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Date: Mon, 5 Feb 2024 18:28:36 -0700
From: Nathan Chancellor <nathan@kernel.org>
To: Heiko Carstens <hca@linux.ibm.com>
Cc: Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>
Subject: Re: [PATCH 1/2] Compiler Attributes: Add __uninitialized macro
Message-ID: <20240206012836.GA2616098@dev-arch.thelio-3990X>
References: <20240205154844.3757121-1-hca@linux.ibm.com>
 <20240205154844.3757121-2-hca@linux.ibm.com>
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On Mon, Feb 05, 2024 at 04:48:43PM +0100, Heiko Carstens wrote:
> With INIT_STACK_ALL_PATTERN or INIT_STACK_ALL_ZERO enabled the kernel will
> be compiled with -ftrivial-auto-var-init=<...> which causes initialization
> of stack variables at function entry time.
> 
> In order to avoid the performance impact that comes with this users can use
> the "uninitialized" attribute to prevent such initialization.
> 
> Therefore provide the __uninitialized macro which can be used for cases
> where INIT_STACK_ALL_PATTERN or INIT_STACK_ALL_ZERO is enabled, but only
> selected variables should not be initialized.
> 
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  include/linux/compiler_attributes.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index 28566624f008..f5859b8c68b4 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -333,6 +333,18 @@
>   */
>  #define __section(section)              __attribute__((__section__(section)))
>  
> +/*
> + * Optional: only supported since gcc >= 12
> + *
> + *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-uninitialized-variable-attribute
> + * clang: https://clang.llvm.org/docs/AttributeReference.html#uninitialized
> + */
> +#if __has_attribute(__uninitialized__)
> +# define __uninitialized		__attribute__((__uninitialized__))
> +#else
> +# define __uninitialized
> +#endif
> +
>  /*
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
> -- 
> 2.40.1
>