[PATCH v5 00/31] kconfig: move compiler capability tests to Kconfig

From: Masahiro Yamada
Date: Mon May 28 2018 - 05:24:35 EST

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[Introduction]

The motivation of this work is to move the compiler option tests to
Kconfig from Makefile. A number of kernel features require the
compiler support. Enabling such features blindly in Kconfig ends up
with a lot of nasty build-time testing in Makefiles. If a chosen
feature turns out unsupported by the compiler, what the build system
can do is either to disable it (silently!) or to forcibly break the
build, despite Kconfig has let the user to enable it. By moving the
compiler capability tests to Kconfig, Kconfig entries will be visible
only when they are available.

[Major Changes in V5]

V5 removed the complexity unnecessary for Kconfig.

- In order to make the implementation simpler, I drop the lazy
argument expansion.
In V5, parameters are expanded before passed to a function.
(the same behavior as v3)

- Replace 'warning', 'error' functions with 'warning-if',
'error-if' functions. The new functions are effective
only when the condition part is 'y'.

- In V4, '$' must be followed by '$' or '('.
'$$' meant an escaped '$'.

V4 caused a build error for ARC architecture due to the
following line:
https://github.com/torvalds/linux/blob/v4.17-rc4/arch/arc/Kconfig#L252

Of course, we could rephrase "D$" to "D cache", but
I treaked the grammar a little bit.

Kconfig decided to not support single-letter variable as in "$X".
Nor curly braces as in "${CC}" are not supported.
This means variable/function references in Kconfig always start
with "$(".
We can use '$' not followed by '(' as-is.
We do not need the "$$" escape sequence.
If necessary, we can use a trick to print '$(' verbatim. See below.

- Fix a wrong behavior of simply expanded variables.
V4 expanded simply expanded variables when used, but it should not.

For example,

dollar := $
X := 1
Y := $(dollar)(X)
$(info,$(Y))

V5 prints '$(X)', not '1'.

- Remove a space after a comma is $( ) context.
Actually, spaces do not matter in most cases.

You can write either

$(cc-option,-fstack-protector)

or

$(cc-option, -fstack-protector)

In fact, both style co-exist in our Makefiles too.
However, there are some cases where they do matter.

I remove spaces after commas for consistency.
If you are unsure, no-space-after-comma is always safe.

[Major Changes in V4]

- In V4, I slightly change the syntax of a function call.
I chose grammatical consistency and simplicity.
Anyway, Kconfig is deviating from Make behavior already.

In v3, a function call looked like this:

$(func-name arg1,arg2,arg3)

In v4, a function is invoked like follows:

$(func-name,arg1,arg2,arg3)

The difference is that the function name and the first argument
are separated by a comma.

- V3 supported single-letter variable like $X.
V4 dropped it because we do not need multiple ways to do the
same thing.
You must always enclose a variable name like $(X).

- Support lazy argument expansion. This is necessary for implementing
'if', 'and', 'or' functions as in Make.

- Add more built-in functions:
'if', 'error', 'filename', 'lineno'

- Error out if a recursive variable references itself eventually.
For example, X = $(X)
ends up with a circular expansion. It must be terminated
since the expansion would continue eternally.

- Update Documentation and unit-tests, accordingly.

[Major Changes in V3]

This version looks more like Make.

- Use = operator instead of 'macro' keyword
to define a user-defined function.

- 'Recursively expanded variable' is implemented as a side-effect.
A variable is a function with zero argument.

- Support simply expanded variable which is defined by := operator

- Support += operator.
Probably, this feature will be useful to accumulate compiler flags.
At least, Clang needs some prerequisite flags such as triplet
to test other compiler flags.

- Support $(info ...) and $(warning ...) built-in functions,
which were useful while I was debugging this.

- Add documentation

- Add unit tests

- Collect helpers to scripts/Kconfig.include

[Old Versions]

V4: https://lkml.org/lkml/2018/5/17/97
V3: https://lkml.org/lkml/2018/4/13/37
V2: https://lkml.org/lkml/2018/2/16/610
V1: https://lkml.org/lkml/2018/2/16/610
RFC: https://lkml.org/lkml/2018/2/8/429

Masahiro Yamada (31):
kbuild: remove kbuild cache
kbuild: remove CONFIG_CROSS_COMPILE support
kconfig: reference environment variables directly and remove 'option
env='
kconfig: remove string expansion in file_lookup()
kconfig: remove string expansion for mainmenu after yyparse()
kconfig: remove sym_expand_string_value()
kconfig: make default prompt of mainmenu less specific
kconfig: add built-in function support
kconfig: add 'shell' built-in function
kconfig: replace $(UNAME_RELEASE) with function call
kconfig: begin PARAM state only when seeing a command keyword
kconfig: support user-defined function and recursively expanded
variable
kconfig: support simply expanded variable
kconfig: support append assignment operator
kconfig: expand lefthand side of assignment statement
kconfig: add 'info', 'warning-if', and 'error-if' built-in functions
kconfig: add 'filename' and 'lineno' built-in variables
kconfig: error out if a recursive variable references itself
Documentation: kconfig: document a new Kconfig macro language
kconfig: test: add Kconfig macro language tests
kconfig: show compiler version text in the top comment
kconfig: add basic helper macros to scripts/Kconfig.include
stack-protector: test compiler capability in Kconfig and drop AUTO
mode
kconfig: add CC_IS_GCC and GCC_VERSION
kconfig: add CC_IS_CLANG and CLANG_VERSION
gcov: remove CONFIG_GCOV_FORMAT_AUTODETECT
kcov: test compiler capability in Kconfig and correct dependency
gcc-plugins: move GCC version check for PowerPC to Kconfig
gcc-plugins: test plugin support in Kconfig and clean up Makefile
gcc-plugins: allow to enable GCC_PLUGINS for COMPILE_TEST
Documentation: kconfig: add recommended way to describe compiler
support

Documentation/kbuild/kconfig-language.txt | 26 +-
Documentation/kbuild/kconfig-macro-language.txt | 242 +++++++++
Kconfig | 10 +-
MAINTAINERS | 3 +-
Makefile | 105 +---
arch/Kconfig | 49 +-
arch/powerpc/Kconfig | 2 +-
arch/sh/Kconfig | 4 +-
arch/sparc/Kconfig | 4 +-
arch/um/Kconfig.common | 4 -
arch/x86/Kconfig | 15 +-
arch/x86/um/Kconfig | 10 +-
init/Kconfig | 40 +-
kernel/gcov/Kconfig | 17 +-
kernel/gcov/Makefile | 2 -
lib/Kconfig.debug | 11 +-
scripts/Kbuild.include | 101 +---
scripts/Kconfig.include | 30 ++
scripts/Makefile.gcc-plugins | 91 +---
scripts/Makefile.kcov | 10 +-
scripts/clang-version.sh | 18 +-
scripts/gcc-plugins/Makefile | 1 +
scripts/gcc-x86_32-has-stack-protector.sh | 7 +-
scripts/gcc-x86_64-has-stack-protector.sh | 5 -
scripts/kconfig/confdata.c | 33 +-
scripts/kconfig/kconf_id.c | 1 -
scripts/kconfig/lkc.h | 5 +-
scripts/kconfig/lkc_proto.h | 15 +-
scripts/kconfig/menu.c | 3 -
scripts/kconfig/preprocess.c | 572 +++++++++++++++++++++
scripts/kconfig/symbol.c | 109 ----
.../tests/no_write_if_dep_unmet/expected_config | 2 +-
.../kconfig/tests/preprocess/builtin_func/Kconfig | 27 +
.../tests/preprocess/builtin_func/__init__.py | 9 +
.../tests/preprocess/builtin_func/expected_stderr | 5 +
.../tests/preprocess/builtin_func/expected_stdout | 1 +
.../tests/preprocess/circular_expansion/Kconfig | 5 +
.../preprocess/circular_expansion/__init__.py | 11 +
.../preprocess/circular_expansion/expected_stderr | 1 +
scripts/kconfig/tests/preprocess/escape/Kconfig | 44 ++
.../kconfig/tests/preprocess/escape/__init__.py | 8 +
.../tests/preprocess/escape/expected_stderr | 10 +
scripts/kconfig/tests/preprocess/variable/Kconfig | 53 ++
.../kconfig/tests/preprocess/variable/__init__.py | 8 +
.../tests/preprocess/variable/expected_stderr | 9 +
scripts/kconfig/util.c | 33 +-
scripts/kconfig/zconf.l | 95 +++-
scripts/kconfig/zconf.y | 46 +-
48 files changed, 1345 insertions(+), 567 deletions(-)
create mode 100644 Documentation/kbuild/kconfig-macro-language.txt
create mode 100644 scripts/Kconfig.include
create mode 100644 scripts/kconfig/preprocess.c
create mode 100644 scripts/kconfig/tests/preprocess/builtin_func/Kconfig
create mode 100644 scripts/kconfig/tests/preprocess/builtin_func/__init__.py
create mode 100644 scripts/kconfig/tests/preprocess/builtin_func/expected_stderr
create mode 100644 scripts/kconfig/tests/preprocess/builtin_func/expected_stdout
create mode 100644 scripts/kconfig/tests/preprocess/circular_expansion/Kconfig
create mode 100644 scripts/kconfig/tests/preprocess/circular_expansion/__init__.py
create mode 100644 scripts/kconfig/tests/preprocess/circular_expansion/expected_stderr
create mode 100644 scripts/kconfig/tests/preprocess/escape/Kconfig
create mode 100644 scripts/kconfig/tests/preprocess/escape/__init__.py
create mode 100644 scripts/kconfig/tests/preprocess/escape/expected_stderr
create mode 100644 scripts/kconfig/tests/preprocess/variable/Kconfig
create mode 100644 scripts/kconfig/tests/preprocess/variable/__init__.py
create mode 100644 scripts/kconfig/tests/preprocess/variable/expected_stderr

--
2.7.4

Next message: Masahiro Yamada: "[PATCH v5 20/31] kconfig: test: add Kconfig macro language tests"
Previous message: Masahiro Yamada: "[PATCH v5 05/31] kconfig: remove string expansion for mainmenu after yyparse()"
Next in thread: Masahiro Yamada: "[PATCH v5 13/31] kconfig: support simply expanded variable"
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