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    SubjectRe: [PATCH v2 2/2] Makefile: infer CROSS_COMPILE from SRCARCH for LLVM=1 LLVM_IAS=1
    On Wed, Jul 21, 2021 at 2:30 AM Nathan Chancellor <nathan@kernel.org> wrote:
    >
    > On 7/20/2021 1:04 AM, Masahiro Yamada wrote:
    > > On Fri, Jul 9, 2021 at 8:25 AM 'Nick Desaulniers' via Clang Built
    > > Linux <clang-built-linux@googlegroups.com> 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@kernel.org>
    > >> Suggested-by: Nathan Chancellor <nathan@kernel.org>
    > >> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
    > >> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
    > >> ---
    > >> 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),)
    > >
    > >
    > > Do you need to check $(LLVM) ?
    > >
    > >
    > > LLVM=1 is a convenient switch to change all the
    > > defaults, but yet you can flip each tool individually.
    > >
    > > Instead of LLVM=1, you still should be able to
    > > get the equivalent setups by:
    > >
    > >
    > > make CC=clang LD=ld.lld AR=llvm-ar OBJCOPY=llvm-objcopy ...
    > >
    > >
    > > The --target option is passed to only
    > > KBUILD_CFLAGS and KBUILD_AFLAGS.
    > >
    > > So, when we talk about --target=,
    > > we only care about whether $(CC) is Clang.
    > > Not caring about $(AR), $(LD), or $(OBJCOPY).
    > >
    > >
    > > scripts/Makefile.clang is already guarded by:
    > >
    > > ifneq ($(findstring clang,$(CC_VERSION_TEXT)),
    >
    > $ make ARCH=arm64 CC=clang LLVM_IAS=1
    >
    > will use the right compiler and assembler but none of the other binary
    > tools because '--prefix=' will not be set so CROSS_COMPILE needs to be
    > specified still, which defeats the purpose of this whole change. This
    > patch is designed to work for the "normal" case of saying "I want to use
    > all of the LLVM tools", not "I want to use clang by itself".


    I disagree.

    LLVM=1 is a shorthand.



    make LLVM=1 LLVM_IAS=1

    should be equivalent to:

    make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \
    OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \
    HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld \
    LLVM_IAS=1



    We do not care about the origin of CC=clang,
    whether it came from LLVM=1 or every tool was explicitly,
    individually specified.



    ifneq ($(LLVM),) is a garbage code
    that checks a pointless thing.







    > >> +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
    > >> --
    > >> 2.32.0.93.g670b81a890-goog
    > >>
    > >> --
    > >> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
    > >> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com.
    > >> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20210708232522.3118208-3-ndesaulniers%40google.com.
    > >
    > >
    > >



    --
    Best Regards
    Masahiro Yamada

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