[FFmpeg-devel] [PATCH] Fix missing used attribute for inline assembly variables

[Thomas Köppe]

It should be under __GNUC__ -- something went wrong with the patch! I'll
make a new one. Sorry about that!

On 30 October 2017 at 19:31, James Almer <jamrial at gmail.com> wrote:

> On 10/30/2017 4:17 PM, Thomas Köppe wrote:
> > Variables used in inline assembly need to be marked with
> attribute((used)).
> > Static constants already were, via the define of DECLARE_ASM_CONST.
> > But DECLARE_ALIGNED does not add this attribute, and some of the
> variables
> > defined with it are const only used in inline assembly, and therefore
> > appeared dead.
> >
> > This change makes FFMPEG linkable with Clang's ThinLTO.
> >
> > ---
> >  libavcodec/cabac.c | 2 +-
> >  libavutil/mem.h    | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavcodec/cabac.c b/libavcodec/cabac.c
> > index dd2b057c6d..7321b48901 100644
> > --- a/libavcodec/cabac.c
> > +++ b/libavcodec/cabac.c
> > @@ -32,7 +32,7 @@
> >  #include "cabac.h"
> >  #include "cabac_functions.h"
> >
> > -const uint8_t ff_h264_cabac_tables[512 + 4*2*64 + 4*64 + 63] = {
> > +DECLARE_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 +
> > 4*64 + 63] = {
> >      9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5,
> >      4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
> >      3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
> > diff --git a/libavutil/mem.h b/libavutil/mem.h
> > index 527cd03191..db06e109be 100644
> > --- a/libavutil/mem.h
> > +++ b/libavutil/mem.h
> > @@ -98,7 +98,7 @@
> >          AV_PRAGMA(DATA_ALIGN(v,n))                      \
> >          static const t __attribute__((aligned(n))) v
> >  #elif defined(__DJGPP__)
>
> Is your intention to change the DJGPP path, or the gnuc/clang path?
>
> > -    #define DECLARE_ALIGNED(n,t,v)      t __attribute__ ((aligned
> > (FFMIN(n, 16)))) v
> > +    #define DECLARE_ALIGNED(n,t,v)      t av_used __attribute__
> ((aligned
> > (FFMIN(n, 16)))) v
> >      #define DECLARE_ASM_CONST(n,t,v)    static const t av_used
> > __attribute__ ((aligned (FFMIN(n, 16)))) v
> >  #elif defined(__GNUC__) || defined(__clang__)
> >      #define DECLARE_ALIGNED(n,t,v)      t __attribute__ ((aligned (n)))
> v
> >
>
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