Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | Linux Kernel Makefiles |
| 2 | |
| 3 | This document describes the Linux kernel Makefiles. |
| 4 | |
| 5 | === Table of Contents |
| 6 | |
| 7 | === 1 Overview |
| 8 | === 2 Who does what |
| 9 | === 3 The kbuild files |
| 10 | --- 3.1 Goal definitions |
| 11 | --- 3.2 Built-in object goals - obj-y |
| 12 | --- 3.3 Loadable module goals - obj-m |
| 13 | --- 3.4 Objects which export symbols |
| 14 | --- 3.5 Library file goals - lib-y |
| 15 | --- 3.6 Descending down in directories |
| 16 | --- 3.7 Compilation flags |
| 17 | --- 3.8 Command line dependency |
| 18 | --- 3.9 Dependency tracking |
| 19 | --- 3.10 Special Rules |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 20 | --- 3.11 $(CC) support functions |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 21 | |
| 22 | === 4 Host Program support |
| 23 | --- 4.1 Simple Host Program |
| 24 | --- 4.2 Composite Host Programs |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 25 | --- 4.3 Defining shared libraries |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 26 | --- 4.4 Using C++ for host programs |
| 27 | --- 4.5 Controlling compiler options for host programs |
| 28 | --- 4.6 When host programs are actually built |
| 29 | --- 4.7 Using hostprogs-$(CONFIG_FOO) |
| 30 | |
| 31 | === 5 Kbuild clean infrastructure |
| 32 | |
| 33 | === 6 Architecture Makefiles |
| 34 | --- 6.1 Set variables to tweak the build to the architecture |
Sam Ravnborg | 5bb7826 | 2005-09-11 22:30:22 +0200 | [diff] [blame] | 35 | --- 6.2 Add prerequisites to archprepare: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 36 | --- 6.3 List directories to visit when descending |
| 37 | --- 6.4 Architecture specific boot images |
| 38 | --- 6.5 Building non-kbuild targets |
| 39 | --- 6.6 Commands useful for building a boot image |
| 40 | --- 6.7 Custom kbuild commands |
| 41 | --- 6.8 Preprocessing linker scripts |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 42 | |
| 43 | === 7 Kbuild Variables |
| 44 | === 8 Makefile language |
| 45 | === 9 Credits |
| 46 | === 10 TODO |
| 47 | |
| 48 | === 1 Overview |
| 49 | |
| 50 | The Makefiles have five parts: |
| 51 | |
| 52 | Makefile the top Makefile. |
| 53 | .config the kernel configuration file. |
| 54 | arch/$(ARCH)/Makefile the arch Makefile. |
| 55 | scripts/Makefile.* common rules etc. for all kbuild Makefiles. |
| 56 | kbuild Makefiles there are about 500 of these. |
| 57 | |
| 58 | The top Makefile reads the .config file, which comes from the kernel |
| 59 | configuration process. |
| 60 | |
| 61 | The top Makefile is responsible for building two major products: vmlinux |
| 62 | (the resident kernel image) and modules (any module files). |
| 63 | It builds these goals by recursively descending into the subdirectories of |
| 64 | the kernel source tree. |
| 65 | The list of subdirectories which are visited depends upon the kernel |
| 66 | configuration. The top Makefile textually includes an arch Makefile |
| 67 | with the name arch/$(ARCH)/Makefile. The arch Makefile supplies |
| 68 | architecture-specific information to the top Makefile. |
| 69 | |
| 70 | Each subdirectory has a kbuild Makefile which carries out the commands |
| 71 | passed down from above. The kbuild Makefile uses information from the |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 72 | .config file to construct various file lists used by kbuild to build |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 73 | any built-in or modular targets. |
| 74 | |
| 75 | scripts/Makefile.* contains all the definitions/rules etc. that |
| 76 | are used to build the kernel based on the kbuild makefiles. |
| 77 | |
| 78 | |
| 79 | === 2 Who does what |
| 80 | |
| 81 | People have four different relationships with the kernel Makefiles. |
| 82 | |
| 83 | *Users* are people who build kernels. These people type commands such as |
| 84 | "make menuconfig" or "make". They usually do not read or edit |
| 85 | any kernel Makefiles (or any other source files). |
| 86 | |
| 87 | *Normal developers* are people who work on features such as device |
| 88 | drivers, file systems, and network protocols. These people need to |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 89 | maintain the kbuild Makefiles for the subsystem they are |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 90 | working on. In order to do this effectively, they need some overall |
| 91 | knowledge about the kernel Makefiles, plus detailed knowledge about the |
| 92 | public interface for kbuild. |
| 93 | |
| 94 | *Arch developers* are people who work on an entire architecture, such |
| 95 | as sparc or ia64. Arch developers need to know about the arch Makefile |
| 96 | as well as kbuild Makefiles. |
| 97 | |
| 98 | *Kbuild developers* are people who work on the kernel build system itself. |
| 99 | These people need to know about all aspects of the kernel Makefiles. |
| 100 | |
| 101 | This document is aimed towards normal developers and arch developers. |
| 102 | |
| 103 | |
| 104 | === 3 The kbuild files |
| 105 | |
| 106 | Most Makefiles within the kernel are kbuild Makefiles that use the |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 107 | kbuild infrastructure. This chapter introduces the syntax used in the |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 108 | kbuild makefiles. |
Sam Ravnborg | 172c3ae | 2006-03-10 00:23:32 +0100 | [diff] [blame] | 109 | The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 110 | be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild' |
Sam Ravnborg | 172c3ae | 2006-03-10 00:23:32 +0100 | [diff] [blame] | 111 | file will be used. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 112 | |
| 113 | Section 3.1 "Goal definitions" is a quick intro, further chapters provide |
| 114 | more details, with real examples. |
| 115 | |
| 116 | --- 3.1 Goal definitions |
| 117 | |
| 118 | Goal definitions are the main part (heart) of the kbuild Makefile. |
| 119 | These lines define the files to be built, any special compilation |
| 120 | options, and any subdirectories to be entered recursively. |
| 121 | |
| 122 | The most simple kbuild makefile contains one line: |
| 123 | |
| 124 | Example: |
| 125 | obj-y += foo.o |
| 126 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 127 | This tell kbuild that there is one object in that directory, named |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 128 | foo.o. foo.o will be built from foo.c or foo.S. |
| 129 | |
| 130 | If foo.o shall be built as a module, the variable obj-m is used. |
| 131 | Therefore the following pattern is often used: |
| 132 | |
| 133 | Example: |
| 134 | obj-$(CONFIG_FOO) += foo.o |
| 135 | |
| 136 | $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). |
| 137 | If CONFIG_FOO is neither y nor m, then the file will not be compiled |
| 138 | nor linked. |
| 139 | |
| 140 | --- 3.2 Built-in object goals - obj-y |
| 141 | |
| 142 | The kbuild Makefile specifies object files for vmlinux |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 143 | in the $(obj-y) lists. These lists depend on the kernel |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 144 | configuration. |
| 145 | |
| 146 | Kbuild compiles all the $(obj-y) files. It then calls |
| 147 | "$(LD) -r" to merge these files into one built-in.o file. |
| 148 | built-in.o is later linked into vmlinux by the parent Makefile. |
| 149 | |
| 150 | The order of files in $(obj-y) is significant. Duplicates in |
| 151 | the lists are allowed: the first instance will be linked into |
| 152 | built-in.o and succeeding instances will be ignored. |
| 153 | |
| 154 | Link order is significant, because certain functions |
| 155 | (module_init() / __initcall) will be called during boot in the |
| 156 | order they appear. So keep in mind that changing the link |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 157 | order may e.g. change the order in which your SCSI |
| 158 | controllers are detected, and thus your disks are renumbered. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 159 | |
| 160 | Example: |
| 161 | #drivers/isdn/i4l/Makefile |
| 162 | # Makefile for the kernel ISDN subsystem and device drivers. |
| 163 | # Each configuration option enables a list of files. |
| 164 | obj-$(CONFIG_ISDN) += isdn.o |
| 165 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o |
| 166 | |
| 167 | --- 3.3 Loadable module goals - obj-m |
| 168 | |
| 169 | $(obj-m) specify object files which are built as loadable |
| 170 | kernel modules. |
| 171 | |
| 172 | A module may be built from one source file or several source |
| 173 | files. In the case of one source file, the kbuild makefile |
| 174 | simply adds the file to $(obj-m). |
| 175 | |
| 176 | Example: |
| 177 | #drivers/isdn/i4l/Makefile |
| 178 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o |
| 179 | |
| 180 | Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm' |
| 181 | |
| 182 | If a kernel module is built from several source files, you specify |
| 183 | that you want to build a module in the same way as above. |
| 184 | |
| 185 | Kbuild needs to know which the parts that you want to build your |
| 186 | module from, so you have to tell it by setting an |
| 187 | $(<module_name>-objs) variable. |
| 188 | |
| 189 | Example: |
| 190 | #drivers/isdn/i4l/Makefile |
| 191 | obj-$(CONFIG_ISDN) += isdn.o |
| 192 | isdn-objs := isdn_net_lib.o isdn_v110.o isdn_common.o |
| 193 | |
| 194 | In this example, the module name will be isdn.o. Kbuild will |
| 195 | compile the objects listed in $(isdn-objs) and then run |
| 196 | "$(LD) -r" on the list of these files to generate isdn.o. |
| 197 | |
| 198 | Kbuild recognises objects used for composite objects by the suffix |
| 199 | -objs, and the suffix -y. This allows the Makefiles to use |
| 200 | the value of a CONFIG_ symbol to determine if an object is part |
| 201 | of a composite object. |
| 202 | |
| 203 | Example: |
| 204 | #fs/ext2/Makefile |
| 205 | obj-$(CONFIG_EXT2_FS) += ext2.o |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 206 | ext2-y := balloc.o bitmap.o |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 207 | ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 208 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 209 | In this example, xattr.o is only part of the composite object |
| 210 | ext2.o if $(CONFIG_EXT2_FS_XATTR) evaluates to 'y'. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 211 | |
| 212 | Note: Of course, when you are building objects into the kernel, |
| 213 | the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, |
| 214 | kbuild will build an ext2.o file for you out of the individual |
| 215 | parts and then link this into built-in.o, as you would expect. |
| 216 | |
| 217 | --- 3.4 Objects which export symbols |
| 218 | |
| 219 | No special notation is required in the makefiles for |
| 220 | modules exporting symbols. |
| 221 | |
| 222 | --- 3.5 Library file goals - lib-y |
| 223 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 224 | Objects listed with obj-* are used for modules, or |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 225 | combined in a built-in.o for that specific directory. |
| 226 | There is also the possibility to list objects that will |
| 227 | be included in a library, lib.a. |
| 228 | All objects listed with lib-y are combined in a single |
| 229 | library for that directory. |
Matt LaPlante | 5d3f083 | 2006-11-30 05:21:10 +0100 | [diff] [blame] | 230 | Objects that are listed in obj-y and additionally listed in |
| 231 | lib-y will not be included in the library, since they will |
| 232 | be accessible anyway. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 233 | For consistency, objects listed in lib-m will be included in lib.a. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 234 | |
| 235 | Note that the same kbuild makefile may list files to be built-in |
| 236 | and to be part of a library. Therefore the same directory |
| 237 | may contain both a built-in.o and a lib.a file. |
| 238 | |
| 239 | Example: |
| 240 | #arch/i386/lib/Makefile |
| 241 | lib-y := checksum.o delay.o |
| 242 | |
| 243 | This will create a library lib.a based on checksum.o and delay.o. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 244 | For kbuild to actually recognize that there is a lib.a being built, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 245 | the directory shall be listed in libs-y. |
| 246 | See also "6.3 List directories to visit when descending". |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 247 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 248 | Use of lib-y is normally restricted to lib/ and arch/*/lib. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 249 | |
| 250 | --- 3.6 Descending down in directories |
| 251 | |
| 252 | A Makefile is only responsible for building objects in its own |
| 253 | directory. Files in subdirectories should be taken care of by |
| 254 | Makefiles in these subdirs. The build system will automatically |
| 255 | invoke make recursively in subdirectories, provided you let it know of |
| 256 | them. |
| 257 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 258 | To do so, obj-y and obj-m are used. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 259 | ext2 lives in a separate directory, and the Makefile present in fs/ |
| 260 | tells kbuild to descend down using the following assignment. |
| 261 | |
| 262 | Example: |
| 263 | #fs/Makefile |
| 264 | obj-$(CONFIG_EXT2_FS) += ext2/ |
| 265 | |
| 266 | If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular) |
| 267 | the corresponding obj- variable will be set, and kbuild will descend |
| 268 | down in the ext2 directory. |
| 269 | Kbuild only uses this information to decide that it needs to visit |
| 270 | the directory, it is the Makefile in the subdirectory that |
| 271 | specifies what is modules and what is built-in. |
| 272 | |
| 273 | It is good practice to use a CONFIG_ variable when assigning directory |
| 274 | names. This allows kbuild to totally skip the directory if the |
| 275 | corresponding CONFIG_ option is neither 'y' nor 'm'. |
| 276 | |
| 277 | --- 3.7 Compilation flags |
| 278 | |
| 279 | EXTRA_CFLAGS, EXTRA_AFLAGS, EXTRA_LDFLAGS, EXTRA_ARFLAGS |
| 280 | |
| 281 | All the EXTRA_ variables apply only to the kbuild makefile |
| 282 | where they are assigned. The EXTRA_ variables apply to all |
| 283 | commands executed in the kbuild makefile. |
| 284 | |
| 285 | $(EXTRA_CFLAGS) specifies options for compiling C files with |
| 286 | $(CC). |
| 287 | |
| 288 | Example: |
| 289 | # drivers/sound/emu10k1/Makefile |
| 290 | EXTRA_CFLAGS += -I$(obj) |
| 291 | ifdef DEBUG |
| 292 | EXTRA_CFLAGS += -DEMU10K1_DEBUG |
| 293 | endif |
| 294 | |
| 295 | |
| 296 | This variable is necessary because the top Makefile owns the |
| 297 | variable $(CFLAGS) and uses it for compilation flags for the |
| 298 | entire tree. |
| 299 | |
| 300 | $(EXTRA_AFLAGS) is a similar string for per-directory options |
| 301 | when compiling assembly language source. |
| 302 | |
| 303 | Example: |
| 304 | #arch/x86_64/kernel/Makefile |
| 305 | EXTRA_AFLAGS := -traditional |
| 306 | |
| 307 | |
| 308 | $(EXTRA_LDFLAGS) and $(EXTRA_ARFLAGS) are similar strings for |
| 309 | per-directory options to $(LD) and $(AR). |
| 310 | |
| 311 | Example: |
| 312 | #arch/m68k/fpsp040/Makefile |
| 313 | EXTRA_LDFLAGS := -x |
| 314 | |
| 315 | CFLAGS_$@, AFLAGS_$@ |
| 316 | |
| 317 | CFLAGS_$@ and AFLAGS_$@ only apply to commands in current |
| 318 | kbuild makefile. |
| 319 | |
| 320 | $(CFLAGS_$@) specifies per-file options for $(CC). The $@ |
| 321 | part has a literal value which specifies the file that it is for. |
| 322 | |
| 323 | Example: |
| 324 | # drivers/scsi/Makefile |
| 325 | CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF |
| 326 | CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \ |
| 327 | -DGDTH_STATISTICS |
| 328 | CFLAGS_seagate.o = -DARBITRATE -DPARITY -DSEAGATE_USE_ASM |
| 329 | |
| 330 | These three lines specify compilation flags for aha152x.o, |
| 331 | gdth.o, and seagate.o |
| 332 | |
| 333 | $(AFLAGS_$@) is a similar feature for source files in assembly |
| 334 | languages. |
| 335 | |
| 336 | Example: |
| 337 | # arch/arm/kernel/Makefile |
| 338 | AFLAGS_head-armv.o := -DTEXTADDR=$(TEXTADDR) -traditional |
| 339 | AFLAGS_head-armo.o := -DTEXTADDR=$(TEXTADDR) -traditional |
| 340 | |
| 341 | --- 3.9 Dependency tracking |
| 342 | |
| 343 | Kbuild tracks dependencies on the following: |
| 344 | 1) All prerequisite files (both *.c and *.h) |
| 345 | 2) CONFIG_ options used in all prerequisite files |
| 346 | 3) Command-line used to compile target |
| 347 | |
| 348 | Thus, if you change an option to $(CC) all affected files will |
| 349 | be re-compiled. |
| 350 | |
| 351 | --- 3.10 Special Rules |
| 352 | |
| 353 | Special rules are used when the kbuild infrastructure does |
| 354 | not provide the required support. A typical example is |
| 355 | header files generated during the build process. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 356 | Another example are the architecture specific Makefiles which |
| 357 | need special rules to prepare boot images etc. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 358 | |
| 359 | Special rules are written as normal Make rules. |
| 360 | Kbuild is not executing in the directory where the Makefile is |
| 361 | located, so all special rules shall provide a relative |
| 362 | path to prerequisite files and target files. |
| 363 | |
| 364 | Two variables are used when defining special rules: |
| 365 | |
| 366 | $(src) |
| 367 | $(src) is a relative path which points to the directory |
| 368 | where the Makefile is located. Always use $(src) when |
| 369 | referring to files located in the src tree. |
| 370 | |
| 371 | $(obj) |
| 372 | $(obj) is a relative path which points to the directory |
| 373 | where the target is saved. Always use $(obj) when |
| 374 | referring to generated files. |
| 375 | |
| 376 | Example: |
| 377 | #drivers/scsi/Makefile |
| 378 | $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl |
| 379 | $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl |
| 380 | |
| 381 | This is a special rule, following the normal syntax |
| 382 | required by make. |
| 383 | The target file depends on two prerequisite files. References |
| 384 | to the target file are prefixed with $(obj), references |
| 385 | to prerequisites are referenced with $(src) (because they are not |
| 386 | generated files). |
| 387 | |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 388 | --- 3.11 $(CC) support functions |
| 389 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 390 | The kernel may be built with several different versions of |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 391 | $(CC), each supporting a unique set of features and options. |
| 392 | kbuild provide basic support to check for valid options for $(CC). |
Daniel Walker | e95be9a | 2006-10-04 02:15:21 -0700 | [diff] [blame] | 393 | $(CC) is usually the gcc compiler, but other alternatives are |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 394 | available. |
| 395 | |
| 396 | as-option |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 397 | as-option is used to check if $(CC) -- when used to compile |
| 398 | assembler (*.S) files -- supports the given option. An optional |
| 399 | second option may be specified if the first option is not supported. |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 400 | |
| 401 | Example: |
| 402 | #arch/sh/Makefile |
| 403 | cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) |
| 404 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 405 | In the above example, cflags-y will be assigned the option |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 406 | -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). |
| 407 | The second argument is optional, and if supplied will be used |
| 408 | if first argument is not supported. |
| 409 | |
Roland McGrath | 0b0bf7a | 2006-07-30 03:04:06 -0700 | [diff] [blame] | 410 | ld-option |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 411 | ld-option is used to check if $(CC) when used to link object files |
Roland McGrath | 0b0bf7a | 2006-07-30 03:04:06 -0700 | [diff] [blame] | 412 | supports the given option. An optional second option may be |
| 413 | specified if first option are not supported. |
| 414 | |
| 415 | Example: |
| 416 | #arch/i386/kernel/Makefile |
| 417 | vsyscall-flags += $(call ld-option, -Wl$(comma)--hash-style=sysv) |
| 418 | |
| 419 | In the above example vsyscall-flags will be assigned the option |
| 420 | -Wl$(comma)--hash-style=sysv if it is supported by $(CC). |
| 421 | The second argument is optional, and if supplied will be used |
| 422 | if first argument is not supported. |
| 423 | |
Andi Kleen | e241491 | 2006-09-26 10:52:30 +0200 | [diff] [blame] | 424 | as-instr |
| 425 | as-instr checks if the assembler reports a specific instruction |
| 426 | and then outputs either option1 or option2 |
| 427 | C escapes are supported in the test instruction |
| 428 | |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 429 | cc-option |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 430 | cc-option is used to check if $(CC) supports a given option, and not |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 431 | supported to use an optional second option. |
| 432 | |
| 433 | Example: |
| 434 | #arch/i386/Makefile |
| 435 | cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) |
| 436 | |
| 437 | In the above example cflags-y will be assigned the option |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 438 | -march=pentium-mmx if supported by $(CC), otherwise -march=i586. |
| 439 | The second argument to cc-option is optional, and if omitted, |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 440 | cflags-y will be assigned no value if first option is not supported. |
| 441 | |
| 442 | cc-option-yn |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 443 | cc-option-yn is used to check if gcc supports a given option |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 444 | and return 'y' if supported, otherwise 'n'. |
| 445 | |
| 446 | Example: |
| 447 | #arch/ppc/Makefile |
| 448 | biarch := $(call cc-option-yn, -m32) |
| 449 | aflags-$(biarch) += -a32 |
| 450 | cflags-$(biarch) += -m32 |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 451 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 452 | In the above example, $(biarch) is set to y if $(CC) supports the -m32 |
| 453 | option. When $(biarch) equals 'y', the expanded variables $(aflags-y) |
| 454 | and $(cflags-y) will be assigned the values -a32 and -m32, |
| 455 | respectively. |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 456 | |
| 457 | cc-option-align |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 458 | gcc versions >= 3.0 changed the type of options used to specify |
| 459 | alignment of functions, loops etc. $(cc-option-align), when used |
| 460 | as prefix to the align options, will select the right prefix: |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 461 | gcc < 3.00 |
| 462 | cc-option-align = -malign |
| 463 | gcc >= 3.00 |
| 464 | cc-option-align = -falign |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 465 | |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 466 | Example: |
| 467 | CFLAGS += $(cc-option-align)-functions=4 |
| 468 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 469 | In the above example, the option -falign-functions=4 is used for |
| 470 | gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 471 | |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 472 | cc-version |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 473 | cc-version returns a numerical version of the $(CC) compiler version. |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 474 | The format is <major><minor> where both are two digits. So for example |
| 475 | gcc 3.41 would return 0341. |
| 476 | cc-version is useful when a specific $(CC) version is faulty in one |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 477 | area, for example -mregparm=3 was broken in some gcc versions |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 478 | even though the option was accepted by gcc. |
| 479 | |
| 480 | Example: |
| 481 | #arch/i386/Makefile |
| 482 | cflags-y += $(shell \ |
| 483 | if [ $(call cc-version) -ge 0300 ] ; then \ |
| 484 | echo "-mregparm=3"; fi ;) |
| 485 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 486 | In the above example, -mregparm=3 is only used for gcc version greater |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 487 | than or equal to gcc 3.0. |
| 488 | |
| 489 | cc-ifversion |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 490 | cc-ifversion tests the version of $(CC) and equals last argument if |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 491 | version expression is true. |
| 492 | |
| 493 | Example: |
| 494 | #fs/reiserfs/Makefile |
| 495 | EXTRA_CFLAGS := $(call cc-ifversion, -lt, 0402, -O1) |
| 496 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 497 | In this example, EXTRA_CFLAGS will be assigned the value -O1 if the |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 498 | $(CC) version is less than 4.2. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 499 | cc-ifversion takes all the shell operators: |
Sam Ravnborg | 20a468b | 2006-01-22 13:34:15 +0100 | [diff] [blame] | 500 | -eq, -ne, -lt, -le, -gt, and -ge |
| 501 | The third parameter may be a text as in this example, but it may also |
| 502 | be an expanded variable or a macro. |
| 503 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 504 | |
| 505 | === 4 Host Program support |
| 506 | |
| 507 | Kbuild supports building executables on the host for use during the |
| 508 | compilation stage. |
| 509 | Two steps are required in order to use a host executable. |
| 510 | |
| 511 | The first step is to tell kbuild that a host program exists. This is |
| 512 | done utilising the variable hostprogs-y. |
| 513 | |
| 514 | The second step is to add an explicit dependency to the executable. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 515 | This can be done in two ways. Either add the dependency in a rule, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 516 | or utilise the variable $(always). |
| 517 | Both possibilities are described in the following. |
| 518 | |
| 519 | --- 4.1 Simple Host Program |
| 520 | |
| 521 | In some cases there is a need to compile and run a program on the |
| 522 | computer where the build is running. |
| 523 | The following line tells kbuild that the program bin2hex shall be |
| 524 | built on the build host. |
| 525 | |
| 526 | Example: |
| 527 | hostprogs-y := bin2hex |
| 528 | |
| 529 | Kbuild assumes in the above example that bin2hex is made from a single |
| 530 | c-source file named bin2hex.c located in the same directory as |
| 531 | the Makefile. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 532 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 533 | --- 4.2 Composite Host Programs |
| 534 | |
| 535 | Host programs can be made up based on composite objects. |
| 536 | The syntax used to define composite objects for host programs is |
| 537 | similar to the syntax used for kernel objects. |
Matt LaPlante | 5d3f083 | 2006-11-30 05:21:10 +0100 | [diff] [blame] | 538 | $(<executable>-objs) lists all objects used to link the final |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 539 | executable. |
| 540 | |
| 541 | Example: |
| 542 | #scripts/lxdialog/Makefile |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 543 | hostprogs-y := lxdialog |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 544 | lxdialog-objs := checklist.o lxdialog.o |
| 545 | |
| 546 | Objects with extension .o are compiled from the corresponding .c |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 547 | files. In the above example, checklist.c is compiled to checklist.o |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 548 | and lxdialog.c is compiled to lxdialog.o. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 549 | Finally, the two .o files are linked to the executable, lxdialog. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 550 | Note: The syntax <executable>-y is not permitted for host-programs. |
| 551 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 552 | --- 4.3 Defining shared libraries |
| 553 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 554 | Objects with extension .so are considered shared libraries, and |
| 555 | will be compiled as position independent objects. |
| 556 | Kbuild provides support for shared libraries, but the usage |
| 557 | shall be restricted. |
| 558 | In the following example the libkconfig.so shared library is used |
| 559 | to link the executable conf. |
| 560 | |
| 561 | Example: |
| 562 | #scripts/kconfig/Makefile |
| 563 | hostprogs-y := conf |
| 564 | conf-objs := conf.o libkconfig.so |
| 565 | libkconfig-objs := expr.o type.o |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 566 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 567 | Shared libraries always require a corresponding -objs line, and |
| 568 | in the example above the shared library libkconfig is composed by |
| 569 | the two objects expr.o and type.o. |
| 570 | expr.o and type.o will be built as position independent code and |
| 571 | linked as a shared library libkconfig.so. C++ is not supported for |
| 572 | shared libraries. |
| 573 | |
| 574 | --- 4.4 Using C++ for host programs |
| 575 | |
| 576 | kbuild offers support for host programs written in C++. This was |
| 577 | introduced solely to support kconfig, and is not recommended |
| 578 | for general use. |
| 579 | |
| 580 | Example: |
| 581 | #scripts/kconfig/Makefile |
| 582 | hostprogs-y := qconf |
| 583 | qconf-cxxobjs := qconf.o |
| 584 | |
| 585 | In the example above the executable is composed of the C++ file |
| 586 | qconf.cc - identified by $(qconf-cxxobjs). |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 587 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 588 | If qconf is composed by a mixture of .c and .cc files, then an |
| 589 | additional line can be used to identify this. |
| 590 | |
| 591 | Example: |
| 592 | #scripts/kconfig/Makefile |
| 593 | hostprogs-y := qconf |
| 594 | qconf-cxxobjs := qconf.o |
| 595 | qconf-objs := check.o |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 596 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 597 | --- 4.5 Controlling compiler options for host programs |
| 598 | |
| 599 | When compiling host programs, it is possible to set specific flags. |
| 600 | The programs will always be compiled utilising $(HOSTCC) passed |
| 601 | the options specified in $(HOSTCFLAGS). |
| 602 | To set flags that will take effect for all host programs created |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 603 | in that Makefile, use the variable HOST_EXTRACFLAGS. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 604 | |
| 605 | Example: |
| 606 | #scripts/lxdialog/Makefile |
| 607 | HOST_EXTRACFLAGS += -I/usr/include/ncurses |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 608 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 609 | To set specific flags for a single file the following construction |
| 610 | is used: |
| 611 | |
| 612 | Example: |
| 613 | #arch/ppc64/boot/Makefile |
| 614 | HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 615 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 616 | It is also possible to specify additional options to the linker. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 617 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 618 | Example: |
| 619 | #scripts/kconfig/Makefile |
| 620 | HOSTLOADLIBES_qconf := -L$(QTDIR)/lib |
| 621 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 622 | When linking qconf, it will be passed the extra option |
| 623 | "-L$(QTDIR)/lib". |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 624 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 625 | --- 4.6 When host programs are actually built |
| 626 | |
| 627 | Kbuild will only build host-programs when they are referenced |
| 628 | as a prerequisite. |
| 629 | This is possible in two ways: |
| 630 | |
| 631 | (1) List the prerequisite explicitly in a special rule. |
| 632 | |
| 633 | Example: |
| 634 | #drivers/pci/Makefile |
| 635 | hostprogs-y := gen-devlist |
| 636 | $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist |
| 637 | ( cd $(obj); ./gen-devlist ) < $< |
| 638 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 639 | The target $(obj)/devlist.h will not be built before |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 640 | $(obj)/gen-devlist is updated. Note that references to |
| 641 | the host programs in special rules must be prefixed with $(obj). |
| 642 | |
| 643 | (2) Use $(always) |
| 644 | When there is no suitable special rule, and the host program |
| 645 | shall be built when a makefile is entered, the $(always) |
| 646 | variable shall be used. |
| 647 | |
| 648 | Example: |
| 649 | #scripts/lxdialog/Makefile |
| 650 | hostprogs-y := lxdialog |
| 651 | always := $(hostprogs-y) |
| 652 | |
| 653 | This will tell kbuild to build lxdialog even if not referenced in |
| 654 | any rule. |
| 655 | |
| 656 | --- 4.7 Using hostprogs-$(CONFIG_FOO) |
| 657 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 658 | A typical pattern in a Kbuild file looks like this: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 659 | |
| 660 | Example: |
| 661 | #scripts/Makefile |
| 662 | hostprogs-$(CONFIG_KALLSYMS) += kallsyms |
| 663 | |
| 664 | Kbuild knows about both 'y' for built-in and 'm' for module. |
| 665 | So if a config symbol evaluate to 'm', kbuild will still build |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 666 | the binary. In other words, Kbuild handles hostprogs-m exactly |
| 667 | like hostprogs-y. But only hostprogs-y is recommended to be used |
| 668 | when no CONFIG symbols are involved. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 669 | |
| 670 | === 5 Kbuild clean infrastructure |
| 671 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 672 | "make clean" deletes most generated files in the obj tree where the kernel |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 673 | is compiled. This includes generated files such as host programs. |
| 674 | Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always), |
| 675 | $(extra-y) and $(targets). They are all deleted during "make clean". |
| 676 | Files matching the patterns "*.[oas]", "*.ko", plus some additional files |
| 677 | generated by kbuild are deleted all over the kernel src tree when |
| 678 | "make clean" is executed. |
| 679 | |
| 680 | Additional files can be specified in kbuild makefiles by use of $(clean-files). |
| 681 | |
| 682 | Example: |
| 683 | #drivers/pci/Makefile |
| 684 | clean-files := devlist.h classlist.h |
| 685 | |
| 686 | When executing "make clean", the two files "devlist.h classlist.h" will |
| 687 | be deleted. Kbuild will assume files to be in same relative directory as the |
| 688 | Makefile except if an absolute path is specified (path starting with '/'). |
| 689 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 690 | To delete a directory hierarchy use: |
| 691 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 692 | Example: |
| 693 | #scripts/package/Makefile |
| 694 | clean-dirs := $(objtree)/debian/ |
| 695 | |
| 696 | This will delete the directory debian, including all subdirectories. |
| 697 | Kbuild will assume the directories to be in the same relative path as the |
| 698 | Makefile if no absolute path is specified (path does not start with '/'). |
| 699 | |
| 700 | Usually kbuild descends down in subdirectories due to "obj-* := dir/", |
| 701 | but in the architecture makefiles where the kbuild infrastructure |
| 702 | is not sufficient this sometimes needs to be explicit. |
| 703 | |
| 704 | Example: |
| 705 | #arch/i386/boot/Makefile |
| 706 | subdir- := compressed/ |
| 707 | |
| 708 | The above assignment instructs kbuild to descend down in the |
| 709 | directory compressed/ when "make clean" is executed. |
| 710 | |
| 711 | To support the clean infrastructure in the Makefiles that builds the |
| 712 | final bootimage there is an optional target named archclean: |
| 713 | |
| 714 | Example: |
| 715 | #arch/i386/Makefile |
| 716 | archclean: |
| 717 | $(Q)$(MAKE) $(clean)=arch/i386/boot |
| 718 | |
| 719 | When "make clean" is executed, make will descend down in arch/i386/boot, |
| 720 | and clean as usual. The Makefile located in arch/i386/boot/ may use |
| 721 | the subdir- trick to descend further down. |
| 722 | |
| 723 | Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is |
| 724 | included in the top level makefile, and the kbuild infrastructure |
| 725 | is not operational at that point. |
| 726 | |
| 727 | Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will |
| 728 | be visited during "make clean". |
| 729 | |
| 730 | === 6 Architecture Makefiles |
| 731 | |
| 732 | The top level Makefile sets up the environment and does the preparation, |
| 733 | before starting to descend down in the individual directories. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 734 | The top level makefile contains the generic part, whereas |
| 735 | arch/$(ARCH)/Makefile contains what is required to set up kbuild |
| 736 | for said architecture. |
| 737 | To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 738 | a few targets. |
| 739 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 740 | When kbuild executes, the following steps are followed (roughly): |
| 741 | 1) Configuration of the kernel => produce .config |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 742 | 2) Store kernel version in include/linux/version.h |
| 743 | 3) Symlink include/asm to include/asm-$(ARCH) |
| 744 | 4) Updating all other prerequisites to the target prepare: |
| 745 | - Additional prerequisites are specified in arch/$(ARCH)/Makefile |
| 746 | 5) Recursively descend down in all directories listed in |
| 747 | init-* core* drivers-* net-* libs-* and build all targets. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 748 | - The values of the above variables are expanded in arch/$(ARCH)/Makefile. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 749 | 6) All object files are then linked and the resulting file vmlinux is |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 750 | located at the root of the obj tree. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 751 | The very first objects linked are listed in head-y, assigned by |
| 752 | arch/$(ARCH)/Makefile. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 753 | 7) Finally, the architecture specific part does any required post processing |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 754 | and builds the final bootimage. |
| 755 | - This includes building boot records |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 756 | - Preparing initrd images and thelike |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 757 | |
| 758 | |
| 759 | --- 6.1 Set variables to tweak the build to the architecture |
| 760 | |
| 761 | LDFLAGS Generic $(LD) options |
| 762 | |
| 763 | Flags used for all invocations of the linker. |
| 764 | Often specifying the emulation is sufficient. |
| 765 | |
| 766 | Example: |
| 767 | #arch/s390/Makefile |
| 768 | LDFLAGS := -m elf_s390 |
| 769 | Note: EXTRA_LDFLAGS and LDFLAGS_$@ can be used to further customise |
| 770 | the flags used. See chapter 7. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 771 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 772 | LDFLAGS_MODULE Options for $(LD) when linking modules |
| 773 | |
| 774 | LDFLAGS_MODULE is used to set specific flags for $(LD) when |
| 775 | linking the .ko files used for modules. |
| 776 | Default is "-r", for relocatable output. |
| 777 | |
| 778 | LDFLAGS_vmlinux Options for $(LD) when linking vmlinux |
| 779 | |
| 780 | LDFLAGS_vmlinux is used to specify additional flags to pass to |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 781 | the linker when linking the final vmlinux image. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 782 | LDFLAGS_vmlinux uses the LDFLAGS_$@ support. |
| 783 | |
| 784 | Example: |
| 785 | #arch/i386/Makefile |
| 786 | LDFLAGS_vmlinux := -e stext |
| 787 | |
| 788 | OBJCOPYFLAGS objcopy flags |
| 789 | |
| 790 | When $(call if_changed,objcopy) is used to translate a .o file, |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 791 | the flags specified in OBJCOPYFLAGS will be used. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 792 | $(call if_changed,objcopy) is often used to generate raw binaries on |
| 793 | vmlinux. |
| 794 | |
| 795 | Example: |
| 796 | #arch/s390/Makefile |
| 797 | OBJCOPYFLAGS := -O binary |
| 798 | |
| 799 | #arch/s390/boot/Makefile |
| 800 | $(obj)/image: vmlinux FORCE |
| 801 | $(call if_changed,objcopy) |
| 802 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 803 | In this example, the binary $(obj)/image is a binary version of |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 804 | vmlinux. The usage of $(call if_changed,xxx) will be described later. |
| 805 | |
| 806 | AFLAGS $(AS) assembler flags |
| 807 | |
| 808 | Default value - see top level Makefile |
| 809 | Append or modify as required per architecture. |
| 810 | |
| 811 | Example: |
| 812 | #arch/sparc64/Makefile |
| 813 | AFLAGS += -m64 -mcpu=ultrasparc |
| 814 | |
| 815 | CFLAGS $(CC) compiler flags |
| 816 | |
| 817 | Default value - see top level Makefile |
| 818 | Append or modify as required per architecture. |
| 819 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 820 | Often, the CFLAGS variable depends on the configuration. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 821 | |
| 822 | Example: |
| 823 | #arch/i386/Makefile |
| 824 | cflags-$(CONFIG_M386) += -march=i386 |
| 825 | CFLAGS += $(cflags-y) |
| 826 | |
| 827 | Many arch Makefiles dynamically run the target C compiler to |
| 828 | probe supported options: |
| 829 | |
| 830 | #arch/i386/Makefile |
| 831 | |
| 832 | ... |
| 833 | cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ |
| 834 | -march=pentium2,-march=i686) |
| 835 | ... |
| 836 | # Disable unit-at-a-time mode ... |
| 837 | CFLAGS += $(call cc-option,-fno-unit-at-a-time) |
| 838 | ... |
| 839 | |
| 840 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 841 | The first example utilises the trick that a config option expands |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 842 | to 'y' when selected. |
| 843 | |
| 844 | CFLAGS_KERNEL $(CC) options specific for built-in |
| 845 | |
| 846 | $(CFLAGS_KERNEL) contains extra C compiler flags used to compile |
| 847 | resident kernel code. |
| 848 | |
| 849 | CFLAGS_MODULE $(CC) options specific for modules |
| 850 | |
| 851 | $(CFLAGS_MODULE) contains extra C compiler flags used to compile code |
| 852 | for loadable kernel modules. |
| 853 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 854 | |
Sam Ravnborg | 5bb7826 | 2005-09-11 22:30:22 +0200 | [diff] [blame] | 855 | --- 6.2 Add prerequisites to archprepare: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 856 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 857 | The archprepare: rule is used to list prerequisites that need to be |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 858 | built before starting to descend down in the subdirectories. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 859 | This is usually used for header files containing assembler constants. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 860 | |
| 861 | Example: |
Sam Ravnborg | 5bb7826 | 2005-09-11 22:30:22 +0200 | [diff] [blame] | 862 | #arch/arm/Makefile |
| 863 | archprepare: maketools |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 864 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 865 | In this example, the file target maketools will be processed |
Sam Ravnborg | 5bb7826 | 2005-09-11 22:30:22 +0200 | [diff] [blame] | 866 | before descending down in the subdirectories. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 867 | See also chapter XXX-TODO that describe how kbuild supports |
| 868 | generating offset header files. |
| 869 | |
| 870 | |
| 871 | --- 6.3 List directories to visit when descending |
| 872 | |
| 873 | An arch Makefile cooperates with the top Makefile to define variables |
| 874 | which specify how to build the vmlinux file. Note that there is no |
| 875 | corresponding arch-specific section for modules; the module-building |
| 876 | machinery is all architecture-independent. |
| 877 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 878 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 879 | head-y, init-y, core-y, libs-y, drivers-y, net-y |
| 880 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 881 | $(head-y) lists objects to be linked first in vmlinux. |
| 882 | $(libs-y) lists directories where a lib.a archive can be located. |
| 883 | The rest lists directories where a built-in.o object file can be |
| 884 | located. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 885 | |
| 886 | $(init-y) objects will be located after $(head-y). |
| 887 | Then the rest follows in this order: |
| 888 | $(core-y), $(libs-y), $(drivers-y) and $(net-y). |
| 889 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 890 | The top level Makefile defines values for all generic directories, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 891 | and arch/$(ARCH)/Makefile only adds architecture specific directories. |
| 892 | |
| 893 | Example: |
| 894 | #arch/sparc64/Makefile |
| 895 | core-y += arch/sparc64/kernel/ |
| 896 | libs-y += arch/sparc64/prom/ arch/sparc64/lib/ |
| 897 | drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ |
| 898 | |
| 899 | |
| 900 | --- 6.4 Architecture specific boot images |
| 901 | |
| 902 | An arch Makefile specifies goals that take the vmlinux file, compress |
| 903 | it, wrap it in bootstrapping code, and copy the resulting files |
| 904 | somewhere. This includes various kinds of installation commands. |
| 905 | The actual goals are not standardized across architectures. |
| 906 | |
| 907 | It is common to locate any additional processing in a boot/ |
| 908 | directory below arch/$(ARCH)/. |
| 909 | |
| 910 | Kbuild does not provide any smart way to support building a |
| 911 | target specified in boot/. Therefore arch/$(ARCH)/Makefile shall |
| 912 | call make manually to build a target in boot/. |
| 913 | |
| 914 | The recommended approach is to include shortcuts in |
| 915 | arch/$(ARCH)/Makefile, and use the full path when calling down |
| 916 | into the arch/$(ARCH)/boot/Makefile. |
| 917 | |
| 918 | Example: |
| 919 | #arch/i386/Makefile |
| 920 | boot := arch/i386/boot |
| 921 | bzImage: vmlinux |
| 922 | $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ |
| 923 | |
| 924 | "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke |
| 925 | make in a subdirectory. |
| 926 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 927 | There are no rules for naming architecture specific targets, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 928 | but executing "make help" will list all relevant targets. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 929 | To support this, $(archhelp) must be defined. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 930 | |
| 931 | Example: |
| 932 | #arch/i386/Makefile |
| 933 | define archhelp |
| 934 | echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 935 | endif |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 936 | |
| 937 | When make is executed without arguments, the first goal encountered |
| 938 | will be built. In the top level Makefile the first goal present |
| 939 | is all:. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 940 | An architecture shall always, per default, build a bootable image. |
| 941 | In "make help", the default goal is highlighted with a '*'. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 942 | Add a new prerequisite to all: to select a default goal different |
| 943 | from vmlinux. |
| 944 | |
| 945 | Example: |
| 946 | #arch/i386/Makefile |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 947 | all: bzImage |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 948 | |
| 949 | When "make" is executed without arguments, bzImage will be built. |
| 950 | |
| 951 | --- 6.5 Building non-kbuild targets |
| 952 | |
| 953 | extra-y |
| 954 | |
| 955 | extra-y specify additional targets created in the current |
| 956 | directory, in addition to any targets specified by obj-*. |
| 957 | |
| 958 | Listing all targets in extra-y is required for two purposes: |
| 959 | 1) Enable kbuild to check changes in command lines |
| 960 | - When $(call if_changed,xxx) is used |
| 961 | 2) kbuild knows what files to delete during "make clean" |
| 962 | |
| 963 | Example: |
| 964 | #arch/i386/kernel/Makefile |
| 965 | extra-y := head.o init_task.o |
| 966 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 967 | In this example, extra-y is used to list object files that |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 968 | shall be built, but shall not be linked as part of built-in.o. |
| 969 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 970 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 971 | --- 6.6 Commands useful for building a boot image |
| 972 | |
| 973 | Kbuild provides a few macros that are useful when building a |
| 974 | boot image. |
| 975 | |
| 976 | if_changed |
| 977 | |
| 978 | if_changed is the infrastructure used for the following commands. |
| 979 | |
| 980 | Usage: |
| 981 | target: source(s) FORCE |
| 982 | $(call if_changed,ld/objcopy/gzip) |
| 983 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 984 | When the rule is evaluated, it is checked to see if any files |
| 985 | needs an update, or the command line has changed since the last |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 986 | invocation. The latter will force a rebuild if any options |
| 987 | to the executable have changed. |
| 988 | Any target that utilises if_changed must be listed in $(targets), |
| 989 | otherwise the command line check will fail, and the target will |
| 990 | always be built. |
| 991 | Assignments to $(targets) are without $(obj)/ prefix. |
| 992 | if_changed may be used in conjunction with custom commands as |
| 993 | defined in 6.7 "Custom kbuild commands". |
Paolo 'Blaisorblade' Giarrusso | 4949057 | 2005-07-28 17:56:17 +0200 | [diff] [blame] | 994 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 995 | Note: It is a typical mistake to forget the FORCE prerequisite. |
Paolo 'Blaisorblade' Giarrusso | 4949057 | 2005-07-28 17:56:17 +0200 | [diff] [blame] | 996 | Another common pitfall is that whitespace is sometimes |
| 997 | significant; for instance, the below will fail (note the extra space |
| 998 | after the comma): |
| 999 | target: source(s) FORCE |
| 1000 | #WRONG!# $(call if_changed, ld/objcopy/gzip) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1001 | |
| 1002 | ld |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1003 | Link target. Often, LDFLAGS_$@ is used to set specific options to ld. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 1004 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1005 | objcopy |
| 1006 | Copy binary. Uses OBJCOPYFLAGS usually specified in |
| 1007 | arch/$(ARCH)/Makefile. |
| 1008 | OBJCOPYFLAGS_$@ may be used to set additional options. |
| 1009 | |
| 1010 | gzip |
| 1011 | Compress target. Use maximum compression to compress target. |
| 1012 | |
| 1013 | Example: |
| 1014 | #arch/i386/boot/Makefile |
| 1015 | LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary |
| 1016 | LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext |
| 1017 | |
| 1018 | targets += setup setup.o bootsect bootsect.o |
| 1019 | $(obj)/setup $(obj)/bootsect: %: %.o FORCE |
| 1020 | $(call if_changed,ld) |
| 1021 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1022 | In this example, there are two possible targets, requiring different |
| 1023 | options to the linker. The linker options are specified using the |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1024 | LDFLAGS_$@ syntax - one for each potential target. |
Matt LaPlante | 5d3f083 | 2006-11-30 05:21:10 +0100 | [diff] [blame] | 1025 | $(targets) are assigned all potential targets, by which kbuild knows |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1026 | the targets and will: |
| 1027 | 1) check for commandline changes |
| 1028 | 2) delete target during make clean |
| 1029 | |
| 1030 | The ": %: %.o" part of the prerequisite is a shorthand that |
| 1031 | free us from listing the setup.o and bootsect.o files. |
| 1032 | Note: It is a common mistake to forget the "target :=" assignment, |
| 1033 | resulting in the target file being recompiled for no |
| 1034 | obvious reason. |
| 1035 | |
| 1036 | |
| 1037 | --- 6.7 Custom kbuild commands |
| 1038 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1039 | When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1040 | of a command is normally displayed. |
| 1041 | To enable this behaviour for custom commands kbuild requires |
| 1042 | two variables to be set: |
| 1043 | quiet_cmd_<command> - what shall be echoed |
| 1044 | cmd_<command> - the command to execute |
| 1045 | |
| 1046 | Example: |
| 1047 | # |
| 1048 | quiet_cmd_image = BUILD $@ |
| 1049 | cmd_image = $(obj)/tools/build $(BUILDFLAGS) \ |
| 1050 | $(obj)/vmlinux.bin > $@ |
| 1051 | |
| 1052 | targets += bzImage |
| 1053 | $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE |
| 1054 | $(call if_changed,image) |
| 1055 | @echo 'Kernel: $@ is ready' |
| 1056 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1057 | When updating the $(obj)/bzImage target, the line |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1058 | |
| 1059 | BUILD arch/i386/boot/bzImage |
| 1060 | |
| 1061 | will be displayed with "make KBUILD_VERBOSE=0". |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 1062 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1063 | |
| 1064 | --- 6.8 Preprocessing linker scripts |
| 1065 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1066 | When the vmlinux image is built, the linker script |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1067 | arch/$(ARCH)/kernel/vmlinux.lds is used. |
| 1068 | The script is a preprocessed variant of the file vmlinux.lds.S |
| 1069 | located in the same directory. |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1070 | kbuild knows .lds files and includes a rule *lds.S -> *lds. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 1071 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1072 | Example: |
| 1073 | #arch/i386/kernel/Makefile |
| 1074 | always := vmlinux.lds |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 1075 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1076 | #Makefile |
| 1077 | export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH) |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 1078 | |
| 1079 | The assignment to $(always) is used to tell kbuild to build the |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1080 | target vmlinux.lds. |
| 1081 | The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1082 | specified options when building the target vmlinux.lds. |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 1083 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1084 | When building the *.lds target, kbuild uses the variables: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1085 | CPPFLAGS : Set in top-level Makefile |
| 1086 | EXTRA_CPPFLAGS : May be set in the kbuild makefile |
| 1087 | CPPFLAGS_$(@F) : Target specific flags. |
| 1088 | Note that the full filename is used in this |
| 1089 | assignment. |
| 1090 | |
| 1091 | The kbuild infrastructure for *lds file are used in several |
| 1092 | architecture specific files. |
| 1093 | |
| 1094 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1095 | === 7 Kbuild Variables |
| 1096 | |
| 1097 | The top Makefile exports the following variables: |
| 1098 | |
| 1099 | VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION |
| 1100 | |
| 1101 | These variables define the current kernel version. A few arch |
| 1102 | Makefiles actually use these values directly; they should use |
| 1103 | $(KERNELRELEASE) instead. |
| 1104 | |
| 1105 | $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic |
| 1106 | three-part version number, such as "2", "4", and "0". These three |
| 1107 | values are always numeric. |
| 1108 | |
| 1109 | $(EXTRAVERSION) defines an even tinier sublevel for pre-patches |
| 1110 | or additional patches. It is usually some non-numeric string |
| 1111 | such as "-pre4", and is often blank. |
| 1112 | |
| 1113 | KERNELRELEASE |
| 1114 | |
| 1115 | $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable |
| 1116 | for constructing installation directory names or showing in |
| 1117 | version strings. Some arch Makefiles use it for this purpose. |
| 1118 | |
| 1119 | ARCH |
| 1120 | |
| 1121 | This variable defines the target architecture, such as "i386", |
| 1122 | "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to |
| 1123 | determine which files to compile. |
| 1124 | |
| 1125 | By default, the top Makefile sets $(ARCH) to be the same as the |
| 1126 | host system architecture. For a cross build, a user may |
| 1127 | override the value of $(ARCH) on the command line: |
| 1128 | |
| 1129 | make ARCH=m68k ... |
| 1130 | |
| 1131 | |
| 1132 | INSTALL_PATH |
| 1133 | |
| 1134 | This variable defines a place for the arch Makefiles to install |
| 1135 | the resident kernel image and System.map file. |
| 1136 | Use this for architecture specific install targets. |
| 1137 | |
| 1138 | INSTALL_MOD_PATH, MODLIB |
| 1139 | |
| 1140 | $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module |
| 1141 | installation. This variable is not defined in the Makefile but |
| 1142 | may be passed in by the user if desired. |
| 1143 | |
| 1144 | $(MODLIB) specifies the directory for module installation. |
| 1145 | The top Makefile defines $(MODLIB) to |
| 1146 | $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may |
| 1147 | override this value on the command line if desired. |
| 1148 | |
Theodore Ts'o | ac031f2 | 2006-06-21 20:53:09 -0400 | [diff] [blame] | 1149 | INSTALL_MOD_STRIP |
| 1150 | |
| 1151 | If this variable is specified, will cause modules to be stripped |
| 1152 | after they are installed. If INSTALL_MOD_STRIP is '1', then the |
| 1153 | default option --strip-debug will be used. Otherwise, |
| 1154 | INSTALL_MOD_STRIP will used as the option(s) to the strip command. |
| 1155 | |
| 1156 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1157 | === 8 Makefile language |
| 1158 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1159 | The kernel Makefiles are designed to be run with GNU Make. The Makefiles |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1160 | use only the documented features of GNU Make, but they do use many |
| 1161 | GNU extensions. |
| 1162 | |
| 1163 | GNU Make supports elementary list-processing functions. The kernel |
| 1164 | Makefiles use a novel style of list building and manipulation with few |
| 1165 | "if" statements. |
| 1166 | |
| 1167 | GNU Make has two assignment operators, ":=" and "=". ":=" performs |
| 1168 | immediate evaluation of the right-hand side and stores an actual string |
| 1169 | into the left-hand side. "=" is like a formula definition; it stores the |
| 1170 | right-hand side in an unevaluated form and then evaluates this form each |
| 1171 | time the left-hand side is used. |
| 1172 | |
| 1173 | There are some cases where "=" is appropriate. Usually, though, ":=" |
| 1174 | is the right choice. |
| 1175 | |
| 1176 | === 9 Credits |
| 1177 | |
| 1178 | Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> |
| 1179 | Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> |
| 1180 | Updates by Sam Ravnborg <sam@ravnborg.org> |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1181 | Language QA by Jan Engelhardt <jengelh@gmx.de> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1182 | |
| 1183 | === 10 TODO |
| 1184 | |
Jan Engelhardt | a07f603 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 1185 | - Describe how kbuild supports shipped files with _shipped. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1186 | - Generating offset header files. |
| 1187 | - Add more variables to section 7? |
| 1188 | |
Bryce Harrington | 39e6e9c | 2006-09-20 12:43:37 -0700 | [diff] [blame] | 1189 | |
| 1190 | |