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 CFED840265 for ; Wed, 19 Jan 2022 12:40:58 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 1A8C768B087; Wed, 19 Jan 2022 14:40:56 +0200 (EET) Received: from mail0.khirnov.net (red.khirnov.net [176.97.15.12]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 5DB5168AF55 for ; Wed, 19 Jan 2022 14:40:50 +0200 (EET) Received: from localhost (localhost [IPv6:::1]) by mail0.khirnov.net (Postfix) with ESMTP id BB48E24017C for ; Wed, 19 Jan 2022 13:40:49 +0100 (CET) Received: from mail0.khirnov.net ([IPv6:::1]) by localhost (mail0.khirnov.net [IPv6:::1]) (amavisd-new, port 10024) with ESMTP id AsFw9Sc1gYYM for ; Wed, 19 Jan 2022 13:40:48 +0100 (CET) Received: from lain.red.khirnov.net (lain.red.khirnov.net [IPv6:2001:67c:1138:4306::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "lain.red.khirnov.net", Issuer "smtp.khirnov.net SMTP CA" (verified OK)) by mail0.khirnov.net (Postfix) with ESMTPS id 40564240179 for ; Wed, 19 Jan 2022 13:40:48 +0100 (CET) Received: by lain.red.khirnov.net (Postfix, from userid 1000) id BA3CA16008E; Wed, 19 Jan 2022 13:40:44 +0100 (CET) From: Anton Khirnov To: FFmpeg development discussions and patches In-Reply-To: <0bd6970d-e2c9-0ff1-3137-5b01dbff3a86@gmail.com> References: <20220119115432.12571-1-anton@khirnov.net> <0bd6970d-e2c9-0ff1-3137-5b01dbff3a86@gmail.com> Mail-Followup-To: FFmpeg development discussions and patches Date: Wed, 19 Jan 2022 13:40:44 +0100 Message-ID: <164259604467.23111.3104146160553486070@lain.red.khirnov.net> User-Agent: alot/0.8.1 MIME-Version: 1.0 Subject: Re: [FFmpeg-devel] [PATCH] configure: link to libatomic when it's present 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: Quoting James Almer (2022-01-19 13:34:20) > > > On 1/19/2022 8:54 AM, Anton Khirnov wrote: > > C11 atomics in some configurations (e.g. 64bit operations on ppc64 with > > GCC) require linking to libatomic. > > --- > > Testing welcome, especially in configurations where > > * libatomic is not present > > * libatomic is actually needed > > --- > > configure | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/configure b/configure > > index 1413122d87..1ff5dbee5b 100755 > > --- a/configure > > +++ b/configure > > @@ -6324,7 +6324,14 @@ check_headers asm/types.h > > # it seems there are versions of clang in some distros that try to use the > > # gcc headers, which explodes for stdatomic > > # so we also check that atomics actually work here > > -check_builtin stdatomic stdatomic.h "atomic_int foo, bar = ATOMIC_VAR_INIT(-1); atomic_store(&foo, 0); foo += bar" > > +# > > +# some configurations also require linking to libatomic, so try > > +# both with -latomic and without > > +for LATOMIC in "-latomic" ""; do > > Shouldn't you try without it first? On my toolchain libatomic is > present, but libraries compile without linking to it just fine. That > changes after this patch, where it starts linking to it explicitly. No, because it may only be needed for some atomic sizes and operations, which the test in configure doesn't necessarily catch. And because we pass as-needed to the linker, the built libraries shouldn't actually require libatomic unless it's really needed. > > > + check_builtin stdatomic stdatomic.h \ > > + "atomic_int foo, bar = ATOMIC_VAR_INIT(-1); atomic_store(&foo, 0); foo += bar" \ > > + $LATOMIC && add_extralibs $LATOMIC && break > > You should probably add it to the required libraries' extralibs only. > Just replace the add_extralibs part with setting stdatomic_extralibs to > $LATOMIC, and then add stdatomic to all the libraries' _suggest lists, > same as we do for libm. Then we need to actively track which libraries actually use atomics, which also depends on which features are enabled. Given that this only fails on less-common arches, this sounds like a recipe for obscure build failures. Given that it's only really linked when needed, it seems better to just add it unconditionally. -- Anton Khirnov _______________________________________________ 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".