Re: [PATCH 1/2] Compiler Attributes: Add __uninitialized macro

Nathan Chancellor
2024-02-06T01:28:38Z

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
>