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doc: clang: Update and correct support notes

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At this point, clang can be used on both 32bit and 64bit targets without
issue. Make note of logic we have that will inform clang of the
architecture to build for.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
This commit is contained in:
Tom Rini 2023-11-21 10:41:07 -05:00 • committed by Heinrich Schuchardt
parent a6ac50cad5
commit 463e341348
1 changed files with 10 additions and 12 deletions
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22
doc/build/clang.rst vendored
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@ -11,14 +11,6 @@ The ARM backend can be instructed not to use the r9 and x18 registers using
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
------------
@ -28,14 +20,20 @@ Required packages can be installed via apt, 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.
We make use of the CROSS_COMPILE variable to derive the build target which is
passed as the --target parameter to clang.
The CROSS_COMPILE variable further determines the paths to other build
tools. As assembler we use the binary pointed to by '$(CROSS_COMPILE)as'
instead of the LLVM integrated assembler (IAS).
Here is an example demonstrating building U-Boot for the Raspberry Pi 2
using clang:
.. code-block:: bash
make HOSTCC=clang rpi_2_defconfig
make HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- \
CC="clang -target arm-linux-gnueabi" -j8
make HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- CC=clang -j8
It can also be used to compile sandbox: