[FFmpeg-devel] [PATCH] Replace br return with ret

[Casey Smalley]

Hi,

Just wondering what current thoughts on the patch was. It looks as
though the change is fine, but if there is still an issue I can submit a
new patch using BTI landing pads instead.

Best regards,

Casey.

On 7/27/23 18:22, Reimar Döffinger wrote:
> 
>
>
>> On 27 Jul 2023, at 15:55, Rémi Denis-Courmont <remi at remlab.net> wrote:
>>
>> Hi,
>>
>> The use of RET vs BR also has microarchitectural side effects. AFAIU, RET should always be paired with an earlier BL/BLR to avoid interfering with branch prediction.
>>
>> So depending on the circumstances, either one of these should be addressed:
>> * Clarify that this is actually a function return , and RET should be used anyway, regardless of BTI.
>> * Keep BR and add BTI J landing pads where appropriate, if this wasn't really a function return.
> Yes BL and RET is best to match up.
>
> For this function:
> % git grep func_tr_32x4
> libavcodec/aarch64/hevcdsp_idct_neon.S:function func_tr_32x4_\name
> libavcodec/aarch64/hevcdsp_idct_neon.S:        bl              func_tr_32x4_firstpass
> libavcodec/aarch64/hevcdsp_idct_neon.S:        bl              func_tr_32x4_secondpass_\bitdepth
> libavcodec/arm/hevcdsp_idct_neon.S:function func_tr_32x4_\name
> libavcodec/arm/hevcdsp_idct_neon.S:        bl              func_tr_32x4_firstpass
> libavcodec/arm/hevcdsp_idct_neon.S:        bl              func_tr_32x4_secondpass_\bitdepth
>
> It is always used with "bl", thus ret is also more correct from
> that aspect.
> Was your comment only on checking that, or did you mean that this should
> be mentioned in the commit message?
> (if you are wondering why the code did not use ret before, I guess it's
> because it was ported from the 32-bit arm assembler and it slipped by code review)
>
> Best regards,
> Reimar
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.