Hello,
I am running into problems when unwinding the stack from a signal handler. The source code for my test application is included. Basically the application computes the Fibonacci sequence and a backtrace is triggered by SIGALRM every second.
I am running x86_64 Centos 4 on 2.6.9-67.ELsmp kernel and g++ version is 4.1.2-42.
The application is compiled with:
g++ -fomit-frame-pointer -o backtrace-test bactrace-test.cc
I would like to know if anyone has come across a similar issue and if there are any solutions for this problem.
Thank you in advance for your help.
Best regards,
Luke
P.S. My brief analysis follows:
(gdb) f 6
#6 uw_frame_state_for (context=0x7fbfffd0b0, fs=<value optimized out>)
at ../../../libgcc/../gcc/config/i386/linux-unwind.h:51
51 ../../../libgcc/../gcc/config/i386/linux-unwind.h: No such file or directory.
in ../../../libgcc/../gcc/config/i386/linux-unwind.h
(gdb) p $rip
$36 = (void (*)()) 0x2a9578a11f <uw_frame_state_for+655>
(gdb) disas
...
0x0000002a9578a115 <uw_frame_state_for+645>: xchg %ax,%ax
0x0000002a9578a118 <uw_frame_state_for+648>: mov 0x98(%r13),%rdx
0x0000002a9578a11f <uw_frame_state_for+655>: cmpb $0x48,(%rdx)
...
The problem is that the value in %rdx is 5.
(gdb) x/20a 0x98 + $r13 - 8*10
0x7fbfffd0f8: 0x7fbffff1c0 0x7fbffff1c8
0x7fbfffd108: 0x7fbffff1d0 0x7fbffff1d8
0x7fbfffd118: 0x7fbffff1e0 0x7fbffff1e8
0x7fbfffd128: 0x7fbffff1f0 0x7fbffff3e0
0x7fbfffd138: 0x0 0x7fbffff3e8 <-- this is what we want in %rdx
0x7fbfffd148: 0x5 0x0 <-- this is what we get in %rdx
0x7fbfffd158: 0x0 0x0
0x7fbfffd168: 0x400708 <_Z3fibi> 0x4000000000000000
0x7fbfffd178: 0x0 0x0
0x7fbfffd188: 0x0 0x0
Looks like we are off by an 8 byte address because the actual location on the stack of the return address is in the previous memory location.
(gdb) x/a 0x7fbffff3e8
0x7fbffff3e8: 0x40073f <_Z3fibi+55>
Attachment:
backtrace-test.cc
Description: backtrace-test.cc
