Compiler Attributes: Add __uninitialized macro

commit fd7eea27a3aed79b63b1726c00bde0d50cf207e2 upstream.

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.

Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20240205154844.3757121-2-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index cdf016596659a3f06d27dd58fb79916ade5a378a..a72b0f756a245b13c6e0c173e37630e3b79c3639 100644 (file)
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -264,6 +264,18 @@
  */
 #define __used                          __attribute__((__used__))
 
+/*
+ * 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-weak-function-attribute
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute