[debian-mysql] Bug#972564: Acknowledgement (mariadb-10.5: FTBFS on armhf: compiler seems to segfault with libnuma enabled?)

[Otto Kekäläinen]

>From IRC:

20:37 < waldi> the log is full of "warning: cast increases required
alignment of target type [-Wcast-align]". i wonder if this would even
work
20:38 < jrtc27> based on the reduced test case it looks to me like it
doesn't like you using `1 << 31` as an int
20:38 < jrtc27> shifting into the sign bit is undefined behaviour
20:39 < jrtc27> I don't know why only armhf would care compared with
other 32-bit architectures that have atomics
20:39 < ansgar> An internal compiler error is still a compiler bug.
20:39 < jrtc27> well
20:39 < jrtc27> it's valid per the C specification
20:39 < jrtc27> but it's poor form that most would regard as a bug in
the compiler too
20:40  * jrtc27 goes to amdahl to try playing with the reduced case
20:43 < jrtc27> hm, no, it's still unhappy
20:45 < jrtc27> ottok: if you want a really ugly workaround to thwart
the optimisers attempts to shoot itself
20:45 < jrtc27> change IF_DBUG_ASSERT(auto l=,) lock.fetch_sub(WRITER,
std::memory_order_release);
20:45 < jrtc27> to volatile uint32_t writer = WRITER;
IF_DBUG_ASSERT(auto l=,) lock.fetch_sub(writer,
std::memory_order_release);
20:46 < jrtc27> (and best to #ifdef it so you don't add overhead to
architectures that don't suffer from such compiler bugs)

For mariadb-10.5 1:10.5.8-1 I applied the patch
https://salsa.debian.org/mariadb-team/mariadb-10.5/-/commit/dcafdab0121977be04bc8038a70c800003399841
and the armhf build now passes with this temporary workaround.