linux-kernel - [PATCH] arch/x86: Propagate $(CLANG_FLAGS) to $(REALMODE

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Date:   Sat, 26 Dec 2020 16:29:30 +0900
From:   John Millikin <jmillikin@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     clang-built-linux@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        John Millikin <john@...n-millikin.com>
Subject: [PATCH] arch/x86: Propagate $(CLANG_FLAGS) to $(REALMODE_FLAGS)

When compiling with Clang, the `$(CLANG_FLAGS)' variable contains
additional flags needed to cross-compile C and Assembly sources:

* `-no-integrated-as' tells clang to assemble with GNU Assembler
  instead of its built-in LLVM assembler. This flag is set by default
  unless `LLVM_IAS=1' is set, because the LLVM assembler can't yet
  parse certain GNU extensions.

* `--target' sets the target architecture when cross-compiling. This
  flag must be set for both compilation and assembly (`KBUILD_AFLAGS')
  to support architecture-specific assembler directives.

Signed-off-by: John Millikin <john@...n-millikin.com>
---
 arch/x86/Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 7116da3980be..725c65532482 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -33,6 +33,11 @@ REALMODE_CFLAGS += -ffreestanding
 REALMODE_CFLAGS += -fno-stack-protector
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
+
+ifdef CONFIG_CC_IS_CLANG
+REALMODE_CFLAGS += $(CLANG_FLAGS)
+endif
+
 export REALMODE_CFLAGS

 # BITS is used as extension for files which are available in a 32 bit
-- 
2.29.2