On 25 Oct 2022, at 14:48, Andreas Rheinhardt wrote: > GCC 11 has a bug: When it creates clones of recursive functions > (to inline some parameters), it clones a recursive function > eight times by default, even when this exceeds the recursion > depth. This happens with encode_block() in libavcodec/svq1enc.c > where a parameter level is always in the range 0..5; > but GCC 11 also creates functions corresponding to level UINT_MAX > and UINT_MAX - 1 (on -O3; -O2 is fine). > > Using such levels would produce undefined behaviour and because > of this GCC emits bogus -Warray-bounds warnings for these clones. > > Since commit d08b2900a9f0935959303da668cb00a8a7245228, certain > symbols that are accessed like ff_svq1_inter_multistage_vlc[level] > are declared with hidden visibility, which allows compilers > to bake the offset implied by level into the instructions > if level is a compile-time constant as it is in the clones. > Yet this leads to insane offsets for level == UINT_MAX which > can be incompatible with the supported offset ranges of relocations. > This happens in the small code model (the default code model for > AArch64). > > This commit therefore works around this bug by disabling cloning > recursive functions for GCC 10 and 11. GCC 10 is affected by the > underlying bug (see > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102513), so the workaround > also targets it, although it only produces three versions of > encode_block(), so it does not seem to trigger the actual issue here. > > The issue has been mitigated in GCC 12.1 (it no longer creates clones > for impossible values; see also commit > 1cb7fd317c84117bbb13b14851d62f77f57bb9ce), so the workaround > does not target it. > > Reported-by: Josh Dekker <j...@itanimul.li> > Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@outlook.com> > --- > libavcodec/svq1enc.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/libavcodec/svq1enc.c b/libavcodec/svq1enc.c > index 75adbe7ea0..7c9430a137 100644 > --- a/libavcodec/svq1enc.c > +++ b/libavcodec/svq1enc.c > @@ -46,6 +46,12 @@ > #include "libavutil/frame.h" > #include "libavutil/mem_internal.h" > > +// Workaround for GCC bug 102513 > +#if AV_GCC_VERSION_AT_LEAST(10, 0) && AV_GCC_VERSION_AT_MOST(12, 0) \ > + && !defined(__clang__) && !defined(__INTEL_COMPILER) > +#pragma GCC optimize ("no-ipa-cp-clone") > +#endif > + > typedef struct SVQ1EncContext { > /* FIXME: Needed for motion estimation, should not be used for anything > * else, the idea is to make the motion estimation eventually independent
Discussed on IRC, LGTM & pushed. -- jd _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
