linux-kernel - [PATCH 0/3] kbuild,kconfig: generate lexer/parser C files instead of copying

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Date:   Sun, 10 Dec 2017 01:02:27 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-kbuild@...r.kernel.org
Cc:     Ulf Magnusson <ulfalizer@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Markus Heiser <markus.heiser@...marit.de>,
        linux-doc@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>,
        Michal Marek <michal.lkml@...kovi.net>,
        SeongJae Park <sj38.park@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Max Filippov <jcmvbkbc@...il.com>
Subject: [PATCH 0/3] kbuild,kconfig: generate lexer/parser C files instead of copying _shipped files

In Linux build system convention, pre-generated files are version-
controlled with a "_shipped" suffix.  During the kernel building,
they are simply shipped (copied) removing the suffix.

>From users' point of view, this approach can reduce external tool
dependency for the kernel build,

>From developers point of view, it is tedious to manually regenerate
such artifacts.  In fact, we see several patches to regenerate
_shipped files.  They are noise commits.

When we update a *.y or *.l file, it would be better to update the
corresponding _shipped file in the same commit, but it is painful.
If you use a different version of flex/bison, it will produce lots of
irrelevant diffs.

We could update _shipped files after adding various changes to the
real sources, but it is not very nice for a git-bisect'ability.
In case of a problem, "git bisect" would point to the commit updating
_shipped files, but the root cause would be in another commit that
has changed the corresponding .l or .y files.

Some months ago, I sent RFC patches to run flex, bison, and gperf
during the build.
https://lkml.org/lkml/2017/8/19/49

Basically Linus agreed this, but he found a problem in gperf, then
use of gperf in kernel was removed.

It took some months for me to come back.  This time, I installed various
versions of flex/bison on my machine, and tested them more carefully.

My current motivation is in Kconfig.
There are several Kconfig patches touching *.y and *.l
(and Linus suggested another improvement for Kconfig)
so I want to remove zconf.lex.c_shipped and zconf.tab.c_shipped now.
Kconfig has no problem for this switch.

dtc and genksyms will be taken care of later because
both of them are having shift/reduce conflicts now.
The ambiguous grammar in dtc has been fixed in upstream, but not
reflected to kernel yet.  We can proceed migration in sub-system base.

Masahiro Yamada (3):
  kbuild: add LEX and YACC variables
  kbuild: prepare to remove C files pre-generated by flex and bison
  kconfig: generate lexer and parser during build instead of shipping

 Documentation/process/changes.rst   |   25 +
 Makefile                            |    4 +-
 scripts/Makefile.lib                |   24 +-
 scripts/kconfig/Makefile            |    1 +
 scripts/kconfig/zconf.lex.c_shipped | 2473 -----------------------------------
 scripts/kconfig/zconf.tab.c_shipped | 2471 ----------------------------------
 6 files changed, 48 insertions(+), 4950 deletions(-)
 delete mode 100644 scripts/kconfig/zconf.lex.c_shipped
 delete mode 100644 scripts/kconfig/zconf.tab.c_shipped

-- 
2.7.4