[Bug sanitizer/101476] AddressSanitizer check failed, points out a (potentially) non-existing stack error

["stsp at users dot sourceforge.net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101476

Stas Sergeev <stsp at users dot sourceforge.net> changed:

           What    |Removed                     |Added
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                 CC|                            |stsp at users dot sourceforge.net

--- Comment #2 from Stas Sergeev <stsp at users dot sourceforge.net> ---
I have the very same crash with the
multi-threaded app. The test-case from
this ticket doesn't reproduce it for
me either, but my app crashes nevertheless.
So I debugged it a bit myself.
gcc-11.2.1.

The crash happens here:
https://github.com/gcc-mirror/gcc/blob/master/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc#L10168
Here asan checks that sigaltstack()
didn't corrupt anything while writing
the "old setting" to "oss" ptr.
Next, some check is later fails here:
https://code.woboq.org/gcc/libsanitizer/asan/asan_thread.cc.html#340
Asan failed to find the canary value
kCurrentStackFrameMagic. The search
was done the following way: it walks
the shadow stack down, and looks for
the kAsanStackLeftRedzoneMagic to find
the bottom of redzone. Then, at the
bottom of redzone, it looks for the
canary value. I checked that the lowest
canary value is overwritten by the call
to GetAltStackSize(). It uses SIGSTKSZ
macro:
https://code.woboq.org/llvm/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp.html#170
which expands into a getconf()
call, so eats up quite a lot.

Now I am not entirely sure what conclusion
can be derived out of that. I think that
the culprit is probably here:
https://code.woboq.org/gcc/libsanitizer/asan/asan_interceptors_memintrinsics.h.html#26
They say that they expect 16 bytes of
a redzone, but it seems to be completely
exhausted with all canaries overwritten.

Does something of the above makes sense?
This is the first time I am looking into
an asan code.