Mark Thompson: > On 23/03/2020 00:52, Andreas Rheinhardt wrote: >> According to C99, there has to be at least one argument for every ... >> in a variadic function-like macro. In practice most (all?) compilers also >> allow to leave it completely out, but it is nevertheless required: In a >> variadic macro "there shall be more arguments in the invocation than there >> are parameters in the macro definition (excluding the ...)." (C99, >> 6.10.3.4). >> >> CBS (not the framework itself, but the macros used in the >> cbs_*_syntax_template.c files) relies on the compiler allowing to leave >> a variadic macro argument out. This leads to warnings when compiling in >> -pedantic mode, e.g. "warning: must specify at least one argument for >> '...' parameter of variadic macro [-Wgnu-zero-variadic-macro-arguments]" >> from Clang. >> >> Most of these warnings can be easily avoided: The syntax_templates >> mostly contain helper macros that expand to more complex variadic macros >> and these helper macros often omit an argument for the .... Modifying >> them to always expand to complex macros with an empty argument for the >> ... at the end fixes most of these warnings: The number of warnings went >> down from 400 to 0 for cbs_av1, from 1114 to 32 for cbs_h2645, from 38 to >> 0 for cbs_jpeg, from 166 to 0 for cbs_mpeg2 and from 110 to 8 for cbs_vp9. >> >> These eight remaining warnings for cbs_vp9 have been fixed by switching >> to another macro in cbs_vp9_syntax_template: The fixed values for the >> sync bytes as well as the trailing bits for byte-alignment are now read >> via the fixed() macro (this also adds a check to ensure that trailing >> bits are indeed zero as they have to be). >> >> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com> >> --- >> There are two ways to fix the remaining 32 warnings from cbs_h2645: >> >> Simply add ", " to all macro calls that make use of the complex macros; >> this has the drawback of adding uglyness to cbs_h26x_syntax_template.c. >> >> Or add new macros for these macro calls: The places that produce >> warnings use the complex macros directly, because they use names >> different from the default names that the helper macros use, but they do >> not use subscripts and therefore leave the variadic argument (designed >> for subscripts) out. I would have implemented the second solution if it >> were not for the problem of the naming of the new macros. >> >> (There is of course also the possibility not to care about the remaining >> ones.) >> >> libavcodec/cbs_av1.c | 16 ++++++++-------- >> libavcodec/cbs_h2645.c | 14 +++++++------- >> libavcodec/cbs_jpeg.c | 2 +- >> libavcodec/cbs_mpeg2.c | 6 +++--- >> libavcodec/cbs_vp9.c | 13 ++++++------- >> libavcodec/cbs_vp9_syntax_template.c | 21 ++++----------------- >> 6 files changed, 29 insertions(+), 43 deletions(-) > > Looks fine to me, keeping the ugliness in the macros rather than the > templates is good. > > Is there any compiler which actually fails here, or is the only case which > finds it the warning in clang pedantic mode? > Both Clang as well as GCC warn in pedantic mode for this (although GCC's warning is not called "gnu-zero-variadic-macro-arguments"; it simply says "warning: ISO C99 requires at least one argument for the "..." in a variadic macro").
Any suggestions for macro names for the remaining stuff (stuff that uses an unusual name, but no subscripts (like last_payload_type_byte and last_payload_size_byte))? If not, I'll apply. I know of no compiler that refuses to compile because of this. - Andreas _______________________________________________ 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".
