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Documentation: add hint about call traces & module symbols to BUG-HUN…

…TING

Here's a couple of small additions to BUG-HUNTING.

1. point out that you can list code in gdb with only one command
	(gdb) l *(<symbol> + offset)

2. give a very brief hint how to decode module symbols in call traces

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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commit dcc85cb61808098d22792db95f1dfa9c8b3bcf6d 1 parent 844fcc5
Richard Kennedy authored Linus Torvalds committed
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@@ -214,6 +214,23 @@ And recompile the kernel with CONFIG_DEBUG_INFO enabled:
gdb vmlinux
(gdb) p vt_ioctl
(gdb) l *(0x<address of vt_ioctl> + 0xda8)
+or, as one command
+ (gdb) l *(vt_ioctl + 0xda8)
+
+If you have a call trace, such as :-
+>Call Trace:
+> [<ffffffff8802c8e9>] :jbd:log_wait_commit+0xa3/0xf5
+> [<ffffffff810482d9>] autoremove_wake_function+0x0/0x2e
+> [<ffffffff8802770b>] :jbd:journal_stop+0x1be/0x1ee
+> ...
+this shows the problem in the :jbd: module. You can load that module in gdb
+and list the relevant code.
+ gdb fs/jbd/jbd.ko
+ (gdb) p log_wait_commit
+ (gdb) l *(0x<address> + 0xa3)
+or
+ (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
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