[FFmpeg-devel] [inline assembly compliance] Issues and patches

[Kieran Kunhya]

On Fri, 3 Apr 2020 at 22:07, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:

> Am Fr., 3. Apr. 2020 um 22:42 Uhr schrieb FRÉDÉRIC RECOULES
> <frederic.recoules at univ-grenoble-alpes.fr>:
>
> > we are academic researchers working in automated program analysis.
> > We are currently interested in checking compliance of inline asm chunks
> > as found in C programs.
> >
> > While benchmarking our tool and technique, we found a number of issues in
> > FFMPEG. We report them to you, as well as adequate patches.
> > Actually, we found 59 significant compliance issues in your code.
> > We join 3 patches for some of them, together with explanations and
> > we can send you other patches on demand.
> >
> >
> > * All these bugs are related to compliance between the block of asm and
> its
> > surrounding "contract" (in gcc-style notation). They are akin to
> undefined or
> > implementation-defined behaviours in C: they currently do not manifest
> > themselves in your program, but at some point in time with compiler
> > optimizations becoming more and more aggressive or changes in
> undocumented
> > compiler choices regarding asm chunks, they can suddenly trigger a
> > (hard-to-find) bug.
>
> So your current patch does not change compilation output (without
> debug symbols) when compared with md5sum or similar?
>

We do not do such a comparison for C undefined behaviour changes so why
should we do such a comparison for this code?

Kieran