From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4B3062F546D; Wed, 17 Sep 2025 02:30:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758076222; cv=none; b=IX7MiagHAJ9PmXCRvgRhbxxa33sxzkOp4D/H2ojfEMpfhWtTx8gSt/qV/N7RD5Z5QWG45cv0msDy2t7SNU+orxS+m8hV9SjDa58MQlvAQBhqAgTNTF04qvbkCVms5DR0WltFJi6w+NqUsRBb+2zSjn2F2xAyZDBXb4gSzWWGbVc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758076222; c=relaxed/simple; bh=9X7QADcxt2zCen4jv6C9mftiuf17xh85fpQtuE7OSM8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=EJUaFu9m55mYJg0hVFuI+S+PnYq68DekKodX9Y+6R4TYbv0IkmDtUroSVf6aTncGckzGgW89MVDInyAqGdhCqgnJkHZBCd8iS/ryPnSXyy9D+3UJe5FfqlOUvefIKSxFCK58uEh8WslE6sM3D5RA2paWi/KUbenHohjkoKGRLSo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=F2IjJp7i; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="F2IjJp7i" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D8F3C4CEFE; Wed, 17 Sep 2025 02:30:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758076221; bh=9X7QADcxt2zCen4jv6C9mftiuf17xh85fpQtuE7OSM8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=F2IjJp7i0geiRr9f92HGSScUadmZ6+qWXyDpkJSiwVyNs91904DNhtSDuJbhhaj0J DJKcETxEWzNzBxsyhW7usZxODZD+xgUjmFC614GNYEbZbQwsw0dpeLBxPsCcNBGAAm /22ayxgBAuSTcnlHABRPG0MUY0z4e8po0p2SiK2dFhh7nhDHJz7GwWhBHU1yJcuQLJ exW4ZkNB5uaXDutsFJDYqObop2XHXw0CvvnXp7EzwCxcF77trENSy7QplSvBv3vKS4 jDuk3O3FlOraGmLgFKmXx7v+Qqg8oWrsCQSC/M4tSYke5eVMO4wboVh9+IgNJL4b2X uYcs479yd3FIA== Date: Tue, 16 Sep 2025 19:30:16 -0700 From: Nathan Chancellor To: Heiko Carstens Cc: Miguel Ojeda , Kees Cook , Nick Desaulniers , Vasily Gorbik , Alexander Gordeev , Juergen Christ , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Sven Schnelle , Christian Borntraeger Subject: Re: [PATCH v2 2/4] compiler_types: Add __assume macro Message-ID: <20250917023016.GA3935228@ax162> References: <20250916134803.874580-1-hca@linux.ibm.com> <20250916134803.874580-3-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250916134803.874580-3-hca@linux.ibm.com> On Tue, Sep 16, 2025 at 03:48:01PM +0200, Heiko Carstens wrote: > Make the statement attribute "assume" with a new __assume macro available. > > The assume attribute is used to indicate that a certain condition is > assumed to be true. Compilers may or may not use this indication to > generate optimized code. If this condition is violated at runtime, the > behavior is undefined. > > Note that the clang documentation states that optimizers may react > differently to this attribute, and this may even have a negative > performance impact. Therefore this attribute should be used with care. > > Signed-off-by: Heiko Carstens LGTM. Reviewed-by: Nathan Chancellor > --- > include/linux/compiler_types.h | 23 +++++++++++++++++++++++ > init/Kconfig | 10 ++++++++++ > 2 files changed, 33 insertions(+) > > diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h > index a910f9fa5341..41c16fb8eb40 100644 > --- a/include/linux/compiler_types.h > +++ b/include/linux/compiler_types.h > @@ -329,6 +329,29 @@ struct ftrace_likely_data { > #define __no_sanitize_or_inline __always_inline > #endif > > +/* > + * The assume attribute is used to indicate that a certain condition is > + * assumed to be true. If this condition is violated at runtime, the behavior > + * is undefined. Compilers may or may not use this indication to generate > + * optimized code. > + * > + * Note that the clang documentation states that optimizers may react > + * differently to this attribute, and this may even have a negative > + * performance impact. Therefore this attribute should be used with care. > + * > + * Optional: only supported since gcc >= 13 > + * Optional: only supported since clang >= 19 > + * > + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#index-assume-statement-attribute > + * clang: https://clang.llvm.org/docs/AttributeReference.html#id13 > + * > + */ > +#ifdef CONFIG_CC_HAS_ASSUME > +# define __assume(expr) __attribute__((__assume__(expr))) > +#else > +# define __assume(expr) > +#endif > + > /* > * Optional: only supported since gcc >= 15 > * Optional: only supported since clang >= 18 > diff --git a/init/Kconfig b/init/Kconfig > index 59ae2b967195..935eff59af97 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -112,6 +112,16 @@ config TOOLS_SUPPORT_RELR > config CC_HAS_ASM_INLINE > def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null) > > +config CC_HAS_ASSUME > + bool > + # clang needs to be at least 19.1.0 since the meaning of the assume > + # attribute changed: > + # https://github.com/llvm/llvm-project/commit/c44fa3e8a9a44c2e9a575768a3c185354b9f6c17 > + default y if CC_IS_CLANG && CLANG_VERSION >= 190100 > + # supported since gcc 13.1.0 > + # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106654 > + default y if CC_IS_GCC && GCC_VERSION >= 130100 > + > config CC_HAS_NO_PROFILE_FN_ATTR > def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror) > > -- > 2.48.1 >