On 7/8/2021 4:25 PM, 'Nick Desaulniers' via Clang Built Linux wrote:
We get constant feedback that the command line invocation of make is too
long. CROSS_COMPILE is helpful when a toolchain has a prefix of the
target triple, or is an absolute path outside of $PATH, but it's mostly
redundant for a given SRCARCH. SRCARCH itself is derived from ARCH
(normalized for a few different targets).
If CROSS_COMPILE is not set, simply set --target= for CLANG_FLAGS,
KBUILD_CFLAGS, and KBUILD_AFLAGS based on $SRCARCH.
Previously, we'd cross compile via:
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make LLVM=1 LLVM_IAS=1
Now:
$ ARCH=arm64 make LLVM=1 LLVM_IAS=1
For native builds (not involving cross compilation) we now explicitly
specify a target triple rather than rely on the implicit host triple.
Link: https://github.com/ClangBuiltLinux/linux/issues/1399
Suggested-by: Arnd Bergmann <arnd@xxxxxxxxxx>
Suggested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
I tested arm, arm64, i386, riscv, and x86_64 and verified that the error
fired for an unsupported arch. Consider this:
Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---
Changes v1 -> v2:
* Fix typos in commit message as per Geert and Masahiro.
* Use SRCARCH instead of ARCH, simplifying x86 handling, as per
Masahiro. Add his sugguested by tag.
* change commit oneline from 'drop' to 'infer.'
* Add detail about explicit host --target and relationship of ARCH to
SRCARCH, as per Masahiro.
Changes RFC -> v1:
* Rebase onto linux-kbuild/for-next
* Keep full target triples since missing the gnueabi suffix messes up
32b ARM. Drop Fangrui's sugguested by tag. Update commit message to
drop references to arm64.
* Flush out TODOS.
* Add note about -EL/-EB, -m32/-m64.
* Add note to Documentation/.
Documentation/kbuild/llvm.rst | 5 +++++
scripts/Makefile.clang | 34 ++++++++++++++++++++++++++++++++--
2 files changed, 37 insertions(+), 2 deletions(-)
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index b18401d2ba82..80c63dd9a6d1 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -46,6 +46,11 @@ example: ::
clang --target=aarch64-linux-gnu foo.c
+When both ``LLVM=1`` and ``LLVM_IAS=1`` are used, ``CROSS_COMPILE`` becomes
+unnecessary and can be inferred from ``ARCH``. Example: ::
+
+ ARCH=arm64 make LLVM=1 LLVM_IAS=1
+
LLVM Utilities
--------------
diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 297932e973d4..956603f56724 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -1,6 +1,36 @@
-ifneq ($(CROSS_COMPILE),)
+# Individual arch/{arch}/Makfiles should use -EL/-EB to set intended endianness
+# and -m32/-m64 to set word size based on Kconfigs instead of relying on the
+# target triple.
+ifeq ($(CROSS_COMPILE),)
+ifneq ($(LLVM),)
+ifeq ($(LLVM_IAS),1)
+ifeq ($(SRCARCH),arm)
+CLANG_FLAGS += --target=arm-linux-gnueabi
+else ifeq ($(SRCARCH),arm64)
+CLANG_FLAGS += --target=aarch64-linux-gnu
+else ifeq ($(SRCARCH),hexagon)
+CLANG_FLAGS += --target=hexagon-linux-gnu
+else ifeq ($(SRCARCH),m68k)
+CLANG_FLAGS += --target=m68k-linux-gnu
+else ifeq ($(SRCARCH),mips)
+CLANG_FLAGS += --target=mipsel-linux-gnu
+else ifeq ($(SRCARCH),powerpc)
+CLANG_FLAGS += --target=powerpc64le-linux-gnu
+else ifeq ($(SRCARCH),riscv)
+CLANG_FLAGS += --target=riscv64-linux-gnu
+else ifeq ($(SRCARCH),s390)
+CLANG_FLAGS += --target=s390x-linux-gnu
+else ifeq ($(SRCARCH),x86)
+CLANG_FLAGS += --target=x86_64-linux-gnu
+else
+$(error Specify CROSS_COMPILE or add '--target=' option to scripts/Makefile.clang)
+endif # SRCARCH
+endif # LLVM_IAS
+endif # LLVM
+else
CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
-endif
+endif # CROSS_COMPILE
+
ifeq ($(LLVM_IAS),1)
CLANG_FLAGS += -integrated-as
else
