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Jeff Kirsher49d86dc2015-02-24 20:22:56 -08001 Linux kernel release 4.x <http://kernel.org/>
Linus Torvalds1da177e2005-04-16 15:20:36 -07002
Jeff Kirsher49d86dc2015-02-24 20:22:56 -08003These are the release notes for Linux version 4. Read them carefully,
Linus Torvalds1da177e2005-04-16 15:20:36 -07004as they tell you what this is all about, explain how to install the
Diego Violacfaf7902016-04-03 04:34:48 -03005kernel, and what to do if something goes wrong.
Linus Torvalds1da177e2005-04-16 15:20:36 -07006
7WHAT IS LINUX?
8
Xose Vazquez Perez4f4e2dc2006-01-14 19:56:28 +01009 Linux is a clone of the operating system Unix, written from scratch by
10 Linus Torvalds with assistance from a loosely-knit team of hackers across
11 the Net. It aims towards POSIX and Single UNIX Specification compliance.
Linus Torvalds1da177e2005-04-16 15:20:36 -070012
Xose Vazquez Perez4f4e2dc2006-01-14 19:56:28 +010013 It has all the features you would expect in a modern fully-fledged Unix,
14 including true multitasking, virtual memory, shared libraries, demand
15 loading, shared copy-on-write executables, proper memory management,
16 and multistack networking including IPv4 and IPv6.
Linus Torvalds1da177e2005-04-16 15:20:36 -070017
18 It is distributed under the GNU General Public License - see the
Diego Violacfaf7902016-04-03 04:34:48 -030019 accompanying COPYING file for more details.
Linus Torvalds1da177e2005-04-16 15:20:36 -070020
21ON WHAT HARDWARE DOES IT RUN?
22
Xose Vazquez Perez4f4e2dc2006-01-14 19:56:28 +010023 Although originally developed first for 32-bit x86-based PCs (386 or higher),
24 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
Jesper Juhl620034c2006-12-07 00:45:58 +010025 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
Xose Vazquez Perez4f4e2dc2006-01-14 19:56:28 +010026 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,
Vineet Guptaad29fff2015-09-14 09:05:42 -070027 Xtensa, Tilera TILE, AVR32, ARC and Renesas M32R architectures.
Xose Vazquez Perez4f4e2dc2006-01-14 19:56:28 +010028
29 Linux is easily portable to most general-purpose 32- or 64-bit architectures
30 as long as they have a paged memory management unit (PMMU) and a port of the
31 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
32 also been ported to a number of architectures without a PMMU, although
33 functionality is then obviously somewhat limited.
Jesper Juhl620034c2006-12-07 00:45:58 +010034 Linux has also been ported to itself. You can now run the kernel as a
35 userspace application - this is called UserMode Linux (UML).
Linus Torvalds1da177e2005-04-16 15:20:36 -070036
37DOCUMENTATION:
38
39 - There is a lot of documentation available both in electronic form on
40 the Internet and in books, both Linux-specific and pertaining to
41 general UNIX questions. I'd recommend looking into the documentation
42 subdirectories on any Linux FTP site for the LDP (Linux Documentation
43 Project) books. This README is not meant to be documentation on the
44 system: there are much better sources available.
45
46 - There are various README files in the Documentation/ subdirectory:
Diego Violacfaf7902016-04-03 04:34:48 -030047 these typically contain kernel-specific installation notes for some
Linus Torvalds1da177e2005-04-16 15:20:36 -070048 drivers for example. See Documentation/00-INDEX for a list of what
49 is contained in each file. Please read the Changes file, as it
50 contains information about the problems, which may result by upgrading
51 your kernel.
52
53 - The Documentation/DocBook/ subdirectory contains several guides for
54 kernel developers and users. These guides can be rendered in a
Randy Dunlap2af238e2008-02-29 14:21:53 -080055 number of formats: PostScript (.ps), PDF, HTML, & man-pages, among others.
56 After installation, "make psdocs", "make pdfdocs", "make htmldocs",
57 or "make mandocs" will render the documentation in the requested format.
Linus Torvalds1da177e2005-04-16 15:20:36 -070058
Randy Dunlap2af238e2008-02-29 14:21:53 -080059INSTALLING the kernel source:
Linus Torvalds1da177e2005-04-16 15:20:36 -070060
61 - If you install the full sources, put the kernel tarball in a
Diego Viola3047bcc2015-12-05 17:50:10 -020062 directory where you have permissions (e.g. your home directory) and
Linus Torvalds1da177e2005-04-16 15:20:36 -070063 unpack it:
64
Yaowei Bai1913c6f2015-03-03 22:08:03 +080065 xz -cd linux-4.X.tar.xz | tar xvf -
Hormsb39f72f2005-10-30 15:03:19 -080066
Michael Witten5b4285f2012-04-01 22:27:30 +000067 Replace "X" with the version number of the latest kernel.
Linus Torvalds1da177e2005-04-16 15:20:36 -070068
69 Do NOT use the /usr/src/linux area! This area has a (usually
70 incomplete) set of kernel headers that are used by the library header
71 files. They should match the library, and not get messed up by
72 whatever the kernel-du-jour happens to be.
73
Jeff Kirsher49d86dc2015-02-24 20:22:56 -080074 - You can also upgrade between 4.x releases by patching. Patches are
Yaowei Bai1913c6f2015-03-03 22:08:03 +080075 distributed in the xz format. To install by patching, get all the
76 newer patch files, enter the top level directory of the kernel source
77 (linux-4.X) and execute:
Linus Torvalds1da177e2005-04-16 15:20:36 -070078
Yaowei Bai1913c6f2015-03-03 22:08:03 +080079 xz -cd ../patch-4.x.xz | patch -p1
Linus Torvalds1da177e2005-04-16 15:20:36 -070080
Michael Witten5b4285f2012-04-01 22:27:30 +000081 Replace "x" for all versions bigger than the version "X" of your current
82 source tree, _in_order_, and you should be ok. You may want to remove
83 the backup files (some-file-name~ or some-file-name.orig), and make sure
84 that there are no failed patches (some-file-name# or some-file-name.rej).
Michael Wittena20e3a72012-04-03 19:20:02 +000085 If there are, either you or I have made a mistake.
Linus Torvalds1da177e2005-04-16 15:20:36 -070086
Jeff Kirsher49d86dc2015-02-24 20:22:56 -080087 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels
Jesper Juhl6ad44222005-11-13 16:07:44 -080088 (also known as the -stable kernels) are not incremental but instead apply
Jeff Kirsher49d86dc2015-02-24 20:22:56 -080089 directly to the base 4.x kernel. For example, if your base kernel is 4.0
90 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1
91 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and
92 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,
93 patch -R) _before_ applying the 4.0.3 patch. You can read more on this in
Michael Witten7f65e922012-04-02 00:53:29 +000094 Documentation/applying-patches.txt
Jesper Juhl6ad44222005-11-13 16:07:44 -080095
Linus Torvalds1da177e2005-04-16 15:20:36 -070096 Alternatively, the script patch-kernel can be used to automate this
97 process. It determines the current kernel version and applies any
98 patches found.
99
Michael Witten3773b452012-04-02 01:07:52 +0000100 linux/scripts/patch-kernel linux
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101
102 The first argument in the command above is the location of the
103 kernel source. Patches are applied from the current directory, but
104 an alternative directory can be specified as the second argument.
105
Linus Torvalds1da177e2005-04-16 15:20:36 -0700106 - Make sure you have no stale .o files and dependencies lying around:
107
Michael Witten3773b452012-04-02 01:07:52 +0000108 cd linux
109 make mrproper
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110
111 You should now have the sources correctly installed.
112
113SOFTWARE REQUIREMENTS
114
Jeff Kirsher49d86dc2015-02-24 20:22:56 -0800115 Compiling and running the 4.x kernels requires up-to-date
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116 versions of various software packages. Consult
117 Documentation/Changes for the minimum version numbers required
118 and how to get updates for these packages. Beware that using
119 excessively old versions of these packages can cause indirect
120 errors that are very difficult to track down, so don't assume that
121 you can just update packages when obvious problems arise during
122 build or operation.
123
124BUILD directory for the kernel:
125
Michael Wittena6144bb2012-04-02 00:31:33 +0000126 When compiling the kernel, all output files will per default be
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127 stored together with the kernel source code.
Diego Viola3047bcc2015-12-05 17:50:10 -0200128 Using the option "make O=output/dir" allows you to specify an alternate
Linus Torvalds1da177e2005-04-16 15:20:36 -0700129 place for the output files (including .config).
130 Example:
Michael Witten88f7a642012-04-02 00:46:58 +0000131
Jeff Kirsher49d86dc2015-02-24 20:22:56 -0800132 kernel source code: /usr/src/linux-4.X
Michael Witten3773b452012-04-02 01:07:52 +0000133 build directory: /home/name/build/kernel
Linus Torvalds1da177e2005-04-16 15:20:36 -0700134
Michael Wittena6144bb2012-04-02 00:31:33 +0000135 To configure and build the kernel, use:
Michael Witten88f7a642012-04-02 00:46:58 +0000136
Jeff Kirsher49d86dc2015-02-24 20:22:56 -0800137 cd /usr/src/linux-4.X
Michael Witten88f7a642012-04-02 00:46:58 +0000138 make O=/home/name/build/kernel menuconfig
139 make O=/home/name/build/kernel
140 sudo make O=/home/name/build/kernel modules_install install
Linus Torvalds1da177e2005-04-16 15:20:36 -0700141
Michael Wittena6144bb2012-04-02 00:31:33 +0000142 Please note: If the 'O=output/dir' option is used, then it must be
Linus Torvalds1da177e2005-04-16 15:20:36 -0700143 used for all invocations of make.
144
145CONFIGURING the kernel:
146
147 Do not skip this step even if you are only upgrading one minor
148 version. New configuration options are added in each release, and
149 odd problems will turn up if the configuration files are not set up
150 as expected. If you want to carry your existing configuration to a
151 new version with minimal work, use "make oldconfig", which will
152 only ask you for the answers to new questions.
153
Michael Witten6d127602012-04-02 00:33:02 +0000154 - Alternative configuration commands are:
Michael Witten88f7a642012-04-02 00:46:58 +0000155
Michael Witten3773b452012-04-02 01:07:52 +0000156 "make config" Plain text interface.
Michael Witten88f7a642012-04-02 00:46:58 +0000157
Michael Witten3773b452012-04-02 01:07:52 +0000158 "make menuconfig" Text based color menus, radiolists & dialogs.
Michael Witten88f7a642012-04-02 00:46:58 +0000159
Michael Witten3773b452012-04-02 01:07:52 +0000160 "make nconfig" Enhanced text based color menus.
Michael Witten88f7a642012-04-02 00:46:58 +0000161
Diego Viola3047bcc2015-12-05 17:50:10 -0200162 "make xconfig" Qt based configuration tool.
Michael Witten88f7a642012-04-02 00:46:58 +0000163
Diego Viola3047bcc2015-12-05 17:50:10 -0200164 "make gconfig" GTK+ based configuration tool.
Michael Witten88f7a642012-04-02 00:46:58 +0000165
Michael Witten3773b452012-04-02 01:07:52 +0000166 "make oldconfig" Default all questions based on the contents of
167 your existing ./.config file and asking about
168 new config symbols.
Michael Witten88f7a642012-04-02 00:46:58 +0000169
Michael Witten3773b452012-04-02 01:07:52 +0000170 "make silentoldconfig"
171 Like above, but avoids cluttering the screen
172 with questions already answered.
173 Additionally updates the dependencies.
Michael Witten88f7a642012-04-02 00:46:58 +0000174
Kees Cookfc0d1b92012-10-24 10:22:43 -0700175 "make olddefconfig"
176 Like above, but sets new symbols to their default
177 values without prompting.
178
Michael Witten3773b452012-04-02 01:07:52 +0000179 "make defconfig" Create a ./.config file by using the default
180 symbol values from either arch/$ARCH/defconfig
181 or arch/$ARCH/configs/${PLATFORM}_defconfig,
182 depending on the architecture.
Michael Witten88f7a642012-04-02 00:46:58 +0000183
Michael Witten3773b452012-04-02 01:07:52 +0000184 "make ${PLATFORM}_defconfig"
185 Create a ./.config file by using the default
186 symbol values from
187 arch/$ARCH/configs/${PLATFORM}_defconfig.
188 Use "make help" to get a list of all available
189 platforms of your architecture.
Michael Witten88f7a642012-04-02 00:46:58 +0000190
Michael Witten3773b452012-04-02 01:07:52 +0000191 "make allyesconfig"
192 Create a ./.config file by setting symbol
193 values to 'y' as much as possible.
Michael Witten88f7a642012-04-02 00:46:58 +0000194
Michael Witten3773b452012-04-02 01:07:52 +0000195 "make allmodconfig"
196 Create a ./.config file by setting symbol
197 values to 'm' as much as possible.
Michael Witten88f7a642012-04-02 00:46:58 +0000198
Michael Witten3773b452012-04-02 01:07:52 +0000199 "make allnoconfig" Create a ./.config file by setting symbol
200 values to 'n' as much as possible.
Michael Witten88f7a642012-04-02 00:46:58 +0000201
Michael Witten3773b452012-04-02 01:07:52 +0000202 "make randconfig" Create a ./.config file by setting symbol
203 values to random values.
Randy Dunlap9dfb5632006-04-18 22:21:53 -0700204
Steven Rostedt80b810b2012-10-05 16:52:50 -0400205 "make localmodconfig" Create a config based on current config and
206 loaded modules (lsmod). Disables any module
207 option that is not needed for the loaded modules.
208
209 To create a localmodconfig for another machine,
210 store the lsmod of that machine into a file
211 and pass it in as a LSMOD parameter.
212
213 target$ lsmod > /tmp/mylsmod
214 target$ scp /tmp/mylsmod host:/tmp
215
216 host$ make LSMOD=/tmp/mylsmod localmodconfig
217
218 The above also works when cross compiling.
219
220 "make localyesconfig" Similar to localmodconfig, except it will convert
221 all module options to built in (=y) options.
222
Randy Dunlap2af238e2008-02-29 14:21:53 -0800223 You can find more information on using the Linux kernel config tools
Li Zefanad444682009-02-20 15:38:43 -0800224 in Documentation/kbuild/kconfig.txt.
Randy Dunlap2af238e2008-02-29 14:21:53 -0800225
Michael Witten3773b452012-04-02 01:07:52 +0000226 - NOTES on "make config":
Michael Witten88f7a642012-04-02 00:46:58 +0000227
Michael Witten3773b452012-04-02 01:07:52 +0000228 - Having unnecessary drivers will make the kernel bigger, and can
229 under some circumstances lead to problems: probing for a
230 nonexistent controller card may confuse your other controllers
Michael Witten88f7a642012-04-02 00:46:58 +0000231
Michael Witten3773b452012-04-02 01:07:52 +0000232 - A kernel with math-emulation compiled in will still use the
233 coprocessor if one is present: the math emulation will just
234 never get used in that case. The kernel will be slightly larger,
235 but will work on different machines regardless of whether they
236 have a math coprocessor or not.
Michael Witten88f7a642012-04-02 00:46:58 +0000237
Michael Witten3773b452012-04-02 01:07:52 +0000238 - The "kernel hacking" configuration details usually result in a
239 bigger or slower kernel (or both), and can even make the kernel
240 less stable by configuring some routines to actively try to
241 break bad code to find kernel problems (kmalloc()). Thus you
242 should probably answer 'n' to the questions for "development",
243 "experimental", or "debugging" features.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700244
Linus Torvalds1da177e2005-04-16 15:20:36 -0700245COMPILING the kernel:
246
Andrew Mortona1365642006-01-08 01:04:09 -0800247 - Make sure you have at least gcc 3.2 available.
248 For more information, refer to Documentation/Changes.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700249
250 Please note that you can still run a.out user programs with this kernel.
251
252 - Do a "make" to create a compressed kernel image. It is also
253 possible to do "make install" if you have lilo installed to suit the
254 kernel makefiles, but you may want to check your particular lilo setup first.
255
Michael Wittena6144bb2012-04-02 00:31:33 +0000256 To do the actual install, you have to be root, but none of the normal
Linus Torvalds1da177e2005-04-16 15:20:36 -0700257 build should require that. Don't take the name of root in vain.
258
259 - If you configured any of the parts of the kernel as `modules', you
260 will also have to do "make modules_install".
261
Randy Dunlap2af238e2008-02-29 14:21:53 -0800262 - Verbose kernel compile/build output:
263
Michael Wittena6144bb2012-04-02 00:31:33 +0000264 Normally, the kernel build system runs in a fairly quiet mode (but not
Randy Dunlap2af238e2008-02-29 14:21:53 -0800265 totally silent). However, sometimes you or other kernel developers need
266 to see compile, link, or other commands exactly as they are executed.
Diego Viola3047bcc2015-12-05 17:50:10 -0200267 For this, use "verbose" build mode. This is done by passing
268 "V=1" to the "make" command, e.g.
Randy Dunlap2af238e2008-02-29 14:21:53 -0800269
Michael Witten3773b452012-04-02 01:07:52 +0000270 make V=1 all
Randy Dunlap2af238e2008-02-29 14:21:53 -0800271
272 To have the build system also tell the reason for the rebuild of each
273 target, use "V=2". The default is "V=0".
274
Diego Violacfaf7902016-04-03 04:34:48 -0300275 - Keep a backup kernel handy in case something goes wrong. This is
Linus Torvalds1da177e2005-04-16 15:20:36 -0700276 especially true for the development releases, since each new release
277 contains new code which has not been debugged. Make sure you keep a
278 backup of the modules corresponding to that kernel, as well. If you
279 are installing a new kernel with the same version number as your
280 working kernel, make a backup of your modules directory before you
281 do a "make modules_install".
Michael Witten88f7a642012-04-02 00:46:58 +0000282
Randy Dunlape3fc4cc2005-09-22 21:44:07 -0700283 Alternatively, before compiling, use the kernel config option
284 "LOCALVERSION" to append a unique suffix to the regular kernel version.
285 LOCALVERSION can be set in the "General Setup" menu.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700286
287 - In order to boot your new kernel, you'll need to copy the kernel
Øyvind A. Holm35db7e92016-07-26 15:21:33 +0200288 image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
Diego Violacfaf7902016-04-03 04:34:48 -0300289 to the place where your regular bootable kernel is found.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700290
291 - Booting a kernel directly from a floppy without the assistance of a
292 bootloader such as LILO, is no longer supported.
293
Michael Wittena6144bb2012-04-02 00:31:33 +0000294 If you boot Linux from the hard drive, chances are you use LILO, which
Linus Torvalds1da177e2005-04-16 15:20:36 -0700295 uses the kernel image as specified in the file /etc/lilo.conf. The
296 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
297 /boot/bzImage. To use the new kernel, save a copy of the old image
298 and copy the new image over the old one. Then, you MUST RERUN LILO
Diego Viola3047bcc2015-12-05 17:50:10 -0200299 to update the loading map! If you don't, you won't be able to boot
Linus Torvalds1da177e2005-04-16 15:20:36 -0700300 the new kernel image.
301
Diego Violacfaf7902016-04-03 04:34:48 -0300302 Reinstalling LILO is usually a matter of running /sbin/lilo.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700303 You may wish to edit /etc/lilo.conf to specify an entry for your
304 old kernel image (say, /vmlinux.old) in case the new one does not
Diego Violacfaf7902016-04-03 04:34:48 -0300305 work. See the LILO docs for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700306
307 After reinstalling LILO, you should be all set. Shutdown the system,
308 reboot, and enjoy!
309
310 If you ever need to change the default root device, video mode,
311 ramdisk size, etc. in the kernel image, use the 'rdev' program (or
312 alternatively the LILO boot options when appropriate). No need to
Diego Violacfaf7902016-04-03 04:34:48 -0300313 recompile the kernel to change these parameters.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700314
Diego Violacfaf7902016-04-03 04:34:48 -0300315 - Reboot with the new kernel and enjoy.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700316
317IF SOMETHING GOES WRONG:
318
319 - If you have problems that seem to be due to kernel bugs, please check
320 the file MAINTAINERS to see if there is a particular person associated
321 with the part of the kernel that you are having trouble with. If there
322 isn't anyone listed there, then the second best thing is to mail
Linus Torvalds99ddcc72007-01-23 14:22:35 -0800323 them to me (torvalds@linux-foundation.org), and possibly to any other
324 relevant mailing-list or to the newsgroup.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700325
326 - In all bug-reports, *please* tell what kernel you are talking about,
327 how to duplicate the problem, and what your setup is (use your common
328 sense). If the problem is new, tell me so, and if the problem is
329 old, please try to tell me when you first noticed it.
330
331 - If the bug results in a message like
332
Michael Witten3773b452012-04-02 01:07:52 +0000333 unable to handle kernel paging request at address C0000010
334 Oops: 0002
335 EIP: 0010:XXXXXXXX
336 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
337 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
338 ds: xxxx es: xxxx fs: xxxx gs: xxxx
339 Pid: xx, process nr: xx
340 xx xx xx xx xx xx xx xx xx xx
Linus Torvalds1da177e2005-04-16 15:20:36 -0700341
342 or similar kernel debugging information on your screen or in your
343 system log, please duplicate it *exactly*. The dump may look
344 incomprehensible to you, but it does contain information that may
345 help debugging the problem. The text above the dump is also
346 important: it tells something about why the kernel dumped code (in
Michael Wittena6144bb2012-04-02 00:31:33 +0000347 the above example, it's due to a bad kernel pointer). More information
Linus Torvalds1da177e2005-04-16 15:20:36 -0700348 on making sense of the dump is in Documentation/oops-tracing.txt
349
350 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
351 as is, otherwise you will have to use the "ksymoops" program to make
Jesper Juhl620034c2006-12-07 00:45:58 +0100352 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
353 This utility can be downloaded from
354 ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
Michael Witten6d127602012-04-02 00:33:02 +0000355 Alternatively, you can do the dump lookup by hand:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700356
357 - In debugging dumps like the above, it helps enormously if you can
358 look up what the EIP value means. The hex value as such doesn't help
359 me or anybody else very much: it will depend on your particular
360 kernel setup. What you should do is take the hex value from the EIP
361 line (ignore the "0010:"), and look it up in the kernel namelist to
362 see which kernel function contains the offending address.
363
364 To find out the kernel function name, you'll need to find the system
365 binary associated with the kernel that exhibited the symptom. This is
366 the file 'linux/vmlinux'. To extract the namelist and match it against
367 the EIP from the kernel crash, do:
368
Michael Witten3773b452012-04-02 01:07:52 +0000369 nm vmlinux | sort | less
Linus Torvalds1da177e2005-04-16 15:20:36 -0700370
371 This will give you a list of kernel addresses sorted in ascending
372 order, from which it is simple to find the function that contains the
373 offending address. Note that the address given by the kernel
374 debugging messages will not necessarily match exactly with the
375 function addresses (in fact, that is very unlikely), so you can't
376 just 'grep' the list: the list will, however, give you the starting
377 point of each kernel function, so by looking for the function that
378 has a starting address lower than the one you are searching for but
379 is followed by a function with a higher address you will find the one
380 you want. In fact, it may be a good idea to include a bit of
381 "context" in your problem report, giving a few lines around the
Diego Violacfaf7902016-04-03 04:34:48 -0300382 interesting one.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700383
384 If you for some reason cannot do the above (you have a pre-compiled
385 kernel image or similar), telling me as much about your setup as
Jesper Juhl620034c2006-12-07 00:45:58 +0100386 possible will help. Please read the REPORTING-BUGS document for details.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700387
Michael Witten6d127602012-04-02 00:33:02 +0000388 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
Linus Torvalds1da177e2005-04-16 15:20:36 -0700389 cannot change values or set break points.) To do this, first compile the
Øyvind A. Holm35db7e92016-07-26 15:21:33 +0200390 kernel with -g; edit arch/x86/Makefile appropriately, then do a "make
Linus Torvalds1da177e2005-04-16 15:20:36 -0700391 clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
392
393 After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
394 You can now use all the usual gdb commands. The command to look up the
395 point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
396 with the EIP value.)
397
398 gdb'ing a non-running kernel currently fails because gdb (wrongly)
399 disregards the starting offset for which the kernel is compiled.
400