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 for assembler sources.

Callers of as-option (and as-instr) likely want to be adding flags to
KBUILD_AFLAGS/aflags-y, not KBUILD_CFLAGS/cflags-y.

Also, change as-option and as-instr to use -x assembler-with-cpp since
kernel sources are .S files that use the compiler as the driver. And
then add -Werror as well.

Link: https://github.com/ClangBuiltLinux/linux/issues/1699
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Changes v2 -> v1:
* Add -x assembler-with-cpp -Werror to both as-option and (new)
  as-instr, as per Masahiro.
* Add Masahiro's SB tag.

Changes v1 -> v2:
* Split off changes to arch/x86/boot/compressed/Makefile into parent
  patch, as per Masahiro.

 scripts/Makefile.compiler | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
index 94d0d40cddb3..a66638b5f4a5 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)
-- 
2.37.2.789.g6183377224-goog

On Wed, Sep 7, 2022 at 1:59 PM Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> 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 for assembler sources.
>
> Callers of as-option (and as-instr) likely want to be adding flags to
> KBUILD_AFLAGS/aflags-y, not KBUILD_CFLAGS/cflags-y.
>
> Also, change as-option and as-instr to use -x assembler-with-cpp since
> kernel sources are .S files that use the compiler as the driver. And
> then add -Werror as well.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1699
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---



01 and 02, applied to linux-kbuild/fixes.
Thanks.




> Changes v2 -> v1:
> * Add -x assembler-with-cpp -Werror to both as-option and (new)
>   as-instr, as per Masahiro.
> * Add Masahiro's SB tag.
>
> Changes v1 -> v2:
> * Split off changes to arch/x86/boot/compressed/Makefile into parent
>   patch, as per Masahiro.
>
>  scripts/Makefile.compiler | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
> index 94d0d40cddb3..a66638b5f4a5 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)
> --
> 2.37.2.789.g6183377224-goog
>


-- 
Best Regards
Masahiro Yamada