894191e7e1
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: J. Dekker <jdek@itanimul.li> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com> Signed-off-by: J. Dekker <jdek@itanimul.li>
FFmpeg README
FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.
Libraries
libavcodecprovides implementation of a wider range of codecs.libavformatimplements streaming protocols, container formats and basic I/O access.libavutilincludes hashers, decompressors and miscellaneous utility functions.libavfilterprovides means to alter decoded audio and video through a directed graph of connected filters.libavdeviceprovides an abstraction to access capture and playback devices.libswresampleimplements audio mixing and resampling routines.libswscaleimplements color conversion and scaling routines.
Tools
- ffmpeg is a command line toolbox to manipulate, convert and stream multimedia content.
- ffplay is a minimalistic multimedia player.
- ffprobe is a simple analysis tool to inspect multimedia content.
- Additional small tools such as
aviocat,ismindexandqt-faststart.
Documentation
The offline documentation is available in the doc/ directory.
The online documentation is available in the main website and in the wiki.
Examples
Coding examples are available in the doc/examples directory.
License
FFmpeg codebase is mainly LGPL-licensed with optional components licensed under GPL. Please refer to the LICENSE file for detailed information.
Contributing
Patches should be submitted to the ffmpeg-devel mailing list using
git format-patch or git send-email. Github pull requests should be
avoided because they are not part of our review process and will be ignored.