alsa-lib potentially racy on ARMv8

[Riku Voipio]

Alsa-lib is a low level library used for sound output. While it compiles on ARMv8, there might be some major problems run-time:

../../include/iatomic.h:1109:2: warning: #warning "Atomic operations are not supported on this architecture." [-Wcpp]

Looking at iatomic.h, without arch-specific atomics, alsa-lib will have empty rmb() amd wmb() macros and similar naive atomic_add/atomic_set macros, meaning that alsa will be badly racy on ARMv8.

Fixing this should be average amount of work, but validating it is tricky as fast model has no sound output.

[Riku Voipio (riku-voipio)]

I can't set the "importance" of bugs in linaro-aarch64 project, so recording here to not to forget: this bug doesn't block anyone, but must be fixed before any distribution releases. Medium importance, perhaps.

[Riku Voipio (riku-voipio)]

I've submitted a patch around this:

http://mailman.alsa-project.org/pipermail/alsa-devel/2014-February/072176.html

It turns out most of these atomics arent' really used, unless you use the pcm meter plugin (that allows you to make meters and scopes out alsa streams).

[Riku Voipio (riku-voipio)]

Accepted upstream:

http://git.alsa-project.org/?p=alsa-lib.git;a=commit;h=326c6802e49e5499e16cf141e1cdb0360fce14aa

[Riku Voipio (riku-voipio)]

Released in alsa-lib 1.0.28