From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8E4E0D52D for ; Mon, 7 Aug 2023 12:43:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691412230; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pgN6ITNOX4XAghEqnE7rc109x2dPHO2XXLtjfGMGEBw=; b=fNiTZ+Ju0r2fCC0CxqgYpD6EbR6b/NAEEkxcljT+CfVuhf7lskS2EBDY9cT95MiXEw3ze8 0UDvvoi1KnBhKad9lMzEdDYlLXqscZ9mFqBd78OPTvVNqfNE149U8u66Jd+TztuChT9DSX jWxk4z1Cd64Tbh8+vQYDLFMQelzm9zc= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-558-VkhQ3GWqNk66vZeVUGT2Qw-1; Mon, 07 Aug 2023 08:43:49 -0400 X-MC-Unique: VkhQ3GWqNk66vZeVUGT2Qw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BD5F6381AE49; Mon, 7 Aug 2023 12:43:43 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.12]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6342E40C2076; Mon, 7 Aug 2023 12:43:40 +0000 (UTC) From: Florian Weimer To: Jakub Jelinek Cc: Marco Elver , Andrew Morton , Kees Cook , Guenter Roeck , Peter Zijlstra , Mark Rutland , Steven Rostedt , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Nathan Chancellor , Nick Desaulniers , Tom Rix , Miguel Ojeda , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Dmitry Vyukov , Alexander Potapenko , kasan-dev@googlegroups.com, linux-toolchains@vger.kernel.org Subject: Re: [PATCH v2 1/3] compiler_types: Introduce the Clang __preserve_most function attribute References: <20230804090621.400-1-elver@google.com> <87il9rgjvw.fsf@oldenburg.str.redhat.com> Date: Mon, 07 Aug 2023 14:43:39 +0200 In-Reply-To: (Jakub Jelinek's message of "Mon, 7 Aug 2023 14:38:05 +0200") Message-ID: <87h6pbf2f8.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 * Jakub Jelinek: > On Mon, Aug 07, 2023 at 02:24:26PM +0200, Marco Elver wrote: >> > | If the arguments are passed in callee-saved registers, then they will >> > | be preserved by the callee across the call. This doesn=E2=80=99t app= ly for >> > | values returned in callee-saved registers. >> > | >> > | =C2=B7 On X86-64 the callee preserves all general purpose register= s, except >> > | for R11. R11 can be used as a scratch register. Floating-point >> > | registers (XMMs/YMMs) are not preserved and need to be saved by = the >> > | caller. >> > | >> > | =C2=B7 On AArch64 the callee preserve all general purpose register= s, except >> > | X0-X8 and X16-X18. >> > >> > Ideally, this would be documented in the respective psABI supplement. >> > I filled in some gaps and filed: >> > >> > Document the ABI for __preserve_most__ function calls >> > >>=20 >> Good idea. I had already created >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110899, and we need >> better spec to proceed for GCC anyway. > > "Registers used for passing arguments > are preserved by the called function, but registers used for > returning results are not." > > You mean just GPRs or also vector SSE or MMX registers? I think this is pretty clear for x86-64: | Floating-point registers (XMMs/YMMs) are not preserved and need to be | saved by the caller. The issue is more with future GPR extensions like APX. Thanks, Florian