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Date: Sat, 26 Dec 2020 20:31:22 -0700 From: Nathan Chancellor <natechancellor@...il.com> To: John Millikin <jmillikin@...il.com> Cc: hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, John Millikin <john@...n-millikin.com> Subject: Re: [PATCH v2] arch/x86: Propagate $(CLANG_FLAGS) to $(REALMODE_FLAGS) On Sat, Dec 26, 2020 at 05:41:25PM +0900, John Millikin wrote: > When cross-compiling with Clang, the `$(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@...n-millikin.com> Reviewed-by: Nathan Chancellor <natechancellor@...il.com> > --- > Changes in v2: > - Reworded the commit message to highlight that this is for > cross-compilation. > - Removed the `ifdef CONFIG_CC_IS_CLANG' guard. > > arch/x86/Makefile | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index 7116da3980be..412b849063ec 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 > -- > 2.29.2 > >
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