From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id E95FD488BE for ; Thu, 21 Mar 2024 21:52:26 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 31D4768D54A; Thu, 21 Mar 2024 23:52:23 +0200 (EET) Received: from mail8.parnet.fi (mail8.parnet.fi [77.234.108.134]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id B935168D4F8 for ; Thu, 21 Mar 2024 23:52:16 +0200 (EET) Received: from mail9.parnet.fi (mail9.parnet.fi [77.234.108.21]) by mail8.parnet.fi with ESMTP id 42LLqEKF031277-42LLqEKG031277 for ; Thu, 21 Mar 2024 23:52:14 +0200 Received: from cone.home.martin.st (host-114-191.parnet.fi [77.234.114.191]) by mail9.parnet.fi (Postfix) with ESMTPS id 7BB68A1467 for ; Thu, 21 Mar 2024 23:52:14 +0200 (EET) Date: Thu, 21 Mar 2024 23:52:12 +0200 (EET) From: =?ISO-8859-15?Q?Martin_Storsj=F6?= To: FFmpeg development discussions and patches In-Reply-To: Message-ID: References: MIME-Version: 1.0 X-FEAS-Client-IP: 77.234.108.21 X-FE-Last-Public-Client-IP: 77.234.108.21 X-FE-Policy-ID: 3:14:2:SYSTEM Subject: Re: [FFmpeg-devel] [PATCH v2] configure: Explicitly check for static_assert X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: 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 >> --- >> 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 <> +#include >> +#include >> +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 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".