On Tue, Aug 10, 2021 at 01:42:37PM -0700, Nick Desaulniers wrote: > 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> Fewer pointless calls to the compiler is always a good thing :) Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx> Small comments inline. > --- > 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 Eliminating -Wno-maybe-uninitialized might warrant a comment in the commit message as I was initially confused then I realized that it is unconditionally added later. > 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 Looks like this was generated against -next as it includes the rust patchset. I was able to apply it to mainline without any complaints but any follow ups should probably be based on Masahiro's tree. > 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
