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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45C45C001DB for ; Fri, 4 Aug 2023 09:10:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229659AbjHDJKH (ORCPT ); Fri, 4 Aug 2023 05:10:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57876 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229661AbjHDJJh (ORCPT ); Fri, 4 Aug 2023 05:09:37 -0400 Received: from mail-wr1-x44a.google.com (mail-wr1-x44a.google.com [IPv6:2a00:1450:4864:20::44a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3F3966588 for ; Fri, 4 Aug 2023 02:06:51 -0700 (PDT) Received: by mail-wr1-x44a.google.com with SMTP id ffacd0b85a97d-314275b653eso1026678f8f.1 for ; Fri, 04 Aug 2023 02:06:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1691140010; x=1691744810; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=mbDuRBO1V21kY8Ln+XMGj8tah/dM0ZngOK9DCSez6Ds=; b=5+NdHYLigl8F6LR7td6fJwq4mY9o+g31biS6M/x67uOl9aEZNMw4T8nENGruiRPiRB +Gw5NEcsPnW4zysL4GKnQBPK9MO8u0Fsh1G5fWlgkmiENC1pguO3W0zZ0X/9KVUs9XYc Tobr1N4uOqLruYOpHjKAtJJ2mDS90eZzDY6tlw9DthEFZ7ugqCsD5LBgD4MRn1hh6V3W c6lem7rrbgF4amzGiob51SzurdoFT2U3i2F0AvVFAwCHWg57HOfRNXyQL4/kaXiOsTGY Q4BSyO6jSC8eDLVGZOooU1CA1YZfiIB3t/WuaZY5AlYApLPEZnbtXoouz1qw8nB4BnEV 78og== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691140010; x=1691744810; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=mbDuRBO1V21kY8Ln+XMGj8tah/dM0ZngOK9DCSez6Ds=; b=a4sqZr5EMnnvKz/Jq59v1cDIiZtDyG24UQUb6KCavuT1VbQu4HX2ks42i/XWD7ySlx frVDHiGfgjILkRzVcnqk3fC7kQEhV58cd/vnn+wMLX9Ur8ZE/eY3/732gnRkkK4yDydt FSNhj9UemrlMSIaPWLaMtuQT7taJ2cxeb8+T3Y5koehrKJSDx/fRv2CWGmHuee5mJdP1 2Y+hGnWSPLe8t3X9CsRbvlnWKl6wkQof/N7UdAiAvcMsWRZwPKBMlB1v8VNKcXKSfcYL ajoN+fMuoxAVHYVxo2wrG8noeRlBCns0X4eTGBFKPgGX7waIVguKgip979JY2G9vOKHJ XLnQ== X-Gm-Message-State: AOJu0YwOw+GI6xZfe3nxeJMdoD1wULsLE08IhBxJRxhjQHWlUfy7JNF4 bTkCjf+yx5joVPhNqZPcszAAynU9pw== X-Google-Smtp-Source: AGHT+IEPvozwf23yi22U6OKa9kIgIghSUiAWRzblYbPC2JjxGfCAqNsiEHfVbqNraFFYkBMktGuoEKz+Fw== X-Received: from elver.muc.corp.google.com ([2a00:79e0:9c:201:2ebf:f3ea:4841:53b6]) (user=elver job=sendgmr) by 2002:adf:f587:0:b0:313:e68e:885d with SMTP id f7-20020adff587000000b00313e68e885dmr6006wro.13.1691140009920; Fri, 04 Aug 2023 02:06:49 -0700 (PDT) Date: Fri, 4 Aug 2023 11:02:56 +0200 Mime-Version: 1.0 X-Mailer: git-send-email 2.41.0.640.ga95def55d0-goog Message-ID: <20230804090621.400-1-elver@google.com> Subject: [PATCH v2 1/3] compiler_types: Introduce the Clang __preserve_most function attribute From: Marco Elver To: elver@google.com, Andrew Morton , Kees Cook Cc: 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-toolchains@vger.kernel.org [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. --- 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 */ /* -- 2.41.0.640.ga95def55d0-goog