* Move README.clang to doc/build/clang.rst and reformat as reStructeredText. * Indicate that -ffixed-r9 and -ffixed-x18 are used to reserve registers for gd. * Minor editing.
Signed-off-by: Heinrich Schuchardt xypron.glpk@gmx.de --- doc/README.clang | 55 -------------------------------- doc/build/clang.rst | 76 +++++++++++++++++++++++++++++++++++++++++++++ doc/build/index.rst | 1 + 3 files changed, 77 insertions(+), 55 deletions(-) delete mode 100644 doc/README.clang create mode 100644 doc/build/clang.rst
diff --git a/doc/README.clang b/doc/README.clang deleted file mode 100644 index 475bb1e2ed..0000000000 --- a/doc/README.clang +++ /dev/null @@ -1,55 +0,0 @@ -The biggest problem when trying to compile U-Boot with clang is that -almost all archs rely on storing gd in a global register and clang user -manual states: "clang does not support global register variables; this -is unlikely to be implemented soon because it requires additional LLVM -backend support." - -Since version 3.4 the ARM backend can be instructed to leave r9 alone. -Global registers themselves are not supported so some inline assembly is -used to get its value. This does lead to larger code then strictly -necessary, but at least works. - -NOTE: target compilation only work for _some_ ARM boards at the moment. -Also AArch64 is not supported currently due to a lack of private libgcc -support. Boards which reassign gd in c will also fail to compile, but there is -in no strict reason to do so in the ARM world, since crt0.S takes care of this. -These assignments can be avoided by changing the init calls but this is not in -mainline yet. - -Debian (based) --------------- -Binary packages can be installed as usual, e.g.: -sudo apt-get install clang - -Note that we still use binutils for some tools so we must continue to set -CROSS_COMPILE. To compile U-Boot with clang on linux without IAS use e.g.: -make HOSTCC=clang rpi_2_defconfig -make HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- \ - CC="clang -target arm-linux-gnueabi" -j8 - -It can also be used to compile sandbox: -make HOSTCC=clang sandbox_defconfig -make HOSTCC=clang CC=clang -j8 - -FreeBSD 11 (Current): --------------------- -Since llvm 3.4 is currently in the base system, the integrated as is -incapable of building U-Boot. Therefore gas from devel/arm-gnueabi-binutils -is used instead. It needs a symlinks to be picked up correctly though: - -ln -s /usr/local/bin/arm-gnueabi-freebsd-as /usr/bin/arm-freebsd-eabi-as - -# The following commands compile U-Boot using the clang xdev toolchain. -# NOTE: CROSS_COMPILE and target differ on purpose! -export CROSS_COMPILE=arm-gnueabi-freebsd- -gmake rpi_2_defconfig -gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd" -j8 - -Given that U-Boot will default to gcc, above commands can be -simplified with a simple wrapper script, listed below. - -/usr/local/bin/arm-gnueabi-freebsd-gcc ---- -#!/bin/sh - -exec clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd "$@" diff --git a/doc/build/clang.rst b/doc/build/clang.rst new file mode 100644 index 0000000000..1d35616eb5 --- /dev/null +++ b/doc/build/clang.rst @@ -0,0 +1,76 @@ +Building with Clang +=================== + +The biggest problem when trying to compile U-Boot with Clang is that almost all +archs rely on storing gd in a global register and the Clang 3.5 user manual +states: "Clang does not support global register variables; this is unlikely to +be implemented soon because it requires additional LLVM backend support." + +The ARM backend can be instructed not to use the r9 and x18 registers using +-ffixed-r9 or -ffixed-x18 respectively. As global registers themselves are not +supported inline assembly is needed to get and set the r9 or x18 value. This +leads to larger code then strictly necessary, but at least works. + +**NOTE:** target compilation only work for _some_ ARM boards at the moment. +Also AArch64 is not supported currently due to a lack of private libgcc +support. Boards which reassign gd in c will also fail to compile, but there is +in no strict reason to do so in the ARM world, since crt0.S takes care of this. +These assignments can be avoided by changing the init calls but this is not in +mainline yet. + + +Debian based +------------ + +Required packages can be installed via apt, e.g. + +.. code-block:: bash + + sudo apt-get install clang + +Note that we still use binutils for some tools so we must continue to set +CROSS_COMPILE. To compile U-Boot with Clang on Linux without IAS use e.g. + +.. code-block:: bash + + make HOSTCC=clang rpi_2_defconfig + make HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- \ + CC="clang -target arm-linux-gnueabi" -j8 + +It can also be used to compile sandbox: + +.. code-block:: bash + + make HOSTCC=clang sandbox_defconfig + make HOSTCC=clang CC=clang -j8 + + +FreeBSD 11 +---------- + +Since llvm 3.4 is currently in the base system, the integrated assembler as +is incapable of building U-Boot. Therefore gas from devel/arm-gnueabi-binutils +is used instead. It needs a symlink to be picked up correctly though: + +.. code-block:: bash + + ln -s /usr/local/bin/arm-gnueabi-freebsd-as /usr/bin/arm-freebsd-eabi-as + +The following commands compile U-Boot using the Clang xdev toolchain. + +**NOTE:** CROSS_COMPILE and target differ on purpose! + +.. code-block:: bash + + export CROSS_COMPILE=arm-gnueabi-freebsd- + gmake rpi_2_defconfig + gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd" -j8 + +Given that U-Boot will default to gcc, above commands can be +simplified with a simple wrapper script - saved as +/usr/local/bin/arm-gnueabi-freebsd-gcc - listed below: + +.. code-block:: bash + + #!/bin/sh + exec clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd "$@" diff --git a/doc/build/index.rst b/doc/build/index.rst index e4e34114af..e0072afb5e 100644 --- a/doc/build/index.rst +++ b/doc/build/index.rst @@ -6,4 +6,5 @@ Build U-Boot .. toctree:: :maxdepth: 2
+ clang tools -- 2.26.2