[PATCH] kbuild: Add KBUILD_CPPFLAGS to as-option invocation

[Nathan Chancellor]

After commit feb843a469fb ("kbuild: add $(CLANG_FLAGS) to
KBUILD_CPPFLAGS"), there is an error while building certain PowerPC
assembly files with clang:

  arch/powerpc/lib/copypage_power7.S: Assembler messages:
  arch/powerpc/lib/copypage_power7.S:34: Error: junk at end of line: `0b01000'
  arch/powerpc/lib/copypage_power7.S:35: Error: junk at end of line: `0b01010'
  arch/powerpc/lib/copypage_power7.S:37: Error: junk at end of line: `0b01000'
  arch/powerpc/lib/copypage_power7.S:38: Error: junk at end of line: `0b01010'
  arch/powerpc/lib/copypage_power7.S:40: Error: junk at end of line: `0b01010'
  clang: error: assembler command failed with exit code 1 (use -v to see invocation)

as-option only uses KBUILD_AFLAGS, so after removing CLANG_FLAGS from
KBUILD_AFLAGS, there is no more '--target=' or '--prefix=' flags. As a
result of those missing flags, the host target
will be tested during as-option calls and likely fail, meaning necessary
flags may not get added when building assembly files, resulting in
errors like seen above.

Add KBUILD_CPPFLAGS to as-option invocations to clear up the errors.
This should have been done in commit d5c8d6e0fa61 ("kbuild: Update
assembler calls to use proper flags and language target"), which
switched from using the assembler target to the assembler-with-cpp
target, so flags that affect preprocessing are passed along in all
relevant tests. as-option now mirrors cc-option.

Fixes: feb843a469fb ("kbuild: add $(CLANG_FLAGS) to KBUILD_CPPFLAGS")
Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
Closes: https://lore.kernel.org/CA+G9fYs=koW9WardsTtora+nMgLR3raHz-LSLr58tgX4T5Mxag@xxxxxxxxxxxxxx/
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---
 scripts/Makefile.compiler | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
index 437013f8def3..e31f18625fcf 100644
--- a/scripts/Makefile.compiler
+++ b/scripts/Makefile.compiler
@@ -32,7 +32,7 @@ try-run = $(shell set -e;		\
 # Usage: aflags-y += $(call as-option,-Wa$(comma)-isa=foo,)
 
 as-option = $(call try-run,\
-	$(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp /dev/null -o "$$TMP",$(1),$(2))
+	$(CC) -Werror $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp /dev/null -o "$$TMP",$(1),$(2))
 
 # as-instr
 # Usage: aflags-y += $(call as-instr,instr,option1,option2)

---
base-commit: feb843a469fb0ab00d2d23cfb9bcc379791011bb
change-id: 20230606-fix-as-option-after-clang_flags-move-be88e993cbaa

Best regards,
-- 
Nathan Chancellor <nathan@xxxxxxxxxx>