[FFmpeg-devel] Re: [DISCUSSION] Adding ARM64EC support to FFmpeg

["Rémi Denis-Courmont via ffmpeg-devel" <ffmpeg-devel@ffmpeg.org>]

Le 23 octobre 2025 00:01:55 GMT+03:00, "Martin Storsjö" <martin@martin.st> a écrit :
>On Wed, 22 Oct 2025, Rémi Denis-Courmont via ffmpeg-devel wrote:
>
>> If you want to compile AArch64 FFmpeg for use in emulated x86 processes, then you need a FFmpeg that exposes the same ABI as the x86 FFmpeg. That's going to require a lot of changes throughout the code base (and I doubt people here will agree to them overall).
>
>Can you elaborate on what changes you think would be needed?

You're supposed to expose the same binary interface as x86. This is obviously not working correctly for CPU flags, which *are* part of the public libavutil interface, AFAIK.

I don't know what else won't work and I'm not going to audit the code.

>In arm64ec mode, the compiler defines __x86_64__ (or _M_X64) and does not define __aarch64__ (or _M_ARM64). It does define __arm64ec__ (or _M_ARM64EC) to distinguish it from regular x86_64 though.

Yes, and it seems extremely unlikely that that would just work. Any inline x86 assembler could break. And even if that did work, it would lack all Arm assembler optimisation so it would likely be worst than just using x86 FFmpeg and passing it through the JIT.

I guess that the code is instead compiled as normal AArch64 just with a different ABI, but then that doesn't work either as noted above.
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