[FFmpeg-devel] [PATCH] Fix missing used attribute for inline assembly variables
michael at niedermayer.cc
Tue Oct 31 18:19:27 EET 2017
On Tue, Oct 31, 2017 at 03:52:14PM +0000, Thomas Köppe wrote:
> +Teresa, who drafted the patch initially.
> On 31 October 2017 at 15:38, Michael Niedermayer <michael at niedermayer.cc>
> > On Tue, Oct 31, 2017 at 12:16:18PM +0000, Thomas Köppe wrote:
> > > Variables used in inline assembly need to be marked with
> > attribute((used)).
> > This should not be the case.
> > Variables referenced through in/out operands should not need that.
> > Only ones accessed directly bypassing operands should need this
> I've added Teresa to the thread, who initially analyzed the problem. (For
> background on ThinLTO, see here cppcon talk:
> > > - #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (n)))
> > v
> > > + #define DECLARE_ALIGNED(n,t,v) t av_used __attribute__
> > ((aligned (n))) v
> > which variables actually are affected/ need this ?
> Without this annotation, and when compiling and linking with ThinLTO, I get
> an undefined reference to "ff_h264_cabac_tables", and also to
> "ff_pw_96", "ff_pw_53",
> "ff_pw_42", "ff_w1111" and many more.
i guess these are all accessed directly, like through MANGLE()
> > Marking all aligned variables as used makes it harder to spot unused
> > variables leading to accumulation of cruft
> I see. Maybe we can annotate only the affected variables more granularly?
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
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