From: Nathan Chancellor <nathan@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, Ard Biesheuvel <ardb@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
clang-built-linux@googlegroups.com,
John Millikin <john@john-millikin.com>,
Sedat Dilek <sedat.dilek@gmail.com>,
Nathan Chancellor <nathan@kernel.org>
Subject: [PATCH 1/3] x86: Propagate $(CLANG_FLAGS) to $(REALMODE_FLAGS)
Date: Thu, 25 Mar 2021 17:04:33 -0700 [thread overview]
Message-ID: <20210326000435.4785-2-nathan@kernel.org> (raw)
In-Reply-To: <20210326000435.4785-1-nathan@kernel.org>
From: John Millikin <john@john-millikin.com>
When cross-compiling with Clang, the `$(CLANG_FLAGS)' variable
contains additional flags needed to build C and assembly sources
for the target platform. Normally this variable is automatically
included in `$(KBUILD_CFLAGS)' by via the top-level Makefile.
The x86 real-mode makefile builds `$(REALMODE_CFLAGS)' from a
plain assignment and therefore drops the Clang flags. This causes
Clang to not recognize x86-specific assembler directives:
arch/x86/realmode/rm/header.S:36:1: error: unknown directive
.type real_mode_header STT_OBJECT ; .size real_mode_header, .-real_mode_header
^
Explicit propagation of `$(CLANG_FLAGS)' to `$(REALMODE_CFLAGS)',
which is inherited by real-mode make rules, fixes cross-compilation
with Clang for x86 targets.
Relevant flags:
* `--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.
* `-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.
Signed-off-by: John Millikin <john@john-millikin.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
arch/x86/Makefile | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 2d6d5a28c3bf..9a73e0cea19c 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -33,6 +33,7 @@ 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))
+REALMODE_CFLAGS += $(CLANG_FLAGS)
export REALMODE_CFLAGS
# BITS is used as extension for files which are available in a 32 bit
--
2.31.0
next prev parent reply other threads:[~2021-03-26 0:05 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-26 0:04 [PATCH 0/3] Fix cross compiling x86 with clang Nathan Chancellor
2021-03-26 0:04 ` Nathan Chancellor [this message]
2021-03-26 8:42 ` [PATCH 1/3] x86: Propagate $(CLANG_FLAGS) to $(REALMODE_FLAGS) Sedat Dilek
2021-03-26 13:13 ` [tip: x86/build] x86/build: " tip-bot2 for John Millikin
2021-03-26 13:38 ` [PATCH 1/3] x86: " John Millikin
2021-03-26 0:04 ` [PATCH 2/3] x86/boot: Add $(CLANG_FLAGS) to compressed KBUILD_CFLAGS Nathan Chancellor
2021-03-26 13:13 ` [tip: x86/build] " tip-bot2 for Nathan Chancellor
2021-03-26 0:04 ` [PATCH 3/3] efi/libstub: Add $(CLANG_FLAGS) to x86 flags Nathan Chancellor
2021-03-26 13:13 ` [tip: x86/build] " tip-bot2 for Nathan Chancellor
2021-03-26 8:43 ` [PATCH 0/3] Fix cross compiling x86 with clang Ard Biesheuvel
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