[PATCH] selftests: Fix clang cross compilation

[Mark Brown <broonie@kernel.org>]

Unlike GCC clang uses a single compiler image to support multiple target
architectures meaning that we can't simply rely on CROSS_COMPILE to select
the output architecture. Instead we must pass --target to the compiler to
tell it what to output, kselftest was not doing this so cross compilation
of kselftest using clang resulted in kselftest being built for the host
architecture.

More work is required to fix tests using custom rules but this gets the
bulk of things building.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/lib.mk | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
index 2a2d240cdc1b..1a5cc3cd97ec 100644
--- a/tools/testing/selftests/lib.mk
+++ b/tools/testing/selftests/lib.mk
@@ -7,10 +7,31 @@ else ifneq ($(filter -%,$(LLVM)),)
 LLVM_SUFFIX := $(LLVM)
 endif
 
-CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
+CLANG_TARGET_FLAGS_arm          := arm-linux-gnueabi
+CLANG_TARGET_FLAGS_arm64        := aarch64-linux-gnu
+CLANG_TARGET_FLAGS_hexagon      := hexagon-linux-musl
+CLANG_TARGET_FLAGS_m68k         := m68k-linux-gnu
+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_x86          := x86_64-linux-gnu
+CLANG_TARGET_FLAGS              := $(CLANG_TARGET_FLAGS_$(ARCH))
+
+ifeq ($(CROSS_COMPILE),)
+ifeq ($(CLANG_TARGET_FLAGS),)
+$(error Specify CROSS_COMPILE or add '--target=' option to lib.mk
+else
+CLANG_FLAGS     += --target=$(CLANG_TARGET_FLAGS)
+endif # CLANG_TARGET_FLAGS
+else
+CLANG_FLAGS     += --target=$(notdir $(CROSS_COMPILE:%-=%))
+endif # CROSS_COMPILE
+
+CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX) $(CLANG_FLAGS) -fintegrated-as
 else
 CC := $(CROSS_COMPILE)gcc
-endif
+endif # LLVM
 
 ifeq (0,$(MAKELEVEL))
     ifeq ($(OUTPUT),)
-- 
2.30.2