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configure: Explicitly check for static_assert, _Static_assert 

C11 provides static assertions via _Static_assert and
provides static_assert as a convenience define for this
in assert.h. Our codebase uses the latter, as _Static_assert
has actually already been deprecated in C23.

Not all toolchains that declare support for C11 actually
support it; e.g. MSVC 19.27 does not support _Static_assert,
but somehow supports static_assert. MSVC 19.27 admits to be
a "preview implementation of the ISO C11 standard",
so this is not surprising (MSVC 19.28 does not come with
this caveat).

Furthermore some FATE boxes [1] use old GCC toolchains (with
only experimental support for C11) where _Static_assert is
supported, but assert.h does not provide the fallback define.
They are broken since the first usage of static_assert.

This commit therefore checks whether static_assert and
_Static_assert work with assert.h included; if not,
configure errors out.

This intentionally drops support for MSVC 19.27. Users like
the old FATE boxes above can still add -Dstatic_assert=_Static_assert
to cflags as a workaround if desired.

[1]: https://fate.ffmpeg.org/report.cgi?time=20240321123620&slot=sh4-debian-qemu-gcc-4.7

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2024-03-21 16:27:58 +01:00
parent ccd2b7f858
commit 0d43adcbef
1 changed files with 13 additions and 0 deletions
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13
configure vendored
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@ -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 assertions"
#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