cc-option, cc-option-yn, and cc-disable-warning all invoke the compiler during build time, and can slow down the build when these checks become stale for our supported compilers, whose minimally supported versions increases over time. See Documentation/process/changes.rst for the current supported minimal versions (GCC 4.9+, clang 10.0.1+). Compiler version support for these flags may be verified on godbolt.org. The following flags are GCC only and supported since at least GCC 4.9. Remove cc-option and cc-disable-warning tests. * -fno-tree-loop-im * -Wno-maybe-uninitialized * -fno-reorder-blocks * -fno-ipa-cp-clone * -fno-partial-inlining * -femit-struct-debug-baseonly * -fno-inline-functions-called-once * -fconserve-stack The following flags are supported by all supported versions of GCC and Clang. Remove their cc-option, cc-option-yn, and cc-disable-warning tests. * -fno-delete-null-pointer-checks * -fno-var-tracking * -mfentry * -Wno-array-bounds The following configs are made dependent on GCC, since they use GCC specific flags. * READABLE_ASM * DEBUG_SECTION_MISMATCH --param=allow-store-data-races=0 was renamed to --allow-store-data-races in the GCC 10 release. Also, base RETPOLINE_CFLAGS and RETPOLINE_VDSO_CFLAGS on CONFIC_CC_IS_* then remove cc-option tests for Clang. Link: https://github.com/ClangBuiltLinux/linux/issues/1436 Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> --- Note: It may be preferred to move the test for -fno-inline-functions-called-once for DEBUG_SECTION_MISMATCH into Kconfig. That one does seem relatively more reasonable to implement in Clang. Makefile | 55 ++++++++++++++++++++++++++--------------------- lib/Kconfig.debug | 2 ++ 2 files changed, 33 insertions(+), 24 deletions(-) diff --git a/Makefile b/Makefile index 027fdf2a14fe..3e3fb4affba1 100644 --- a/Makefile +++ b/Makefile @@ -730,9 +730,10 @@ endif # KBUILD_EXTMOD # Defaults to vmlinux, but the arch makefile usually adds further targets all: vmlinux -CFLAGS_GCOV := -fprofile-arcs -ftest-coverage \ - $(call cc-option,-fno-tree-loop-im) \ - $(call cc-disable-warning,maybe-uninitialized,) +CFLAGS_GCOV := -fprofile-arcs -ftest-coverage +ifdef CONFIG_CC_IS_GCC +CFLAGS_GCOV += -fno-tree-loop-im +endif export CFLAGS_GCOV # The arch Makefiles can override CC_FLAGS_FTRACE. We may also append it later. @@ -740,12 +741,14 @@ ifdef CONFIG_FUNCTION_TRACER CC_FLAGS_FTRACE := -pg endif -RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register -RETPOLINE_VDSO_CFLAGS_GCC := -mindirect-branch=thunk-inline -mindirect-branch-register -RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk -RETPOLINE_VDSO_CFLAGS_CLANG := -mretpoline -RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG))) -RETPOLINE_VDSO_CFLAGS := $(call cc-option,$(RETPOLINE_VDSO_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_VDSO_CFLAGS_CLANG))) +ifdef CONFIG_CC_IS_GCC +RETPOLINE_CFLAGS := $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register) +RETPOLINE_VDSO_CFLAGS := $(call cc-option,-mindirect-branch=thunk-inline -mindirect-branch-register) +endif +ifdef CONFIG_CC_IS_CLANG +RETPOLINE_CFLAGS := -mretpoline-external-thunk +RETPOLINE_VDSO_CFLAGS := -mretpoline +endif export RETPOLINE_CFLAGS export RETPOLINE_VDSO_CFLAGS @@ -798,7 +801,7 @@ include/config/auto.conf: endif # may-sync-config endif # need-config -KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) +KBUILD_CFLAGS += -fno-delete-null-pointer-checks KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,) KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) @@ -844,17 +847,17 @@ KBUILD_RUSTFLAGS += -Copt-level=z endif # Tell gcc to never replace conditional load with a non-conditional one -KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0) +ifdef CONFIG_CC_IS_GCC +KBUILD_CFLAGS += $(call cc-option,--allow-store-data-races,--param=allow-store-data-races=0) KBUILD_CFLAGS += $(call cc-option,-fno-allow-store-data-races) +endif ifdef CONFIG_READABLE_ASM # Disable optimizations that make assembler listings hard to read. # reorder blocks reorders the control in the function # ipa clone creates specialized cloned functions # partial inlining inlines only parts of functions -KBUILD_CFLAGS += $(call cc-option,-fno-reorder-blocks,) \ - $(call cc-option,-fno-ipa-cp-clone,) \ - $(call cc-option,-fno-partial-inlining) +KBUILD_CFLAGS += -fno-reorder-blocks -fno-ipa-cp-clone -fno-partial-inlining endif ifneq ($(CONFIG_FRAME_WARN),0) @@ -959,8 +962,10 @@ DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) endif ifdef CONFIG_DEBUG_INFO_REDUCED -DEBUG_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \ - $(call cc-option,-fno-var-tracking) +DEBUG_CFLAGS += -fno-var-tracking +ifdef CONFIG_CC_IS_GCC +DEBUG_CFLAGS += -femit-struct-debug-baseonly +endif endif ifdef CONFIG_DEBUG_INFO_COMPRESSED @@ -997,10 +1002,8 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT endif endif ifdef CONFIG_HAVE_FENTRY - ifeq ($(call cc-option-yn, -mfentry),y) - CC_FLAGS_FTRACE += -mfentry - CC_FLAGS_USING += -DCC_USING_FENTRY - endif + CC_FLAGS_FTRACE += -mfentry + CC_FLAGS_USING += -DCC_USING_FENTRY endif export CC_FLAGS_FTRACE KBUILD_CFLAGS += $(CC_FLAGS_FTRACE) $(CC_FLAGS_USING) @@ -1009,7 +1012,7 @@ endif # We trigger additional mismatches with less inlining ifdef CONFIG_DEBUG_SECTION_MISMATCH -KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once) +KBUILD_CFLAGS += -fno-inline-functions-called-once endif ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION @@ -1088,14 +1091,16 @@ KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation) # We'll want to enable this eventually, but it's not going away for 5.7 at least KBUILD_CFLAGS += $(call cc-disable-warning, zero-length-bounds) -KBUILD_CFLAGS += $(call cc-disable-warning, array-bounds) +KBUILD_CFLAGS += -Wno-array-bounds KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow) # Another good warning that we'll want to enable eventually KBUILD_CFLAGS += $(call cc-disable-warning, restrict) # Enabled with W=2, disabled by default as noisy -KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized) +ifdef CONFIG_CC_IS_GCC +KBUILD_CFLAGS += -Wno-maybe-uninitialized +endif # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += -fno-strict-overflow @@ -1104,7 +1109,9 @@ KBUILD_CFLAGS += -fno-strict-overflow KBUILD_CFLAGS += -fno-stack-check # conserve stack if available -KBUILD_CFLAGS += $(call cc-option,-fconserve-stack) +ifdef CONFIG_CC_IS_GCC +KBUILD_CFLAGS += -fconserve-stack +endif # Prohibit date/time macros, which would make the build non-deterministic KBUILD_CFLAGS += -Werror=date-time diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index b6b951b0ed46..a4a431606be2 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -364,6 +364,7 @@ config STRIP_ASM_SYMS config READABLE_ASM bool "Generate readable assembler code" depends on DEBUG_KERNEL + depends on CC_IS_GCC help Disable some compiler optimizations that tend to generate human unreadable assembler output. This may make the kernel slightly slower, but it helps @@ -382,6 +383,7 @@ config HEADERS_INSTALL config DEBUG_SECTION_MISMATCH bool "Enable full Section mismatch analysis" + depends on CC_IS_GCC help The section mismatch analysis checks if there are illegal references from one section to another section. -- 2.32.0.605.g8dce9f2422-goog
