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Most of the CPU architectures have different variants, but kernel
usually only accepts parts of them via the ARCH variable, the others
should be customized via kernel config files.
To simplify testing, a new XARCH variable is added to extend the
kernel's ARCH with a few variants of the same architecture, and it is
used to customize variant specific variables, at last XARCH is converted
to the kernel's ARCH:
e.g. make run XARCH=<one of the supported variants>
| \
| `-> variant specific variables:
| IMAGE, DEFCONFIG, QEMU_ARCH, QEMU_ARGS, CFLAGS ...
\
`---> kernel's ARCH
XARCH and ARCH are carefully mapped to allow users to pass architecture
variants via XARCH or pass architecture via ARCH from cmdline.
PowerPC is the first user and also a very good reference architecture of
this mapping, it has variants with different combinations of
32-bit/64-bit and bit endian/little endian.
To use this mapping, the other architectures can refer to PowerPC, If
the target architecture only has one variant, XARCH is simply an alias
of ARCH, no additional mapping required.
Suggested-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/lkml/20230702171715.GD16233@1wt.eu/
Link: https://lore.kernel.org/lkml/20230730061801.GA7690@1wt.eu/
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.