| Message ID | 20210729165039.23896-3-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | infer CROSS_COMPILE from SRCARCH for CC=clang LLVM_IAS=1 | expand |
On Thu, Jul 29, 2021 at 6:50 PM '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> Looks good to me, Acked-by: Arnd Bergmann <arnd@arndb.de> > +else > +$(error Specify CROSS_COMPILE or add '--target=' option to scripts/Makefile.clang) > +endif # SRCARCH > +endif # LLVM_IAS Now in theory I suppose we could just have the fallback use --target="$(SRCARCH)-linux-gnu" to avoid having to change this for every new architecture. I think in most cases, this would just work, even though a lot of the one you listed have different patterns. Arnd
I realized that the title of this commit is not really right. We are not inferring CROSS_COMPILE, we are inferring '--target='. On 7/29/2021 9:50 AM, Nick Desaulniers 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 I feel like the beginning of this needs a little work. 1. "...invocation of make is too long when compiling with LLVM" would be a little more accurate. 2. "it's mostly redundant for a given SRCARCH" is not quite true in my eyes. For example, you could have aarch64-linux-, aarch64-elf-, or aarch64-linux-gnu-, and to my knowledge, all of these can compile a working Linux kernel. Again, saying "with LLVM", even mentioning its multitargeted nature, might make it a little more accurate to the casual passerby. > (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> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Tested-by: Nathan Chancellor <nathan@kernel.org> > --- > Changes v2 -> v3: > * Drop check/requirement for LLVM=1, as per Masahiro. > * Change oneliner from LLVM=1 LLVM_IAS=1 to CC=clang LLVM_IAS=1. > * Don't carry forward Nathan's RB/TB tags. :( Sorry Nathan, but thank > you for testing+reviewing v2. > * Update wording of docs slightly. > > 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 | 6 ++++++ > scripts/Makefile.clang | 32 ++++++++++++++++++++++++++++++-- > 2 files changed, 36 insertions(+), 2 deletions(-) > > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst > index b18401d2ba82..aef1587fc09b 100644 > --- a/Documentation/kbuild/llvm.rst > +++ b/Documentation/kbuild/llvm.rst > @@ -46,6 +46,12 @@ example: :: > > clang --target=aarch64-linux-gnu foo.c > > +When both ``CC=clang`` (set via ``LLVM=1``) and ``LLVM_IAS=1`` are used, > +``CROSS_COMPILE`` becomes unnecessary and can be inferred from ``ARCH``. I am not a fan of this sentence because it implies that something like 'make ARCH=arm64 CC=clang LLVM_IAS=1' will work fine, which is not true. We still need CROSS_COMPILE for binutils in this configuration. CROSS_COMPILE provides the value for '--target=' and the prefix for the GNU tools such as ld, objcopy, and readelf. I think this direction is a regression because we are just talking about the first use of CROSS_COMPILE rather than the second at the same time. With LLVM=1 LLVM_IAS=1, we KNOW that the user will be using all LLVM tools. Sure, they are free to override LD, OBJCOPY, READELF, etc with the GNU variants but they have to provide the prefix because LLVM=1 overrides the $(CROSS_COMPILE)<tool> assignments so it is irrelevant to us. As Masahiro mentioned, the user is free to individually specify all the tools by their individual variables such as LD=ld.lld BUT at that point, the user should be aware of what they are doing and specify CROSS_COMPILE. While I understand that the LLVM=1 LLVM_IAS=1 case works perfectly fine with this series, I am of the belief that making it work for CC=clang LLVM_IAS=1 is a mistake because there is no way for that configuration to work for cross compiling without CROSS_COMPILE. At the same time, not a hill I am willing to die on, hence the tags above. > +Example: :: > + > + ARCH=arm64 make LLVM=1 LLVM_IAS=1 > + > LLVM Utilities > -------------- > > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang > index 297932e973d4..a1b46811bdc6 100644 > --- a/scripts/Makefile.clang > +++ b/scripts/Makefile.clang > @@ -1,6 +1,34 @@ > -ifneq ($(CROSS_COMPILE),) > +# Individual arch/{arch}/Makfiles should use -EL/-EB to set intended endianness Makefiles > +# and -m32/-m64 to set word size based on Kconfigs instead of relying on the > +# target triple. > +ifeq ($(CROSS_COMPILE),) > +ifeq ($(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 > +else > CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) > -endif > +endif # CROSS_COMPILE > + > ifeq ($(LLVM_IAS),1) > CLANG_FLAGS += -integrated-as > else >
On Thu, Jul 29, 2021 at 2:00 PM Nathan Chancellor <nathan@kernel.org> wrote: > > While I understand that the LLVM=1 LLVM_IAS=1 case works perfectly fine > with this series, I am of the belief that making it work for CC=clang > LLVM_IAS=1 is a mistake because there is no way for that configuration > to work for cross compiling without CROSS_COMPILE. So with v3 of this change, rather than: $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang -j72 If you wanted to omit CROSS_COMPILE, you'd need: $ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=ld.lld OBJCOPY=llvm-objcopy STRIP=llvm-strip or $ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=aarch64-linux-gnu-ld OBJCOPY=aarch64-linux-gnu-objcopy STRIP=aarch64-linux-gnu-strip That's straight up worse IMO and defeats the purpose of "shortening the command line," which should be the goal. Not "making CC=clang maximally flexible." We don't want folks generally using CC=clang; preferably they'd use LLVM=1. I need to rewrite our docs to make that more explicit and straightforward. And if folks would prefer to use CC=clang for whatever reason, let them explicitly state CROSS_COMPILE then. So I agree with Nathan, and hope Masahiro will reconsider that perhaps the v2 variant that required LLVM=1 maybe makes more sense. Either way, I need to fix the comment in the new script, commit message, and docs, so v4 is necessary. I'm tempted to add a rewrite of our docs to say "just use LLVM=1" front and center, then get into finer grain details below, moving this second patch to be the third in a series. Let's see what Masahiro's thoughts are though first. (I do appreciate them, even when I disagree).
On Fri, Jul 30, 2021 at 2:19 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > maximally flexible." We don't want folks generally using CC=clang; > preferably they'd use LLVM=1. I need to rewrite our docs to make that > more explicit and straightforward. And if folks would prefer to use > CC=clang for whatever reason, let them explicitly state CROSS_COMPILE > then. Perhaps it would be nice to clarify the "level of support" for `CC=clang` too, in particular long-term when `LLVM=1` works for all architectures. In other words, is `CC=clang` going to remain supported/maintained, or it will be something that will still compile/boot but not expected to be used by anyone in production, or dropped altogether (not the `CC` option itself, of course, I refer to the mix of toolchains)? Thanks, Cheers, Miguel
On Fri, Jul 30, 2021 at 6:00 AM Nathan Chancellor <nathan@kernel.org> wrote: > > I realized that the title of this commit is not really right. We are not > inferring CROSS_COMPILE, we are inferring '--target='. > > On 7/29/2021 9:50 AM, Nick Desaulniers 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 > > I feel like the beginning of this needs a little work. > > 1. "...invocation of make is too long when compiling with LLVM" would be > a little more accurate. > > 2. "it's mostly redundant for a given SRCARCH" is not quite true in my > eyes. For example, you could have aarch64-linux-, aarch64-elf-, or > aarch64-linux-gnu-, and to my knowledge, all of these can compile a > working Linux kernel. Again, saying "with LLVM", even mentioning its > multitargeted nature, might make it a little more accurate to the casual > passerby. > > > (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> > > Reviewed-by: Nathan Chancellor <nathan@kernel.org> > Tested-by: Nathan Chancellor <nathan@kernel.org> > > > --- > > Changes v2 -> v3: > > * Drop check/requirement for LLVM=1, as per Masahiro. > > * Change oneliner from LLVM=1 LLVM_IAS=1 to CC=clang LLVM_IAS=1. > > * Don't carry forward Nathan's RB/TB tags. :( Sorry Nathan, but thank > > you for testing+reviewing v2. > > * Update wording of docs slightly. > > > > 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 | 6 ++++++ > > scripts/Makefile.clang | 32 ++++++++++++++++++++++++++++++-- > > 2 files changed, 36 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst > > index b18401d2ba82..aef1587fc09b 100644 > > --- a/Documentation/kbuild/llvm.rst > > +++ b/Documentation/kbuild/llvm.rst > > @@ -46,6 +46,12 @@ example: :: > > > > clang --target=aarch64-linux-gnu foo.c > > > > +When both ``CC=clang`` (set via ``LLVM=1``) and ``LLVM_IAS=1`` are used, > > +``CROSS_COMPILE`` becomes unnecessary and can be inferred from ``ARCH``. > > I am not a fan of this sentence because it implies that something like > 'make ARCH=arm64 CC=clang LLVM_IAS=1' will work fine, which is not true. > We still need CROSS_COMPILE for binutils in this configuration. Agree. That sentence is misleading, and moreover, it is wrong. > > CROSS_COMPILE provides the value for '--target=' and the prefix for the > GNU tools such as ld, objcopy, and readelf. I think this direction is a > regression because we are just talking about the first use of > CROSS_COMPILE rather than the second at the same time. > > With LLVM=1 LLVM_IAS=1, we KNOW that the user will be using all LLVM > tools. Sure, they are free to override LD, OBJCOPY, READELF, etc with > the GNU variants but they have to provide the prefix because LLVM=1 > overrides the $(CROSS_COMPILE)<tool> assignments so it is irrelevant to > us. As Masahiro mentioned, the user is free to individually specify all > the tools by their individual variables such as LD=ld.lld BUT at that > point, the user should be aware of what they are doing and specify > CROSS_COMPILE. > > While I understand that the LLVM=1 LLVM_IAS=1 case works perfectly fine > with this series, I am of the belief that making it work for CC=clang > LLVM_IAS=1 is a mistake because there is no way for that configuration > to work for cross compiling without CROSS_COMPILE. LLVM=1 is a too strong requirement. LLVM=1 switches not only target tools (CC=clang, LD=ld.lld, AR=llvm-ar...) but also host tools (HOSTCC=clang, HOSTCXX=g++...). Obviously host-tools are don't-care here. Specifying the target tools individually, as in make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \ OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf ... is a perfectly correct command that makes CROSS_COMPILE unnecessary. There is no reason to stop inferring --target for this case. The problem is NOT removing the LLVM=1 check but the wrong documentation. Let's write a precise document. For example, the following document exactly explains what is happening in the code, and is still clear. diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst index b18401d2ba82..a0d862bd73ac 100644 --- a/Documentation/kbuild/llvm.rst +++ b/Documentation/kbuild/llvm.rst @@ -63,6 +63,26 @@ They can be enabled individually. The full list of the parameters: :: Currently, the integrated assembler is disabled by default. You can pass ``LLVM_IAS=1`` to enable it. + +Omitting CROSS_COMPILE +---------------------- + +As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``. + +Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive +``--prefix=<path>`` to search for the back-end GNU assembler. + +If CROSS_COMPILE is not specified, the ``--target=<triple>`` is inferred from +``ARCH``. + +It means, if you use only LLVM tools, `CROSS_COMPILE`` becomes unnecessary. + +For example, to cross-compile the arm64 kernel:: + + ARCH=arm64 make LLVM=1 LLVM_IAS=1 + + Supported Architectures ----------------------- BTW, I noticed LLVM_IAS=1 check is also unneeded for the same reason. So, it should go away.
On Fri, Jul 30, 2021 at 9:19 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Jul 29, 2021 at 2:00 PM Nathan Chancellor <nathan@kernel.org> wrote: > > > > While I understand that the LLVM=1 LLVM_IAS=1 case works perfectly fine > > with this series, I am of the belief that making it work for CC=clang > > LLVM_IAS=1 is a mistake because there is no way for that configuration > > to work for cross compiling without CROSS_COMPILE. > > So with v3 of this change, rather than: > > $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang -j72 > > If you wanted to omit CROSS_COMPILE, you'd need: > > $ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=ld.lld OBJCOPY=llvm-objcopy > STRIP=llvm-strip > > or > > $ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=aarch64-linux-gnu-ld > OBJCOPY=aarch64-linux-gnu-objcopy STRIP=aarch64-linux-gnu-strip or $ ARCH=arm64 make LLVM=1 LLVM_IAS=1 still works. > That's straight up worse IMO and defeats the purpose of "shortening > the command line," which should be the goal. Not "making CC=clang > maximally flexible." We don't want folks generally using CC=clang; > preferably they'd use LLVM=1. I need to rewrite our docs to make that > more explicit and straightforward. And if folks would prefer to use > CC=clang for whatever reason, let them explicitly state CROSS_COMPILE > then. > > So I agree with Nathan, and hope Masahiro will reconsider that perhaps > the v2 variant that required LLVM=1 maybe makes more sense. We can always infer the target triple from ARCH unless CROSS_COMPILE is given. Doing this all the time makes nothing wrong. "Whether CROSS_COMPILE is unneeded" is a different thing. > Either way, I need to fix the comment in the new script, commit > message, and docs, so v4 is necessary. > > I'm tempted to add a rewrite of our docs to say "just use LLVM=1" > front and center, then get into finer grain details below, moving this > second patch to be the third in a series. Let's see what Masahiro's > thoughts are though first. (I do appreciate them, even when I > disagree). I am not sure about that. LLVM=1 is a very strong all-or-nothing flag, but technically there is no reason to force it. (At least, target-tools and host-tools look independent to each other to me) When you send v4, one more request: Please drop LLVM_IAS=1 check as well.
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst index b18401d2ba82..aef1587fc09b 100644 --- a/Documentation/kbuild/llvm.rst +++ b/Documentation/kbuild/llvm.rst @@ -46,6 +46,12 @@ example: :: clang --target=aarch64-linux-gnu foo.c +When both ``CC=clang`` (set via ``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..a1b46811bdc6 100644 --- a/scripts/Makefile.clang +++ b/scripts/Makefile.clang @@ -1,6 +1,34 @@ -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),) +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 +$(error Specify CROSS_COMPILE or add '--target=' option to scripts/Makefile.clang) +endif # SRCARCH +endif # LLVM_IAS +else CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) -endif +endif # CROSS_COMPILE + ifeq ($(LLVM_IAS),1) CLANG_FLAGS += -integrated-as else
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 v2 -> v3: * Drop check/requirement for LLVM=1, as per Masahiro. * Change oneliner from LLVM=1 LLVM_IAS=1 to CC=clang LLVM_IAS=1. * Don't carry forward Nathan's RB/TB tags. :( Sorry Nathan, but thank you for testing+reviewing v2. * Update wording of docs slightly. 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 | 6 ++++++ scripts/Makefile.clang | 32 ++++++++++++++++++++++++++++++-- 2 files changed, 36 insertions(+), 2 deletions(-)