On Fri, Feb 18, 2022 at 2:41 AM Nathan Chancellor nathan@kernel.org wrote:
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@chromium.org 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@addtoit.com Cc: Richard Weinberger richard@nod.at Cc: Anton Ivanov anton.ivanov@cambridgegreys.com Cc: Masahiro Yamada masahiroy@kernel.org Cc: Nick Desaulniers ndesaulniers@google.com Cc: Nathan Chancellor nathan@kernel.org Cc: David Gow davidgow@google.com Cc: linux-um@lists.infradead.org Cc: linux-kbuild@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: kunit-dev@googlegroups.com Cc: llvm@lists.linux.dev Signed-off-by: Kees Cook keescook@chromium.org
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:
Ah, you are right!
$ 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))
LGTM.
I also thought of not passing --target at all for ARCH=um, but we decided to override --target all the time (for reproducibility?). Anyway, Nathan's way is clean, and looks OK to me.
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
-- Best Regards Masahiro Yamada