Free in death_handler.cpp:93 enless loop?

[hrehfeld]

My program is rather complex, so I'm not sure this is caused by deathhandler exclusively. I'm also using asan. Any ideas why this might happen?

What's good info to provide?

$ gdb -ex run myapp
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff396a4d4 in dlsym () from /usr/lib/libdl.so.2
(gdb) bt
#0  0x00007ffff396a4d4 in dlsym () from /usr/lib/libdl.so.2
#1  0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#2  0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#3  0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#4  0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#5  0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#6  0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#7  0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#8  0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#9  0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#10 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#11 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#12 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#13 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#14 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#15 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#16 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#17 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#18 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#19 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#20 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#21 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#22 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#23 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#24 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#25 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#26 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#27 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#28 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#29 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#30 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#31 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#32 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#33 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#34 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#35 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#36 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#37 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#38 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#39 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#40 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#41 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
#42 0x00007ffff396a520 in dlsym () from /usr/lib/libdl.so.2
#43 0x0000555555dea1c6 in free (ptr=0x7ffff76fb840 <alloc_memory_for_dlsym+32>) at /home/hrehfeld/projects/mplan-repos3-git/mplan/ext/DeathHandler/death_handler.cc:93
#44 0x00007ffff396abad in ?? () from /usr/lib/libdl.so.2
...

[vmarkovtsev]

Fair enough, it crashes inside the first attempt to load the original free(). I need to have a flag to break the crash loop in that case. Thanks for the report.
On the other hand, since it fails to allocate memory, I am not sure that we'll succeed writing any signaling output.

[hrehfeld]

But why does this happen in the first place? ASAN? CUDA? Everything seems fine when I just comment out the constructor:

//Debug::DeathHandler dh;

This is on Archlinux with g++ (GCC) 10.2.0

[vmarkovtsev]

You see, alloc_memory_for_dlsym suggests that dlsym uses dynamic memory, but DeathHandler overwrites malloc and free to call dlsym during the first invocation. Chicken and egg. It was different back in 2013 when I was a fresh graduate and wrote this project, hehe.

[vmarkovtsev]

How about now?

The current code does not support ASLR, so you'll probably not see the line numbers. I will eventually fix that, too.