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

[stsp at users dot sourceforge.net]

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

--- Comment #4 from Stas Sergeev <stsp at users dot sourceforge.net> ---
Thread 3 "X ev" hit Breakpoint 4, __sanitizer::UnsetAlternateSignalStack () at
../../../../libsanitizer/sanitizer_common/sanitizer_posix_libcdep.cpp:190
190     void UnsetAlternateSignalStack() {
(gdb) n
194       altstack.ss_size = GetAltStackSize();  // Some sane value required on
Darwin.
(gdb) p /x $rsp
$128 = 0x7fffee0a0ce0
(gdb) p &oldstack
$129 = (stack_t *) 0x7fffee0a0d00
(gdb) p /x *(int *)0x7fffee0a0cc0  <== canary address
$130 = 0x41b58ab3
(gdb) p 0x7fffee0a0ce0-0x7fffee0a0cc0
$132 = 32

Here we can see that before a
call to GetAltStackSize(), rsp
is 32 bytes above the lowest
canary value. After the call,
there is no more canary because
32 bytes are quickly overwritten
by a call to getconf().