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Date: Mon, 28 May 2018 21:23:40 +0900
From: Masahiro Yamada <yamada.masahiro@...ionext.com>
To: Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Kees Cook <keescook@...omium.org>,
Nicholas Piggin <npiggin@...il.com>,
"Luis R . Rodriguez" <mcgrof@...e.com>,
Randy Dunlap <rdunlap@...radead.org>,
Ulf Magnusson <ulfalizer@...il.com>,
Sam Ravnborg <sam@...nborg.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH v5 00/31] kconfig: move compiler capability tests to Kconfig
2018-05-28 18:21 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.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
--
Best Regards
Masahiro Yamada
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