linux-kernel - [PATCH 3/3] efi/libstub: Add $(CLANG

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Message-Id: <20210326000435.4785-4-nathan@kernel.org>
Date:   Thu, 25 Mar 2021 17:04:35 -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 3/3] efi/libstub: Add $(CLANG_FLAGS) to x86 flags

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

arch/x86/include/asm/page_64.h:52:7: error: invalid output constraint
'=D' in asm

This happens because the x86 flags in the EFI stub are not derived from
KBUILD_CFLAGS like the other architectures are and the clang flags that
set the target architecture ('--target=') and the path to the GNU cross
tools ('--prefix=') are not present, meaning that the host architecture
is targeted.

These flags are available as $(CLANG_FLAGS) from the main Makefile so
add them to the cflags for x86 so that cross compiling works as
expected.

Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 drivers/firmware/efi/libstub/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index c23466e05e60..d0537573501e 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -13,7 +13,8 @@ cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
 				   -Wno-pointer-sign \
 				   $(call cc-disable-warning, address-of-packed-member) \
 				   $(call cc-disable-warning, gnu) \
-				   -fno-asynchronous-unwind-tables
+				   -fno-asynchronous-unwind-tables \
+				   $(CLANG_FLAGS)
 
 # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
 # disable the stackleak plugin
-- 
2.31.0