277 lines
13 KiB
Text
277 lines
13 KiB
Text
NOTE: ksymoops is useless on 2.6. 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 Documentation/serial-console.txt),
|
|
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
|
|
|
|
|
|
---------------------------------------------------------------------------
|
|
Tainted kernels:
|
|
|
|
Some oops reports contain the string 'Tainted: ' after the program
|
|
counter. This indicates that the kernel has been tainted by some
|
|
mechanism. The string is followed by a series of position-sensitive
|
|
characters, each representing a particular tainted value.
|
|
|
|
1: 'G' if all modules loaded have a GPL or compatible license, 'P' if
|
|
any proprietary module has been loaded. Modules without a
|
|
MODULE_LICENSE or with a MODULE_LICENSE that is not recognised by
|
|
insmod as GPL compatible are assumed to be proprietary.
|
|
|
|
2: 'F' if any module was force loaded by "insmod -f", ' ' if all
|
|
modules were loaded normally.
|
|
|
|
3: 'S' if the oops occurred on an SMP kernel running on hardware that
|
|
hasn't been certified as safe to run multiprocessor.
|
|
Currently this occurs only on various Athlons that are not
|
|
SMP capable.
|
|
|
|
4: 'R' if a module was force unloaded by "rmmod -f", ' ' if all
|
|
modules were unloaded normally.
|
|
|
|
5: 'M' if any processor has reported a Machine Check Exception,
|
|
' ' if no Machine Check Exceptions have occurred.
|
|
|
|
6: 'B' if a page-release function has found a bad page reference or
|
|
some unexpected page flags.
|
|
|
|
7: 'U' if a user or user application specifically requested that the
|
|
Tainted flag be set, ' ' otherwise.
|
|
|
|
8: 'D' if the kernel has died recently, i.e. there was an OOPS or BUG.
|
|
|
|
9: 'A' if the ACPI table has been overridden.
|
|
|
|
10: 'W' if a warning has previously been issued by the kernel.
|
|
(Though some warnings may set more specific taint flags.)
|
|
|
|
11: 'C' if a staging driver has been loaded.
|
|
|
|
12: 'I' if the kernel is working around a severe bug in the platform
|
|
firmware (BIOS or similar).
|
|
|
|
13: 'O' if an externally-built ("out-of-tree") module has been loaded.
|
|
|
|
14: 'E' if an unsigned module has been loaded in a kernel supporting
|
|
module signature.
|
|
|
|
15: 'L' if a soft lockup has previously occurred on the system.
|
|
|
|
The primary reason for the 'Tainted: ' string is to tell kernel
|
|
debuggers if this is a clean kernel or if anything unusual has
|
|
occurred. Tainting is permanent: even if an offending module is
|
|
unloaded, the tainted value remains to indicate that the kernel is not
|
|
trustworthy.
|