[PATCH] kbuild: clang: Support building UM with SUBARCH=i386

Kees Cook
2025-03-03T21:52:46Z

The UM builds distinguish i386 from x86_64 via SUBARCH, but we don't
support building i386 directly with Clang. To make SUBARCH work for
i386 UM, we need to explicitly test for it.

This lets me run i386 KUnit tests with Clang:

$ ./tools/testing/kunit/kunit.py run \
--make_options LLVM=1 \
--make_options SUBARCH=i386
...

Fixes: c7500c1b53bf ("um: Allow builds with Clang")
Signed-off-by: Kees Cook <kees@kernel.org>
---
I could not find a cleaner way to do this without hardcoding a test
for i386 UM. Does anyone see a more sane way to accomplish this? The
comment above the CLANG_TARGET_FLAGS seems like it can't be done with
UM's Makefile...

Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: llvm@lists.linux.dev
Cc: linux-kbuild@vger.kernel.org
---
scripts/Makefile.clang | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 2435efae67f5..fa6f9a9be4ac 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -12,8 +12,12 @@ CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
CLANG_TARGET_FLAGS_sparc := sparc64-linux-gnu
CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
+ifeq ($(SRCARCH):$(SUBARCH),um:i386)
+CLANG_TARGET_FLAGS := i386-linux-gnu
+else
CLANG_TARGET_FLAGS_um := $(CLANG_TARGET_FLAGS_$(SUBARCH))
CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
+endif

ifeq ($(CLANG_TARGET_FLAGS),)
$(error add '--target=' option to scripts/Makefile.clang)
--
2.34.1