| 446 | actually being 8 bytes or more as opposed to a simple pointer to the routine. |
| 447 | This is typically defined as follows |
| 448 | Routine Descriptor offset 0=Pointer to Function |
| 449 | Routine Descriptor offset 4=Pointer to Table of Contents |
| 450 | The table of contents/TOC is roughly equivalent to a GOT pointer. |
| 451 | & it means that shared libraries etc. can be shared between several |
| 452 | environments each with their own TOC. |
| 453 | |
| 454 | |
| 455 | static-chain: This is used in nested functions a concept adopted from pascal |
| 456 | by gcc not used in ansi C or C++ ( although quite useful ), basically it |
| 457 | is a pointer used to reference local variables of enclosing functions. |
| 458 | You might come across this stuff once or twice in your lifetime. |
| 459 | |
| 460 | e.g. |
| 461 | The function below should return 11 though gcc may get upset & toss warnings |
| 462 | about unused variables. |
| 463 | int FunctionA(int a) |
| 464 | { |
| 465 | int b; |
| 466 | FunctionC(int c) |
| 467 | { |
| 468 | b=c+1; |
| 469 | } |
| 470 | FunctionC(10); |
| 471 | return(b); |
| 472 | } |
| 473 | |
| 474 | |
| 475 | s/390 & z/Architecture Register usage |
| 476 | ===================================== |
| 477 | r0 used by syscalls/assembly call-clobbered |
| 478 | r1 used by syscalls/assembly call-clobbered |
| 479 | r2 argument 0 / return value 0 call-clobbered |
| 480 | r3 argument 1 / return value 1 (if long long) call-clobbered |
| 481 | r4 argument 2 call-clobbered |
| 482 | r5 argument 3 call-clobbered |
Heiko Carstens | d8c351a | 2007-02-05 21:17:34 +0100 | [diff] [blame] | 483 | r6 argument 4 saved |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 484 | r7 pointer-to arguments 5 to ... saved |
| 485 | r8 this & that saved |
| 486 | r9 this & that saved |
| 487 | r10 static-chain ( if nested function ) saved |
| 488 | r11 frame-pointer ( if function used alloca ) saved |
| 489 | r12 got-pointer saved |
| 490 | r13 base-pointer saved |
| 491 | r14 return-address saved |
| 492 | r15 stack-pointer saved |
| 493 | |
| 494 | f0 argument 0 / return value ( float/double ) call-clobbered |
| 495 | f2 argument 1 call-clobbered |
| 496 | f4 z/Architecture argument 2 saved |
| 497 | f6 z/Architecture argument 3 saved |
| 498 | The remaining floating points |
| 499 | f1,f3,f5 f7-f15 are call-clobbered. |
| 500 | |
| 501 | Notes: |
| 502 | ------ |
| 503 | 1) The only requirement is that registers which are used |
| 504 | by the callee are saved, e.g. the compiler is perfectly |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 505 | capable of using r11 for purposes other than a frame a |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 506 | frame pointer if a frame pointer is not needed. |
| 507 | 2) In functions with variable arguments e.g. printf the calling procedure |
| 508 | is identical to one without variable arguments & the same number of |
| 509 | parameters. However, the prologue of this function is somewhat more |
| 510 | hairy owing to it having to move these parameters to the stack to |
| 511 | get va_start, va_arg & va_end to work. |
| 512 | 3) Access registers are currently unused by gcc but are used in |
| 513 | the kernel. Possibilities exist to use them at the moment for |
| 514 | temporary storage but it isn't recommended. |
| 515 | 4) Only 4 of the floating point registers are used for |
| 516 | parameter passing as older machines such as G3 only have only 4 |
| 517 | & it keeps the stack frame compatible with other compilers. |
| 518 | However with IEEE floating point emulation under linux on the |
| 519 | older machines you are free to use the other 12. |
| 520 | 5) A long long or double parameter cannot be have the |
| 521 | first 4 bytes in a register & the second four bytes in the |
| 522 | outgoing args area. It must be purely in the outgoing args |
| 523 | area if crossing this boundary. |
| 524 | 6) Floating point parameters are mixed with outgoing args |
| 525 | on the outgoing args area in the order the are passed in as parameters. |
| 526 | 7) Floating point arguments 2 & 3 are saved in the outgoing args area for |
| 527 | z/Architecture |
| 528 | |
| 529 | |
| 530 | Stack Frame Layout |
| 531 | ------------------ |
| 532 | s/390 z/Architecture |
| 533 | 0 0 back chain ( a 0 here signifies end of back chain ) |
| 534 | 4 8 eos ( end of stack, not used on Linux for S390 used in other linkage formats ) |
| 535 | 8 16 glue used in other s/390 linkage formats for saved routine descriptors etc. |
| 536 | 12 24 glue used in other s/390 linkage formats for saved routine descriptors etc. |
| 537 | 16 32 scratch area |
| 538 | 20 40 scratch area |
| 539 | 24 48 saved r6 of caller function |
| 540 | 28 56 saved r7 of caller function |
| 541 | 32 64 saved r8 of caller function |
| 542 | 36 72 saved r9 of caller function |
| 543 | 40 80 saved r10 of caller function |
| 544 | 44 88 saved r11 of caller function |
| 545 | 48 96 saved r12 of caller function |
| 546 | 52 104 saved r13 of caller function |
| 547 | 56 112 saved r14 of caller function |
| 548 | 60 120 saved r15 of caller function |
| 549 | 64 128 saved f4 of caller function |
| 550 | 72 132 saved f6 of caller function |
| 551 | 80 undefined |
| 552 | 96 160 outgoing args passed from caller to callee |
| 553 | 96+x 160+x possible stack alignment ( 8 bytes desirable ) |
| 554 | 96+x+y 160+x+y alloca space of caller ( if used ) |
| 555 | 96+x+y+z 160+x+y+z automatics of caller ( if used ) |
| 556 | 0 back-chain |
| 557 | |
| 558 | A sample program with comments. |
| 559 | =============================== |
| 560 | |
| 561 | Comments on the function test |
| 562 | ----------------------------- |
| 563 | 1) It didn't need to set up a pointer to the constant pool gpr13 as it isn't used |
| 564 | ( :-( ). |
| 565 | 2) This is a frameless function & no stack is bought. |
| 566 | 3) The compiler was clever enough to recognise that it could return the |
| 567 | value in r2 as well as use it for the passed in parameter ( :-) ). |
| 568 | 4) The basr ( branch relative & save ) trick works as follows the instruction |
| 569 | has a special case with r0,r0 with some instruction operands is understood as |
| 570 | the literal value 0, some risc architectures also do this ). So now |
| 571 | we are branching to the next address & the address new program counter is |
| 572 | in r13,so now we subtract the size of the function prologue we have executed |
| 573 | + the size of the literal pool to get to the top of the literal pool |
| 574 | 0040037c int test(int b) |
| 575 | { # Function prologue below |
| 576 | 40037c: 90 de f0 34 stm %r13,%r14,52(%r15) # Save registers r13 & r14 |
| 577 | 400380: 0d d0 basr %r13,%r0 # Set up pointer to constant pool using |
| 578 | 400382: a7 da ff fa ahi %r13,-6 # basr trick |
| 579 | return(5+b); |
| 580 | # Huge main program |
| 581 | 400386: a7 2a 00 05 ahi %r2,5 # add 5 to r2 |
| 582 | |
| 583 | # Function epilogue below |
| 584 | 40038a: 98 de f0 34 lm %r13,%r14,52(%r15) # restore registers r13 & 14 |
| 585 | 40038e: 07 fe br %r14 # return |
| 586 | } |
| 587 | |
| 588 | Comments on the function main |
| 589 | ----------------------------- |
| 590 | 1) The compiler did this function optimally ( 8-) ) |
| 591 | |
| 592 | Literal pool for main. |
| 593 | 400390: ff ff ff ec .long 0xffffffec |
| 594 | main(int argc,char *argv[]) |
| 595 | { # Function prologue below |
| 596 | 400394: 90 bf f0 2c stm %r11,%r15,44(%r15) # Save necessary registers |
| 597 | 400398: 18 0f lr %r0,%r15 # copy stack pointer to r0 |
| 598 | 40039a: a7 fa ff a0 ahi %r15,-96 # Make area for callee saving |
| 599 | 40039e: 0d d0 basr %r13,%r0 # Set up r13 to point to |
| 600 | 4003a0: a7 da ff f0 ahi %r13,-16 # literal pool |
| 601 | 4003a4: 50 00 f0 00 st %r0,0(%r15) # Save backchain |
| 602 | |
| 603 | return(test(5)); # Main Program Below |
| 604 | 4003a8: 58 e0 d0 00 l %r14,0(%r13) # load relative address of test from |
| 605 | # literal pool |
| 606 | 4003ac: a7 28 00 05 lhi %r2,5 # Set first parameter to 5 |
| 607 | 4003b0: 4d ee d0 00 bas %r14,0(%r14,%r13) # jump to test setting r14 as return |
| 608 | # address using branch & save instruction. |
| 609 | |
| 610 | # Function Epilogue below |
| 611 | 4003b4: 98 bf f0 8c lm %r11,%r15,140(%r15)# Restore necessary registers. |
| 612 | 4003b8: 07 fe br %r14 # return to do program exit |
| 613 | } |
| 614 | |
| 615 | |
| 616 | Compiler updates |
| 617 | ---------------- |
| 618 | |
| 619 | main(int argc,char *argv[]) |
| 620 | { |
| 621 | 4004fc: 90 7f f0 1c stm %r7,%r15,28(%r15) |
| 622 | 400500: a7 d5 00 04 bras %r13,400508 <main+0xc> |
| 623 | 400504: 00 40 04 f4 .long 0x004004f4 |
| 624 | # compiler now puts constant pool in code to so it saves an instruction |
| 625 | 400508: 18 0f lr %r0,%r15 |
| 626 | 40050a: a7 fa ff a0 ahi %r15,-96 |
| 627 | 40050e: 50 00 f0 00 st %r0,0(%r15) |
| 628 | return(test(5)); |
| 629 | 400512: 58 10 d0 00 l %r1,0(%r13) |
| 630 | 400516: a7 28 00 05 lhi %r2,5 |
| 631 | 40051a: 0d e1 basr %r14,%r1 |
| 632 | # compiler adds 1 extra instruction to epilogue this is done to |
| 633 | # avoid processor pipeline stalls owing to data dependencies on g5 & |
| 634 | # above as register 14 in the old code was needed directly after being loaded |
| 635 | # by the lm %r11,%r15,140(%r15) for the br %14. |
| 636 | 40051c: 58 40 f0 98 l %r4,152(%r15) |
| 637 | 400520: 98 7f f0 7c lm %r7,%r15,124(%r15) |
| 638 | 400524: 07 f4 br %r4 |
| 639 | } |
| 640 | |
| 641 | |
| 642 | Hartmut ( our compiler developer ) also has been threatening to take out the |
| 643 | stack backchain in optimised code as this also causes pipeline stalls, you |
| 644 | have been warned. |
| 645 | |
| 646 | 64 bit z/Architecture code disassembly |
| 647 | -------------------------------------- |
| 648 | |
| 649 | If you understand the stuff above you'll understand the stuff |
| 650 | below too so I'll avoid repeating myself & just say that |
| 651 | some of the instructions have g's on the end of them to indicate |
| 652 | they are 64 bit & the stack offsets are a bigger, |
| 653 | the only other difference you'll find between 32 & 64 bit is that |
| 654 | we now use f4 & f6 for floating point arguments on 64 bit. |
| 655 | 00000000800005b0 <test>: |
| 656 | int test(int b) |
| 657 | { |
| 658 | return(5+b); |
| 659 | 800005b0: a7 2a 00 05 ahi %r2,5 |
| 660 | 800005b4: b9 14 00 22 lgfr %r2,%r2 # downcast to integer |
| 661 | 800005b8: 07 fe br %r14 |
| 662 | 800005ba: 07 07 bcr 0,%r7 |
| 663 | |
| 664 | |
| 665 | } |
| 666 | |
| 667 | 00000000800005bc <main>: |
| 668 | main(int argc,char *argv[]) |
| 669 | { |
| 670 | 800005bc: eb bf f0 58 00 24 stmg %r11,%r15,88(%r15) |
| 671 | 800005c2: b9 04 00 1f lgr %r1,%r15 |
| 672 | 800005c6: a7 fb ff 60 aghi %r15,-160 |
| 673 | 800005ca: e3 10 f0 00 00 24 stg %r1,0(%r15) |
| 674 | return(test(5)); |
| 675 | 800005d0: a7 29 00 05 lghi %r2,5 |
| 676 | # brasl allows jumps > 64k & is overkill here bras would do fune |
| 677 | 800005d4: c0 e5 ff ff ff ee brasl %r14,800005b0 <test> |
| 678 | 800005da: e3 40 f1 10 00 04 lg %r4,272(%r15) |
| 679 | 800005e0: eb bf f0 f8 00 04 lmg %r11,%r15,248(%r15) |
| 680 | 800005e6: 07 f4 br %r4 |
| 681 | } |
| 682 | |
| 683 | |
| 684 | |
| 685 | Compiling programs for debugging on Linux for s/390 & z/Architecture |
| 686 | ==================================================================== |
| 687 | -gdwarf-2 now works it should be considered the default debugging |
| 688 | format for s/390 & z/Architecture as it is more reliable for debugging |
| 689 | shared libraries, normal -g debugging works much better now |
| 690 | Thanks to the IBM java compiler developers bug reports. |
| 691 | |
| 692 | This is typically done adding/appending the flags -g or -gdwarf-2 to the |
| 693 | CFLAGS & LDFLAGS variables Makefile of the program concerned. |
| 694 | |
| 695 | If using gdb & you would like accurate displays of registers & |
| 696 | stack traces compile without optimisation i.e make sure |
| 697 | that there is no -O2 or similar on the CFLAGS line of the Makefile & |
| 698 | the emitted gcc commands, obviously this will produce worse code |
| 699 | ( not advisable for shipment ) but it is an aid to the debugging process. |
| 700 | |
| 701 | This aids debugging because the compiler will copy parameters passed in |
| 702 | in registers onto the stack so backtracing & looking at passed in |
| 703 | parameters will work, however some larger programs which use inline functions |
| 704 | will not compile without optimisation. |
| 705 | |
| 706 | Debugging with optimisation has since much improved after fixing |
| 707 | some bugs, please make sure you are using gdb-5.0 or later developed |
| 708 | after Nov'2000. |
| 709 | |
| 710 | Figuring out gcc compile errors |
| 711 | =============================== |
| 712 | If you are getting a lot of syntax errors compiling a program & the problem |
| 713 | isn't blatantly obvious from the source. |
| 714 | It often helps to just preprocess the file, this is done with the -E |
| 715 | option in gcc. |
| 716 | What this does is that it runs through the very first phase of compilation |
| 717 | ( compilation in gcc is done in several stages & gcc calls many programs to |
| 718 | achieve its end result ) with the -E option gcc just calls the gcc preprocessor (cpp). |
| 719 | The c preprocessor does the following, it joins all the files #included together |
| 720 | recursively ( #include files can #include other files ) & also the c file you wish to compile. |
| 721 | It puts a fully qualified path of the #included files in a comment & it |
| 722 | does macro expansion. |
| 723 | This is useful for debugging because |
| 724 | 1) You can double check whether the files you expect to be included are the ones |
| 725 | that are being included ( e.g. double check that you aren't going to the i386 asm directory ). |
| 726 | 2) Check that macro definitions aren't clashing with typedefs, |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 727 | 3) Check that definitions aren't being used before they are being included. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 728 | 4) Helps put the line emitting the error under the microscope if it contains macros. |
| 729 | |
| 730 | For convenience the Linux kernel's makefile will do preprocessing automatically for you |
| 731 | by suffixing the file you want built with .i ( instead of .o ) |
| 732 | |
| 733 | e.g. |
| 734 | from the linux directory type |
| 735 | make arch/s390/kernel/signal.i |
| 736 | this will build |
| 737 | |
| 738 | s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer |
| 739 | -fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce -E arch/s390/kernel/signal.c |
| 740 | > arch/s390/kernel/signal.i |
| 741 | |
| 742 | Now look at signal.i you should see something like. |
| 743 | |
| 744 | |
| 745 | # 1 "/home1/barrow/linux/include/asm/types.h" 1 |
| 746 | typedef unsigned short umode_t; |
| 747 | typedef __signed__ char __s8; |
| 748 | typedef unsigned char __u8; |
| 749 | typedef __signed__ short __s16; |
| 750 | typedef unsigned short __u16; |
| 751 | |
| 752 | If instead you are getting errors further down e.g. |
| 753 | unknown instruction:2515 "move.l" or better still unknown instruction:2515 |
| 754 | "Fixme not implemented yet, call Martin" you are probably are attempting to compile some code |
| 755 | meant for another architecture or code that is simply not implemented, with a fixme statement |
| 756 | stuck into the inline assembly code so that the author of the file now knows he has work to do. |
| 757 | To look at the assembly emitted by gcc just before it is about to call gas ( the gnu assembler ) |
| 758 | use the -S option. |
| 759 | Again for your convenience the Linux kernel's Makefile will hold your hand & |
| 760 | do all this donkey work for you also by building the file with the .s suffix. |
| 761 | e.g. |
| 762 | from the Linux directory type |
| 763 | make arch/s390/kernel/signal.s |
| 764 | |
| 765 | s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer |
| 766 | -fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce -S arch/s390/kernel/signal.c |
| 767 | -o arch/s390/kernel/signal.s |
| 768 | |
| 769 | |
| 770 | This will output something like, ( please note the constant pool & the useful comments |
| 771 | in the prologue to give you a hand at interpreting it ). |
| 772 | |
| 773 | .LC54: |
| 774 | .string "misaligned (__u16 *) in __xchg\n" |
| 775 | .LC57: |
| 776 | .string "misaligned (__u32 *) in __xchg\n" |
| 777 | .L$PG1: # Pool sys_sigsuspend |
| 778 | .LC192: |
| 779 | .long -262401 |
| 780 | .LC193: |
| 781 | .long -1 |
| 782 | .LC194: |
| 783 | .long schedule-.L$PG1 |
| 784 | .LC195: |
| 785 | .long do_signal-.L$PG1 |
| 786 | .align 4 |
| 787 | .globl sys_sigsuspend |
| 788 | .type sys_sigsuspend,@function |
| 789 | sys_sigsuspend: |
| 790 | # leaf function 0 |
| 791 | # automatics 16 |
| 792 | # outgoing args 0 |
| 793 | # need frame pointer 0 |
| 794 | # call alloca 0 |
| 795 | # has varargs 0 |
| 796 | # incoming args (stack) 0 |
| 797 | # function length 168 |
| 798 | STM 8,15,32(15) |
| 799 | LR 0,15 |
| 800 | AHI 15,-112 |
| 801 | BASR 13,0 |
| 802 | .L$CO1: AHI 13,.L$PG1-.L$CO1 |
| 803 | ST 0,0(15) |
| 804 | LR 8,2 |
| 805 | N 5,.LC192-.L$PG1(13) |
| 806 | |
| 807 | Adding -g to the above output makes the output even more useful |
| 808 | e.g. typing |
| 809 | make CC:="s390-gcc -g" kernel/sched.s |
| 810 | |
| 811 | which compiles. |
| 812 | s390-gcc -g -D__KERNEL__ -I/home/barrow/linux-2.3/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -fno-strict-aliasing -pipe -fno-strength-reduce -S kernel/sched.c -o kernel/sched.s |
| 813 | |
| 814 | also outputs stabs ( debugger ) info, from this info you can find out the |
| 815 | offsets & sizes of various elements in structures. |
| 816 | e.g. the stab for the structure |
| 817 | struct rlimit { |
| 818 | unsigned long rlim_cur; |
| 819 | unsigned long rlim_max; |
| 820 | }; |
| 821 | is |
| 822 | .stabs "rlimit:T(151,2)=s8rlim_cur:(0,5),0,32;rlim_max:(0,5),32,32;;",128,0,0,0 |
| 823 | from this stab you can see that |
| 824 | rlimit_cur starts at bit offset 0 & is 32 bits in size |
| 825 | rlimit_max starts at bit offset 32 & is 32 bits in size. |
| 826 | |
| 827 | |
| 828 | Debugging Tools: |
| 829 | ================ |
| 830 | |
| 831 | objdump |
| 832 | ======= |
| 833 | This is a tool with many options the most useful being ( if compiled with -g). |
| 834 | objdump --source <victim program or object file> > <victims debug listing > |
| 835 | |
| 836 | |
| 837 | The whole kernel can be compiled like this ( Doing this will make a 17MB kernel |
| 838 | & a 200 MB listing ) however you have to strip it before building the image |
| 839 | using the strip command to make it a more reasonable size to boot it. |
| 840 | |
| 841 | A source/assembly mixed dump of the kernel can be done with the line |
| 842 | objdump --source vmlinux > vmlinux.lst |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 843 | Also, if the file isn't compiled -g, this will output as much debugging information |
| 844 | as it can (e.g. function names). This is very slow as it spends lots |
| 845 | of time searching for debugging info. The following self explanatory line should be used |
| 846 | instead if the code isn't compiled -g, as it is much faster: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 847 | objdump --disassemble-all --syms vmlinux > vmlinux.lst |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 848 | |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 849 | As hard drive space is valuable most of us use the following approach. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 850 | 1) Look at the emitted psw on the console to find the crash address in the kernel. |
| 851 | 2) Look at the file System.map ( in the linux directory ) produced when building |
| 852 | the kernel to find the closest address less than the current PSW to find the |
| 853 | offending function. |
| 854 | 3) use grep or similar to search the source tree looking for the source file |
| 855 | with this function if you don't know where it is. |
| 856 | 4) rebuild this object file with -g on, as an example suppose the file was |
| 857 | ( /arch/s390/kernel/signal.o ) |
| 858 | 5) Assuming the file with the erroneous function is signal.c Move to the base of the |
| 859 | Linux source tree. |
| 860 | 6) rm /arch/s390/kernel/signal.o |
| 861 | 7) make /arch/s390/kernel/signal.o |
| 862 | 8) watch the gcc command line emitted |
Matt LaPlante | 3f6dee9 | 2006-10-03 22:45:33 +0200 | [diff] [blame] | 863 | 9) type it in again or alternatively cut & paste it on the console adding the -g option. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 864 | 10) objdump --source arch/s390/kernel/signal.o > signal.lst |
| 865 | This will output the source & the assembly intermixed, as the snippet below shows |
| 866 | This will unfortunately output addresses which aren't the same |
| 867 | as the kernel ones you should be able to get around the mental arithmetic |
| 868 | by playing with the --adjust-vma parameter to objdump. |
| 869 | |
| 870 | |
| 871 | |
| 872 | |
Adrian Bunk | 4448aaf | 2005-11-08 21:34:42 -0800 | [diff] [blame] | 873 | static inline void spin_lock(spinlock_t *lp) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 874 | { |
| 875 | a0: 18 34 lr %r3,%r4 |
| 876 | a2: a7 3a 03 bc ahi %r3,956 |
| 877 | __asm__ __volatile(" lhi 1,-1\n" |
| 878 | a6: a7 18 ff ff lhi %r1,-1 |
| 879 | aa: 1f 00 slr %r0,%r0 |
| 880 | ac: ba 01 30 00 cs %r0,%r1,0(%r3) |
| 881 | b0: a7 44 ff fd jm aa <sys_sigsuspend+0x2e> |
| 882 | saveset = current->blocked; |
| 883 | b4: d2 07 f0 68 mvc 104(8,%r15),972(%r4) |
| 884 | b8: 43 cc |
| 885 | return (set->sig[0] & mask) != 0; |
| 886 | } |
| 887 | |
| 888 | 6) If debugging under VM go down to that section in the document for more info. |
| 889 | |
| 890 | |
| 891 | I now have a tool which takes the pain out of --adjust-vma |
| 892 | & you are able to do something like |
| 893 | make /arch/s390/kernel/traps.lst |
| 894 | & it automatically generates the correctly relocated entries for |
| 895 | the text segment in traps.lst. |
| 896 | This tool is now standard in linux distro's in scripts/makelst |
| 897 | |
| 898 | strace: |
| 899 | ------- |
| 900 | Q. What is it ? |
| 901 | A. It is a tool for intercepting calls to the kernel & logging them |
| 902 | to a file & on the screen. |
| 903 | |
| 904 | Q. What use is it ? |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 905 | A. You can use it to find out what files a particular program opens. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 906 | |
| 907 | |
| 908 | |
| 909 | Example 1 |
| 910 | --------- |
| 911 | If you wanted to know does ping work but didn't have the source |
| 912 | strace ping -c 1 127.0.0.1 |
| 913 | & then look at the man pages for each of the syscalls below, |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 914 | ( In fact this is sometimes easier than looking at some spaghetti |
Matt LaPlante | 2fe0ae7 | 2006-10-03 22:50:39 +0200 | [diff] [blame] | 915 | source which conditionally compiles for several architectures ). |
| 916 | Not everything that it throws out needs to make sense immediately. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 917 | |
| 918 | Just looking quickly you can see that it is making up a RAW socket |
| 919 | for the ICMP protocol. |
| 920 | Doing an alarm(10) for a 10 second timeout |
| 921 | & doing a gettimeofday call before & after each read to see |
| 922 | how long the replies took, & writing some text to stdout so the user |
| 923 | has an idea what is going on. |
| 924 | |
| 925 | socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) = 3 |
| 926 | getuid() = 0 |
| 927 | setuid(0) = 0 |
| 928 | stat("/usr/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory) |
| 929 | stat("/usr/share/locale/libc/C", 0xbffff134) = -1 ENOENT (No such file or directory) |
| 930 | stat("/usr/local/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory) |
| 931 | getpid() = 353 |
| 932 | setsockopt(3, SOL_SOCKET, SO_BROADCAST, [1], 4) = 0 |
| 933 | setsockopt(3, SOL_SOCKET, SO_RCVBUF, [49152], 4) = 0 |
| 934 | fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(3, 1), ...}) = 0 |
| 935 | mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40008000 |
| 936 | ioctl(1, TCGETS, {B9600 opost isig icanon echo ...}) = 0 |
| 937 | write(1, "PING 127.0.0.1 (127.0.0.1): 56 d"..., 42PING 127.0.0.1 (127.0.0.1): 56 data bytes |
| 938 | ) = 42 |
| 939 | sigaction(SIGINT, {0x8049ba0, [], SA_RESTART}, {SIG_DFL}) = 0 |
| 940 | sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {SIG_DFL}) = 0 |
| 941 | gettimeofday({948904719, 138951}, NULL) = 0 |
| 942 | sendto(3, "\10\0D\201a\1\0\0\17#\2178\307\36"..., 64, 0, {sin_family=AF_INET, |
| 943 | sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 64 |
| 944 | sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0 |
| 945 | sigaction(SIGALRM, {0x8049ba0, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0 |
| 946 | alarm(10) = 0 |
| 947 | recvfrom(3, "E\0\0T\0005\0\0@\1|r\177\0\0\1\177"..., 192, 0, |
| 948 | {sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84 |
| 949 | gettimeofday({948904719, 160224}, NULL) = 0 |
| 950 | recvfrom(3, "E\0\0T\0006\0\0\377\1\275p\177\0"..., 192, 0, |
| 951 | {sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84 |
| 952 | gettimeofday({948904719, 166952}, NULL) = 0 |
| 953 | write(1, "64 bytes from 127.0.0.1: icmp_se"..., |
| 954 | 5764 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=28.0 ms |
| 955 | |
| 956 | Example 2 |
| 957 | --------- |
| 958 | strace passwd 2>&1 | grep open |
| 959 | produces the following output |
| 960 | open("/etc/ld.so.cache", O_RDONLY) = 3 |
| 961 | open("/opt/kde/lib/libc.so.5", O_RDONLY) = -1 ENOENT (No such file or directory) |
| 962 | open("/lib/libc.so.5", O_RDONLY) = 3 |
| 963 | open("/dev", O_RDONLY) = 3 |
| 964 | open("/var/run/utmp", O_RDONLY) = 3 |
| 965 | open("/etc/passwd", O_RDONLY) = 3 |
| 966 | open("/etc/shadow", O_RDONLY) = 3 |
| 967 | open("/etc/login.defs", O_RDONLY) = 4 |
| 968 | open("/dev/tty", O_RDONLY) = 4 |
| 969 | |
| 970 | The 2>&1 is done to redirect stderr to stdout & grep is then filtering this input |
| 971 | through the pipe for each line containing the string open. |
| 972 | |
| 973 | |
| 974 | Example 3 |
| 975 | --------- |
Matt LaPlante | 53cb472 | 2006-10-03 22:55:17 +0200 | [diff] [blame] | 976 | Getting sophisticated |
| 977 | telnetd crashes & I don't know why |
| 978 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 979 | Steps |
| 980 | ----- |
| 981 | 1) Replace the following line in /etc/inetd.conf |
| 982 | telnet stream tcp nowait root /usr/sbin/in.telnetd -h |
| 983 | with |
| 984 | telnet stream tcp nowait root /blah |
| 985 | |
| 986 | 2) Create the file /blah with the following contents to start tracing telnetd |
| 987 | #!/bin/bash |
| 988 | /usr/bin/strace -o/t1 -f /usr/sbin/in.telnetd -h |
| 989 | 3) chmod 700 /blah to make it executable only to root |
| 990 | 4) |
| 991 | killall -HUP inetd |
| 992 | or ps aux | grep inetd |
| 993 | get inetd's process id |
| 994 | & kill -HUP inetd to restart it. |
| 995 | |
| 996 | Important options |
| 997 | ----------------- |
| 998 | -o is used to tell strace to output to a file in our case t1 in the root directory |
| 999 | -f is to follow children i.e. |
| 1000 | e.g in our case above telnetd will start the login process & subsequently a shell like bash. |
| 1001 | You will be able to tell which is which from the process ID's listed on the left hand side |
| 1002 | of the strace output. |
| 1003 | -p<pid> will tell strace to attach to a running process, yup this can be done provided |
| 1004 | it isn't being traced or debugged already & you have enough privileges, |
| 1005 | the reason 2 processes cannot trace or debug the same program is that strace |
| 1006 | becomes the parent process of the one being debugged & processes ( unlike people ) |
| 1007 | can have only one parent. |
| 1008 | |
| 1009 | |
| 1010 | However the file /t1 will get big quite quickly |
| 1011 | to test it telnet 127.0.0.1 |
| 1012 | |
| 1013 | now look at what files in.telnetd execve'd |
| 1014 | 413 execve("/usr/sbin/in.telnetd", ["/usr/sbin/in.telnetd", "-h"], [/* 17 vars */]) = 0 |
| 1015 | 414 execve("/bin/login", ["/bin/login", "-h", "localhost", "-p"], [/* 2 vars */]) = 0 |
| 1016 | |
| 1017 | Whey it worked!. |
| 1018 | |
| 1019 | |
| 1020 | Other hints: |
| 1021 | ------------ |
| 1022 | If the program is not very interactive ( i.e. not much keyboard input ) |
| 1023 | & is crashing in one architecture but not in another you can do |
| 1024 | an strace of both programs under as identical a scenario as you can |
| 1025 | on both architectures outputting to a file then. |
| 1026 | do a diff of the two traces using the diff program |
| 1027 | i.e. |
| 1028 | diff output1 output2 |
| 1029 | & maybe you'll be able to see where the call paths differed, this |
| 1030 | is possibly near the cause of the crash. |
| 1031 | |
| 1032 | More info |
| 1033 | --------- |
| 1034 | Look at man pages for strace & the various syscalls |
| 1035 | e.g. man strace, man alarm, man socket. |
| 1036 | |
| 1037 | |
| 1038 | Performance Debugging |
| 1039 | ===================== |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1040 | gcc is capable of compiling in profiling code just add the -p option |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1041 | to the CFLAGS, this obviously affects program size & performance. |
| 1042 | This can be used by the gprof gnu profiling tool or the |
| 1043 | gcov the gnu code coverage tool ( code coverage is a means of testing |
| 1044 | code quality by checking if all the code in an executable in exercised by |
| 1045 | a tester ). |
| 1046 | |
| 1047 | |
| 1048 | Using top to find out where processes are sleeping in the kernel |
| 1049 | ---------------------------------------------------------------- |
| 1050 | To do this copy the System.map from the root directory where |
| 1051 | the linux kernel was built to the /boot directory on your |
| 1052 | linux machine. |
| 1053 | Start top |
| 1054 | Now type fU<return> |
| 1055 | You should see a new field called WCHAN which |
| 1056 | tells you where each process is sleeping here is a typical output. |
| 1057 | |
| 1058 | 6:59pm up 41 min, 1 user, load average: 0.00, 0.00, 0.00 |
| 1059 | 28 processes: 27 sleeping, 1 running, 0 zombie, 0 stopped |
| 1060 | CPU states: 0.0% user, 0.1% system, 0.0% nice, 99.8% idle |
| 1061 | Mem: 254900K av, 45976K used, 208924K free, 0K shrd, 28636K buff |
| 1062 | Swap: 0K av, 0K used, 0K free 8620K cached |
| 1063 | |
| 1064 | PID USER PRI NI SIZE RSS SHARE WCHAN STAT LIB %CPU %MEM TIME COMMAND |
| 1065 | 750 root 12 0 848 848 700 do_select S 0 0.1 0.3 0:00 in.telnetd |
| 1066 | 767 root 16 0 1140 1140 964 R 0 0.1 0.4 0:00 top |
| 1067 | 1 root 8 0 212 212 180 do_select S 0 0.0 0.0 0:00 init |
| 1068 | 2 root 9 0 0 0 0 down_inte SW 0 0.0 0.0 0:00 kmcheck |
| 1069 | |
| 1070 | The time command |
| 1071 | ---------------- |
| 1072 | Another related command is the time command which gives you an indication |
| 1073 | of where a process is spending the majority of its time. |
| 1074 | e.g. |
| 1075 | time ping -c 5 nc |
| 1076 | outputs |
| 1077 | real 0m4.054s |
| 1078 | user 0m0.010s |
| 1079 | sys 0m0.010s |
| 1080 | |
| 1081 | Debugging under VM |
| 1082 | ================== |
| 1083 | |
| 1084 | Notes |
| 1085 | ----- |
| 1086 | Addresses & values in the VM debugger are always hex never decimal |
| 1087 | Address ranges are of the format <HexValue1>-<HexValue2> or <HexValue1>.<HexValue2> |
Paolo Ornati | 670e9f3 | 2006-10-03 22:57:56 +0200 | [diff] [blame] | 1088 | e.g. The address range 0x2000 to 0x3000 can be described as 2000-3000 or 2000.1000 |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1089 | |
| 1090 | The VM Debugger is case insensitive. |
| 1091 | |
| 1092 | VM's strengths are usually other debuggers weaknesses you can get at any resource |
| 1093 | no matter how sensitive e.g. memory management resources,change address translation |
| 1094 | in the PSW. For kernel hacking you will reap dividends if you get good at it. |
| 1095 | |
| 1096 | The VM Debugger displays operators but not operands, probably because some |
| 1097 | of it was written when memory was expensive & the programmer was probably proud that |
| 1098 | it fitted into 2k of memory & the programmers & didn't want to shock hardcore VM'ers by |
| 1099 | changing the interface :-), also the debugger displays useful information on the same line & |
| 1100 | the author of the code probably felt that it was a good idea not to go over |
| 1101 | the 80 columns on the screen. |
| 1102 | |
| 1103 | As some of you are probably in a panic now this isn't as unintuitive as it may seem |
| 1104 | as the 390 instructions are easy to decode mentally & you can make a good guess at a lot |
| 1105 | of them as all the operands are nibble ( half byte aligned ) & if you have an objdump listing |
| 1106 | also it is quite easy to follow, if you don't have an objdump listing keep a copy of |
| 1107 | the s/390 Reference Summary & look at between pages 2 & 7 or alternatively the |
| 1108 | s/390 principles of operation. |
| 1109 | e.g. even I can guess that |
| 1110 | 0001AFF8' LR 180F CC 0 |
| 1111 | is a ( load register ) lr r0,r15 |
| 1112 | |
| 1113 | Also it is very easy to tell the length of a 390 instruction from the 2 most significant |
| 1114 | bits in the instruction ( not that this info is really useful except if you are trying to |
| 1115 | make sense of a hexdump of code ). |
| 1116 | Here is a table |
| 1117 | Bits Instruction Length |
| 1118 | ------------------------------------------ |
| 1119 | 00 2 Bytes |
| 1120 | 01 4 Bytes |
| 1121 | 10 4 Bytes |
| 1122 | 11 6 Bytes |
| 1123 | |
| 1124 | |
| 1125 | |
| 1126 | |
| 1127 | The debugger also displays other useful info on the same line such as the |
| 1128 | addresses being operated on destination addresses of branches & condition codes. |
| 1129 | e.g. |
| 1130 | 00019736' AHI A7DAFF0E CC 1 |
| 1131 | 000198BA' BRC A7840004 -> 000198C2' CC 0 |
| 1132 | 000198CE' STM 900EF068 >> 0FA95E78 CC 2 |
| 1133 | |
| 1134 | |
| 1135 | |
| 1136 | Useful VM debugger commands |
| 1137 | --------------------------- |
| 1138 | |
| 1139 | I suppose I'd better mention this before I start |
| 1140 | to list the current active traces do |
| 1141 | Q TR |
| 1142 | there can be a maximum of 255 of these per set |
| 1143 | ( more about trace sets later ). |
| 1144 | To stop traces issue a |
| 1145 | TR END. |
| 1146 | To delete a particular breakpoint issue |
| 1147 | TR DEL <breakpoint number> |
| 1148 | |
| 1149 | The PA1 key drops to CP mode so you can issue debugger commands, |
| 1150 | Doing alt c (on my 3270 console at least ) clears the screen. |
| 1151 | hitting b <enter> comes back to the running operating system |
| 1152 | from cp mode ( in our case linux ). |
| 1153 | It is typically useful to add shortcuts to your profile.exec file |
| 1154 | if you have one ( this is roughly equivalent to autoexec.bat in DOS ). |
| 1155 | file here are a few from mine. |
| 1156 | /* this gives me command history on issuing f12 */ |
| 1157 | set pf12 retrieve |
| 1158 | /* this continues */ |
| 1159 | set pf8 imm b |
| 1160 | /* goes to trace set a */ |
| 1161 | set pf1 imm tr goto a |
| 1162 | /* goes to trace set b */ |
| 1163 | set pf2 imm tr goto b |
| 1164 | /* goes to trace set c */ |
| 1165 | set pf3 imm tr goto c |
| 1166 | |
| 1167 | |
| 1168 | |
| 1169 | Instruction Tracing |
| 1170 | ------------------- |
| 1171 | Setting a simple breakpoint |
| 1172 | TR I PSWA <address> |
| 1173 | To debug a particular function try |
| 1174 | TR I R <function address range> |
| 1175 | TR I on its own will single step. |
| 1176 | TR I DATA <MNEMONIC> <OPTIONAL RANGE> will trace for particular mnemonics |
| 1177 | e.g. |
| 1178 | TR I DATA 4D R 0197BC.4000 |
| 1179 | will trace for BAS'es ( opcode 4D ) in the range 0197BC.4000 |
| 1180 | if you were inclined you could add traces for all branch instructions & |
| 1181 | suffix them with the run prefix so you would have a backtrace on screen |
| 1182 | when a program crashes. |
| 1183 | TR BR <INTO OR FROM> will trace branches into or out of an address. |
| 1184 | e.g. |
| 1185 | TR BR INTO 0 is often quite useful if a program is getting awkward & deciding |
| 1186 | to branch to 0 & crashing as this will stop at the address before in jumps to 0. |
| 1187 | TR I R <address range> RUN cmd d g |
| 1188 | single steps a range of addresses but stays running & |
| 1189 | displays the gprs on each step. |
| 1190 | |
| 1191 | |
| 1192 | |
| 1193 | Displaying & modifying Registers |
| 1194 | -------------------------------- |
| 1195 | D G will display all the gprs |
| 1196 | Adding a extra G to all the commands is necessary to access the full 64 bit |
| 1197 | content in VM on z/Architecture obviously this isn't required for access registers |
| 1198 | as these are still 32 bit. |
| 1199 | e.g. DGG instead of DG |
| 1200 | D X will display all the control registers |
| 1201 | D AR will display all the access registers |
| 1202 | D AR4-7 will display access registers 4 to 7 |
| 1203 | CPU ALL D G will display the GRPS of all CPUS in the configuration |
| 1204 | D PSW will display the current PSW |
| 1205 | st PSW 2000 will put the value 2000 into the PSW & |
| 1206 | cause crash your machine. |
| 1207 | D PREFIX displays the prefix offset |
| 1208 | |
| 1209 | |
| 1210 | Displaying Memory |
| 1211 | ----------------- |
| 1212 | To display memory mapped using the current PSW's mapping try |
| 1213 | D <range> |
| 1214 | To make VM display a message each time it hits a particular address & continue try |
| 1215 | D I<range> will disassemble/display a range of instructions. |
| 1216 | ST addr 32 bit word will store a 32 bit aligned address |
| 1217 | D T<range> will display the EBCDIC in an address ( if you are that way inclined ) |
| 1218 | D R<range> will display real addresses ( without DAT ) but with prefixing. |
| 1219 | There are other complex options to display if you need to get at say home space |
| 1220 | but are in primary space the easiest thing to do is to temporarily |
| 1221 | modify the PSW to the other addressing mode, display the stuff & then |
| 1222 | restore it. |
| 1223 | |
| 1224 | |
| 1225 | |
| 1226 | Hints |
| 1227 | ----- |
| 1228 | If you want to issue a debugger command without halting your virtual machine with the |
| 1229 | PA1 key try prefixing the command with #CP e.g. |
| 1230 | #cp tr i pswa 2000 |
| 1231 | also suffixing most debugger commands with RUN will cause them not |
| 1232 | to stop just display the mnemonic at the current instruction on the console. |
| 1233 | If you have several breakpoints you want to put into your program & |
| 1234 | you get fed up of cross referencing with System.map |
| 1235 | you can do the following trick for several symbols. |
| 1236 | grep do_signal System.map |
| 1237 | which emits the following among other things |
| 1238 | 0001f4e0 T do_signal |
| 1239 | now you can do |
| 1240 | |
| 1241 | TR I PSWA 0001f4e0 cmd msg * do_signal |
| 1242 | This sends a message to your own console each time do_signal is entered. |
| 1243 | ( As an aside I wrote a perl script once which automatically generated a REXX |
| 1244 | script with breakpoints on every kernel procedure, this isn't a good idea |
| 1245 | because there are thousands of these routines & VM can only set 255 breakpoints |
| 1246 | at a time so you nearly had to spend as long pruning the file down as you would |
| 1247 | entering the msg's by hand ),however, the trick might be useful for a single object file. |
| 1248 | On linux'es 3270 emulator x3270 there is a very useful option under the file ment |
| 1249 | Save Screens In File this is very good of keeping a copy of traces. |
| 1250 | |
| 1251 | From CMS help <command name> will give you online help on a particular command. |
| 1252 | e.g. |
| 1253 | HELP DISPLAY |
| 1254 | |
| 1255 | Also CP has a file called profile.exec which automatically gets called |
| 1256 | on startup of CMS ( like autoexec.bat ), keeping on a DOS analogy session |
| 1257 | CP has a feature similar to doskey, it may be useful for you to |
| 1258 | use profile.exec to define some keystrokes. |
| 1259 | e.g. |
| 1260 | SET PF9 IMM B |
| 1261 | This does a single step in VM on pressing F8. |
| 1262 | SET PF10 ^ |
| 1263 | This sets up the ^ key. |
| 1264 | which can be used for ^c (ctrl-c),^z (ctrl-z) which can't be typed directly into some 3270 consoles. |
| 1265 | SET PF11 ^- |
| 1266 | This types the starting keystrokes for a sysrq see SysRq below. |
| 1267 | SET PF12 RETRIEVE |
| 1268 | This retrieves command history on pressing F12. |
| 1269 | |
| 1270 | |
| 1271 | Sometimes in VM the display is set up to scroll automatically this |
| 1272 | can be very annoying if there are messages you wish to look at |
| 1273 | to stop this do |
| 1274 | TERM MORE 255 255 |
| 1275 | This will nearly stop automatic screen updates, however it will |
| 1276 | cause a denial of service if lots of messages go to the 3270 console, |
| 1277 | so it would be foolish to use this as the default on a production machine. |
| 1278 | |
| 1279 | |
| 1280 | Tracing particular processes |
| 1281 | ---------------------------- |
| 1282 | The kernel's text segment is intentionally at an address in memory that it will |
| 1283 | very seldom collide with text segments of user programs ( thanks Martin ), |
| 1284 | this simplifies debugging the kernel. |
| 1285 | However it is quite common for user processes to have addresses which collide |
| 1286 | this can make debugging a particular process under VM painful under normal |
| 1287 | circumstances as the process may change when doing a |
| 1288 | TR I R <address range>. |
| 1289 | Thankfully after reading VM's online help I figured out how to debug |
| 1290 | I particular process. |
| 1291 | |
| 1292 | Your first problem is to find the STD ( segment table designation ) |
| 1293 | of the program you wish to debug. |
| 1294 | There are several ways you can do this here are a few |
| 1295 | 1) objdump --syms <program to be debugged> | grep main |
| 1296 | To get the address of main in the program. |
| 1297 | tr i pswa <address of main> |
| 1298 | Start the program, if VM drops to CP on what looks like the entry |
| 1299 | point of the main function this is most likely the process you wish to debug. |
| 1300 | Now do a D X13 or D XG13 on z/Architecture. |
| 1301 | On 31 bit the STD is bits 1-19 ( the STO segment table origin ) |
| 1302 | & 25-31 ( the STL segment table length ) of CR13. |
| 1303 | now type |
| 1304 | TR I R STD <CR13's value> 0.7fffffff |
| 1305 | e.g. |
| 1306 | TR I R STD 8F32E1FF 0.7fffffff |
| 1307 | Another very useful variation is |
| 1308 | TR STORE INTO STD <CR13's value> <address range> |
| 1309 | for finding out when a particular variable changes. |
| 1310 | |
| 1311 | An alternative way of finding the STD of a currently running process |
| 1312 | is to do the following, ( this method is more complex but |
Matt LaPlante | 6c28f2c | 2006-10-03 22:46:31 +0200 | [diff] [blame] | 1313 | could be quite convenient if you aren't updating the kernel much & |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1314 | so your kernel structures will stay constant for a reasonable period of |
| 1315 | time ). |
| 1316 | |
| 1317 | grep task /proc/<pid>/status |
| 1318 | from this you should see something like |
| 1319 | task: 0f160000 ksp: 0f161de8 pt_regs: 0f161f68 |
| 1320 | This now gives you a pointer to the task structure. |
| 1321 | Now make CC:="s390-gcc -g" kernel/sched.s |
| 1322 | To get the task_struct stabinfo. |
| 1323 | ( task_struct is defined in include/linux/sched.h ). |
| 1324 | Now we want to look at |
| 1325 | task->active_mm->pgd |
| 1326 | on my machine the active_mm in the task structure stab is |
| 1327 | active_mm:(4,12),672,32 |
| 1328 | its offset is 672/8=84=0x54 |
| 1329 | the pgd member in the mm_struct stab is |
| 1330 | pgd:(4,6)=*(29,5),96,32 |
| 1331 | so its offset is 96/8=12=0xc |
| 1332 | |
| 1333 | so we'll |
| 1334 | hexdump -s 0xf160054 /dev/mem | more |
| 1335 | i.e. task_struct+active_mm offset |
| 1336 | to look at the active_mm member |
| 1337 | f160054 0fee cc60 0019 e334 0000 0000 0000 0011 |
| 1338 | hexdump -s 0x0feecc6c /dev/mem | more |
| 1339 | i.e. active_mm+pgd offset |
| 1340 | feecc6c 0f2c 0000 0000 0001 0000 0001 0000 0010 |
| 1341 | we get something like |
| 1342 | now do |
| 1343 | TR I R STD <pgd|0x7f> 0.7fffffff |
| 1344 | i.e. the 0x7f is added because the pgd only |
| 1345 | gives the page table origin & we need to set the low bits |
| 1346 | to the maximum possible segment table length. |
| 1347 | TR I R STD 0f2c007f 0.7fffffff |
| 1348 | on z/Architecture you'll probably need to do |
| 1349 | TR I R STD <pgd|0x7> 0.ffffffffffffffff |
| 1350 | to set the TableType to 0x1 & the Table length to 3. |
| 1351 | |
| 1352 | |
| 1353 | |
| 1354 | Tracing Program Exceptions |
| 1355 | -------------------------- |
| 1356 | If you get a crash which says something like |
| 1357 | illegal operation or specification exception followed by a register dump |
| 1358 | You can restart linux & trace these using the tr prog <range or value> trace option. |
| 1359 | |
| 1360 | |
| 1361 | |
| 1362 | The most common ones you will normally be tracing for is |
| 1363 | 1=operation exception |
| 1364 | 2=privileged operation exception |
| 1365 | 4=protection exception |
| 1366 | 5=addressing exception |
| 1367 | 6=specification exception |
| 1368 | 10=segment translation exception |
| 1369 | 11=page translation exception |
| 1370 | |
| 1371 | The full list of these is on page 22 of the current s/390 Reference Summary. |
| 1372 | e.g. |
| 1373 | tr prog 10 will trace segment translation exceptions. |
| 1374 | tr prog on its own will trace all program interruption codes. |
| 1375 | |
| 1376 | Trace Sets |
| 1377 | ---------- |
| 1378 | On starting VM you are initially in the INITIAL trace set. |
| 1379 | You can do a Q TR to verify this. |
| 1380 | If you have a complex tracing situation where you wish to wait for instance |
| 1381 | till a driver is open before you start tracing IO, but know in your |
| 1382 | heart that you are going to have to make several runs through the code till you |
| 1383 | have a clue whats going on. |
| 1384 | |
| 1385 | What you can do is |
| 1386 | TR I PSWA <Driver open address> |
| 1387 | hit b to continue till breakpoint |
| 1388 | reach the breakpoint |
| 1389 | now do your |
| 1390 | TR GOTO B |
| 1391 | TR IO 7c08-7c09 inst int run |
| 1392 | or whatever the IO channels you wish to trace are & hit b |
| 1393 | |
| 1394 | To got back to the initial trace set do |
| 1395 | TR GOTO INITIAL |
| 1396 | & the TR I PSWA <Driver open address> will be the only active breakpoint again. |
| 1397 | |
| 1398 | |
| 1399 | Tracing linux syscalls under VM |
| 1400 | ------------------------------- |
| 1401 | Syscalls are implemented on Linux for S390 by the Supervisor call instruction (SVC) there 256 |
| 1402 | possibilities of these as the instruction is made up of a 0xA opcode & the second byte being |
| 1403 | the syscall number. They are traced using the simple command. |
| 1404 | TR SVC <Optional value or range> |
Randy Dunlap | 58cc855 | 2009-01-06 14:42:42 -0800 | [diff] [blame] | 1405 | the syscalls are defined in linux/arch/s390/include/asm/unistd.h |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1406 | e.g. to trace all file opens just do |
| 1407 | TR SVC 5 ( as this is the syscall number of open ) |
| 1408 | |
| 1409 | |
| 1410 | SMP Specific commands |
| 1411 | --------------------- |
| 1412 | To find out how many cpus you have |
| 1413 | Q CPUS displays all the CPU's available to your virtual machine |
| 1414 | To find the cpu that the current cpu VM debugger commands are being directed at do |
Paolo Ornati | 670e9f3 | 2006-10-03 22:57:56 +0200 | [diff] [blame] | 1415 | Q CPU to change the current cpu VM debugger commands are being directed at do |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1416 | CPU <desired cpu no> |
| 1417 | |
| 1418 | On a SMP guest issue a command to all CPUs try prefixing the command with cpu all. |
| 1419 | To issue a command to a particular cpu try cpu <cpu number> e.g. |
| 1420 | CPU 01 TR I R 2000.3000 |
| 1421 | If you are running on a guest with several cpus & you have a IO related problem |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1422 | & cannot follow the flow of code but you know it isn't smp related. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1423 | from the bash prompt issue |
| 1424 | shutdown -h now or halt. |
| 1425 | do a Q CPUS to find out how many cpus you have |
| 1426 | detach each one of them from cp except cpu 0 |
| 1427 | by issuing a |
| 1428 | DETACH CPU 01-(number of cpus in configuration) |
| 1429 | & boot linux again. |
| 1430 | TR SIGP will trace inter processor signal processor instructions. |
| 1431 | DEFINE CPU 01-(number in configuration) |
| 1432 | will get your guests cpus back. |
| 1433 | |
| 1434 | |
| 1435 | Help for displaying ascii textstrings |
| 1436 | ------------------------------------- |
| 1437 | On the very latest VM Nucleus'es VM can now display ascii |
| 1438 | ( thanks Neale for the hint ) by doing |
| 1439 | D TX<lowaddr>.<len> |
| 1440 | e.g. |
| 1441 | D TX0.100 |
| 1442 | |
| 1443 | Alternatively |
| 1444 | ============= |
| 1445 | Under older VM debuggers ( I love EBDIC too ) you can use this little program I wrote which |
| 1446 | will convert a command line of hex digits to ascii text which can be compiled under linux & |
| 1447 | you can copy the hex digits from your x3270 terminal to your xterm if you are debugging |
| 1448 | from a linuxbox. |
| 1449 | |
| 1450 | This is quite useful when looking at a parameter passed in as a text string |
| 1451 | under VM ( unless you are good at decoding ASCII in your head ). |
| 1452 | |
| 1453 | e.g. consider tracing an open syscall |
| 1454 | TR SVC 5 |
| 1455 | We have stopped at a breakpoint |
| 1456 | 000151B0' SVC 0A05 -> 0001909A' CC 0 |
| 1457 | |
| 1458 | D 20.8 to check the SVC old psw in the prefix area & see was it from userspace |
| 1459 | ( for the layout of the prefix area consult P18 of the s/390 390 Reference Summary |
| 1460 | if you have it available ). |
| 1461 | V00000020 070C2000 800151B2 |
| 1462 | The problem state bit wasn't set & it's also too early in the boot sequence |
| 1463 | for it to be a userspace SVC if it was we would have to temporarily switch the |
| 1464 | psw to user space addressing so we could get at the first parameter of the open in |
| 1465 | gpr2. |
| 1466 | Next do a |
| 1467 | D G2 |
| 1468 | GPR 2 = 00014CB4 |
| 1469 | Now display what gpr2 is pointing to |
| 1470 | D 00014CB4.20 |
| 1471 | V00014CB4 2F646576 2F636F6E 736F6C65 00001BF5 |
| 1472 | V00014CC4 FC00014C B4001001 E0001000 B8070707 |
| 1473 | Now copy the text till the first 00 hex ( which is the end of the string |
| 1474 | to an xterm & do hex2ascii on it. |
| 1475 | hex2ascii 2F646576 2F636F6E 736F6C65 00 |
| 1476 | outputs |
| 1477 | Decoded Hex:=/ d e v / c o n s o l e 0x00 |
| 1478 | We were opening the console device, |
| 1479 | |
| 1480 | You can compile the code below yourself for practice :-), |
| 1481 | /* |
| 1482 | * hex2ascii.c |
| 1483 | * a useful little tool for converting a hexadecimal command line to ascii |
| 1484 | * |
| 1485 | * Author(s): Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com) |
| 1486 | * (C) 2000 IBM Deutschland Entwicklung GmbH, IBM Corporation. |
| 1487 | */ |
| 1488 | #include <stdio.h> |
| 1489 | |
| 1490 | int main(int argc,char *argv[]) |
| 1491 | { |
| 1492 | int cnt1,cnt2,len,toggle=0; |
| 1493 | int startcnt=1; |
| 1494 | unsigned char c,hex; |
| 1495 | |
| 1496 | if(argc>1&&(strcmp(argv[1],"-a")==0)) |
| 1497 | startcnt=2; |
| 1498 | printf("Decoded Hex:="); |
| 1499 | for(cnt1=startcnt;cnt1<argc;cnt1++) |
| 1500 | { |
| 1501 | len=strlen(argv[cnt1]); |
| 1502 | for(cnt2=0;cnt2<len;cnt2++) |
| 1503 | { |
| 1504 | c=argv[cnt1][cnt2]; |
| 1505 | if(c>='0'&&c<='9') |
| 1506 | c=c-'0'; |
| 1507 | if(c>='A'&&c<='F') |
| 1508 | c=c-'A'+10; |
| 1509 | if(c>='a'&&c<='f') |
| 1510 | c=c-'a'+10; |
| 1511 | switch(toggle) |
| 1512 | { |
| 1513 | case 0: |
| 1514 | hex=c<<4; |
| 1515 | toggle=1; |
| 1516 | break; |
| 1517 | case 1: |
| 1518 | hex+=c; |
| 1519 | if(hex<32||hex>127) |
| 1520 | { |
| 1521 | if(startcnt==1) |
| 1522 | printf("0x%02X ",(int)hex); |
| 1523 | else |
| 1524 | printf("."); |
| 1525 | } |
| 1526 | else |
| 1527 | { |
| 1528 | printf("%c",hex); |
| 1529 | if(startcnt==1) |
| 1530 | printf(" "); |
| 1531 | } |
| 1532 | toggle=0; |
| 1533 | break; |
| 1534 | } |
| 1535 | } |
| 1536 | } |
| 1537 | printf("\n"); |
| 1538 | } |
| 1539 | |
| 1540 | |
| 1541 | |
| 1542 | |
| 1543 | Stack tracing under VM |
| 1544 | ---------------------- |
| 1545 | A basic backtrace |
| 1546 | ----------------- |
| 1547 | |
| 1548 | Here are the tricks I use 9 out of 10 times it works pretty well, |
| 1549 | |
| 1550 | When your backchain reaches a dead end |
| 1551 | -------------------------------------- |
| 1552 | This can happen when an exception happens in the kernel & the kernel is entered twice |
| 1553 | if you reach the NULL pointer at the end of the back chain you should be |
| 1554 | able to sniff further back if you follow the following tricks. |
| 1555 | 1) A kernel address should be easy to recognise since it is in |
| 1556 | primary space & the problem state bit isn't set & also |
| 1557 | The Hi bit of the address is set. |
| 1558 | 2) Another backchain should also be easy to recognise since it is an |
| 1559 | address pointing to another address approximately 100 bytes or 0x70 hex |
| 1560 | behind the current stackpointer. |
| 1561 | |
| 1562 | |
| 1563 | Here is some practice. |
| 1564 | boot the kernel & hit PA1 at some random time |
| 1565 | d g to display the gprs, this should display something like |
| 1566 | GPR 0 = 00000001 00156018 0014359C 00000000 |
| 1567 | GPR 4 = 00000001 001B8888 000003E0 00000000 |
| 1568 | GPR 8 = 00100080 00100084 00000000 000FE000 |
| 1569 | GPR 12 = 00010400 8001B2DC 8001B36A 000FFED8 |
| 1570 | Note that GPR14 is a return address but as we are real men we are going to |
| 1571 | trace the stack. |
| 1572 | display 0x40 bytes after the stack pointer. |
| 1573 | |
| 1574 | V000FFED8 000FFF38 8001B838 80014C8E 000FFF38 |
| 1575 | V000FFEE8 00000000 00000000 000003E0 00000000 |
| 1576 | V000FFEF8 00100080 00100084 00000000 000FE000 |
| 1577 | V000FFF08 00010400 8001B2DC 8001B36A 000FFED8 |
| 1578 | |
| 1579 | |
| 1580 | Ah now look at whats in sp+56 (sp+0x38) this is 8001B36A our saved r14 if |
| 1581 | you look above at our stackframe & also agrees with GPR14. |
| 1582 | |
| 1583 | now backchain |
| 1584 | d 000FFF38.40 |
| 1585 | we now are taking the contents of SP to get our first backchain. |
| 1586 | |
| 1587 | V000FFF38 000FFFA0 00000000 00014995 00147094 |
| 1588 | V000FFF48 00147090 001470A0 000003E0 00000000 |
| 1589 | V000FFF58 00100080 00100084 00000000 001BF1D0 |
| 1590 | V000FFF68 00010400 800149BA 80014CA6 000FFF38 |
| 1591 | |
| 1592 | This displays a 2nd return address of 80014CA6 |
| 1593 | |
| 1594 | now do d 000FFFA0.40 for our 3rd backchain |
| 1595 | |
| 1596 | V000FFFA0 04B52002 0001107F 00000000 00000000 |
| 1597 | V000FFFB0 00000000 00000000 FF000000 0001107F |
| 1598 | V000FFFC0 00000000 00000000 00000000 00000000 |
| 1599 | V000FFFD0 00010400 80010802 8001085A 000FFFA0 |
| 1600 | |
| 1601 | |
| 1602 | our 3rd return address is 8001085A |
| 1603 | |
| 1604 | as the 04B52002 looks suspiciously like rubbish it is fair to assume that the kernel entry routines |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1605 | for the sake of optimisation don't set up a backchain. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1606 | |
| 1607 | now look at System.map to see if the addresses make any sense. |
| 1608 | |
| 1609 | grep -i 0001b3 System.map |
| 1610 | outputs among other things |
| 1611 | 0001b304 T cpu_idle |
| 1612 | so 8001B36A |
| 1613 | is cpu_idle+0x66 ( quiet the cpu is asleep, don't wake it ) |
| 1614 | |
| 1615 | |
| 1616 | grep -i 00014 System.map |
| 1617 | produces among other things |
| 1618 | 00014a78 T start_kernel |
| 1619 | so 0014CA6 is start_kernel+some hex number I can't add in my head. |
| 1620 | |
| 1621 | grep -i 00108 System.map |
| 1622 | this produces |
| 1623 | 00010800 T _stext |
| 1624 | so 8001085A is _stext+0x5a |
| 1625 | |
| 1626 | Congrats you've done your first backchain. |
| 1627 | |
| 1628 | |
| 1629 | |
| 1630 | s/390 & z/Architecture IO Overview |
| 1631 | ================================== |
| 1632 | |
| 1633 | I am not going to give a course in 390 IO architecture as this would take me quite a |
| 1634 | while & I'm no expert. Instead I'll give a 390 IO architecture summary for Dummies if you have |
| 1635 | the s/390 principles of operation available read this instead. If nothing else you may find a few |
| 1636 | useful keywords in here & be able to use them on a web search engine like altavista to find |
| 1637 | more useful information. |
| 1638 | |
| 1639 | Unlike other bus architectures modern 390 systems do their IO using mostly |
| 1640 | fibre optics & devices such as tapes & disks can be shared between several mainframes, |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1641 | also S390 can support up to 65536 devices while a high end PC based system might be choking |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1642 | with around 64. Here is some of the common IO terminology |
| 1643 | |
| 1644 | Subchannel: |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1645 | This is the logical number most IO commands use to talk to an IO device there can be up to |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1646 | 0x10000 (65536) of these in a configuration typically there is a few hundred. Under VM |
| 1647 | for simplicity they are allocated contiguously, however on the native hardware they are not |
| 1648 | they typically stay consistent between boots provided no new hardware is inserted or removed. |
| 1649 | Under Linux for 390 we use these as IRQ's & also when issuing an IO command (CLEAR SUBCHANNEL, |
| 1650 | HALT SUBCHANNEL,MODIFY SUBCHANNEL,RESUME SUBCHANNEL,START SUBCHANNEL,STORE SUBCHANNEL & |
| 1651 | TEST SUBCHANNEL ) we use this as the ID of the device we wish to talk to, the most |
| 1652 | important of these instructions are START SUBCHANNEL ( to start IO ), TEST SUBCHANNEL ( to check |
| 1653 | whether the IO completed successfully ), & HALT SUBCHANNEL ( to kill IO ), a subchannel |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1654 | can have up to 8 channel paths to a device this offers redundancy if one is not available. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1655 | |
| 1656 | |
| 1657 | Device Number: |
| 1658 | This number remains static & Is closely tied to the hardware, there are 65536 of these |
| 1659 | also they are made up of a CHPID ( Channel Path ID, the most significant 8 bits ) |
| 1660 | & another lsb 8 bits. These remain static even if more devices are inserted or removed |
| 1661 | from the hardware, there is a 1 to 1 mapping between Subchannels & Device Numbers provided |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1662 | devices aren't inserted or removed. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1663 | |
| 1664 | Channel Control Words: |
| 1665 | CCWS are linked lists of instructions initially pointed to by an operation request block (ORB), |
| 1666 | which is initially given to Start Subchannel (SSCH) command along with the subchannel number |
| 1667 | for the IO subsystem to process while the CPU continues executing normal code. |
| 1668 | These come in two flavours, Format 0 ( 24 bit for backward ) |
| 1669 | compatibility & Format 1 ( 31 bit ). These are typically used to issue read & write |
| 1670 | ( & many other instructions ) they consist of a length field & an absolute address field. |
| 1671 | For each IO typically get 1 or 2 interrupts one for channel end ( primary status ) when the |
| 1672 | channel is idle & the second for device end ( secondary status ) sometimes you get both |
| 1673 | concurrently, you check how the IO went on by issuing a TEST SUBCHANNEL at each interrupt, |
| 1674 | from which you receive an Interruption response block (IRB). If you get channel & device end |
| 1675 | status in the IRB without channel checks etc. your IO probably went okay. If you didn't you |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 1676 | probably need a doctor to examine the IRB & extended status word etc. |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1677 | If an error occurs, more sophisticated control units have a facility known as |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1678 | concurrent sense this means that if an error occurs Extended sense information will |
| 1679 | be presented in the Extended status word in the IRB if not you have to issue a |
| 1680 | subsequent SENSE CCW command after the test subchannel. |
| 1681 | |
| 1682 | |
| 1683 | TPI( Test pending interrupt) can also be used for polled IO but in multitasking multiprocessor |
| 1684 | systems it isn't recommended except for checking special cases ( i.e. non looping checks for |
| 1685 | pending IO etc. ). |
| 1686 | |
| 1687 | Store Subchannel & Modify Subchannel can be used to examine & modify operating characteristics |
| 1688 | of a subchannel ( e.g. channel paths ). |
| 1689 | |
| 1690 | Other IO related Terms: |
| 1691 | Sysplex: S390's Clustering Technology |
| 1692 | QDIO: S390's new high speed IO architecture to support devices such as gigabit ethernet, |
| 1693 | this architecture is also designed to be forward compatible with up & coming 64 bit machines. |
| 1694 | |
| 1695 | |
| 1696 | General Concepts |
| 1697 | |
| 1698 | Input Output Processors (IOP's) are responsible for communicating between |
| 1699 | the mainframe CPU's & the channel & relieve the mainframe CPU's from the |
| 1700 | burden of communicating with IO devices directly, this allows the CPU's to |
| 1701 | concentrate on data processing. |
| 1702 | |
| 1703 | IOP's can use one or more links ( known as channel paths ) to talk to each |
| 1704 | IO device. It first checks for path availability & chooses an available one, |
| 1705 | then starts ( & sometimes terminates IO ). |
Matt LaPlante | 992caac | 2006-10-03 22:52:05 +0200 | [diff] [blame] | 1706 | There are two types of channel path: ESCON & the Parallel IO interface. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1707 | |
| 1708 | IO devices are attached to control units, control units provide the |
| 1709 | logic to interface the channel paths & channel path IO protocols to |
| 1710 | the IO devices, they can be integrated with the devices or housed separately |
| 1711 | & often talk to several similar devices ( typical examples would be raid |
| 1712 | controllers or a control unit which connects to 1000 3270 terminals ). |
| 1713 | |
| 1714 | |
| 1715 | +---------------------------------------------------------------+ |
| 1716 | | +-----+ +-----+ +-----+ +-----+ +----------+ +----------+ | |
| 1717 | | | CPU | | CPU | | CPU | | CPU | | Main | | Expanded | | |
| 1718 | | | | | | | | | | | Memory | | Storage | | |
| 1719 | | +-----+ +-----+ +-----+ +-----+ +----------+ +----------+ | |
| 1720 | |---------------------------------------------------------------+ |
| 1721 | | IOP | IOP | IOP | |
| 1722 | |--------------------------------------------------------------- |
| 1723 | | C | C | C | C | C | C | C | C | C | C | C | C | C | C | C | C | |
| 1724 | ---------------------------------------------------------------- |
| 1725 | || || |
| 1726 | || Bus & Tag Channel Path || ESCON |
| 1727 | || ====================== || Channel |
| 1728 | || || || || Path |
| 1729 | +----------+ +----------+ +----------+ |
| 1730 | | | | | | | |
| 1731 | | CU | | CU | | CU | |
| 1732 | | | | | | | |
| 1733 | +----------+ +----------+ +----------+ |
| 1734 | | | | | | |
| 1735 | +----------+ +----------+ +----------+ +----------+ +----------+ |
| 1736 | |I/O Device| |I/O Device| |I/O Device| |I/O Device| |I/O Device| |
| 1737 | +----------+ +----------+ +----------+ +----------+ +----------+ |
| 1738 | CPU = Central Processing Unit |
| 1739 | C = Channel |
| 1740 | IOP = IP Processor |
| 1741 | CU = Control Unit |
| 1742 | |
| 1743 | The 390 IO systems come in 2 flavours the current 390 machines support both |
| 1744 | |
Matt LaPlante | 992caac | 2006-10-03 22:52:05 +0200 | [diff] [blame] | 1745 | The Older 360 & 370 Interface,sometimes called the Parallel I/O interface, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1746 | sometimes called Bus-and Tag & sometimes Original Equipment Manufacturers |
| 1747 | Interface (OEMI). |
| 1748 | |
Matt LaPlante | 992caac | 2006-10-03 22:52:05 +0200 | [diff] [blame] | 1749 | This byte wide Parallel channel path/bus has parity & data on the "Bus" cable |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1750 | & control lines on the "Tag" cable. These can operate in byte multiplex mode for |
| 1751 | sharing between several slow devices or burst mode & monopolize the channel for the |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1752 | whole burst. Up to 256 devices can be addressed on one of these cables. These cables are |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1753 | about one inch in diameter. The maximum unextended length supported by these cables is |
| 1754 | 125 Meters but this can be extended up to 2km with a fibre optic channel extended |
| 1755 | such as a 3044. The maximum burst speed supported is 4.5 megabytes per second however |
| 1756 | some really old processors support only transfer rates of 3.0, 2.0 & 1.0 MB/sec. |
| 1757 | One of these paths can be daisy chained to up to 8 control units. |
| 1758 | |
| 1759 | |
| 1760 | ESCON if fibre optic it is also called FICON |
| 1761 | Was introduced by IBM in 1990. Has 2 fibre optic cables & uses either leds or lasers |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1762 | for communication at a signaling rate of up to 200 megabits/sec. As 10bits are transferred |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1763 | for every 8 bits info this drops to 160 megabits/sec & to 18.6 Megabytes/sec once |
| 1764 | control info & CRC are added. ESCON only operates in burst mode. |
| 1765 | |
| 1766 | ESCONs typical max cable length is 3km for the led version & 20km for the laser version |
| 1767 | known as XDF ( extended distance facility ). This can be further extended by using an |
| 1768 | ESCON director which triples the above mentioned ranges. Unlike Bus & Tag as ESCON is |
| 1769 | serial it uses a packet switching architecture the standard Bus & Tag control protocol |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 1770 | is however present within the packets. Up to 256 devices can be attached to each control |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1771 | unit that uses one of these interfaces. |
| 1772 | |
| 1773 | Common 390 Devices include: |
| 1774 | Network adapters typically OSA2,3172's,2116's & OSA-E gigabit ethernet adapters, |
| 1775 | Consoles 3270 & 3215 ( a teletype emulated under linux for a line mode console ). |
| 1776 | DASD's direct access storage devices ( otherwise known as hard disks ). |
| 1777 | Tape Drives. |
| 1778 | CTC ( Channel to Channel Adapters ), |
Matt LaPlante | 992caac | 2006-10-03 22:52:05 +0200 | [diff] [blame] | 1779 | ESCON or Parallel Cables used as a very high speed serial link |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1780 | between 2 machines. We use 2 cables under linux to do a bi-directional serial link. |
| 1781 | |
| 1782 | |
| 1783 | Debugging IO on s/390 & z/Architecture under VM |
| 1784 | =============================================== |
| 1785 | |
| 1786 | Now we are ready to go on with IO tracing commands under VM |
| 1787 | |
| 1788 | A few self explanatory queries: |
| 1789 | Q OSA |
| 1790 | Q CTC |
| 1791 | Q DISK ( This command is CMS specific ) |
| 1792 | Q DASD |
| 1793 | |
| 1794 | |
| 1795 | |
| 1796 | |
| 1797 | |
| 1798 | |
| 1799 | Q OSA on my machine returns |
| 1800 | OSA 7C08 ON OSA 7C08 SUBCHANNEL = 0000 |
| 1801 | OSA 7C09 ON OSA 7C09 SUBCHANNEL = 0001 |
| 1802 | OSA 7C14 ON OSA 7C14 SUBCHANNEL = 0002 |
| 1803 | OSA 7C15 ON OSA 7C15 SUBCHANNEL = 0003 |
| 1804 | |
Matt LaPlante | 992caac | 2006-10-03 22:52:05 +0200 | [diff] [blame] | 1805 | If you have a guest with certain privileges you may be able to see devices |
| 1806 | which don't belong to you. To avoid this, add the option V. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1807 | e.g. |
| 1808 | Q V OSA |
| 1809 | |
| 1810 | Now using the device numbers returned by this command we will |
| 1811 | Trace the io starting up on the first device 7c08 & 7c09 |
| 1812 | In our simplest case we can trace the |
| 1813 | start subchannels |
| 1814 | like TR SSCH 7C08-7C09 |
| 1815 | or the halt subchannels |
| 1816 | or TR HSCH 7C08-7C09 |
| 1817 | MSCH's ,STSCH's I think you can guess the rest |
| 1818 | |
| 1819 | Ingo's favourite trick is tracing all the IO's & CCWS & spooling them into the reader of another |
| 1820 | VM guest so he can ftp the logfile back to his own machine.I'll do a small bit of this & give you |
| 1821 | a look at the output. |
| 1822 | |
| 1823 | 1) Spool stdout to VM reader |
| 1824 | SP PRT TO (another vm guest ) or * for the local vm guest |
| 1825 | 2) Fill the reader with the trace |
| 1826 | TR IO 7c08-7c09 INST INT CCW PRT RUN |
| 1827 | 3) Start up linux |
| 1828 | i 00c |
| 1829 | 4) Finish the trace |
| 1830 | TR END |
| 1831 | 5) close the reader |
| 1832 | C PRT |
| 1833 | 6) list reader contents |
| 1834 | RDRLIST |
| 1835 | 7) copy it to linux4's minidisk |
| 1836 | RECEIVE / LOG TXT A1 ( replace |
| 1837 | 8) |
| 1838 | filel & press F11 to look at it |
Matt LaPlante | 53cb472 | 2006-10-03 22:55:17 +0200 | [diff] [blame] | 1839 | You should see something like: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1840 | |
| 1841 | 00020942' SSCH B2334000 0048813C CC 0 SCH 0000 DEV 7C08 |
| 1842 | CPA 000FFDF0 PARM 00E2C9C4 KEY 0 FPI C0 LPM 80 |
| 1843 | CCW 000FFDF0 E4200100 00487FE8 0000 E4240100 ........ |
| 1844 | IDAL 43D8AFE8 |
| 1845 | IDAL 0FB76000 |
| 1846 | 00020B0A' I/O DEV 7C08 -> 000197BC' SCH 0000 PARM 00E2C9C4 |
| 1847 | 00021628' TSCH B2354000 >> 00488164 CC 0 SCH 0000 DEV 7C08 |
| 1848 | CCWA 000FFDF8 DEV STS 0C SCH STS 00 CNT 00EC |
| 1849 | KEY 0 FPI C0 CC 0 CTLS 4007 |
| 1850 | 00022238' STSCH B2344000 >> 00488108 CC 0 SCH 0000 DEV 7C08 |
| 1851 | |
| 1852 | If you don't like messing up your readed ( because you possibly booted from it ) |
| 1853 | you can alternatively spool it to another readers guest. |
| 1854 | |
| 1855 | |
| 1856 | Other common VM device related commands |
| 1857 | --------------------------------------------- |
| 1858 | These commands are listed only because they have |
| 1859 | been of use to me in the past & may be of use to |
| 1860 | you too. For more complete info on each of the commands |
| 1861 | use type HELP <command> from CMS. |
| 1862 | detaching devices |
| 1863 | DET <devno range> |
| 1864 | ATT <devno range> <guest> |
| 1865 | attach a device to guest * for your own guest |
| 1866 | READY <devno> cause VM to issue a fake interrupt. |
| 1867 | |
| 1868 | The VARY command is normally only available to VM administrators. |
| 1869 | VARY ON PATH <path> TO <devno range> |
| 1870 | VARY OFF PATH <PATH> FROM <devno range> |
| 1871 | This is used to switch on or off channel paths to devices. |
| 1872 | |
| 1873 | Q CHPID <channel path ID> |
| 1874 | This displays state of devices using this channel path |
| 1875 | D SCHIB <subchannel> |
| 1876 | This displays the subchannel information SCHIB block for the device. |
| 1877 | this I believe is also only available to administrators. |
| 1878 | DEFINE CTC <devno> |
| 1879 | defines a virtual CTC channel to channel connection |
| 1880 | 2 need to be defined on each guest for the CTC driver to use. |
| 1881 | COUPLE devno userid remote devno |
| 1882 | Joins a local virtual device to a remote virtual device |
| 1883 | ( commonly used for the CTC driver ). |
| 1884 | |
| 1885 | Building a VM ramdisk under CMS which linux can use |
| 1886 | def vfb-<blocksize> <subchannel> <number blocks> |
| 1887 | blocksize is commonly 4096 for linux. |
| 1888 | Formatting it |
| 1889 | format <subchannel> <driver letter e.g. x> (blksize <blocksize> |
| 1890 | |
| 1891 | Sharing a disk between multiple guests |
| 1892 | LINK userid devno1 devno2 mode password |
| 1893 | |
| 1894 | |
| 1895 | |
| 1896 | GDB on S390 |
| 1897 | =========== |
| 1898 | N.B. if compiling for debugging gdb works better without optimisation |
| 1899 | ( see Compiling programs for debugging ) |
| 1900 | |
| 1901 | invocation |
| 1902 | ---------- |
| 1903 | gdb <victim program> <optional corefile> |
| 1904 | |
| 1905 | Online help |
| 1906 | ----------- |
| 1907 | help: gives help on commands |
| 1908 | e.g. |
| 1909 | help |
| 1910 | help display |
| 1911 | Note gdb's online help is very good use it. |
| 1912 | |
| 1913 | |
| 1914 | Assembly |
| 1915 | -------- |
| 1916 | info registers: displays registers other than floating point. |
| 1917 | info all-registers: displays floating points as well. |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 1918 | disassemble: disassembles |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1919 | e.g. |
| 1920 | disassemble without parameters will disassemble the current function |
| 1921 | disassemble $pc $pc+10 |
| 1922 | |
| 1923 | Viewing & modifying variables |
| 1924 | ----------------------------- |
| 1925 | print or p: displays variable or register |
| 1926 | e.g. p/x $sp will display the stack pointer |
| 1927 | |
| 1928 | display: prints variable or register each time program stops |
| 1929 | e.g. |
| 1930 | display/x $pc will display the program counter |
| 1931 | display argc |
| 1932 | |
| 1933 | undisplay : undo's display's |
| 1934 | |
| 1935 | info breakpoints: shows all current breakpoints |
| 1936 | |
Matt LaPlante | fff9289 | 2006-10-03 22:47:42 +0200 | [diff] [blame] | 1937 | info stack: shows stack back trace ( if this doesn't work too well, I'll show you the |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1938 | stacktrace by hand below ). |
| 1939 | |
| 1940 | info locals: displays local variables. |
| 1941 | |
| 1942 | info args: display current procedure arguments. |
| 1943 | |
| 1944 | set args: will set argc & argv each time the victim program is invoked. |
| 1945 | |
| 1946 | set <variable>=value |
| 1947 | set argc=100 |
| 1948 | set $pc=0 |
| 1949 | |
| 1950 | |
| 1951 | |
| 1952 | Modifying execution |
| 1953 | ------------------- |
| 1954 | step: steps n lines of sourcecode |
| 1955 | step steps 1 line. |
| 1956 | step 100 steps 100 lines of code. |
| 1957 | |
| 1958 | next: like step except this will not step into subroutines |
| 1959 | |
| 1960 | stepi: steps a single machine code instruction. |
| 1961 | e.g. stepi 100 |
| 1962 | |
| 1963 | nexti: steps a single machine code instruction but will not step into subroutines. |
| 1964 | |
| 1965 | finish: will run until exit of the current routine |
| 1966 | |
| 1967 | run: (re)starts a program |
| 1968 | |
| 1969 | cont: continues a program |
| 1970 | |
| 1971 | quit: exits gdb. |
| 1972 | |
| 1973 | |
| 1974 | breakpoints |
| 1975 | ------------ |
| 1976 | |
| 1977 | break |
| 1978 | sets a breakpoint |
| 1979 | e.g. |
| 1980 | |
| 1981 | break main |
| 1982 | |
| 1983 | break *$pc |
| 1984 | |
| 1985 | break *0x400618 |
| 1986 | |
Matt LaPlante | 19f5946 | 2009-04-27 15:06:31 +0200 | [diff] [blame] | 1987 | Here's a really useful one for large programs |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1988 | rbr |
| 1989 | Set a breakpoint for all functions matching REGEXP |
| 1990 | e.g. |
| 1991 | rbr 390 |
| 1992 | will set a breakpoint with all functions with 390 in their name. |
| 1993 | |
| 1994 | info breakpoints |
| 1995 | lists all breakpoints |
| 1996 | |
| 1997 | delete: delete breakpoint by number or delete them all |
| 1998 | e.g. |
| 1999 | delete 1 will delete the first breakpoint |
| 2000 | delete will delete them all |
| 2001 | |
| 2002 | watch: This will set a watchpoint ( usually hardware assisted ), |
| 2003 | This will watch a variable till it changes |
| 2004 | e.g. |
| 2005 | watch cnt, will watch the variable cnt till it changes. |
| 2006 | As an aside unfortunately gdb's, architecture independent watchpoint code |
| 2007 | is inconsistent & not very good, watchpoints usually work but not always. |
| 2008 | |
| 2009 | info watchpoints: Display currently active watchpoints |
| 2010 | |
| 2011 | condition: ( another useful one ) |
| 2012 | Specify breakpoint number N to break only if COND is true. |
| 2013 | Usage is `condition N COND', where N is an integer and COND is an |
| 2014 | expression to be evaluated whenever breakpoint N is reached. |
| 2015 | |
| 2016 | |
| 2017 | |
| 2018 | User defined functions/macros |
| 2019 | ----------------------------- |
| 2020 | define: ( Note this is very very useful,simple & powerful ) |
| 2021 | usage define <name> <list of commands> end |
| 2022 | |
| 2023 | examples which you should consider putting into .gdbinit in your home directory |
| 2024 | define d |
| 2025 | stepi |
| 2026 | disassemble $pc $pc+10 |
| 2027 | end |
| 2028 | |
| 2029 | define e |
| 2030 | nexti |
| 2031 | disassemble $pc $pc+10 |
| 2032 | end |
| 2033 | |
| 2034 | |
| 2035 | Other hard to classify stuff |
| 2036 | ---------------------------- |
| 2037 | signal n: |
| 2038 | sends the victim program a signal. |
| 2039 | e.g. signal 3 will send a SIGQUIT. |
| 2040 | |
| 2041 | info signals: |
| 2042 | what gdb does when the victim receives certain signals. |
| 2043 | |
| 2044 | list: |
| 2045 | e.g. |
| 2046 | list lists current function source |
Matt LaPlante | 6c28f2c | 2006-10-03 22:46:31 +0200 | [diff] [blame] | 2047 | list 1,10 list first 10 lines of current file. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2048 | list test.c:1,10 |
| 2049 | |
| 2050 | |
| 2051 | directory: |
| 2052 | Adds directories to be searched for source if gdb cannot find the source. |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 2053 | (note it is a bit sensitive about slashes) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2054 | e.g. To add the root of the filesystem to the searchpath do |
| 2055 | directory // |
| 2056 | |
| 2057 | |
| 2058 | call <function> |
| 2059 | This calls a function in the victim program, this is pretty powerful |
| 2060 | e.g. |
| 2061 | (gdb) call printf("hello world") |
| 2062 | outputs: |
| 2063 | $1 = 11 |
| 2064 | |
| 2065 | You might now be thinking that the line above didn't work, something extra had to be done. |
| 2066 | (gdb) call fflush(stdout) |
| 2067 | hello world$2 = 0 |
| 2068 | As an aside the debugger also calls malloc & free under the hood |
| 2069 | to make space for the "hello world" string. |
| 2070 | |
| 2071 | |
| 2072 | |
| 2073 | hints |
| 2074 | ----- |
| 2075 | 1) command completion works just like bash |
| 2076 | ( if you are a bad typist like me this really helps ) |
| 2077 | e.g. hit br <TAB> & cursor up & down :-). |
| 2078 | |
| 2079 | 2) if you have a debugging problem that takes a few steps to recreate |
| 2080 | put the steps into a file called .gdbinit in your current working directory |
| 2081 | if you have defined a few extra useful user defined commands put these in |
| 2082 | your home directory & they will be read each time gdb is launched. |
| 2083 | |
| 2084 | A typical .gdbinit file might be. |
| 2085 | break main |
| 2086 | run |
| 2087 | break runtime_exception |
| 2088 | cont |
| 2089 | |
| 2090 | |
| 2091 | stack chaining in gdb by hand |
| 2092 | ----------------------------- |
| 2093 | This is done using a the same trick described for VM |
| 2094 | p/x (*($sp+56))&0x7fffffff get the first backchain. |
| 2095 | |
| 2096 | For z/Architecture |
| 2097 | Replace 56 with 112 & ignore the &0x7fffffff |
| 2098 | in the macros below & do nasty casts to longs like the following |
| 2099 | as gdb unfortunately deals with printed arguments as ints which |
| 2100 | messes up everything. |
| 2101 | i.e. here is a 3rd backchain dereference |
| 2102 | p/x *(long *)(***(long ***)$sp+112) |
| 2103 | |
| 2104 | |
| 2105 | this outputs |
| 2106 | $5 = 0x528f18 |
| 2107 | on my machine. |
| 2108 | Now you can use |
| 2109 | info symbol (*($sp+56))&0x7fffffff |
| 2110 | you might see something like. |
| 2111 | rl_getc + 36 in section .text telling you what is located at address 0x528f18 |
| 2112 | Now do. |
| 2113 | p/x (*(*$sp+56))&0x7fffffff |
| 2114 | This outputs |
| 2115 | $6 = 0x528ed0 |
| 2116 | Now do. |
| 2117 | info symbol (*(*$sp+56))&0x7fffffff |
| 2118 | rl_read_key + 180 in section .text |
| 2119 | now do |
| 2120 | p/x (*(**$sp+56))&0x7fffffff |
| 2121 | & so on. |
| 2122 | |
| 2123 | Disassembling instructions without debug info |
| 2124 | --------------------------------------------- |
Matt LaPlante | 6c28f2c | 2006-10-03 22:46:31 +0200 | [diff] [blame] | 2125 | gdb typically complains if there is a lack of debugging |
| 2126 | symbols in the disassemble command with |
| 2127 | "No function contains specified address." To get around |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2128 | this do |
| 2129 | x/<number lines to disassemble>xi <address> |
| 2130 | e.g. |
| 2131 | x/20xi 0x400730 |
| 2132 | |
| 2133 | |
| 2134 | |
| 2135 | Note: Remember gdb has history just like bash you don't need to retype the |
| 2136 | whole line just use the up & down arrows. |
| 2137 | |
| 2138 | |
| 2139 | |
| 2140 | For more info |
| 2141 | ------------- |
| 2142 | From your linuxbox do |
| 2143 | man gdb or info gdb. |
| 2144 | |
| 2145 | core dumps |
| 2146 | ---------- |
| 2147 | What a core dump ?, |
| 2148 | A core dump is a file generated by the kernel ( if allowed ) which contains the registers, |
| 2149 | & all active pages of the program which has crashed. |
| 2150 | From this file gdb will allow you to look at the registers & stack trace & memory of the |
| 2151 | program as if it just crashed on your system, it is usually called core & created in the |
| 2152 | current working directory. |
| 2153 | This is very useful in that a customer can mail a core dump to a technical support department |
| 2154 | & the technical support department can reconstruct what happened. |
Nicolas Kaiser | 2254f5a | 2006-12-04 15:40:23 +0100 | [diff] [blame] | 2155 | Provided they have an identical copy of this program with debugging symbols compiled in & |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2156 | the source base of this build is available. |
| 2157 | In short it is far more useful than something like a crash log could ever hope to be. |
| 2158 | |
| 2159 | In theory all that is missing to restart a core dumped program is a kernel patch which |
| 2160 | will do the following. |
| 2161 | 1) Make a new kernel task structure |
| 2162 | 2) Reload all the dumped pages back into the kernel's memory management structures. |
| 2163 | 3) Do the required clock fixups |
| 2164 | 4) Get all files & network connections for the process back into an identical state ( really difficult ). |
| 2165 | 5) A few more difficult things I haven't thought of. |
| 2166 | |
| 2167 | |
| 2168 | |
| 2169 | Why have I never seen one ?. |
| 2170 | Probably because you haven't used the command |
| 2171 | ulimit -c unlimited in bash |
| 2172 | to allow core dumps, now do |
| 2173 | ulimit -a |
| 2174 | to verify that the limit was accepted. |
| 2175 | |
| 2176 | A sample core dump |
| 2177 | To create this I'm going to do |
| 2178 | ulimit -c unlimited |
| 2179 | gdb |
| 2180 | to launch gdb (my victim app. ) now be bad & do the following from another |
| 2181 | telnet/xterm session to the same machine |
| 2182 | ps -aux | grep gdb |
| 2183 | kill -SIGSEGV <gdb's pid> |
| 2184 | or alternatively use killall -SIGSEGV gdb if you have the killall command. |
| 2185 | Now look at the core dump. |
Paolo Ornati | 670e9f3 | 2006-10-03 22:57:56 +0200 | [diff] [blame] | 2186 | ./gdb core |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2187 | Displays the following |
| 2188 | GNU gdb 4.18 |
| 2189 | Copyright 1998 Free Software Foundation, Inc. |
| 2190 | GDB is free software, covered by the GNU General Public License, and you are |
| 2191 | welcome to change it and/or distribute copies of it under certain conditions. |
| 2192 | Type "show copying" to see the conditions. |
| 2193 | There is absolutely no warranty for GDB. Type "show warranty" for details. |
| 2194 | This GDB was configured as "s390-ibm-linux"... |
| 2195 | Core was generated by `./gdb'. |
| 2196 | Program terminated with signal 11, Segmentation fault. |
| 2197 | Reading symbols from /usr/lib/libncurses.so.4...done. |
| 2198 | Reading symbols from /lib/libm.so.6...done. |
| 2199 | Reading symbols from /lib/libc.so.6...done. |
| 2200 | Reading symbols from /lib/ld-linux.so.2...done. |
| 2201 | #0 0x40126d1a in read () from /lib/libc.so.6 |
| 2202 | Setting up the environment for debugging gdb. |
| 2203 | Breakpoint 1 at 0x4dc6f8: file utils.c, line 471. |
| 2204 | Breakpoint 2 at 0x4d87a4: file top.c, line 2609. |
| 2205 | (top-gdb) info stack |
| 2206 | #0 0x40126d1a in read () from /lib/libc.so.6 |
| 2207 | #1 0x528f26 in rl_getc (stream=0x7ffffde8) at input.c:402 |
| 2208 | #2 0x528ed0 in rl_read_key () at input.c:381 |
| 2209 | #3 0x5167e6 in readline_internal_char () at readline.c:454 |
| 2210 | #4 0x5168ee in readline_internal_charloop () at readline.c:507 |
| 2211 | #5 0x51692c in readline_internal () at readline.c:521 |
John Anthony Kazos Jr | be2a608 | 2007-05-09 08:50:42 +0200 | [diff] [blame] | 2212 | #6 0x5164fe in readline (prompt=0x7ffff810 "\177ÿøx\177ÿ÷Ø\177ÿøxÀ") |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2213 | at readline.c:349 |
Matt LaPlante | 19f5946 | 2009-04-27 15:06:31 +0200 | [diff] [blame] | 2214 | #7 0x4d7a8a in command_line_input (prompt=0x564420 "(gdb) ", repeat=1, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2215 | annotation_suffix=0x4d6b44 "prompt") at top.c:2091 |
| 2216 | #8 0x4d6cf0 in command_loop () at top.c:1345 |
| 2217 | #9 0x4e25bc in main (argc=1, argv=0x7ffffdf4) at main.c:635 |
| 2218 | |
| 2219 | |
| 2220 | LDD |
| 2221 | === |
| 2222 | This is a program which lists the shared libraries which a library needs, |
| 2223 | Note you also get the relocations of the shared library text segments which |
| 2224 | help when using objdump --source. |
| 2225 | e.g. |
| 2226 | ldd ./gdb |
| 2227 | outputs |
| 2228 | libncurses.so.4 => /usr/lib/libncurses.so.4 (0x40018000) |
| 2229 | libm.so.6 => /lib/libm.so.6 (0x4005e000) |
| 2230 | libc.so.6 => /lib/libc.so.6 (0x40084000) |
| 2231 | /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000) |
| 2232 | |
| 2233 | |
| 2234 | Debugging shared libraries |
| 2235 | ========================== |
| 2236 | Most programs use shared libraries, however it can be very painful |
| 2237 | when you single step instruction into a function like printf for the |
| 2238 | first time & you end up in functions like _dl_runtime_resolve this is |
| 2239 | the ld.so doing lazy binding, lazy binding is a concept in ELF where |
| 2240 | shared library functions are not loaded into memory unless they are |
| 2241 | actually used, great for saving memory but a pain to debug. |
| 2242 | To get around this either relink the program -static or exit gdb type |
| 2243 | export LD_BIND_NOW=true this will stop lazy binding & restart the gdb'ing |
| 2244 | the program in question. |
| 2245 | |
| 2246 | |
| 2247 | |
| 2248 | Debugging modules |
| 2249 | ================= |
| 2250 | As modules are dynamically loaded into the kernel their address can be |
| 2251 | anywhere to get around this use the -m option with insmod to emit a load |
| 2252 | map which can be piped into a file if required. |
| 2253 | |
| 2254 | The proc file system |
| 2255 | ==================== |
| 2256 | What is it ?. |
| 2257 | It is a filesystem created by the kernel with files which are created on demand |
| 2258 | by the kernel if read, or can be used to modify kernel parameters, |
| 2259 | it is a powerful concept. |
| 2260 | |
| 2261 | e.g. |
| 2262 | |
| 2263 | cat /proc/sys/net/ipv4/ip_forward |
| 2264 | On my machine outputs |
| 2265 | 0 |
| 2266 | telling me ip_forwarding is not on to switch it on I can do |
| 2267 | echo 1 > /proc/sys/net/ipv4/ip_forward |
| 2268 | cat it again |
| 2269 | cat /proc/sys/net/ipv4/ip_forward |
| 2270 | On my machine now outputs |
| 2271 | 1 |
| 2272 | IP forwarding is on. |
| 2273 | There is a lot of useful info in here best found by going in & having a look around, |
| 2274 | so I'll take you through some entries I consider important. |
| 2275 | |
| 2276 | All the processes running on the machine have there own entry defined by |
| 2277 | /proc/<pid> |
| 2278 | So lets have a look at the init process |
| 2279 | cd /proc/1 |
| 2280 | |
| 2281 | cat cmdline |
| 2282 | emits |
| 2283 | init [2] |
| 2284 | |
| 2285 | cd /proc/1/fd |
| 2286 | This contains numerical entries of all the open files, |
| 2287 | some of these you can cat e.g. stdout (2) |
| 2288 | |
| 2289 | cat /proc/29/maps |
| 2290 | on my machine emits |
| 2291 | |
| 2292 | 00400000-00478000 r-xp 00000000 5f:00 4103 /bin/bash |
| 2293 | 00478000-0047e000 rw-p 00077000 5f:00 4103 /bin/bash |
| 2294 | 0047e000-00492000 rwxp 00000000 00:00 0 |
| 2295 | 40000000-40015000 r-xp 00000000 5f:00 14382 /lib/ld-2.1.2.so |
| 2296 | 40015000-40016000 rw-p 00014000 5f:00 14382 /lib/ld-2.1.2.so |
| 2297 | 40016000-40017000 rwxp 00000000 00:00 0 |
| 2298 | 40017000-40018000 rw-p 00000000 00:00 0 |
| 2299 | 40018000-4001b000 r-xp 00000000 5f:00 14435 /lib/libtermcap.so.2.0.8 |
| 2300 | 4001b000-4001c000 rw-p 00002000 5f:00 14435 /lib/libtermcap.so.2.0.8 |
| 2301 | 4001c000-4010d000 r-xp 00000000 5f:00 14387 /lib/libc-2.1.2.so |
| 2302 | 4010d000-40111000 rw-p 000f0000 5f:00 14387 /lib/libc-2.1.2.so |
| 2303 | 40111000-40114000 rw-p 00000000 00:00 0 |
| 2304 | 40114000-4011e000 r-xp 00000000 5f:00 14408 /lib/libnss_files-2.1.2.so |
| 2305 | 4011e000-4011f000 rw-p 00009000 5f:00 14408 /lib/libnss_files-2.1.2.so |
| 2306 | 7fffd000-80000000 rwxp ffffe000 00:00 0 |
| 2307 | |
| 2308 | |
| 2309 | Showing us the shared libraries init uses where they are in memory |
| 2310 | & memory access permissions for each virtual memory area. |
| 2311 | |
| 2312 | /proc/1/cwd is a softlink to the current working directory. |
| 2313 | /proc/1/root is the root of the filesystem for this process. |
| 2314 | |
| 2315 | /proc/1/mem is the current running processes memory which you |
| 2316 | can read & write to like a file. |
| 2317 | strace uses this sometimes as it is a bit faster than the |
Matt LaPlante | 2fe0ae7 | 2006-10-03 22:50:39 +0200 | [diff] [blame] | 2318 | rather inefficient ptrace interface for peeking at DATA. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2319 | |
| 2320 | |
| 2321 | cat status |
| 2322 | |
| 2323 | Name: init |
| 2324 | State: S (sleeping) |
| 2325 | Pid: 1 |
| 2326 | PPid: 0 |
| 2327 | Uid: 0 0 0 0 |
| 2328 | Gid: 0 0 0 0 |
| 2329 | Groups: |
| 2330 | VmSize: 408 kB |
| 2331 | VmLck: 0 kB |
| 2332 | VmRSS: 208 kB |
| 2333 | VmData: 24 kB |
| 2334 | VmStk: 8 kB |
| 2335 | VmExe: 368 kB |
| 2336 | VmLib: 0 kB |
| 2337 | SigPnd: 0000000000000000 |
| 2338 | SigBlk: 0000000000000000 |
| 2339 | SigIgn: 7fffffffd7f0d8fc |
| 2340 | SigCgt: 00000000280b2603 |
| 2341 | CapInh: 00000000fffffeff |
| 2342 | CapPrm: 00000000ffffffff |
| 2343 | CapEff: 00000000fffffeff |
| 2344 | |
| 2345 | User PSW: 070de000 80414146 |
| 2346 | task: 004b6000 tss: 004b62d8 ksp: 004b7ca8 pt_regs: 004b7f68 |
| 2347 | User GPRS: |
| 2348 | 00000400 00000000 0000000b 7ffffa90 |
| 2349 | 00000000 00000000 00000000 0045d9f4 |
| 2350 | 0045cafc 7ffffa90 7fffff18 0045cb08 |
| 2351 | 00010400 804039e8 80403af8 7ffff8b0 |
| 2352 | User ACRS: |
| 2353 | 00000000 00000000 00000000 00000000 |
| 2354 | 00000001 00000000 00000000 00000000 |
| 2355 | 00000000 00000000 00000000 00000000 |
| 2356 | 00000000 00000000 00000000 00000000 |
| 2357 | Kernel BackChain CallChain BackChain CallChain |
| 2358 | 004b7ca8 8002bd0c 004b7d18 8002b92c |
| 2359 | 004b7db8 8005cd50 004b7e38 8005d12a |
| 2360 | 004b7f08 80019114 |
| 2361 | Showing among other things memory usage & status of some signals & |
| 2362 | the processes'es registers from the kernel task_structure |
| 2363 | as well as a backchain which may be useful if a process crashes |
| 2364 | in the kernel for some unknown reason. |
| 2365 | |
| 2366 | Some driver debugging techniques |
| 2367 | ================================ |
| 2368 | debug feature |
| 2369 | ------------- |
| 2370 | Some of our drivers now support a "debug feature" in |
| 2371 | /proc/s390dbf see s390dbf.txt in the linux/Documentation directory |
| 2372 | for more info. |
| 2373 | e.g. |
| 2374 | to switch on the lcs "debug feature" |
| 2375 | echo 5 > /proc/s390dbf/lcs/level |
| 2376 | & then after the error occurred. |
| 2377 | cat /proc/s390dbf/lcs/sprintf >/logfile |
| 2378 | the logfile now contains some information which may help |
| 2379 | tech support resolve a problem in the field. |
| 2380 | |
| 2381 | |
| 2382 | |
| 2383 | high level debugging network drivers |
| 2384 | ------------------------------------ |
| 2385 | ifconfig is a quite useful command |
| 2386 | it gives the current state of network drivers. |
| 2387 | |
| 2388 | If you suspect your network device driver is dead |
| 2389 | one way to check is type |
| 2390 | ifconfig <network device> |
| 2391 | e.g. tr0 |
| 2392 | You should see something like |
| 2393 | tr0 Link encap:16/4 Mbps Token Ring (New) HWaddr 00:04:AC:20:8E:48 |
| 2394 | inet addr:9.164.185.132 Bcast:9.164.191.255 Mask:255.255.224.0 |
| 2395 | UP BROADCAST RUNNING MULTICAST MTU:2000 Metric:1 |
| 2396 | RX packets:246134 errors:0 dropped:0 overruns:0 frame:0 |
| 2397 | TX packets:5 errors:0 dropped:0 overruns:0 carrier:0 |
| 2398 | collisions:0 txqueuelen:100 |
| 2399 | |
| 2400 | if the device doesn't say up |
| 2401 | try |
| 2402 | /etc/rc.d/init.d/network start |
| 2403 | ( this starts the network stack & hopefully calls ifconfig tr0 up ). |
| 2404 | ifconfig looks at the output of /proc/net/dev & presents it in a more presentable form |
| 2405 | Now ping the device from a machine in the same subnet. |
| 2406 | if the RX packets count & TX packets counts don't increment you probably |
| 2407 | have problems. |
| 2408 | next |
| 2409 | cat /proc/net/arp |
| 2410 | Do you see any hardware addresses in the cache if not you may have problems. |
| 2411 | Next try |
| 2412 | ping -c 5 <broadcast_addr> i.e. the Bcast field above in the output of |
| 2413 | ifconfig. Do you see any replies from machines other than the local machine |
| 2414 | if not you may have problems. also if the TX packets count in ifconfig |
| 2415 | hasn't incremented either you have serious problems in your driver |
| 2416 | (e.g. the txbusy field of the network device being stuck on ) |
| 2417 | or you may have multiple network devices connected. |
| 2418 | |
| 2419 | |
| 2420 | chandev |
| 2421 | ------- |
| 2422 | There is a new device layer for channel devices, some |
| 2423 | drivers e.g. lcs are registered with this layer. |
| 2424 | If the device uses the channel device layer you'll be |
| 2425 | able to find what interrupts it uses & the current state |
| 2426 | of the device. |
| 2427 | See the manpage chandev.8 &type cat /proc/chandev for more info. |
| 2428 | |
| 2429 | |
| 2430 | |
| 2431 | Starting points for debugging scripting languages etc. |
| 2432 | ====================================================== |
| 2433 | |
| 2434 | bash/sh |
| 2435 | |
| 2436 | bash -x <scriptname> |
| 2437 | e.g. bash -x /usr/bin/bashbug |
| 2438 | displays the following lines as it executes them. |
| 2439 | + MACHINE=i586 |
| 2440 | + OS=linux-gnu |
| 2441 | + CC=gcc |
| 2442 | + CFLAGS= -DPROGRAM='bash' -DHOSTTYPE='i586' -DOSTYPE='linux-gnu' -DMACHTYPE='i586-pc-linux-gnu' -DSHELL -DHAVE_CONFIG_H -I. -I. -I./lib -O2 -pipe |
| 2443 | + RELEASE=2.01 |
| 2444 | + PATCHLEVEL=1 |
| 2445 | + RELSTATUS=release |
| 2446 | + MACHTYPE=i586-pc-linux-gnu |
| 2447 | |
Matt LaPlante | 2fe0ae7 | 2006-10-03 22:50:39 +0200 | [diff] [blame] | 2448 | perl -d <scriptname> runs the perlscript in a fully interactive debugger |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2449 | <like gdb>. |
| 2450 | Type 'h' in the debugger for help. |
| 2451 | |
| 2452 | for debugging java type |
| 2453 | jdb <filename> another fully interactive gdb style debugger. |
| 2454 | & type ? in the debugger for help. |
| 2455 | |
| 2456 | |
| 2457 | |
| 2458 | Dumptool & Lcrash ( lkcd ) |
| 2459 | ========================== |
| 2460 | Michael Holzheu & others here at IBM have a fairly mature port of |
| 2461 | SGI's lcrash tool which allows one to look at kernel structures in a |
| 2462 | running kernel. |
| 2463 | |
| 2464 | It also complements a tool called dumptool which dumps all the kernel's |
| 2465 | memory pages & registers to either a tape or a disk. |
| 2466 | This can be used by tech support or an ambitious end user do |
| 2467 | post mortem debugging of a machine like gdb core dumps. |
| 2468 | |
| 2469 | Going into how to use this tool in detail will be explained |
| 2470 | in other documentation supplied by IBM with the patches & the |
| 2471 | lcrash homepage http://oss.sgi.com/projects/lkcd/ & the lcrash manpage. |
| 2472 | |
| 2473 | How they work |
| 2474 | ------------- |
| 2475 | Lcrash is a perfectly normal program,however, it requires 2 |
| 2476 | additional files, Kerntypes which is built using a patch to the |
| 2477 | linux kernel sources in the linux root directory & the System.map. |
| 2478 | |
Paolo Ornati | 670e9f3 | 2006-10-03 22:57:56 +0200 | [diff] [blame] | 2479 | Kerntypes is an objectfile whose sole purpose in life |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2480 | is to provide stabs debug info to lcrash, to do this |
| 2481 | Kerntypes is built from kerntypes.c which just includes the most commonly |
| 2482 | referenced header files used when debugging, lcrash can then read the |
| 2483 | .stabs section of this file. |
| 2484 | |
| 2485 | Debugging a live system it uses /dev/mem |
| 2486 | alternatively for post mortem debugging it uses the data |
| 2487 | collected by dumptool. |
| 2488 | |
| 2489 | |
| 2490 | |
| 2491 | SysRq |
| 2492 | ===== |
| 2493 | This is now supported by linux for s/390 & z/Architecture. |
| 2494 | To enable it do compile the kernel with |
| 2495 | Kernel Hacking -> Magic SysRq Key Enabled |
| 2496 | echo "1" > /proc/sys/kernel/sysrq |
| 2497 | also type |
| 2498 | echo "8" >/proc/sys/kernel/printk |
| 2499 | To make printk output go to console. |
| 2500 | On 390 all commands are prefixed with |
| 2501 | ^- |
| 2502 | e.g. |
| 2503 | ^-t will show tasks. |
| 2504 | ^-? or some unknown command will display help. |
| 2505 | The sysrq key reading is very picky ( I have to type the keys in an |
| 2506 | xterm session & paste them into the x3270 console ) |
| 2507 | & it may be wise to predefine the keys as described in the VM hints above |
| 2508 | |
| 2509 | This is particularly useful for syncing disks unmounting & rebooting |
| 2510 | if the machine gets partially hung. |
| 2511 | |
| 2512 | Read Documentation/sysrq.txt for more info |
| 2513 | |
| 2514 | References: |
| 2515 | =========== |
| 2516 | Enterprise Systems Architecture Reference Summary |
| 2517 | Enterprise Systems Architecture Principles of Operation |
| 2518 | Hartmut Penners s390 stack frame sheet. |
| 2519 | IBM Mainframe Channel Attachment a technology brief from a CISCO webpage |
| 2520 | Various bits of man & info pages of Linux. |
| 2521 | Linux & GDB source. |
| 2522 | Various info & man pages. |
| 2523 | CMS Help on tracing commands. |
| 2524 | Linux for s/390 Elf Application Binary Interface |
| 2525 | Linux for z/Series Elf Application Binary Interface ( Both Highly Recommended ) |
| 2526 | z/Architecture Principles of Operation SA22-7832-00 |
| 2527 | Enterprise Systems Architecture/390 Reference Summary SA22-7209-01 & the |
| 2528 | Enterprise Systems Architecture/390 Principles of Operation SA22-7201-05 |
| 2529 | |
| 2530 | Special Thanks |
| 2531 | ============== |
| 2532 | Special thanks to Neale Ferguson who maintains a much |
| 2533 | prettier HTML version of this page at |
Justin P. Mattock | 0ea6e61 | 2010-07-23 20:51:24 -0700 | [diff] [blame^] | 2534 | http://linuxvm.org/penguinvm/ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 2535 | Bob Grainger Stefan Bader & others for reporting bugs |