Re: [Libunwind-devel] Re: Backtrace from signal handler on arm from threads

[Henrik Grindal Bakken]

Arun Sharma <address@hidden> writes:

> On Wed, Feb 2, 2011 at 1:19 AM, Henrik Grindal Bakken <address@hidden> wrote:
>> Program received signal SIGSEGV, Segmentation fault.
>> 0x4026da98 in __errno_location () from /lib/libc.so.6
>>
>> (gdb) bt
>> #0  0x4026da98 in __errno_location () from /lib/libc.so.6
>> #1  0x40294d0c in vfprintf () from /lib/libc.so.6
>> #2  0x40299284 in ?? () from /lib/libc.so.6
>> #3  0x40299284 in ?? () from /lib/libc.so.6
>
> gdb is not able to unwind probably for the same reason why libunwind
> is not able to. Where did this libc.so.6 come from? You might have to
> use readelf -wf to figure out if there is missing unwind info around
> 0x40299284.

The libc is from my cross-compiled toolchain (built using crosstool-ng).

I'm not all that experienced in interpreting readelf output, I'm afraid.
<URL:http://folk.uio.no/hgb/readelf.output.gz> is the output of readelf
on the libc-2.12.1.so (aka libc.so.6).

Actually, a second attempt now, I had the following results:

[hgbsnoopy:~] $ gdb backtrace 
GNU gdb (GDB) 7.1
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "arm-unknown-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /tools/backtrace...Reading symbols from 
/tools/backtrace.debug...done.
done.
(gdb) run
Starting program: /tools/backtrace 
warning: Unable to find libthread_db matching inferior's thread library, thread 
debugging will not be available.
warning: Unable to find libthread_db matching inferior's thread library, thread 
debugging will not be available.
Thread dummytask has TID 26713
foo: 1
zot: 2
bar: 2
foo: 3
zot: 4
bar: 4
foo: 5
zot: 6
bar: 6
foo: 7
zot: 8
bar: 8
Thread dummytask has TID 26712
[New LWP 26713]

Program received signal SIGSEGV, Segmentation fault.
[Switching to LWP 26713]
0x0000b540 in bar (i=8) at product/backtrace/cfg/bar.c:10
10      product/backtrace/cfg/bar.c: No such file or directory.
        in product/backtrace/cfg/bar.c
(gdb) sig SIGSEGV
Continuing with signal SIGSEGV.
Received signal SIGSEGV (11) in thread 0x00031460, TID 26713
Illegal memory access at: 0x8
Registers:
R0:     00000007 R1:   00000000 R2:    00000001 R3:   00000008
R4:     00006859 R5:   00000001 R6:    00031674 R7:   00000000
R8:     00000000 R9:   befe7a98 R10:   00000001 FP:   00030bec
PC:     0000b540 IP:   00030638 SP:    00030bd0 LR:   402467e4
ERR:    00000817 CPSR: 20000010 FAULT: 00000008 TRAP: 0000000e
OLDMSK: 00000000

Program received signal SIGSEGV, Segmentation fault.
0x4028392c in __sigprocmask (how=2, set=0x400a35a4, oset=0x357d0)
    at ../sysdeps/unix/sysv/linux/sigprocmask.c:42
42      ../sysdeps/unix/sysv/linux/sigprocmask.c: No such file or directory.
        in ../sysdeps/unix/sysv/linux/sigprocmask.c
(gdb) bt
#0  0x4028392c in __sigprocmask (how=2, set=0x400a35a4, oset=0x357d0)
    at ../sysdeps/unix/sysv/linux/sigprocmask.c:42
#1  0x4006e7ac in ?? () from /extra/lib/libunwind-arm.so.7
#2  0x4006f248 in ?? () from /extra/lib/libunwind-arm.so.7
#3  0x40072a60 in _Uarm_step () from /extra/lib/libunwind-arm.so.7
#4  0x0000bdec in obtain_backtrace (dest=0x39bf4, destsize=32, context=0x39d10)
    at platform/backtrace/libunwind/obtain_backtrace.c:31
#5  0x0000ba64 in sig_handler_bt_exit (sig=11, psi=0x39c90, ctxarg=0x39d10)
    at platform/signal_handler/linux/signal_handler.c:333
#6  <signal handler called>
#7  0x0000b540 in bar (i=8) at product/backtrace/cfg/bar.c:10
#8  0x0000b470 in zot (i=8) at product/backtrace/cfg/foo.c:7
#9  0x0000b4d8 in foo (i=8) at product/backtrace/cfg/foo.c:13
#10 0x0000b558 in bar (i=7) at product/backtrace/cfg/bar.c:11
#11 0x0000b470 in zot (i=6) at product/backtrace/cfg/foo.c:7
#12 0x0000b4d8 in foo (i=6) at product/backtrace/cfg/foo.c:13
#13 0x0000b558 in bar (i=5) at product/backtrace/cfg/bar.c:11
#14 0x0000b470 in zot (i=4) at product/backtrace/cfg/foo.c:7
#15 0x0000b4d8 in foo (i=4) at product/backtrace/cfg/foo.c:13
#16 0x0000b558 in bar (i=3) at product/backtrace/cfg/bar.c:11
#17 0x0000b470 in zot (i=2) at product/backtrace/cfg/foo.c:7
#18 0x0000b4d8 in foo (i=2) at product/backtrace/cfg/foo.c:13
#19 0x0000b2a0 in t (arg=0x0) at product/backtrace/cfg/main.c:102
---Type <return> to continue, or q <return> to quit---
#20 0x0000cd1c in pthread_wrapper (varg=0x1e478)
    at platform/ttos/linux/task.c:275
#21 0x4023dc4c in ?? () from /lib/libpthread.so.0
#22 0x4023dc4c in ?? () from /lib/libpthread.so.0
#23 0x4023dc4c in ?? () from /lib/libpthread.so.0


>> Has anyone else had any luck using libunwind with multithreaded arm
>> applications?
>
> Works just fine on x86.

Yes, that's my experience too.  But not on arm.


-- 
Henrik Grindal Bakken <address@hidden>
PGP ID: 8D436E52
Fingerprint: 131D 9590 F0CF 47EF 7963  02AF 9236 D25A 8D43 6E52