Re: can the kernel show user task stack backtrace ?

2009-07-31 Thread Norbert van Bolhuis 


Thanks for the answers!

libSegFault.so seems to do what I want. I'll replace
sysctl -w kernel.print-fatal-signals=1
with
export LD_PRELOAD=/lib/libSegFault.so
since it better suits my needs.

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can the kernel show user task stack backtrace ?

2009-07-30 Thread Norbert van Bolhuis 


Afaik the kernel only shows the stack backtrace of the kernel stack
(of a task).

I wonder if there would be anything wrong with letting it show
the user task stack backtrace in certain cases.

Read the rest to see what I mean.


If kernel.print-fatal-signals has been enabled a crashing
application makes the kernel show this:
ca2/943: potentially unexpected fatal signal 11.

NIP: 144c LR: 1444 CTR: 
REGS: ce73df50 TRAP: 0300   Not tainted  (2.6.28)
MSR: d032 EE,PR,ME,IR,DR  CR: 22000422  XER: 2000
DAR: d003, DSISR: 2200
TASK = ceb7a3e0[943] 'ca2' THREAD: ce73c000

GPR00: 000e bf963b30 48025450 000a 0ff0ac2c 22000422 0001 0ff5e6b0
GPR08: 0001 d003 1032   1001896c 0ffe9000 
GPR16: 0ffca59c  1009b940 100a8b6a 100bf234 bfea22b8 100bf224 
GPR24: 100bf008 1009b960 4801e858 4802dd34 4802e7e0  0ffec8d8 bf963b30
Call Trace:
Segmentation fault
#

It's a real pity the user task stack backtrace isn't shown.
We're dealing with some complex (3rd party) applications and I like to see a
user task stack backtrace.

(Of course the way to go here is to use a debugger (gdb) and
 do a backtrace (with the coredump file).
 However, debugging takes some time. Besides the info is there
 it only needs to be shown. Often just this info is enough to
 pinpoint the problem)

Obviously the arch/powerpc/kernel/process.c:show_stack function
isn't meant for doing this. It only shows the kernel stack.

Btw. this doesn't work in my case since validate_sp returns 0 (because
sp is assigned the user-space stack (bf963b30) while kernel stack starts at 
ce73c000).
Though if it would work it isn't very usefull I guess since the crashing app
not enters kernel-mode (via sys-calls).

If I change arch/powerpc/kernel/process.c:show_stack (of kernel 2.6.28) like 
this:

do {
#if 0
if (!validate_sp(sp, tsk, STACK_FRAME_OVERHEAD))
return;
#endif
 .
 .
 .
} while ((count++  kstack_depth_to_print)  (sp != 0));


the following is shown:

ca2/943: potentially unexpected fatal signal 11.

NIP: 144c LR: 1444 CTR: c001fd7c

REGS: ce73df50 TRAP: 0300   Not tainted  (2.6.28)
MSR: f932 EE,PR,FP,ME,IR,DR  CR: 22000422  XER: 2000
DAR: d003, DSISR: 2200
TASK = cf09b340[943] 'ca2' THREAD: ce73c000
GPR00: 000e bfd65b30 48025450 000a 0ff0ac2c 22000422 0001 0ff5e6b0
GPR08: 0001 d003 1032   1001896c 0ffe9000 
GPR16: 0ffca59c  1009b940 100a8b6a 100bf234 bfb532b8 100bf224 
GPR24: 100bf008 1009b960 4801e858 4802dd34 4802e7e0  0ffec8d8 bfd65b30
Call Trace:
[bfd65b30] [1444] 0x1444 (unreliable)
[bfd65b60] [1490] 0x1490
[bfd65b90] [14cc] 0x14cc
[bfd65ba0] [0feb39c8] 0xfeb39c8
[bfd65dd0] [0feb3ad4] 0xfeb3ad4
[bfd65de0] [] 0x00
Segmentation fault
#

which is what I want.


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Re: can the kernel show user task stack backtrace ?

2009-07-30 Thread Alessandro Rubini 
 We're dealing with some complex (3rd party) applications and I like to see a
 user task stack backtrace.
 
 (Of course the way to go here is to use a debugger (gdb) and
   do a backtrace (with the coredump file).

Actually, you can intercept SIGSEGV and print your own stack from within
the signal handler. You can also open /proc/self/maps and print it, to
ease understanding the various pointers in there, especially if the
application is using a number of shared libs.

This is usually easier than getting to a core dump, although there is
less information than what the core offers.

I have the code for ARM and I've it on ppc once, but I must dig for the actual
code.

/alessandro
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Re: can the kernel show user task stack backtrace ?

2009-07-30 Thread Nicholas Mc Guire 
On Thu, 30 Jul 2009, Alessandro Rubini wrote:

  We're dealing with some complex (3rd party) applications and I like to see a
  user task stack backtrace.
  
  (Of course the way to go here is to use a debugger (gdb) and
do a backtrace (with the coredump file).
 
 Actually, you can intercept SIGSEGV and print your own stack from within
 the signal handler. You can also open /proc/self/maps and print it, to
 ease understanding the various pointers in there, especially if the
 application is using a number of shared libs.
 
 This is usually easier than getting to a core dump, although there is
 less information than what the core offers.
 
 I have the code for ARM and I've it on ppc once, but I must dig for the actual
 code.

I think libSegFault.so (part of glibc) can do that by simply preloading it 

LD_PRELOAD=/lib/libSegFault.so ./your_segfaulting_app

should do the trick.

hofrat
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