From: Nick Desaulniers <ndesaulniers@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Miguel Ojeda <ojeda@kernel.org>,
Fangrui Song <maskray@google.com>,
Michal Marek <michal.lkml@markovi.net>,
Arnd Bergmann <arnd@kernel.org>,
linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
clang-built-linux@googlegroups.com,
Geert Uytterhoeven <geert@linux-m68k.org>,
Christoph Hellwig <hch@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Nick Desaulniers <ndesaulniers@google.com>
Subject: [PATCH v6 3/3] Documentation/llvm: update CROSS_COMPILE inferencing
Date: Mon, 2 Aug 2021 11:39:10 -0700 [thread overview]
Message-ID: <20210802183910.1802120-4-ndesaulniers@google.com> (raw)
In-Reply-To: <20210802183910.1802120-1-ndesaulniers@google.com>
As noted by Masahiro, document how we can generally infer CROSS_COMPILE
(and the more specific details about --target and --prefix) based on
ARCH.
Change use of env vars to command line parameters.
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Changes v5 -> v6:
* Pick up Fangrui's RB tag.
* Change use of env vars to command line parameters for consistency.
Documentation/kbuild/llvm.rst | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index b18401d2ba82..f8a360958f4c 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -38,7 +38,7 @@ Cross Compiling
A single Clang compiler binary will typically contain all supported backends,
which can help simplify cross compiling. ::
- ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
+ make ARCH=arm64 CC=clang CROSS_COMPILE=aarch64-linux-gnu-
``CROSS_COMPILE`` is not used to prefix the Clang compiler binary, instead
``CROSS_COMPILE`` is used to set a command line flag: ``--target=<triple>``. For
@@ -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 linker.
+
+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::
+
+ make ARCH=arm64 LLVM=1 LLVM_IAS=1
+
Supported Architectures
-----------------------
--
2.32.0.554.ge1b32706d8-goog
next prev parent reply other threads:[~2021-08-02 18:39 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-02 18:39 [PATCH v6 0/3] infer --target from SRCARCH for CC=clang Nick Desaulniers
2021-08-02 18:39 ` [PATCH v6 1/3] Makefile: move initial clang flag handling into scripts/Makefile.clang Nick Desaulniers
2021-08-02 21:06 ` Fāng-ruì Sòng
2021-08-02 21:14 ` Nick Desaulniers
2021-08-05 12:55 ` Masahiro Yamada
2021-08-02 18:39 ` [PATCH v6 2/3] Makefile: infer --target from ARCH for CC=clang Nick Desaulniers
2021-08-05 13:58 ` Masahiro Yamada
2021-08-05 18:17 ` Miguel Ojeda
2021-08-02 18:39 ` Nick Desaulniers [this message]
2021-08-02 19:16 ` [PATCH v6 3/3] Documentation/llvm: update CROSS_COMPILE inferencing Nathan Chancellor
2021-08-05 13:57 ` Masahiro Yamada
2021-08-05 18:27 ` Nick Desaulniers
2021-08-05 18:29 ` Nick Desaulniers
2021-08-05 23:26 ` Masahiro Yamada
2021-08-10 0:05 ` [PATCH v6 0/3] infer --target from SRCARCH for CC=clang Masahiro Yamada
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