On Thu, Feb 17, 2022 at 01:54:58PM +0900, Masahiro Yamada wrote:
> On Thu, Feb 17, 2022 at 9:28 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> >
> > Add x86-64 target for Clang+um and update user-offsets.c to use
> > Clang-friendly assembler, similar to the fix from commit cf0c3e68aa81
> > ("kbuild: fix asm-offset generation to work with clang").
> >
> > This lets me run KUnit tests with Clang:
> >
> > $ ./tools/testing/kunit/kunit.py config --make_options LLVM=1
> > ...
> > $ ./tools/testing/kunit/kunit.py run --make_options LLVM=1
> > ...
> >
> > Cc: Jeff Dike <jdike@xxxxxxxxxxx>
> > Cc: Richard Weinberger <richard@xxxxxx>
> > Cc: Anton Ivanov <anton.ivanov@xxxxxxxxxxxxxxxxxx>
> > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> > Cc: David Gow <davidgow@xxxxxxxxxx>
> > Cc: linux-um@xxxxxxxxxxxxxxxxxxx
> > Cc: linux-kbuild@xxxxxxxxxxxxxxx
> > Cc: linux-kselftest@xxxxxxxxxxxxxxx
> > Cc: kunit-dev@xxxxxxxxxxxxxxxx
> > Cc: llvm@xxxxxxxxxxxxxxx
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> > arch/x86/um/user-offsets.c | 4 ++--
> > scripts/Makefile.clang | 1 +
> > 2 files changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> > index bae61554abcc..d9071827b515 100644
> > --- a/arch/x86/um/user-offsets.c
> > +++ b/arch/x86/um/user-offsets.c
> > @@ -10,10 +10,10 @@
> > #include <asm/types.h>
> >
> > #define DEFINE(sym, val) \
> > - asm volatile("\n->" #sym " %0 " #val : : "i" (val))
> > + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val))
> >
> > #define DEFINE_LONGS(sym, val) \
> > - asm volatile("\n->" #sym " %0 " #val : : "i" (val/sizeof(unsigned long)))
> > + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val/sizeof(unsigned long)))
> >
> > void foo(void)
> > {
> > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> > index 51fc23e2e9e5..857b23de51c6 100644
> > --- a/scripts/Makefile.clang
> > +++ b/scripts/Makefile.clang
> > @@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
> > CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
> > CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
> > CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
> > +CLANG_TARGET_FLAGS_um := x86_64-linux-gnu
>
>
> Does this work for the i386 host?
>
> UML supports i386 and x86_64 as the host architecture as of now,
> but this always compiles UML for x86_64?
I think the current code will work because arch/x86/Makefile.um includes
-m32 for CONFIG_X86_32, which will implicitly change x86_64-linux-gnu
into a 32-bit target triple:
$ echo | clang --target=x86_64-linux-gnu -x c -c -o test.o -
$ file test.o
test.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped
$ echo | clang --target=x86_64-linux-gnu -m32 -x c -c -o test.o -
$ file test.o
test.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
In fact, we rely on this for ARCH=i386 LLVM=1 right now, as it uses
x86_64-linux-gnu for the target flag.
While UML only supports x86, maybe it is worth using SUBARCH instead of
hardcoding the triple? No strong opinion around that though.
diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 51fc23e2e9e5..87285b76adb2 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
+CLANG_TARGET_FLAGS_um := $(CLANG_TARGET_FLAGS_$(SUBARCH))
CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
ifeq ($(CROSS_COMPILE),)
> > CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
> >
> > ifeq ($(CROSS_COMPILE),)
> > --
> > 2.30.2
> >
>
>
> --
> Best Regards
> Masahiro Yamada
