Bug#870676: ffmpeg requires NEON on armhf, which is not part of the ARMv7 ABI

[James Cowgill]

Hi,

On 06/08/17 04:01, Edmund Grimley Evans wrote:
> As far as I know, the best way to implement run-time detection of
> hardware capabilities is with getauxval(AT_HWCAP) and
> getauxval(AT_HWCAP2).
> 
> There is some kind of NEON detection in ffmeg. See, for example:
> 
> https://sources.debian.net/src/ffmpeg/7:3.3.3-1/libavutil/arm/cpu.c/
> 
> That code appears to use /proc rather than getauxval. Is there a good
> reason for that?

I guess you would have to ask upstream to get an answer to this
question.

> In case someone reading this has access to hardware (or a simulator)
> without NEON but is not familiar with ffmpeg, what is a quick and easy
> way of checking whether ffmpeg is working?

I think the runtime is working, but this is the testcase from the SIGBUS
bug which you can use:

ffmpeg -f lavfi -i testsrc=s=32x32:d=0.1 -strict -2 -c:v libx264rgb -f avi libx264rgb.avi -y -hide_banner -nostdin
ffmpeg -strict -2 -i libx264rgb.avi -t 1 -c:v rawvideo -c:a pcm_s32le -f nut /dev/null -y -hide_banner -nostdin

Since the SIGBUS bug occurs in NEON code, if the runtime detection is
working, this will _only_ fail on machines with NEON and work on
non-NEON machines.

Thanks,
James

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