diff mbox series

[1/2] Compiler Attributes: Add __uninitialized macro

Message ID 20240205154844.3757121-2-hca@linux.ibm.com
State New
Headers
Series Compiler Attributes, s390: Provide and use __uninitialized macro |

Commit Message

Heiko Carstens Feb. 5, 2024, 3:48 p.m. UTC 
  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>
---
 include/linux/compiler_attributes.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Comments

Kees Cook Feb. 5, 2024, 4:21 p.m. UTC | #1 
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>

Thanks! We had something similar a while back with syscall entry:
efa90c11f62e ("stack: Constrain and fix stack offset randomization with Clang builds")

Acked-by: Kees Cook <keescook@chromium.org>
Nathan Chancellor Feb. 6, 2024, 1:28 a.m. UTC | #2 
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
>
diff mbox series

Patch

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