| Message ID | 20210730215708.276437-4-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | infer --target from SRCARCH for CC=clang | expand |
On 2021-07-30, Nick Desaulniers wrote: >As noted by Masahiro, document how we can generally infer CROSS_COMPILE >(and the more specific details about --target and --prefix) based on >ARCH. > >Suggested-by: Masahiro Yamada <masahiroy@kernel.org> >Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> >--- > Documentation/kbuild/llvm.rst | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > >diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst >index b18401d2ba82..4292f0686316 100644 >--- a/Documentation/kbuild/llvm.rst >+++ b/Documentation/kbuild/llvm.rst >@@ -63,6 +63,23 @@ 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 GNU assembler. and the GNU linker. Reviewed-by: Fangrui Song <maskray@google.com> >+If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred >+from ``ARCH``. >+ >+That 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 Is ARCH=arm64 make LLVM=1 LLVM_IAS=1 preferred over make ARCH=arm64 LLVM=1 LLVM_IAS=1 ? > Supported Architectures > ----------------------- > >-- >2.32.0.554.ge1b32706d8-goog >
On Sat, Jul 31, 2021 at 8:12 AM Fangrui Song <maskray@google.com> wrote: > > On 2021-07-30, Nick Desaulniers wrote: > >As noted by Masahiro, document how we can generally infer CROSS_COMPILE > >(and the more specific details about --target and --prefix) based on > >ARCH. > > > >Suggested-by: Masahiro Yamada <masahiroy@kernel.org> > >Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > >--- > > Documentation/kbuild/llvm.rst | 17 +++++++++++++++++ > > 1 file changed, 17 insertions(+) > > > >diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst > >index b18401d2ba82..4292f0686316 100644 > >--- a/Documentation/kbuild/llvm.rst > >+++ b/Documentation/kbuild/llvm.rst > >@@ -63,6 +63,23 @@ 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 GNU assembler. > > and the GNU linker. > > Reviewed-by: Fangrui Song <maskray@google.com> > > >+If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred > >+from ``ARCH``. > >+ > >+That 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 > > Is ARCH=arm64 make LLVM=1 LLVM_IAS=1 > > preferred over > > make ARCH=arm64 LLVM=1 LLVM_IAS=1 > > ? I do not think so. For consistency, make ARCH=arm64 LLVM=1 LLVM_IAS=1 or ARCH=arm64 LLVM=1 LLVM_IAS=1 make might be preferred. But, in the same doc, I see an example, which mixes up the env variables and a make variable. ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
On Fri, Jul 30, 2021 at 4:12 PM 'Fangrui Song' via Clang Built Linux <clang-built-linux@googlegroups.com> wrote: > > On 2021-07-30, Nick Desaulniers wrote: > >As noted by Masahiro, document how we can generally infer CROSS_COMPILE > >(and the more specific details about --target and --prefix) based on > >ARCH. > > > >Suggested-by: Masahiro Yamada <masahiroy@kernel.org> > >Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > >--- > > Documentation/kbuild/llvm.rst | 17 +++++++++++++++++ > > 1 file changed, 17 insertions(+) > > > >diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst > >index b18401d2ba82..4292f0686316 100644 > >--- a/Documentation/kbuild/llvm.rst > >+++ b/Documentation/kbuild/llvm.rst > >@@ -63,6 +63,23 @@ 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 GNU assembler. > > and the GNU linker. Sure, I'll add this, but wanted to note that generally the compiler is not used as the driver for kernel builds; the linker is invoked directly. IIRC, there were a few spots where the compiler is used as the driver; I think some of the various VDSO's are still built that way, but it's not common. > > Reviewed-by: Fangrui Song <maskray@google.com> > > >+If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred > >+from ``ARCH``. > >+ > >+That 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 > > Is ARCH=arm64 make LLVM=1 LLVM_IAS=1 > > preferred over > > make ARCH=arm64 LLVM=1 LLVM_IAS=1 > > ? Will respond to this against Masahiro's reply.
On Fri, Jul 30, 2021 at 5:05 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > On Sat, Jul 31, 2021 at 8:12 AM Fangrui Song <maskray@google.com> wrote: > > > > On 2021-07-30, Nick Desaulniers wrote: > > >+For example, to cross-compile the arm64 kernel:: > > >+ > > >+ ARCH=arm64 make LLVM=1 LLVM_IAS=1 > > > > Is ARCH=arm64 make LLVM=1 LLVM_IAS=1 > > > > preferred over > > > > make ARCH=arm64 LLVM=1 LLVM_IAS=1 > > > > ? > > > I do not think so. > > For consistency, > > make ARCH=arm64 LLVM=1 LLVM_IAS=1 > > or > > ARCH=arm64 LLVM=1 LLVM_IAS=1 make > > might be preferred. > > > > But, in the same doc, I see an example, which > mixes up the env variables and a make variable. > > ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang Perhaps it's just muscle memory from when I started working on Nexus phone kernels ~5 years ago; that's how our build scripts invoked make (with ARCH and CROSS_COMPILE as env vars). IIRC, GNU make has the notion of `origin` for variables. https://www.gnu.org/software/make/manual/html_node/Origin-Function.html So "before `make`" would be "environment" and "after `make`" would be "command line." I'm rereading the section on assignment to see if one of the assignment operators was affected by origin. https://www.gnu.org/software/make/manual/html_node/Setting.html https://www.gnu.org/software/make/manual/html_node/Flavors.html#Flavors I could have sworn that due to one of the assignment operators (perhaps `?=`) that the orderings weren't commutative. $ make ARCH=arm64 LLVM=1 LLVM_IAS=1 -j72 works $ ARCH=arm64 LLVM=1 LLVM_IAS=1 make -j72 also works. Hmm...maybe I misremembered the issue then. Ok, I will reorder all instances to use the command line rather than env vars in v6.
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst index b18401d2ba82..4292f0686316 100644 --- a/Documentation/kbuild/llvm.rst +++ b/Documentation/kbuild/llvm.rst @@ -63,6 +63,23 @@ 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 GNU assembler. + +If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred +from ``ARCH``. + +That 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 -----------------------
As noted by Masahiro, document how we can generally infer CROSS_COMPILE (and the more specific details about --target and --prefix) based on ARCH. Suggested-by: Masahiro Yamada <masahiroy@kernel.org> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- Documentation/kbuild/llvm.rst | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)