linux-kernel - [PATCH 2/3] x86/boot: Add $(CLANG_FLAGS) to compressed KBUILD

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Date:   Thu, 25 Mar 2021 17:04:34 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH 2/3] x86/boot: Add $(CLANG_FLAGS) to compressed KBUILD_CFLAGS

When cross compiling x86 on an ARM machine with clang, there are several
errors along the lines of:

arch/x86/include/asm/string_64.h:27:10: error: invalid output constraint
'=&c' in asm

This happens because the compressed boot Makefile reassigns KBUILD_CFLAGS
and drops the clang flags that set the target architecture ('--target=')
and the path to the GNU cross tools ('--prefix='), meaning that the host
architecture is targeted.

These flags are available as $(CLANG_FLAGS) from the main Makefile so
add them to the compressed boot folder's KBUILD_CFLAGS so that cross
compiling works as expected.

Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 arch/x86/boot/compressed/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index e0bc3988c3fa..6e5522aebbbd 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -46,6 +46,7 @@ KBUILD_CFLAGS += -D__DISABLE_EXPORTS
 # Disable relocation relaxation in case the link is not PIE.
 KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)
 KBUILD_CFLAGS += -include $(srctree)/include/linux/hidden.h
+KBUILD_CFLAGS += $(CLANG_FLAGS)
 
 # sev-es.c indirectly inludes inat-table.h which is generated during
 # compilation and stored in $(objtree). Add the directory to the includes so
-- 
2.31.0