-Table of contents
-=================
-
-Last updated: 20 December 2005
-
-Contents
-========
-
-- Introduction
-- Devices not appearing
-- Finding patch that caused a bug
--- Finding using git-bisect
--- Finding it the old way
-- Fixing the bug
-
-Introduction
-============
-
-Always try the latest kernel from kernel.org and build from source. If you are
-not confident in doing that please report the bug to your distribution vendor
-instead of to a kernel developer.
-
-Finding bugs is not always easy. Have a go though. If you can't find it don't
-give up. Report as much as you have found to the relevant maintainer. See
-MAINTAINERS for who that is for the subsystem you have worked on.
-
-Before you submit a bug report read REPORTING-BUGS.
-
-Devices not appearing
-=====================
-
-Often this is caused by udev. Check that first before blaming it on the
-kernel.
-
-Finding patch that caused a bug
-===============================
-
-
-
-Finding using git-bisect
-------------------------
-
-Using the provided tools with git makes finding bugs easy provided the bug is
-reproducible.
-
-Steps to do it:
-- start using git for the kernel source
-- read the man page for git-bisect
-- have fun
-
-Finding it the old way
-----------------------
-
[Sat Mar 2 10:32:33 PST 1996 KERNEL_BUG-HOWTO lm@sgi.com (Larry McVoy)]
This is how to track down a bug if you know nothing about kernel hacking.
because Linux snapshots will let you do this - something that you can't
do with vendor supplied releases.
-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.
-
-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
-
-NB.: 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 ip_queue_xmit+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
-
-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.
-
-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?
-
-Please do read Documentation/SubmittingPatches though to help your code get
-accepted.
git://git.onelab.eu / linux-2.6.git / blobdiff