OpenBSD saves me again! — Debug a memory corruption issue

Yesterday, I came across a third-part library issue, which crashes at allocating memory:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f594a5a9b6b in _int_malloc () from /usr/lib/
(gdb) bt
#0  0x00007f594a5a9b6b in _int_malloc () from /usr/lib/
#1  0x00007f594a5ab503 in malloc () from /usr/lib/
#2  0x00007f594b13f159 in operator new (sz=5767168) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/

It is obvious that the memory tags are corrupted, but who is the murder? Since the library involves a lot of maths computation, it is not an easy task to grasp the code quickly. So I need to find another way:

(1) Open all warnings during compilation: -Wall. Nothing found.

(2) Use valgrind, but unfortunately, valgrind crashes itself:

valgrind: the 'impossible' happened:
   Killed by fatal signal

host stacktrace:
==43326==    at 0x58053139: get_bszB_as_is (m_mallocfree.c:303)
==43326==    by 0x58053139: get_bszB (m_mallocfree.c:315)
==43326==    by 0x58053139: vgPlain_arena_malloc (m_mallocfree.c:1799)
==43326==    by 0x5800BA84: vgMemCheck_new_block (mc_malloc_wrappers.c:372)
==43326==    by 0x5800BD39: vgMemCheck___builtin_vec_new (mc_malloc_wrappers.c:427)
==43326==    by 0x5809F785: do_client_request (scheduler.c:1866)
==43326==    by 0x5809F785: vgPlain_scheduler (scheduler.c:1433)
==43326==    by 0x580AED50: thread_wrapper (syswrap-linux.c:103)
==43326==    by 0x580AED50: run_a_thread_NORETURN (syswrap-linux.c:156)

sched status:

(3) Change compiler, use clang instead of gcc, and hope it can give me some clues. Still no effect.

(4) Switch Operating System from Linux to OpenBSD, the program crashes again. But this time, it tells me where the memory corruption occurs:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000014b07f01e52d in addMod (r=<error reading variable>, a=4693443247995522, b=28622907746665631,

I figure out the issue quickly, and not bother to understand the whole code. OpenBSD saves me again, thanks!


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