@@ -7,6 +7,8 @@ else ifneq ($(filter -%,$(LLVM)),)
LLVM_SUFFIX := $(LLVM)
endif
+CLANG := $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
+
CLANG_TARGET_FLAGS_arm := arm-linux-gnueabi
CLANG_TARGET_FLAGS_arm64 := aarch64-linux-gnu
CLANG_TARGET_FLAGS_hexagon := hexagon-linux-musl
@@ -18,7 +20,13 @@ 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_x86_64 := x86_64-linux-gnu
-CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(ARCH))
+
+# Default to host architecture if ARCH is not explicitly given.
+ifeq ($(ARCH),)
+CLANG_TARGET_FLAGS := $(shell $(CLANG) -print-target-triple)
+else
+CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(ARCH))
+endif
ifeq ($(CROSS_COMPILE),)
ifeq ($(CLANG_TARGET_FLAGS),)
@@ -30,7 +38,7 @@ else
CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
endif # CROSS_COMPILE
-CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX) $(CLANG_FLAGS) -fintegrated-as
+CC := $(CLANG) $(CLANG_FLAGS) -fintegrated-as
else
CC := $(CROSS_COMPILE)gcc
endif # LLVM
Align the behavior for gcc and clang builds by interpreting unset `ARCH` and `CROSS_COMPILE` variables in `LLVM` builds as a sign that the user wants to build for the host architecture. This patch preserves the properties that setting the `ARCH` variable to an unknown value will trigger an error that complains about insufficient information, and that a set `CROSS_COMPILE` variable will override the target triple that is determined based on presence/absence of `ARCH`. When compiling with clang, i.e., `LLVM` is set, an unset `ARCH` variable in combination with an unset `CROSS_COMPILE` variable, i.e., compiling for the host architecture, leads to compilation failures since `lib.mk` can not determine the clang target triple. In this case, the following error message is displayed for each subsystem that does not set `ARCH` in its own Makefile before including `lib.mk` (lines wrapped at 75 chrs): make[1]: Entering directory '/mnt/build/linux/tools/testing/selftests/ sysctl' ../lib.mk:33: *** Specify CROSS_COMPILE or add '--target=' option to lib.mk. Stop. make[1]: Leaving directory '/mnt/build/linux/tools/testing/selftests/ sysctl' In the same scenario a gcc build would default to the host architecture, i.e., it would use plain `gcc`. Fixes: 795285ef2425 ("selftests: Fix clang cross compilation") Reviewed-by: Mark Brown <broonie@kernel.org> Signed-off-by: Valentin Obst <kernel@valentinobst.de> --- I am not entirely sure whether this behavior is in fact known and intended and whether the way to obtain the host target triple is sufficiently general. The flag was introduced in llvm-8 with [1], it will be an error in older clang versions. The target triple you get with `-print-target-triple` may not be the same that you would get when explicitly setting ARCH to you host architecture. For example on my x86_64 system it get `x86_64-pc-linux-gnu` instead of `x86_64-linux-gnu`, similar deviations were observed when testing other clang binaries on compiler-explorer, e.g., [2]. An alternative could be to simply do: ARCH ?= $(shell uname -m) before using it to select the target. Possibly with some post processing, but at that point we would likely be replicating `scripts/subarch.include`. This is what some subsystem Makefiles do before including `lib.mk`. This change might make it possible to remove the explicit setting of `ARCH` from the few subsystem Makefiles that do it. [1]: https://reviews.llvm.org/D50755 [2]: https://godbolt.org/z/r7Gn9bvv1 Changes in v1: - Shortened commit message. - Link to RFC: https://lore.kernel.org/r/20240303-selftests-libmk-llvm-rfc-v1-1-9ab53e365e31@valentinobst.de --- tools/testing/selftests/lib.mk | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) --- base-commit: 4cece764965020c22cff7665b18a012006359095 change-id: 20240303-selftests-libmk-llvm-rfc-5fe3cfa9f094 Best regards, -- Valentin Obst <kernel@valentinobst.de>