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

[Thomas Köppe]

(I must have forgotten to rebase first!)

On 30 October 2017 at 20:14, Thomas Köppe <tkoeppe at google.com> wrote:

> 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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>>
>
>