| Message ID | 20210326000435.4785-2-nathan@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | Fix cross compiling x86 with clang | expand |
On Fri, Mar 26, 2021 at 1:04 AM Nathan Chancellor <nathan@kernel.org> wrote: > > 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> I had John's v2 of this patch in my custom 5.11 patchset. Thanks for bringing this up again, Nathan. Later, I will test the triple patchset series. Feel free to add for this one: Tested-by: Sedat Dilek <sedat.dilek@gmail.com> - Sedat - > --- > 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 += $(CLANG_FLAGS) > export REALMODE_CFLAGS > > # BITS is used as extension for files which are available in a 32 bit > -- > 2.31.0 >
On 3/26/21 09:04, Nathan Chancellor wrote: > From: John Millikin <john@john-millikin.com> > > When cross-compiling with Clang, the `$(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 > Just wanted to say "thank you" for picking this up -- I ran into some real-life situations and didn't have time to debug why my patch was failing the Git validity check (presumed to be an email client misconfiguration).
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