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Now, we got a basic ability to test compiler capability in Kconfig.
config CC_HAS_STACKPROTECTOR
def_bool $(shell,($(CC) -Werror -fstack-protector -E -x c /dev/null -o /dev/null 2>/dev/null) && echo y || echo n)
This works, but it is ugly to repeat this long boilerplate.
We want to describe like this:
config CC_HAS_STACKPROTECTOR
bool
default $(cc-option,-fstack-protector)
It is straight-forward to add a new function, but I do not like to
hard-code specialized functions like that. Hence, here is another
feature, user-defined function. This works as a textual shorthand
with parameterization.
A user-defined function is defined by using the = operator, and can
be referenced in the same way as built-in functions. A user-defined
function in Make is referenced like $(call my-func,arg1,arg2), but I
omitted the 'call' to make the syntax shorter.
The definition of a user-defined function contains $(1), $(2), etc.
in its body to reference the parameters. It is grammatically valid
to pass more or fewer arguments when calling it. We already exploit
this feature in our makefiles; scripts/Kbuild.include defines cc-option
which takes two arguments at most, but most of the callers pass only
one argument.
By the way, a variable is supported as a subset of this feature since
a variable is "a user-defined function with zero argument". In this
context, I mean "variable" as recursively expanded variable. I will
add a different flavored variable in the next commit.
The code above can be written as follows:
[Example Code]
success = $(shell,($(1)) >/dev/null 2>&1 && echo y || echo n)
cc-option = $(success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null)
config CC_HAS_STACKPROTECTOR
def_bool $(cc-option,-fstack-protector)
[Result]
$ make -s alldefconfig && tail -n 1 .config
CONFIG_CC_HAS_STACKPROTECTOR=y
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
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.