From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can cause as-option to fail unexpectedly when CONFIG_WERROR is set, because clang will emit -Werror,-Wunused-command-line-argument for various -m and -f flags in KBUILD_CFLAGS for assembler sources. Callers of as-option and as-instr should be adding flags to KBUILD_AFLAGS / aflags-y, not KBUILD_CFLAGS / cflags-y. Use KBUILD_AFLAGS in all macros to clear up the initial problem. Unfortunately, -Wunused-command-line-argument can still be triggered with clang by the presence of warning flags or macro definitions because '-x assembler' is used, instead of '-x assembler-with-cpp', which will consume these flags. Switch to '-x assembler-with-cpp' in places where '-x assembler' is used, as the compiler is always used as the driver for out of line assembler sources in the kernel. Finally, add -Werror to these macros so that they behave consistently whether or not CONFIG_WERROR is set. Link: https://github.com/ClangBuiltLinux/linux/issues/1699 Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> [nathan: Reworded and expanded on problems in commit message Use '-x assembler-with-cpp' in a couple more places] Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> --- Benchmarking '-x assembler' vs. '-x assembler-with-cpp' does show that invoking the preprocessor incurs some overhead but my kernel builds do not show any noticeable slowdowns due to how infrequently these macros are used. $ hyperfine -L lang assembler,assembler-with-cpp -N -w 5 "/usr/bin/gcc -x {lang} -c -o /dev/null /dev/null" Benchmark 1: /usr/bin/gcc -x assembler -c -o /dev/null /dev/null Time (mean ± σ): 5.5 ms ± 0.5 ms [User: 4.1 ms, System: 1.3 ms] Range (min … max): 4.3 ms … 6.3 ms 472 runs Benchmark 2: /usr/bin/gcc -x assembler-with-cpp -c -o /dev/null /dev/null Time (mean ± σ): 12.7 ms ± 1.0 ms [User: 9.1 ms, System: 3.6 ms] Range (min … max): 9.6 ms … 14.2 ms 225 runs Summary '/usr/bin/gcc -x assembler -c -o /dev/null /dev/null' ran 2.29 ± 0.28 times faster than '/usr/bin/gcc -x assembler-with-cpp -c -o /dev/null /dev/null' $ hyperfine -L lang assembler,assembler-with-cpp -N -w 5 "/usr/bin/clang -x {lang} -c -o /dev/null /dev/null" Benchmark 1: /usr/bin/clang -x assembler -c -o /dev/null /dev/null Time (mean ± σ): 21.0 ms ± 1.1 ms [User: 9.6 ms, System: 11.1 ms] Range (min … max): 13.9 ms … 22.0 ms 138 runs Benchmark 2: /usr/bin/clang -x assembler-with-cpp -c -o /dev/null /dev/null Time (mean ± σ): 56.9 ms ± 3.2 ms [User: 27.2 ms, System: 29.5 ms] Range (min … max): 53.9 ms … 62.1 ms 48 runs Summary '/usr/bin/clang -x assembler -c -o /dev/null /dev/null' ran 2.71 ± 0.20 times faster than '/usr/bin/clang -x assembler-with-cpp -c -o /dev/null /dev/null' --- scripts/Kconfig.include | 2 +- scripts/Makefile.compiler | 8 ++++---- scripts/as-version.sh | 2 +- 3 files changed, 6 insertions(+), 6 deletions(-) diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include index 274125307ebd..5a84b6443875 100644 --- a/scripts/Kconfig.include +++ b/scripts/Kconfig.include @@ -33,7 +33,7 @@ ld-option = $(success,$(LD) -v $(1)) # $(as-instr,<instr>) # Return y if the assembler supports <instr>, n otherwise -as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler -o /dev/null -) +as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler-with-cpp -o /dev/null -) # check if $(CC) and $(LD) exist $(error-if,$(failure,command -v $(CC)),C compiler '$(CC)' not found) diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler index 3d8adfd34af1..7aa1fbc4aafe 100644 --- a/scripts/Makefile.compiler +++ b/scripts/Makefile.compiler @@ -29,16 +29,16 @@ try-run = $(shell set -e; \ fi) # as-option -# Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,) +# Usage: aflags-y += $(call as-option,-Wa$(comma)-isa=foo,) as-option = $(call try-run,\ - $(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) + $(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp /dev/null -o "$$TMP",$(1),$(2)) # as-instr -# Usage: cflags-y += $(call as-instr,instr,option1,option2) +# Usage: aflags-y += $(call as-instr,instr,option1,option2) as-instr = $(call try-run,\ - printf "%b\n" "$(1)" | $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3)) + printf "%b\n" "$(1)" | $(CC) -Werror $(KBUILD_AFLAGS) -c -x assembler-with-cpp -o "$$TMP" -,$(2),$(3)) # __cc-option # Usage: MY_CFLAGS += $(call __cc-option,$(CC),$(MY_CFLAGS),-march=winchip-c6,-march=i586) diff --git a/scripts/as-version.sh b/scripts/as-version.sh index 1a21495e9ff0..af717476152d 100755 --- a/scripts/as-version.sh +++ b/scripts/as-version.sh @@ -45,7 +45,7 @@ orig_args="$@" # Get the first line of the --version output. IFS=' ' -set -- $(LC_ALL=C "$@" -Wa,--version -c -x assembler /dev/null -o /dev/null 2>/dev/null) +set -- $(LC_ALL=C "$@" -Wa,--version -c -x assembler-with-cpp /dev/null -o /dev/null 2>/dev/null) # Split the line on spaces. IFS=' ' -- 2.39.0
