From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B8314C001DF for ; Fri, 4 Aug 2023 15:59:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=dMVYw3lJr52QeGqPPwd19eIh0Dp2388rL7/NfhprsY0=; b=2rwom9qlHDBC8p GbPg1bDUESSk1lHw1KYQ6FlXFqdFDF2/2vkKwULDX1iOiy1wHXb3t6XwhYWHmWeKUZZ/FaUlnzix7 2NXgo4IW5x4H5333GQGXUnoxGbDEizRR/txwYIBZzSX1SO2dP4q3LbW/5o85+CCKhFiYJBZFfRW7L y0keQWi0sZHhjvWR+jarwXphS7LBJBPJj6afIooMtgn8nju4ILKEDcQRNvhjjHllI4VQSgqbk+vcA +l4BaCeZBY3Fnu38/cHDvOxbxMfsF3bUsP87NxeiHI3F9H4yi7tXhw9vx3j+IIRzniaCBMFsr18Xz UG+HrTdVRlRk+eDj77tA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qRxCW-00CkYt-34; Fri, 04 Aug 2023 15:58:52 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qRxCT-00CkY3-0p for linux-arm-kernel@lists.infradead.org; Fri, 04 Aug 2023 15:58:51 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5AA9062099; Fri, 4 Aug 2023 15:58:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 275F2C433C7; Fri, 4 Aug 2023 15:58:45 +0000 (UTC) Date: Fri, 4 Aug 2023 11:58:43 -0400 From: Steven Rostedt To: Marco Elver Cc: Andrew Morton , Kees Cook , Guenter Roeck , Peter Zijlstra , Mark Rutland , 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 Message-ID: <20230804115843.5be5f2b2@gandalf.local.home> In-Reply-To: <20230804090621.400-1-elver@google.com> References: <20230804090621.400-1-elver@google.com> X-Mailer: Claws Mail 3.19.1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230804_085849_381873_A9E42606 X-CRM114-Status: GOOD ( 32.28 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 4 Aug 2023 11:02:56 +0200 Marco Elver wrote: > [1]: "On X86-64 and AArch64 targets, this attribute changes the calling > convention of a function. The preserve_most calling convention attempts > to make the code in the caller as unintrusive as possible. This > convention behaves identically to the C calling convention on how > arguments and return values are passed, but it uses a different set of > caller/callee-saved registers. This alleviates the burden of saving and > recovering a large register set before and after the call in the > caller." > > [1] https://clang.llvm.org/docs/AttributeReference.html#preserve-most > > Introduce the attribute to compiler_types.h as __preserve_most. > > Use of this attribute results in better code generation for calls to > very rarely called functions, such as error-reporting functions, or > rarely executed slow paths. > > Beware that the attribute conflicts with instrumentation calls inserted > on function entry which do not use __preserve_most themselves. Notably, > function tracing which assumes the normal C calling convention for the > given architecture. Where the attribute is supported, __preserve_most > will imply notrace. It is recommended to restrict use of the attribute > to functions that should or already disable tracing. > > Signed-off-by: Marco Elver > --- > v2: > * Imply notrace, to avoid any conflicts with tracing which is inserted > on function entry. See added comments. Acked-by: Steven Rostedt (Google) -- Steve > --- > include/linux/compiler_types.h | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h > index 547ea1ff806e..12c4540335b7 100644 > --- a/include/linux/compiler_types.h > +++ b/include/linux/compiler_types.h > @@ -106,6 +106,33 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { } > #define __cold > #endif > > +/* > + * On x86-64 and arm64 targets, __preserve_most changes the calling convention > + * of a function to make the code in the caller as unintrusive as possible. This > + * convention behaves identically to the C calling convention on how arguments > + * and return values are passed, but uses a different set of caller- and callee- > + * saved registers. > + * > + * The purpose is to alleviates the burden of saving and recovering a large > + * register set before and after the call in the caller. This is beneficial for > + * rarely taken slow paths, such as error-reporting functions that may be called > + * from hot paths. > + * > + * Note: This may conflict with instrumentation inserted on function entry which > + * does not use __preserve_most or equivalent convention (if in assembly). Since > + * function tracing assumes the normal C calling convention, where the attribute > + * is supported, __preserve_most implies notrace. > + * > + * Optional: not supported by gcc. > + * > + * clang: https://clang.llvm.org/docs/AttributeReference.html#preserve-most > + */ > +#if __has_attribute(__preserve_most__) > +# define __preserve_most notrace __attribute__((__preserve_most__)) > +#else > +# define __preserve_most > +#endif > + > /* Builtins */ > > /* _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel