From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792959664; b=hBq+ZuXTks0i6cwynFquQHGctPDG8D0fscKu9huft6GMMXfkhWid2IMa+kRTPvcz9Fx0 xIuB5HC+y3MIOUuxk5vToRC0MEFrqfJAgCUtbfSguthHbJo8Wk2jGG8TwP2rKapvWuOqz 3AXuc353k+clEc64HI4WdovFfvdYZtiN34/yB3OU4zSwGZPmnLdb+eB1VGWQtl6XBbE7X hbK/jjjRRr9gyB9yxFrM08Yw8ljed08sJzHA6rOEt6Hg3tPg8BK5kmbzObNmuq8eYERrq DexJnBe1FZK5Egs8XO3qeX/wQh4sTdOwtQzHVJSEgcbBygvCdRagQ6CLhnvmHQHaKXQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792959664; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition: Content-Transfer-Encoding:In-Reply-To; bh=xISrLrkizMl7yJxaTlfZqoeJnZK8a6hbzOaniZGY6+w=; b=0qPiiQGmg0zPEEs4pC56E3zIHfnUkBwu8geS3H1nEZoUJfJGGIssHMTY8u102x1U/XVv lYnDMdGU6JaNTEOCqIjrz6CQk5vyey4cd2/lU4mUIyZA5XRCfADhwH+dXZkw2erDH14zd 3ZezYU1HnwYhTbP2tGtnj5WOOmPJS+3jCqh6VOqkk04JpFnxkrK9wP4jPjfQvKX4c5i87 c6IuKebHix1lhQi/iyX9RmCXld54hDYHSFxEJO3z8U4+Zxoc4poNrhxtvGMTMJcD9bKE8 MYx82xzZONhbiUgm/ilk9vk9Hrbaabgxudl5HHFfF+ZKTMiPbZxjZg02V9YP31tGwTQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=O3mJJaGU; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A2221606A31B for ; Sun, 25 Oct 2026 20:21:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=O3mJJaGU Received: by smtp.kernel.org (Postfix) with ESMTPSA id B47991F01825; Sun, 25 Oct 2026 20:21:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792959664; bh=xISrLrkizMl7yJxaTlfZqoeJnZK8a6hbzOaniZGY6+w=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=O3mJJaGUydflanSZMujzW4Lz5+ki/LlS/8cAwnZMQdOGkLDkb/3oEpKev5dDk1sbf l31fhyRiyvVAKdogj1+4+8nu9nbS3HsEhEXNAxWhDCJNEYC0b5rSHKTDMNwdfW402F uhev+vAUtUlZmKzJ7hjp/bMAMSmu2lMwQFeZx2a8RdMKqZnq3hdbmY/Eege111tAyf NEw6jyb+3eUjwq2eJVKHh+X3g7upRDnSWYoI9weMVNQQsaR6vpqFkvzp7v/UwKdeuR RUfGWM4gRMUUG7AwHGe7gKbAHocKmp2ki63HTYcBp5cO4FB3K8QJIq469eLzpzFF8T sA8yUNQiOhhMg== Date: Sun, 25 Oct 2026 13:20:59 -0700 From: Nathan Chancellor To: Antoni =?utf-8?Q?Kuczy=C5=84ski?= Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Subject: Re: [PATCH] x86/build/64: Prevent native builds from generating SSE/AVX code Message-ID: <20261025202059.GA1945927@ax162> References: <20261025174336.8857-1-antoni.kucz@gmail.com> <20261025194411.GA56787@ax162> <20261025200735.61814-1-antoni.kucz@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261025200735.61814-1-antoni.kucz@gmail.com> On Sun, Oct 25, 2026 at 09:07:35PM +0100, Antoni Kuczyński wrote: > On Sun, Oct 25, 2026 at 12:44:11PM -0700, Nathan Chancellor wrote: > > This option has been in the kernel for quite some time and I am sure > > people are using it. I wonder why this has not come up sooner. Just > > unlucky timing or configuration? > > Configuration, on my side, sorry for the noise. Following up on your > question I found that "gcc" in my PATH was the icecc (icecream 1.4.0) > wrapper. To be able to distribute the compilation, icecc replaces > -march=native with an explicit list of options for the local CPU: > > /usr/bin/gcc -mno-sse -mno-avx -Os -march=ivybridge -mmmx -mpopcnt > -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -mavx ... > > so the expanded -msse/-mavx come after the kernel's -mno-* flags and > win. Plain GCC 14.2 does not have this problem: the reproducer from > the changelog built with /usr/bin/gcc-14 emits no SIMD instructions, > as explicit -mno-* options take precedence over what -march=native > enables. > > So the changelog's explanation and the Fixes:/stable tags are wrong, > please drop this patch. I will report the issue to icecream instead. Ah yeah, that makes a lot more sense. I guess the easiest solution is probably something like this patch internally where the expanded value of '-march=native' is moved to the front of the GCC command so that any overrides can happen naturally. > > Maintaining two copies of these flags (and having them appear in the > > command line twice) seems objectively worse than just adding an extra > > 'ifdef CONFIG_X86_64' and moving the block up so that this happens in > > the naturally expected order? > > Agreed, and FWIW your diff on top of current master also fixes the > icecc build here: -march=native now comes before the -mno-* flags and > arch/x86/boot/startup/gdt_idt.o contains no SIMD instructions. If you > think that ordering is worth having on its own merits, I am happy to > send it as a cleanup without Fixes:/stable, but I understand if it is > not worth the churn for an icecc-only problem. I guess that is up to the x86 maintainers. I would personally be fine with it since the workaround is basically an extra ifdef and comment, which I do not see an substantial maintenance burden, but they might feel otherwise. -- Cheers, Nathan