[Crash-utility] About the use of 'gcore'
Patrick Agrain
patrick.agrain at alcatel-lucent.com
Mon Jan 6 09:15:02 UTC 2014
Hello all,
First of all, I wish a Happy New Year (with less crash, but still
enhanced tools...)
Thanks for the links, they were very useful.
I dig further in the way of analyzing the User Space, but it seems that
I'm linked to a dead-end way.
Below is a snapshot of kernel / userland stack dump.
What I've done :
- Crash is triggered by a page fault inside a kernel module (write 0 in
0xFFFFFFFF, classic).
- Using gcore to create the 'core.<pid>.bash (which is the user task
running at time of crash).
- Evaluating an EBP (between { }) chaining value (hypothesis), EIP value
(between [ ]) is then just pushed beside
The purpose of this study is to find a method to analyze futur crashes
from kernel space down to user space applications.
Do you have an idea about the cause of this non-dumping of the memory in
user-space ?
Should I use other extension as 'gcore' ?
Thank in advance.
Best regards,
Patrick Agrain
-------
===============================================================================
--------------------- Go down into User Space Territory
-----------------------
Last pt_regs of kernel stack is:
| pt_regs
00000001 094a5408 00000003 ..~......TJ..... |
bx cx dx
c2699fc0: 00000003 094a5408 bfd1b704 00000004 .....TJ......... | si di
bp ax
c2699fd0: 0000007b ffff007b c07e0000 00000033 {...{.....~.3... | ds es
fs gs
c2699fe0: 00000004 b776a416 00000073 00000246 ......v.s...F... |
orig_eax ip cs flags
c2699ff0: bfd1b6d8 0000007b | sp ss
v cccccccc cccccccc ....{........... | padding
|
|----------------------------------------------------------------|
|
(gdb) x/32xw 0xbfd1b680 |
0xbfd1b680: 0xbfd1b6d0 0x0000000f 0x094b4568 0x080c90b9 |
0xbfd1b690: 0x094b4568 0x080cd160 0x00001936 0x00000001 |
0xbfd1b6a0: 0x094ab9c8 0x00000000 0x094b4b48 0xbfd1b7c8 |
0xbfd1b6b0: 0x080ce9e8 0x094b4b48 0x094b4b48 0xbfd1b728 |
0xbfd1b6c0: 0x094aed28 0x00000020 0x00000000 0x00000070 |
0xbfd1b6d0: 0x094b4588 0x080cc080 |
0xb7698b43 <--|
0xb7757ff4
0xbfd1b6e0: 0xb76343b4 0x00000001 0x094a5408 0x00000003
0xbfd1b6f0: 0xb77584e0 0x080cc080 0xbfd1b728 0xb77584e0
|------------------------------------------ Hypothesis : this is an EBP
value...
v
0xbfd1b700: 0x00000003 {0xbfd1b72c} [0xb7635c90] 0xb77584e0
0xbfd1b710: 0x094a5408 0x00000003 0x094b4b48 0xbfd1b7c8
0xbfd1b720: 0xb7757ff4 0xb77584e0 0x0000000a {0xbfd1b750}
0xbfd1b730: [0xb7634e80] 0xb77584e0 0x094a5408 0x00000003
0xbfd1b740: 0x0000000a 0xb7757ff4 0xb77584e0 0x0000000a
0xbfd1b750: {0xbfd1b768} [0xb7637d2a] 0xb77584e0 0x0000000a
0xbfd1b760: 0xb7757ff4 0xb77584e0 {0xbfd1b788} [0xb76312b5]>-|
0xbfd1b770: 0xb77584e0 0x0000000a 0xb75c9940 0x094a3e48 |
0xbfd1b780: 0x00000001 0x00000000 0x00000000 0x0809b64b |
|
Disassemble Try: EIP at 0xb76312b5
<---------------------------------------------|
(gdb) disassemble 0xb7631200, 0xb7631300
Dump of assembler code from 0xb7631200 to 0xb7631300:
0xb7631200: Cannot access memory at address 0xb7631200
(gdb)
----------
Le 17/12/2013 19:12, Buland Kumar Singh a écrit :
> Hi Patrick,
>
> The following links may also be helpful to understand gdb and
> it's usage for application core analysis.
>
> http://web.eecs.umich.edu/~sugih/pointers/gdb_core.html
> <http://web.eecs.umich.edu/%7Esugih/pointers/gdb_core.html>
> https://sourceware.org/gdb/onlinedocs/gdb/
>
> -- BKS
>
>
> On 17 December 2013 21:36, Patrick Agrain
> <patrick.agrain at alcatel-lucent.com
> <mailto:patrick.agrain at alcatel-lucent.com>> wrote:
>
> Hello all,
>
> Now that we have dumped the kernel stack, I'm intesresting in the
> user process from which we came just before the 'panic'.
> Googling around, I found mention of the 'gcore' extension.
>
> I compiled version 1.22 and installed it.
> Using it on crash 6.1.0-1.el6, I get a file core.845.bash on
> process 'bash' (in which I trigger a kernel panic) :
>
> crash> gcore -v 1 845
> gcore: Opening file core.845.bash ...
> gcore: done.
> gcore: Writing ELF header ...
> gcore: done.
> gcore: Retrieving and writing note information ...
> gcore: done.
> gcore: Writing PT_NOTE program header ...
> gcore: done.
> gcore: Writing PT_LOAD program headers ...
> gcore: done.
> gcore: Writing PT_LOAD segment ...
> gcore: PT_LOAD[0]: 8048000 - 8048000
> gcore: PT_LOAD[1]: 80e2000 - 80e9000
> gcore: PT_LOAD[2]: 80e9000 - 80ed000
> gcore: PT_LOAD[3]: 94a2000 - 94d1000
> gcore: PT_LOAD[4]: b7374000 - b7374000
> gcore: PT_LOAD[5]: b7375000 - b7376000
> gcore: PT_LOAD[6]: b7376000 - b7377000
> gcore: PT_LOAD[7]: b7377000 - b7377000
> gcore: PT_LOAD[8]: b737e000 - b737e000
> gcore: PT_LOAD[9]: b737f000 - b737f000
> gcore: PT_LOAD[10]: b73bb000 - b73bb000
> gcore: PT_LOAD[11]: b75bb000 - b75bb000
> gcore: PT_LOAD[12]: b75c7000 - b75c8000
> gcore: PT_LOAD[13]: b75c8000 - b75c9000
> gcore: PT_LOAD[14]: b75c9000 - b75ca000
> gcore: PT_LOAD[15]: b75ca000 - b75ca000
> gcore: PT_LOAD[16]: b7756000 - b7758000
> gcore: PT_LOAD[17]: b7758000 - b7759000
> gcore: PT_LOAD[18]: b7759000 - b775c000
> gcore: PT_LOAD[19]: b775c000 - b775c000
> gcore: PT_LOAD[20]: b775f000 - b7760000
> gcore: PT_LOAD[21]: b7760000 - b7761000
> gcore: PT_LOAD[22]: b7761000 - b7761000
> gcore: PT_LOAD[23]: b7764000 - b7765000
> gcore: PT_LOAD[24]: b7769000 - b776a000
> gcore: PT_LOAD[25]: b776a000 - b776b000
> gcore: PT_LOAD[26]: b776b000 - b776b000
> gcore: PT_LOAD[27]: b7789000 - b778a000
> gcore: PT_LOAD[28]: b778a000 - b778b000
> gcore: PT_LOAD[29]: bfd07000 - bfd1d000
> gcore: done.
> Saved core.845.bash
> crash>
>
>
> So far, so good... But
>
> Question: Are there anywhere some hints about how to use this
> core.<pid> file ?
>
> Thanks in advance.
> Regards,
> Patrick Agrain
>
> --
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> Crash-utility at redhat.com <mailto:Crash-utility at redhat.com>
> https://www.redhat.com/mailman/listinfo/crash-utility
>
>
>
>
> --
> BKS
>
>
> --
> Crash-utility mailing list
> Crash-utility at redhat.com
> https://www.redhat.com/mailman/listinfo/crash-utility
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