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 EF3A6C001B0 for ; Tue, 8 Aug 2023 17:53:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234115AbjHHRx4 (ORCPT ); Tue, 8 Aug 2023 13:53:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233894AbjHHRxa (ORCPT ); Tue, 8 Aug 2023 13:53:30 -0400 Received: from mail-wm1-x349.google.com (mail-wm1-x349.google.com [IPv6:2a00:1450:4864:20::349]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 302AA2956F for ; Tue, 8 Aug 2023 09:23:52 -0700 (PDT) Received: by mail-wm1-x349.google.com with SMTP id 5b1f17b1804b1-3fe210c47acso32080545e9.3 for ; Tue, 08 Aug 2023 09:23:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1691511824; x=1692116624; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=hmnOfvRNRbQKO2Fig5tO7oMJZvMK80sR98XXmZHYIOg=; b=RarQiWbSLFNVWbsaPmvVR8B9n/vSl/5FCPVCXAJmHHpiVCEBWBPvMcorW1/bzDGbBc mk7irX8Tiv3Vjb46PZiPJYYLalii7S0OdMY4H9i3dgdnnBNSJc1a8JAkpO6iWPpv+MlB Yq13DoM3m+RP0U3hnzWYUyz9/b6bMV8R+4gbE9OrTdxoaiHeNPX2OSqDXEqnyGM4q71C c8cyvA5W6ov5E2IiKg7MNsigjy7p4juvHZgUWz9uD8v8hcu6gsVvfaUxH1cTfSO5D09z fCgTrwMNN+dmyYQ/i1a5XGBy5EYOWjDULgq8CoRBdAA5W/h4YoQzjdGx+V1eLSzRbixH OLMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691511824; x=1692116624; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=hmnOfvRNRbQKO2Fig5tO7oMJZvMK80sR98XXmZHYIOg=; b=Dt13J+pPDRxLU649SffG5JMLP39xMjjlpkX29e8XpXFEm6BX9/f47ppEPY1jmJl2PR 9ddLPWVDbFX/Ezpc35oVSyBVjEATHVR0/4Q5IL7Dqw+uzSKWPNbWR61ffPseehvcZU5C Lzxv3aSyZVgRdCNKCnAsyjmrQQ02gt7rd5ak51JPV3f2se5acTi/mDd7BWhrcIjaj0i0 ImKhIDpxef6vJuyTFjSrAh8OcIIN/77Tj6mx9t/2HLj6/LI8MnIEuIQ/J4p2up55IGwt CBBlvBd3kqu0um4vTcMYbUcEHJ368jgSLzVIDY9bHGnf+JL/nnwcYZpAH8ue6I+hIdYT taVQ== X-Gm-Message-State: AOJu0YwQOaHzQc/o+2W5IRiKYKZ2WMf02HxDIcwjuRE/wG+e5RU/nC+1 lFtrgP61DdTUcIBiNg/DHlEV6wjyBQ== X-Google-Smtp-Source: AGHT+IFO91+Sq0a4bROaXXMkpleB+MNLqFDhhb5O1iR8Zhdu/8OTj2ivFrTXYjJox8ukr1691thj7vV+Eg== X-Received: from elver.muc.corp.google.com ([2a00:79e0:9c:201:39c0:833d:c267:7f64]) (user=elver job=sendgmr) by 2002:adf:f0cb:0:b0:317:5e4f:9097 with SMTP id x11-20020adff0cb000000b003175e4f9097mr74564wro.7.1691490086705; Tue, 08 Aug 2023 03:21:26 -0700 (PDT) Date: Tue, 8 Aug 2023 12:17:25 +0200 Mime-Version: 1.0 X-Mailer: git-send-email 2.41.0.640.ga95def55d0-goog Message-ID: <20230808102049.465864-1-elver@google.com> Subject: [PATCH v3 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 , Sami Tolvanen , 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-kernel@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. If the arguments are passed in callee-saved registers, then they will be preserved by the callee across the call. This doesn't apply for values returned in callee-saved registers. * On X86-64 the callee preserves all general purpose registers, 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. * On AArch64 the callee preserve all general purpose registers, except x0-X8 and X16-X18." [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. The attribute may be supported by a future GCC version (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110899). Signed-off-by: Marco Elver Reviewed-by: Miguel Ojeda Acked-by: Steven Rostedt (Google) --- v3: * Quote more from LLVM documentation about which registers are callee/caller with preserve_most. * Code comment to restrict use where tracing is meant to be disabled. v2: * Imply notrace, to avoid any conflicts with tracing which is inserted on function entry. See added comments. --- include/linux/compiler_types.h | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 547ea1ff806e..c88488715a39 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -106,6 +106,34 @@ 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. It is recommended to restrict + * use of the attribute to functions that should or already disable tracing. + * + * 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