[FFmpeg-devel] [RFC] x86 external assembler requirements

[Ivan Kalvachev]

On 6/9/17, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> On Fri, Jun 9, 2017 at 2:51 PM, James Darnley <jdarnley at obe.tv> wrote:
>> I propose that we drop support for all assemblers older than NASM version
>> 2.11.
>> That was released on 2013-12-31 with several point releases over the
>> following
>> year with 2.11.08 being released on 2015-02-21.
>>
>> The following patch does just that.  Please do not be concerned about the
>> ZMM
>> register use.  This patch does not address the use of AVX-512
>> instructions.  In
>> a future patch I will add a different check for enabling/disabling
>> AVX-512.
>>
>> The NASM changelog can be found here:
>> http://www.nasm.us/doc/nasmdocc.html
>>
>> Releases and their dates can be seen here:
>> http://www.nasm.us/pub/nasm/releasebuilds/?C=M;O=D
>>
>> Other than the discussion about the oldest version to support we should
>> discuss
>> the command line options for configure and the internal variable names.
>> At
>> present they all use "yasm" somewhere.  If we are to drop support for that
>> then
>> we should change the option names to prevent confusion.
>>
>> We could just change them to "nasm" and be done.  We could provide
>> compatability
>> options.  We could adopt Libav's generic "x86asm".

It's better to use generic name.

I do not like "x86asm", as 'gnu as' also fits that description,
but it is better than changing the name every time some
compiler takes the lead. E.g. zasm might be the next
champion of AVX512 assembly. ;)



>> James Darnley (1):
>>   configure: require NASM version 2.11 or newer for external x86
>>     assembly
>>
>>  configure | 17 ++++-------------
>>  1 file changed, 4 insertions(+), 13 deletions(-)
>>
>> Brought to you by my inability to configure FFmpeg with NASM 2.13.
>>
>
> Maybe you should just pick the patches from Libav, that still
> implement an automatic fallback to YASM if NASM is not found or too
> old? We would eventually get to them in the merges anyway.
> Many people building FFmpeg for years with YASM may not have an
> appropriate NASM installed, and forcing a switch here may not be
> ideal.

+1