git
/
linux
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

compiler_types: Add __assume macro 

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 <hca@linux.ibm.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
This commit is contained in:
Heiko Carstens 2025-09-16 15:48:01 +02:00 committed by Alexander Gordeev
parent a9f859b516
commit f72e2cff13
2 changed files with 33 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
include/linux/compiler_types.h
View File

@ -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

10
init/Kconfig
View File

@ -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)