[PATCH v2 7/9] LoongArch: Tweak CFLAGS for Clang compatibility

From: WANG Xuerui
Date: Sat Jun 24 2023 - 14:42:58 EST


From: WANG Xuerui <git@xxxxxxxxxx>

Now the arch code is mostly ready for LLVM/Clang consumption, it is time
to re-organize the CFLAGS a little to actually enable the LLVM build.

In particular, -mexplicit-relocs and -mdirect-extern-access are not
necessary nor supported on Clang; feature detection via cc-option would
not work, because that way the broken combo of "new GNU as + old GCC"
would seem to get "fixed", but actually produce broken kernels.
Explicitly depending on CONFIG_CC_IS_CLANG is thus necessary to not
regress UX for those building their own kernels.

A build with !RELOCATABLE && !MODULE is confirmed working within a QEMU
environment; support for the two features are currently blocked on
LLVM/Clang, and will come later.

Signed-off-by: WANG Xuerui <git@xxxxxxxxxx>
---
arch/loongarch/Makefile | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index 366771016b99..82c619791a63 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -51,7 +51,9 @@ LDFLAGS_vmlinux += -static -n -nostdlib

# When the assembler supports explicit relocation hint, we must use it.
# GCC may have -mexplicit-relocs off by default if it was built with an old
-# assembler, so we force it via an option.
+# assembler, so we force it via an option. For LLVM/Clang the desired behavior
+# is the default, and the flag is not supported, so don't pass it if Clang is
+# being used.
#
# When the assembler does not supports explicit relocation hint, we can't use
# it. Disable it if the compiler supports it.
@@ -61,8 +63,10 @@ LDFLAGS_vmlinux += -static -n -nostdlib
# combination of a "new" assembler and "old" compiler is not supported. Either
# upgrade the compiler or downgrade the assembler.
ifdef CONFIG_AS_HAS_EXPLICIT_RELOCS
+ifndef CONFIG_CC_IS_CLANG
cflags-y += -mexplicit-relocs
KBUILD_CFLAGS_KERNEL += -mdirect-extern-access
+endif
else
cflags-y += $(call cc-option,-mno-explicit-relocs)
KBUILD_AFLAGS_KERNEL += -Wa,-mla-global-with-pcrel
--
2.40.0