Martin Storsjö: > On Thu, 21 Mar 2024, Andreas Rheinhardt wrote: > >> Andreas Rheinhardt: >>> C11 provides static assertions via _Static_assert and >>> provides static_assert as a convenience define for this >>> in assert.h. MSVC 19.27 declares support for C11, but does >>> not support _Static_assert, but somehow supports >>> static_assert. That's therefore what we use. >>> >>> But apparently there are some old GCC toolchains where >>> _Static_assert is supported, but assert.h does not provide >>> the fallback define. Some fate boxes are affected by this >>> [1]. >>> >>> This commit therefore checks whether static_assert works >>> with assert.h included; if not, it errors out. Users like >>> the above can still add -Dstatic_assert=_Static_assert >>> to cflags as a workaround. >>> >>> [1]: >>> https://fate.ffmpeg.org/report.cgi?time=20240321123620&slot=sh4-debian-qemu-gcc-4.7 >>> >>> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@outlook.com> >>> --- >>> This is what a test without fallback looks like. >>> Posted to gather opinions on what people prefer. >>> >>> configure | 13 +++++++++++++ >>> 1 file changed, 13 insertions(+) >>> >>> diff --git a/configure b/configure >>> index 6d7b33b0ff..c2d2c70c20 100755 >>> --- a/configure >>> +++ b/configure >>> @@ -5589,6 +5589,19 @@ check_cxxflags_cc -std=$stdcxx ctype.h >>> "__cplusplus >= 201103L" || >>> check_cflags_cc -std=$stdc ctype.h "__STDC_VERSION__ >= 201112L" || >>> { check_cflags_cc -std=c11 ctype.h "__STDC_VERSION__ >= 201112L" >>> && stdc="c11" || die "Compiler lacks C11 support"; } >>> >>> +test_cc <<EOF || die "Compiler lacks support for C11 static_assert" >>> +#include <assert.h> >>> +#include <stddef.h> >>> +struct Foo { >>> + int a; >>> + void *ptr; >>> +} obj; >>> +static_assert(offsetof(struct Foo, a) == 0, >>> + "First element of struct does not have offset 0"); >>> +static_assert(offsetof(struct Foo, ptr) >= offsetof(struct Foo, a) + >>> sizeof(obj.a), >>> + "elements not properly ordered in struct"); >>> +EOF >>> + >>> check_cppflags -D_FILE_OFFSET_BITS=64 >>> check_cppflags -D_LARGEFILE_SOURCE >>> >> >> Jan has tested old toolchains and found out that his GCC 4.7 has proper >> C11 headers; so this seems to be unique to Michael's setup. This makes >> me prefer this patch instead of the version with the fallback. (Michael >> can simply add -Dstatic_assert=_Static_assert to his cflags.) >> Of course others are still invited to share their opinions. > > Both patches seem to work fine with MSVC 19.27 - I vaguely prefer the v2 > version, which is simpler. > > > But to me, we could also just revert the change to > libavcodec/ccaption_dec.c, and declare that we require MSVC 19.28 > instead. MSVC 19.27, when executed with -std:c11 without -nologo, it > prints this: > > /std:c11 is a preview implementation of the ISO C11 standard, and > we're eager to hear about bugs and suggestions for improvements. > However, note that these features are provided as-is without support. > > And I don't have any specific reasons for wanting to use this compiler - > I just tested the lowest version that was supposed to be supported > earlier and noted that it had broken recently. So to me, reverting to > requiring _Static_assert would be quite ok as well. >
We can actually do both: Test for static_assert and for _Static_assert (to exclude MSVC 19.27; is 19.28 still supposed to be a preview implementation?). The reason I prefer static_assert in the codebase is that _Static_assert is actually deprecated with C23 (although I don't think it will be removed any time). - 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".
