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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Wed, 30 May 2018 09:38:38 +0900
Message-ID: <CAK7LNAT0S-4qq1T3q25H0BGsJSUpTsgV_+TGKBiPW-MUKyqzsQ@mail.gmail.com>
Subject: Re: [PATCH v5 00/31] kconfig: move compiler capability tests to Kconfig
To:     Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        "Luis R . Rodriguez" <mcgrof@suse.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Ulf Magnusson <ulfalizer@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>
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2018-05-28 21:23 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
> 2018-05-28 18:21 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
>>
>> [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
>>
>
>
>
> I pushed this series to
>
> git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
> kconfig-shell-v5
>


I pushed this series to the for-next branch.
Unless a significant problem is reported,
I'd like to merge this series in the upcoming MW.
At least, I need to keep it in linux-next for a while.

Your comments and tags are still appreciated.
I will add tags (or replace patches if necessary) later,
but I want this series tested in linux-next
to expose to more developers' eyes.

It passed my local test.  O-day bot did not report anything so far.


-- 
Best Regards
Masahiro Yamada