Re: [PATCH v2] um: Allow builds with Clang

On Thu, Feb 24, 2022 at 2:58 PM Kees Cook keescook@chromium.org wrote:

Add x86-64 target for Clang+um and update user-offsets.c to use Clang-friendly assembly, 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 Reviewed-by: Nathan Chancellor nathan@kernel.org Link: https://lore.kernel.org/lkml/Yg2YubZxvYvx7%2Fnm@dev-arch.archlinux-ax161/ Tested-by: David Gow davidgow@google.com Link: https://lore.kernel.org/lkml/CABVgOSk=oFxsbSbQE-v65VwR2+mXeGXDDjzq8t7FShwjJ3... Signed-off-by: Kees Cook keescook@chromium.org

---

v1: https://lore.kernel.org/lkml/20220217002843.2312603-1-keescook@chromium.org/ v2:

• tweak commit log phrasing and alphabetize targets (nathan)
• fix a missing implicit fallthrough under 32-bit builds
• add review tags

---

arch/um/os-Linux/execvp.c | 1 + arch/x86/um/user-offsets.c | 4 ++-- scripts/Makefile.clang | 1 + 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/um/os-Linux/execvp.c b/arch/um/os-Linux/execvp.c index 84a0777c2a45..c09a5fd5e225 100644 --- a/arch/um/os-Linux/execvp.c +++ b/arch/um/os-Linux/execvp.c @@ -93,6 +93,7 @@ int execvp_noalloc(char *buf, const char *file, char *const argv[]) up finding no executable we can use, we want to diagnose that we did find one but were denied access. */ got_eacces = 1;

•                                   break;
                            case ENOENT:
                            case ESTALE:
                            case ENOTDIR:
  

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))
  

Another way might be #include <linux/kbuild.h> and delete this macro definition.

#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)))
  

This generates wrong comments.

In include/generated/user_constants.h, I see this:

#define HOST_BX 5 /* RBX */

(Here, the value of RBX is 40.)

#define DEFINE_LONGS(sym, val) asm volatile("\n.ascii "->" #sym " %0 " #val "/sizeof(unsigned long)"": : "i" (val/sizeof(unsigned long)))

creates valid comments:

#define HOST_BX 5 /* RBX/sizeof(unsigned long) */

Another way might be to do this indirectly.

#define DEFINE_LONGS(sym, val) DEFINE(sym, val / sizeof(unsigned long))

The comments in include/generated/user_constans.h do not retain the original macro names, though...

void foo(void) { diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang index 51fc23e2e9e5..6e49344c6db2 100644 --- a/scripts/Makefile.clang +++ b/scripts/Makefile.clang @@ -9,6 +9,7 @@ CLANG_TARGET_FLAGS_mips := mipsel-linux-gnu CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu +CLANG_TARGET_FLAGS_um := x86_64-linux-gnu

Personally, I like Nathan's idea, but we can live with the hard-coding since we see no efforts for UML on other host arch.

CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))

-- 2.30.2