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.
// Martin
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