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104daea149
To get access to environment variables, Kconfig needs to define a
symbol using "option env=" syntax. It is tedious to add a symbol entry
for each environment variable given that we need to define much more
such as 'CC', 'AS', 'srctree' etc. to evaluate the compiler capability
in Kconfig.
Adding '$' for symbol references is grammatically inconsistent.
Looking at the code, the symbols prefixed with 'S' are expanded by:
- conf_expand_value()
This is used to expand 'arch/$ARCH/defconfig' and 'defconfig_list'
- sym_expand_string_value()
This is used to expand strings in 'source' and 'mainmenu'
All of them are fixed values independent of user configuration. So,
they can be changed into the direct expansion instead of symbols.
This change makes the code much cleaner. The bounce symbols 'SRCARCH',
'ARCH', 'SUBARCH', 'KERNELVERSION' are gone.
sym_init() hard-coding 'UNAME_RELEASE' is also gone. 'UNAME_RELEASE'
should be replaced with an environment variable.
ARCH_DEFCONFIG is a normal symbol, so it should be simply referenced
without '$' prefix.
The new syntax is addicted by Make. The variable reference needs
parentheses, like $(FOO), but you can omit them for single-letter
variables, like $F. Yet, in Makefiles, people tend to use the
parenthetical form for consistency / clarification.
At this moment, only the environment variable is supported, but I will
extend the concept of 'variable' later on.
The variables are expanded in the lexer so we can simplify the token
handling on the parser side.
For example, the following code works.
[Example code]
config MY_TOOLCHAIN_LIST
string
default "My tools: CC=$(CC), AS=$(AS), CPP=$(CPP)"
[Result]
$ make -s alldefconfig && tail -n 1 .config
CONFIG_MY_TOOLCHAIN_LIST="My tools: CC=gcc, AS=as, CPP=gcc -E"
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.