diff options
| -rw-r--r-- | Makefile | 7 | ||||
| -rw-r--r-- | arch/Kconfig | 12 | ||||
| -rw-r--r-- | include/linux/compiler_types.h | 10 |
3 files changed, 24 insertions, 5 deletions
@@ -974,8 +974,15 @@ export CC_FLAGS_CFI endif ifneq ($(CONFIG_FUNCTION_ALIGNMENT),0) +# Set the minimal function alignment. Use the newer GCC option +# -fmin-function-alignment if it is available, or fall back to -falign-funtions. +# See also CONFIG_CC_HAS_SANE_FUNCTION_ALIGNMENT. +ifdef CONFIG_CC_HAS_MIN_FUNCTION_ALIGNMENT +KBUILD_CFLAGS += -fmin-function-alignment=$(CONFIG_FUNCTION_ALIGNMENT) +else KBUILD_CFLAGS += -falign-functions=$(CONFIG_FUNCTION_ALIGNMENT) endif +endif # arch Makefile may override CC so keep this after arch Makefile is included NOSTDINC_FLAGS += -nostdinc diff --git a/arch/Kconfig b/arch/Kconfig index a5af0edd3eb8..bd6c6335efac 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1507,4 +1507,16 @@ config FUNCTION_ALIGNMENT default 4 if FUNCTION_ALIGNMENT_4B default 0 +config CC_HAS_MIN_FUNCTION_ALIGNMENT + # Detect availability of the GCC option -fmin-function-alignment which + # guarantees minimal alignment for all functions, unlike + # -falign-functions which the compiler ignores for cold functions. + def_bool $(cc-option, -fmin-function-alignment=8) + +config CC_HAS_SANE_FUNCTION_ALIGNMENT + # Set if the guaranteed alignment with -fmin-function-alignment is + # available or extra care is required in the kernel. Clang provides + # strict alignment always, even with -falign-functions. + def_bool CC_HAS_MIN_FUNCTION_ALIGNMENT || CC_IS_CLANG + endmenu diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 0caf354cb94b..fb8888678687 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -99,17 +99,17 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { } * gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-cold-label-attribute * * When -falign-functions=N is in use, we must avoid the cold attribute as - * contemporary versions of GCC drop the alignment for cold functions. Worse, - * GCC can implicitly mark callees of cold functions as cold themselves, so - * it's not sufficient to add __function_aligned here as that will not ensure - * that callees are correctly aligned. + * GCC drops the alignment for cold functions. Worse, GCC can implicitly mark + * callees of cold functions as cold themselves, so it's not sufficient to add + * __function_aligned here as that will not ensure that callees are correctly + * aligned. * * See: * * https://lore.kernel.org/lkml/Y77%2FqVgvaJidFpYt@FVFF77S0Q05N * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345#c9 */ -#if !defined(CONFIG_CC_IS_GCC) || (CONFIG_FUNCTION_ALIGNMENT == 0) +#if defined(CONFIG_CC_HAS_SANE_FUNCTION_ALIGNMENT) || (CONFIG_FUNCTION_ALIGNMENT == 0) #define __cold __attribute__((__cold__)) #else #define __cold |