diff options
author | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2016-11-07 17:03:19 -0200 |
---|---|---|
committer | Jonathan Corbet <corbet@lwn.net> | 2016-11-07 16:50:33 -0700 |
commit | f226e460875da8e00febf55e5ec3438e498ca676 (patch) | |
tree | e3226e34e0120ba45e78edd3d22b4ffbb31b79e0 | |
parent | 337c188dff4a850643ee299c38b2591bbda937a7 (diff) | |
download | linux-rt-f226e460875da8e00febf55e5ec3438e498ca676.tar.gz |
admin-guide: merge oops-tracing with bug-hunting
Now that oops-tracing.rst has only information about
stack dumps found on OOPS, and bug-hunting.rst has only
information about how to identify the source code line
associated with a stack dump, let's merge them and
improve the information inside it.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
-rw-r--r-- | Documentation/admin-guide/bug-hunting.rst | 358 | ||||
-rw-r--r-- | Documentation/admin-guide/index.rst | 1 | ||||
-rw-r--r-- | Documentation/admin-guide/oops-tracing.rst | 241 |
3 files changed, 293 insertions, 307 deletions
diff --git a/Documentation/admin-guide/bug-hunting.rst b/Documentation/admin-guide/bug-hunting.rst index d245d4677ae2..08c4b1308189 100644 --- a/Documentation/admin-guide/bug-hunting.rst +++ b/Documentation/admin-guide/bug-hunting.rst @@ -1,68 +1,113 @@ Bug hunting -+++++++++++ - -Last updated: 28 October 2016 - -Fixing the bug -============== - -Nobody is going to tell you how to fix bugs. Seriously. You need to work it -out. But below are some hints on how to use the tools. - -objdump -------- - -To debug a kernel, use objdump and look for the hex offset from the crash -output to find the valid line of code/assembler. Without debug symbols, you -will see the assembler code for the routine shown, but if your kernel has -debug symbols the C code will also be available. (Debug symbols can be enabled -in the kernel hacking menu of the menu configuration.) For example:: - - $ objdump -r -S -l --disassemble net/dccp/ipv4.o +=========== + +Kernel bug reports often come with a stack dump like the one below:: + + ------------[ cut here ]------------ + WARNING: CPU: 1 PID: 28102 at kernel/module.c:1108 module_put+0x57/0x70 + Modules linked in: dvb_usb_gp8psk(-) dvb_usb dvb_core nvidia_drm(PO) nvidia_modeset(PO) snd_hda_codec_hdmi snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core snd_pcm snd_timer snd soundcore nvidia(PO) [last unloaded: rc_core] + CPU: 1 PID: 28102 Comm: rmmod Tainted: P WC O 4.8.4-build.1 #1 + Hardware name: MSI MS-7309/MS-7309, BIOS V1.12 02/23/2009 + 00000000 c12ba080 00000000 00000000 c103ed6a c1616014 00000001 00006dc6 + c1615862 00000454 c109e8a7 c109e8a7 00000009 ffffffff 00000000 f13f6a10 + f5f5a600 c103ee33 00000009 00000000 00000000 c109e8a7 f80ca4d0 c109f617 + Call Trace: + [<c12ba080>] ? dump_stack+0x44/0x64 + [<c103ed6a>] ? __warn+0xfa/0x120 + [<c109e8a7>] ? module_put+0x57/0x70 + [<c109e8a7>] ? module_put+0x57/0x70 + [<c103ee33>] ? warn_slowpath_null+0x23/0x30 + [<c109e8a7>] ? module_put+0x57/0x70 + [<f80ca4d0>] ? gp8psk_fe_set_frontend+0x460/0x460 [dvb_usb_gp8psk] + [<c109f617>] ? symbol_put_addr+0x27/0x50 + [<f80bc9ca>] ? dvb_usb_adapter_frontend_exit+0x3a/0x70 [dvb_usb] + [<f80bb3bf>] ? dvb_usb_exit+0x2f/0xd0 [dvb_usb] + [<c13d03bc>] ? usb_disable_endpoint+0x7c/0xb0 + [<f80bb48a>] ? dvb_usb_device_exit+0x2a/0x50 [dvb_usb] + [<c13d2882>] ? usb_unbind_interface+0x62/0x250 + [<c136b514>] ? __pm_runtime_idle+0x44/0x70 + [<c13620d8>] ? __device_release_driver+0x78/0x120 + [<c1362907>] ? driver_detach+0x87/0x90 + [<c1361c48>] ? bus_remove_driver+0x38/0x90 + [<c13d1c18>] ? usb_deregister+0x58/0xb0 + [<c109fbb0>] ? SyS_delete_module+0x130/0x1f0 + [<c1055654>] ? task_work_run+0x64/0x80 + [<c1000fa5>] ? exit_to_usermode_loop+0x85/0x90 + [<c10013f0>] ? do_fast_syscall_32+0x80/0x130 + [<c1549f43>] ? sysenter_past_esp+0x40/0x6a + ---[ end trace 6ebc60ef3981792f ]--- + +Such stack traces provide enough information to identify the line inside the +Kernel's source code where the bug happened. Depending on the severity of +the issue, it may also contain the word **Oops**, as on this one:: + + BUG: unable to handle kernel NULL pointer dereference at (null) + IP: [<c06969d4>] iret_exc+0x7d0/0xa59 + *pdpt = 000000002258a001 *pde = 0000000000000000 + Oops: 0002 [#1] PREEMPT SMP + ... + +Despite being an **Oops** or some other sort of stack trace, the offended +line is usually required to identify and handle the bug. Along this chapter, +we'll refer to "Oops" for all kinds of stack traces that need to be analized. .. note:: - You need to be at the top level of the kernel tree for this to pick up - your C files. - -If you don't have access to the code you can also debug on some crash dumps -e.g. crash dump output as shown by Dave Miller:: - - EIP is at +0x14/0x4c0 - ... - Code: 44 24 04 e8 6f 05 00 00 e9 e8 fe ff ff 8d 76 00 8d bc 27 00 00 - 00 00 55 57 56 53 81 ec bc 00 00 00 8b ac 24 d0 00 00 00 8b 5d 08 - <8b> 83 3c 01 00 00 89 44 24 14 8b 45 28 85 c0 89 44 24 18 0f 85 - - Put the bytes into a "foo.s" file like this: - - .text - .globl foo - foo: - .byte .... /* bytes from Code: part of OOPS dump */ - - Compile it with "gcc -c -o foo.o foo.s" then look at the output of - "objdump --disassemble foo.o". - - Output: - - ip_queue_xmit: - push %ebp - push %edi - push %esi - push %ebx - sub $0xbc, %esp - mov 0xd0(%esp), %ebp ! %ebp = arg0 (skb) - mov 0x8(%ebp), %ebx ! %ebx = skb->sk - mov 0x13c(%ebx), %eax ! %eax = inet_sk(sk)->opt + ``ksymoops`` is useless on 2.6 or upper. Please use the Oops in its original + format (from ``dmesg``, etc). Ignore any references in this or other docs to + "decoding the Oops" or "running it through ksymoops". + If you post an Oops from 2.6+ that has been run through ``ksymoops``, + people will just tell you to repost it. + +Where is the Oops message is located? +------------------------------------- + +Normally the Oops text is read from the kernel buffers by klogd and +handed to ``syslogd`` which writes it to a syslog file, typically +``/var/log/messages`` (depends on ``/etc/syslog.conf``). On systems with +systemd, it may also be stored by the ``journald`` daemon, and accessed +by running ``journalctl`` command. + +Sometimes ``klogd`` dies, in which case you can run ``dmesg > file`` to +read the data from the kernel buffers and save it. Or you can +``cat /proc/kmsg > file``, however you have to break in to stop the transfer, +``kmsg`` is a "never ending file". + +If the machine has crashed so badly that you cannot enter commands or +the disk is not available then you have three options: + +(1) Hand copy the text from the screen and type it in after the machine + has restarted. Messy but it is the only option if you have not + planned for a crash. Alternatively, you can take a picture of + the screen with a digital camera - not nice, but better than + nothing. If the messages scroll off the top of the console, you + may find that booting with a higher resolution (eg, ``vga=791``) + will allow you to read more of the text. (Caveat: This needs ``vesafb``, + so won't help for 'early' oopses) + +(2) Boot with a serial console (see + :ref:`Documentation/admin-guide/serial-console.rst <serial_console>`), + run a null modem to a second machine and capture the output there + using your favourite communication program. Minicom works well. + +(3) Use Kdump (see Documentation/kdump/kdump.txt), + extract the kernel ring buffer from old memory with using dmesg + gdbmacro in Documentation/kdump/gdbmacros.txt. + +Finding the bug's location +-------------------------- + +Reporting a bug works best if you point the location of the bug at the +Kernel source file. There are two methods for doing that. Usually, using +``gdb`` is easier, but the Kernel should be pre-compiled with debug info. gdb ---- +^^^ -In addition, you can use GDB to figure out the exact file and line +The GNU debug (``gdb``) is the best way to figure out the exact file and line number of the OOPS from the ``vmlinux`` file. -The usage of gdb requires a kernel compiled with ``CONFIG_DEBUG_INFO``. +The usage of gdb works best on a kernel compiled with ``CONFIG_DEBUG_INFO``. This can be set by running:: $ ./scripts/config -d COMPILE_TEST -e DEBUG_KERNEL -e DEBUG_INFO @@ -84,6 +129,7 @@ offset from the OOPS:: And recompile the kernel with ``CONFIG_DEBUG_INFO`` enabled:: + $ ./scripts/config -d COMPILE_TEST -e DEBUG_KERNEL -e DEBUG_INFO $ make vmlinux $ gdb vmlinux (gdb) l *vt_ioctl+0xda8 @@ -125,17 +171,199 @@ in gdb and list the relevant code:: $ gdb fs/jbd/jbd.ko (gdb) l *log_wait_commit+0xa3 -Another very useful option of the Kernel Hacking section in menuconfig is -Debug memory allocations. This will help you see whether data has been -initialised and not set before use etc. To see the values that get assigned -with this look at ``mm/slab.c`` and search for ``POISON_INUSE``. When using -this an Oops will often show the poisoned data instead of zero which is the -default. +.. note:: + + You can also do the same for any function call at the stack trace, + like this one:: + + [<f80bc9ca>] ? dvb_usb_adapter_frontend_exit+0x3a/0x70 [dvb_usb] + + The position where the above call happened can be seen with:: + + $ gdb drivers/media/usb/dvb-usb/dvb-usb.o + (gdb) l *dvb_usb_adapter_frontend_exit+0x3a + +objdump +^^^^^^^ + +To debug a kernel, use objdump and look for the hex offset from the crash +output to find the valid line of code/assembler. Without debug symbols, you +will see the assembler code for the routine shown, but if your kernel has +debug symbols the C code will also be available. (Debug symbols can be enabled +in the kernel hacking menu of the menu configuration.) For example:: + + $ objdump -r -S -l --disassemble net/dccp/ipv4.o + +.. note:: -Once you have worked out a fix please submit it upstream. After all open -source is about sharing what you do and don't you want to be recognised for -your genius? + You need to be at the top level of the kernel tree for this to pick up + your C files. + +If you don't have access to the code you can also debug on some crash dumps +e.g. crash dump output as shown by Dave Miller:: + + EIP is at +0x14/0x4c0 + ... + Code: 44 24 04 e8 6f 05 00 00 e9 e8 fe ff ff 8d 76 00 8d bc 27 00 00 + 00 00 55 57 56 53 81 ec bc 00 00 00 8b ac 24 d0 00 00 00 8b 5d 08 + <8b> 83 3c 01 00 00 89 44 24 14 8b 45 28 85 c0 89 44 24 18 0f 85 + + Put the bytes into a "foo.s" file like this: + + .text + .globl foo + foo: + .byte .... /* bytes from Code: part of OOPS dump */ + + Compile it with "gcc -c -o foo.o foo.s" then look at the output of + "objdump --disassemble foo.o". + + Output: + + ip_queue_xmit: + push %ebp + push %edi + push %esi + push %ebx + sub $0xbc, %esp + mov 0xd0(%esp), %ebp ! %ebp = arg0 (skb) + mov 0x8(%ebp), %ebx ! %ebx = skb->sk + mov 0x13c(%ebx), %eax ! %eax = inet_sk(sk)->opt + +Reporting the bug +----------------- + +Once you find where the bug happened, by inspecting its location, +you could either try to fix it yourself or report it upstream. + +In order to report it upstream, you should identify the mailing list +used for the development of the affected code. This can be done by using +the ``get_maintainer.pl`` script. + +For example, if you find a bug at the gspca's conex.c file, you can get +their maintainers with:: + + $ ./scripts/get_maintainer.pl -f drivers/media/usb/gspca/sonixj.c + Hans Verkuil <hverkuil@xs4all.nl> (odd fixer:GSPCA USB WEBCAM DRIVER,commit_signer:1/1=100%) + Mauro Carvalho Chehab <mchehab@kernel.org> (maintainer:MEDIA INPUT INFRASTRUCTURE (V4L/DVB),commit_signer:1/1=100%) + Tejun Heo <tj@kernel.org> (commit_signer:1/1=100%) + Bhaktipriya Shridhar <bhaktipriya96@gmail.com> (commit_signer:1/1=100%,authored:1/1=100%,added_lines:4/4=100%,removed_lines:9/9=100%) + linux-media@vger.kernel.org (open list:GSPCA USB WEBCAM DRIVER) + linux-kernel@vger.kernel.org (open list) + +Please notice that it will point to: + +- The last developers that touched on the source code. On the above example, + Tejun and Bhaktipriya (in this specific case, none really envolved on the + development of this file); +- The driver maintainer (Hans Verkuil); +- The subsystem maintainer (Mauro Carvalho Chehab) +- The driver and/or subsystem mailing list (linux-media@vger.kernel.org); +- the Linux Kernel mailing list (linux-kernel@vger.kernel.org). + +Usually, the fastest way to have your bug fixed is to report it to mailing +list used for the development of the code (linux-media ML) copying the driver maintainer (Hans). + +If you are totally stumped as to whom to send the report, and +``get_maintainer.pl`` didn't provide you anything useful, send it to +linux-kernel@vger.kernel.org. + +Thanks for your help in making Linux as stable as humanly possible. + +Fixing the bug +-------------- + +If you know programming, you could help us by not only reporting the bug, +but also providing us with a solution. After all open source is about +sharing what you do and don't you want to be recognised for your genius? + +If you decide to take this way, once you have worked out a fix please submit +it upstream. Please do read ref:`Documentation/process/submitting-patches.rst <submittingpatches>` though to help your code get accepted. + + +--------------------------------------------------------------------------- + +Notes on Oops tracing with ``klogd`` +------------------------------------ + +In order to help Linus and the other kernel developers there has been +substantial support incorporated into ``klogd`` for processing protection +faults. In order to have full support for address resolution at least +version 1.3-pl3 of the ``sysklogd`` package should be used. + +When a protection fault occurs the ``klogd`` daemon automatically +translates important addresses in the kernel log messages to their +symbolic equivalents. This translated kernel message is then +forwarded through whatever reporting mechanism ``klogd`` is using. The +protection fault message can be simply cut out of the message files +and forwarded to the kernel developers. + +Two types of address resolution are performed by ``klogd``. The first is +static translation and the second is dynamic translation. Static +translation uses the System.map file in much the same manner that +ksymoops does. In order to do static translation the ``klogd`` daemon +must be able to find a system map file at daemon initialization time. +See the klogd man page for information on how ``klogd`` searches for map +files. + +Dynamic address translation is important when kernel loadable modules +are being used. Since memory for kernel modules is allocated from the +kernel's dynamic memory pools there are no fixed locations for either +the start of the module or for functions and symbols in the module. + +The kernel supports system calls which allow a program to determine +which modules are loaded and their location in memory. Using these +system calls the klogd daemon builds a symbol table which can be used +to debug a protection fault which occurs in a loadable kernel module. + +At the very minimum klogd will provide the name of the module which +generated the protection fault. There may be additional symbolic +information available if the developer of the loadable module chose to +export symbol information from the module. + +Since the kernel module environment can be dynamic there must be a +mechanism for notifying the ``klogd`` daemon when a change in module +environment occurs. There are command line options available which +allow klogd to signal the currently executing daemon that symbol +information should be refreshed. See the ``klogd`` manual page for more +information. + +A patch is included with the sysklogd distribution which modifies the +``modules-2.0.0`` package to automatically signal klogd whenever a module +is loaded or unloaded. Applying this patch provides essentially +seamless support for debugging protection faults which occur with +kernel loadable modules. + +The following is an example of a protection fault in a loadable module +processed by ``klogd``:: + + Aug 29 09:51:01 blizard kernel: Unable to handle kernel paging request at virtual address f15e97cc + Aug 29 09:51:01 blizard kernel: current->tss.cr3 = 0062d000, %cr3 = 0062d000 + Aug 29 09:51:01 blizard kernel: *pde = 00000000 + Aug 29 09:51:01 blizard kernel: Oops: 0002 + Aug 29 09:51:01 blizard kernel: CPU: 0 + Aug 29 09:51:01 blizard kernel: EIP: 0010:[oops:_oops+16/3868] + Aug 29 09:51:01 blizard kernel: EFLAGS: 00010212 + Aug 29 09:51:01 blizard kernel: eax: 315e97cc ebx: 003a6f80 ecx: 001be77b edx: 00237c0c + Aug 29 09:51:01 blizard kernel: esi: 00000000 edi: bffffdb3 ebp: 00589f90 esp: 00589f8c + Aug 29 09:51:01 blizard kernel: ds: 0018 es: 0018 fs: 002b gs: 002b ss: 0018 + Aug 29 09:51:01 blizard kernel: Process oops_test (pid: 3374, process nr: 21, stackpage=00589000) + Aug 29 09:51:01 blizard kernel: Stack: 315e97cc 00589f98 0100b0b4 bffffed4 0012e38e 00240c64 003a6f80 00000001 + Aug 29 09:51:01 blizard kernel: 00000000 00237810 bfffff00 0010a7fa 00000003 00000001 00000000 bfffff00 + Aug 29 09:51:01 blizard kernel: bffffdb3 bffffed4 ffffffda 0000002b 0007002b 0000002b 0000002b 00000036 + Aug 29 09:51:01 blizard kernel: Call Trace: [oops:_oops_ioctl+48/80] [_sys_ioctl+254/272] [_system_call+82/128] + Aug 29 09:51:01 blizard kernel: Code: c7 00 05 00 00 00 eb 08 90 90 90 90 90 90 90 90 89 ec 5d c3 + +--------------------------------------------------------------------------- + +:: + + Dr. G.W. Wettstein Oncology Research Div. Computing Facility + Roger Maris Cancer Center INTERNET: greg@wind.rmcc.com + 820 4th St. N. + Fargo, ND 58122 + Phone: 701-234-7556 diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst index 86a6ab98d6b6..2681cbd24cdd 100644 --- a/Documentation/admin-guide/index.rst +++ b/Documentation/admin-guide/index.rst @@ -27,7 +27,6 @@ problems and bugs in particular. security-bugs bug-hunting bug-bisect - oops-tracing tainted-kernels ramoops dynamic-debug-howto diff --git a/Documentation/admin-guide/oops-tracing.rst b/Documentation/admin-guide/oops-tracing.rst deleted file mode 100644 index 1f5e2b716631..000000000000 --- a/Documentation/admin-guide/oops-tracing.rst +++ /dev/null @@ -1,241 +0,0 @@ -OOPS tracing -============ - -.. note:: - - ``ksymoops`` is useless on 2.6 or upper. Please use the Oops in its original - format (from ``dmesg``, etc). Ignore any references in this or other docs to - "decoding the Oops" or "running it through ksymoops". - If you post an Oops from 2.6+ that has been run through ``ksymoops``, - people will just tell you to repost it. - -Quick Summary -------------- - -Find the Oops and send it to the maintainer of the kernel area that seems to be -involved with the problem. Don't worry too much about getting the wrong person. -If you are unsure send it to the person responsible for the code relevant to -what you were doing. If it occurs repeatably try and describe how to recreate -it. That's worth even more than the oops. - -If you are totally stumped as to whom to send the report, send it to -linux-kernel@vger.kernel.org. Thanks for your help in making Linux as -stable as humanly possible. - -Where is the Oops? ----------------------- - -Normally the Oops text is read from the kernel buffers by klogd and -handed to ``syslogd`` which writes it to a syslog file, typically -``/var/log/messages`` (depends on ``/etc/syslog.conf``). Sometimes ``klogd`` -dies, in which case you can run ``dmesg > file`` to read the data from the -kernel buffers and save it. Or you can ``cat /proc/kmsg > file``, however you -have to break in to stop the transfer, ``kmsg`` is a "never ending file". -If the machine has crashed so badly that you cannot enter commands or -the disk is not available then you have three options : - -(1) Hand copy the text from the screen and type it in after the machine - has restarted. Messy but it is the only option if you have not - planned for a crash. Alternatively, you can take a picture of - the screen with a digital camera - not nice, but better than - nothing. If the messages scroll off the top of the console, you - may find that booting with a higher resolution (eg, ``vga=791``) - will allow you to read more of the text. (Caveat: This needs ``vesafb``, - so won't help for 'early' oopses) - -(2) Boot with a serial console (see - :ref:`Documentation/admin-guide/serial-console.rst <serial_console>`), - run a null modem to a second machine and capture the output there - using your favourite communication program. Minicom works well. - -(3) Use Kdump (see Documentation/kdump/kdump.txt), - extract the kernel ring buffer from old memory with using dmesg - gdbmacro in Documentation/kdump/gdbmacros.txt. - - -Full Information ----------------- - -.. note:: - - the message from Linus below applies to 2.4 kernel. I have preserved it - for historical reasons, and because some of the information in it still - applies. Especially, please ignore any references to ksymoops. - - :: - - From: Linus Torvalds <torvalds@osdl.org> - - How to track down an Oops.. [originally a mail to linux-kernel] - - The main trick is having 5 years of experience with those pesky oops - messages ;-) - -Actually, there are things you can do that make this easier. I have two -separate approaches:: - - gdb /usr/src/linux/vmlinux - gdb> disassemble <offending_function> - -That's the easy way to find the problem, at least if the bug-report is -well made (like this one was - run through ``ksymoops`` to get the -information of which function and the offset in the function that it -happened in). - -Oh, it helps if the report happens on a kernel that is compiled with the -same compiler and similar setups. - -The other thing to do is disassemble the "Code:" part of the bug report: -ksymoops will do this too with the correct tools, but if you don't have -the tools you can just do a silly program:: - - char str[] = "\xXX\xXX\xXX..."; - main(){} - -and compile it with ``gcc -g`` and then do ``disassemble str`` (where the ``XX`` -stuff are the values reported by the Oops - you can just cut-and-paste -and do a replace of spaces to ``\x`` - that's what I do, as I'm too lazy -to write a program to automate this all). - -Alternatively, you can use the shell script in ``scripts/decodecode``. -Its usage is:: - - decodecode < oops.txt - -The hex bytes that follow "Code:" may (in some architectures) have a series -of bytes that precede the current instruction pointer as well as bytes at and -following the current instruction pointer. In some cases, one instruction -byte or word is surrounded by ``<>`` or ``()``, as in ``<86>`` or ``(f00d)``. -These ``<>`` or ``()`` markings indicate the current instruction pointer. - -Example from i386, split into multiple lines for readability:: - - Code: f9 0f 8d f9 00 00 00 8d 42 0c e8 dd 26 11 c7 a1 60 ea 2b f9 8b 50 08 a1 - 64 ea 2b f9 8d 34 82 8b 1e 85 db 74 6d 8b 15 60 ea 2b f9 <8b> 43 04 39 42 54 - 7e 04 40 89 42 54 8b 43 04 3b 05 00 f6 52 c0 - -Finally, if you want to see where the code comes from, you can do:: - - cd /usr/src/linux - make fs/buffer.s # or whatever file the bug happened in - -and then you get a better idea of what happens than with the gdb -disassembly. - -Now, the trick is just then to combine all the data you have: the C -sources (and general knowledge of what it **should** do), the assembly -listing and the code disassembly (and additionally the register dump you -also get from the "oops" message - that can be useful to see **what** the -corrupted pointers were, and when you have the assembler listing you can -also match the other registers to whatever C expressions they were used -for). - -Essentially, you just look at what doesn't match (in this case it was the -"Code" disassembly that didn't match with what the compiler generated). -Then you need to find out **why** they don't match. Often it's simple - you -see that the code uses a NULL pointer and then you look at the code and -wonder how the NULL pointer got there, and if it's a valid thing to do -you just check against it.. - -Now, if somebody gets the idea that this is time-consuming and requires -some small amount of concentration, you're right. Which is why I will -mostly just ignore any panic reports that don't have the symbol table -info etc looked up: it simply gets too hard to look it up (I have some -programs to search for specific patterns in the kernel code segment, and -sometimes I have been able to look up those kinds of panics too, but -that really requires pretty good knowledge of the kernel just to be able -to pick out the right sequences etc..) - -**Sometimes** it happens that I just see the disassembled code sequence -from the panic, and I know immediately where it's coming from. That's when -I get worried that I've been doing this for too long ;-) - - Linus - - ---------------------------------------------------------------------------- - -Notes on Oops tracing with ``klogd`` ------------------------------------- - -In order to help Linus and the other kernel developers there has been -substantial support incorporated into ``klogd`` for processing protection -faults. In order to have full support for address resolution at least -version 1.3-pl3 of the ``sysklogd`` package should be used. - -When a protection fault occurs the ``klogd`` daemon automatically -translates important addresses in the kernel log messages to their -symbolic equivalents. This translated kernel message is then -forwarded through whatever reporting mechanism ``klogd`` is using. The -protection fault message can be simply cut out of the message files -and forwarded to the kernel developers. - -Two types of address resolution are performed by ``klogd``. The first is -static translation and the second is dynamic translation. Static -translation uses the System.map file in much the same manner that -ksymoops does. In order to do static translation the ``klogd`` daemon -must be able to find a system map file at daemon initialization time. -See the klogd man page for information on how ``klogd`` searches for map -files. - -Dynamic address translation is important when kernel loadable modules -are being used. Since memory for kernel modules is allocated from the -kernel's dynamic memory pools there are no fixed locations for either -the start of the module or for functions and symbols in the module. - -The kernel supports system calls which allow a program to determine -which modules are loaded and their location in memory. Using these -system calls the klogd daemon builds a symbol table which can be used -to debug a protection fault which occurs in a loadable kernel module. - -At the very minimum klogd will provide the name of the module which -generated the protection fault. There may be additional symbolic -information available if the developer of the loadable module chose to -export symbol information from the module. - -Since the kernel module environment can be dynamic there must be a -mechanism for notifying the ``klogd`` daemon when a change in module -environment occurs. There are command line options available which -allow klogd to signal the currently executing daemon that symbol -information should be refreshed. See the ``klogd`` manual page for more -information. - -A patch is included with the sysklogd distribution which modifies the -``modules-2.0.0`` package to automatically signal klogd whenever a module -is loaded or unloaded. Applying this patch provides essentially -seamless support for debugging protection faults which occur with -kernel loadable modules. - -The following is an example of a protection fault in a loadable module -processed by ``klogd``:: - - Aug 29 09:51:01 blizard kernel: Unable to handle kernel paging request at virtual address f15e97cc - Aug 29 09:51:01 blizard kernel: current->tss.cr3 = 0062d000, %cr3 = 0062d000 - Aug 29 09:51:01 blizard kernel: *pde = 00000000 - Aug 29 09:51:01 blizard kernel: Oops: 0002 - Aug 29 09:51:01 blizard kernel: CPU: 0 - Aug 29 09:51:01 blizard kernel: EIP: 0010:[oops:_oops+16/3868] - Aug 29 09:51:01 blizard kernel: EFLAGS: 00010212 - Aug 29 09:51:01 blizard kernel: eax: 315e97cc ebx: 003a6f80 ecx: 001be77b edx: 00237c0c - Aug 29 09:51:01 blizard kernel: esi: 00000000 edi: bffffdb3 ebp: 00589f90 esp: 00589f8c - Aug 29 09:51:01 blizard kernel: ds: 0018 es: 0018 fs: 002b gs: 002b ss: 0018 - Aug 29 09:51:01 blizard kernel: Process oops_test (pid: 3374, process nr: 21, stackpage=00589000) - Aug 29 09:51:01 blizard kernel: Stack: 315e97cc 00589f98 0100b0b4 bffffed4 0012e38e 00240c64 003a6f80 00000001 - Aug 29 09:51:01 blizard kernel: 00000000 00237810 bfffff00 0010a7fa 00000003 00000001 00000000 bfffff00 - Aug 29 09:51:01 blizard kernel: bffffdb3 bffffed4 ffffffda 0000002b 0007002b 0000002b 0000002b 00000036 - Aug 29 09:51:01 blizard kernel: Call Trace: [oops:_oops_ioctl+48/80] [_sys_ioctl+254/272] [_system_call+82/128] - Aug 29 09:51:01 blizard kernel: Code: c7 00 05 00 00 00 eb 08 90 90 90 90 90 90 90 90 89 ec 5d c3 - ---------------------------------------------------------------------------- - -:: - - Dr. G.W. Wettstein Oncology Research Div. Computing Facility - Roger Maris Cancer Center INTERNET: greg@wind.rmcc.com - 820 4th St. N. - Fargo, ND 58122 - Phone: 701-234-7556 - - ---------------------------------------------------------------------------- - |