[PATCH v2] um: Allow builds with Clang

[Kees Cook <keescook@chromium.org>]

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+kUg@mail.gmail.com/
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))
 
 #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..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
 CLANG_TARGET_FLAGS_x86		:= x86_64-linux-gnu
 CLANG_TARGET_FLAGS		:= $(CLANG_TARGET_FLAGS_$(SRCARCH))
 
-- 
2.30.2