Full support of functions for atomic memory access in gcc?

[Manuel Prinz <manuel@debian.org>]

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Dear porters,

I'm trying to fix some long-standing issues in one of my packages
(src:openmpi). It does not build on s390 since no atomic primitives are
provided by upstream. Upstream agreed to solve this by using the
build-in primitives when compiled with gcc but I was unable to find out
if those are supported on s390.

Could you please enlighten me whether or not there is support for that
on s390? (Only read memory barriers would be sufficient.) Also, are high
resolution timers available?

Any hint or pointers to further documentation would be great, as I'm not
very familiar with the issue at hand at the moment! Thanks in advance!

Best regards,
Manuel