There is something weird going on here. I'm seeing the same thing with
Ubuntu 24.04's gcc 13.2.0-23ubuntu4, after hitting some issues with x264
(which declared a local variable with __attribute__((aligned(64))) but
then it actually wasn't aligned as such, and some AVX512 function then
segfaults due to unaligned access).
In my case I can compile the following example on Ubuntu 22.04, and the
resulting binary asserts:
#undef NDEBUG
#include <assert.h>
#include <stdio.h>
#include <stdint.h>
int main(void)
{
char c __attribute__((__aligned__(64)));
uintptr_t addr = (uintptr_t)&c;
printf("explicitly aligned char: %#lx\n", addr);
assert(addr % 64 == 0);
return 0;
}
$ gcc -fsanitize=address asan-align.c -o asan-align
$ ./asan-align
explicitly aligned char: 0x7f6e19000020
asan-align: asan-align.c:11: main: Assertion `addr % 64 == 0' failed.
Aborted
However, running _exactly_ the same binary on Ubuntu 22.04 does not
assert. E.g.:
$ ./asan-align
explicitly aligned char: 0x7ffd1fea4e40
So it looks like there is something that causes main()'s stack to be
differently aligned. Whether that is due to Ubuntu 22.04 and 24.04
having different crt*.o files, or due to some AddressSanitizer
difference, is not clear to me yet.
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https://bugs.launchpad.net/bugs/2023424
Title:
GCC 13 on Lunar exhibits AddressSanitizer/UndefinedBehaviorSanitizer
bug that doesn't manifest elsewhere
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