9:26 a.m.
On 06/15/2011 12:56 AM, Shashidhara Shamaiah wrote:
Hi,
I was investigating a 64 bit linux kernel dump . I have following doubts
regarding usage of crash.
1) I wanted to access the intermediate kernel stack frames. To know the
status of the frame and the point of failure.
When I tried to access a stack frame I get an error message "crash:
prohibited gdb command: frame". Can you please let me know if there is
any other way of accessing the kernel stack frames using
crash.
Try 'bt -f'
Try also 'help bt' to discover other nice parameters as well.
2) When I run bt in crash, I get a stack trace. Another person from a
different team reported a slightly different stack trace to mine. Below
are the stack traces. The register contents are quite different between
the two
My stack trace
PID: 13366 TASK: ffff88031b60d580 CPU: 1 COMMAND: "telnet"
#0 [ffff88031ce759d0] machine_kexec at ffffffff81024486
#1 [ffff88031ce75a40] crash_kexec at ffffffff8107e230
#2 [ffff88031ce75b20] oops_end at ffffffff8100fa38
#3 [ffff88031ce75b50] no_context at ffffffff8102d801
#4 [ffff88031ce75ba0] __bad_area_nosemaphore at ffffffff8102d9c9
#5 [ffff88031ce75c70] bad_area at ffffffff8102da41
#6 [ffff88031ce75ca0] do_page_fault at ffffffff8102dd19
#7 [ffff88031ce75cf0] page_fault at ffffffff812d7425
#8 [ffff88031ce75d78] n_tty_read at ffffffff811f03b3
#9 [ffff88031ce75ec0] tty_read at ffffffff811ebf7e
#10 [ffff88031ce75f10] vfs_read at ffffffff810ebcc8
#11 [ffff88031ce75f40] sys_read at ffffffff810ebe48
#12 [ffff88031ce75f80] system_call_fastpath at ffffffff8100bbc2
RIP: 00007ffff716b9e0 RSP: 00007fffffffdfc0 RFLAGS: 00010212
RAX: 0000000000000000 RBX: ffffffff8100bbc2 RCX: 0000000000000000
RDX: 0000000000001ff6 RSI: 000000000061c02a RDI: 0000000000000000
RBP: 0000000000001ff6 R8: 0000000000000000 R9: 0000000000000000
R10: 0000000000616680 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 000000000061c02a R15: 00000000006178a0
ORIG_RAX: 0000000000000000 CS: 0033 SS: 002b
Reported stack trace
PID: 13366 TASK: ffff88031b60d580 CPU: 1 COMMAND: "telnet"
#0 [ffff88031ce759d0] machine_kexec at ffffffff81024486
#1 [ffff88031ce75a40] crash_kexec at ffffffff8107e230
#2 [ffff88031ce75ad8] n_tty_read at ffffffff811f03b3
#3 [ffff88031ce75b20] oops_end at ffffffff8100fa38
#4 [ffff88031ce75b50] no_context at ffffffff8102d801
#5 [ffff88031ce75ba0] __bad_area_nosemaphore at ffffffff8102d9c9
#6 [ffff88031ce75c20] native_sched_clock at ffffffff810120aa
#7 [ffff88031ce75c70] bad_area at ffffffff8102da41
#8 [ffff88031ce75ca0] do_page_fault at ffffffff8102dd19
#9 [ffff88031ce75cf0] page_fault at ffffffff812d7425
[exception RIP: n_tty_read+1420]
RIP: ffffffff811f03b3 RSP: ffff88031ce75da8 RFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8802cbd54a68 RCX: 000000000061c044
RDX: 0000000000000005 RSI: ffff88031ce75e87 RDI: ffff8802cbd54d1c
RBP: ffff88031ce75eb8 R8: 0000000000000000 R9: 0000000000000000
R10: 0000000000616680 R11: 0000000000000246 R12: 000000000061c044
R13: ffff8802cbd54800 R14: 0000000000000000 R15: 7fffffffffffffff
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 #10
[ffff88031ce75ec0] tty_read at ffffffff811ebf7e
#11 [ffff88031ce75f10] vfs_read at ffffffff810ebcc8
#12 [ffff88031ce75f40] sys_read at ffffffff810ebe48
#13 [ffff88031ce75f80] system_call_fastpath at ffffffff8100bbc2
3) I want to retrieve the address of a data structure in the current
context. How can it be done? I tried using struct command, but it did
not help
You need to use bt -f and find what pointer you are looking for and
then: struct <struct name> pointer
most of times just doing: <struct name> pointer
works out
fbl
4) When I run the command readelf -a vmcore, I get an error message
"readelf: Error: Not an ELF file - it has the wrong magic bytes at the
start."
Please help regarding the above queries.
Thanks and Regards
Shashidhara
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