In Linux build system convention, we do not run tools such as
flex, bison, gperf during the kernel building.  Instead, manage
generated C files in the repository with _shipped suffixes.
They are simply shipped (copied) removing the _shipped suffixes
during the kernel building.

Commit 7373f4f83c71 ("kbuild: add implicit rules for parser generation")
added a mechanism to regenerate intermediate C files easily.
The build rules are surrounded with ifdef REGENERATE_PARSERS.
So, we need to pass REGENERATE_PARSERS=1 from the command line
when we want to update them.

Here is one question.  Is it acceptable to use those rules all the time?
That is, generate those C files by flex, bison, gperf during the
kernel building.

This means, the build system depends on more external tools.

From the users' point of view, they will need to install

flex, bison, gperf in order to build the kernel.

From the developers' point of view, the advantage is

we do not need to version-control generated files, i.e. _shipped files
will be deleted.

I'd like to know if this is acceptable or not.

For example, currently some files are simply shipped (copied)
when building the kconfig program.

  $ make mrproper; make defconfig
    HOSTCC  scripts/basic/fixdep
    HOSTCC  scripts/kconfig/conf.o
    SHIPPED scripts/kconfig/zconf.tab.c
    SHIPPED scripts/kconfig/zconf.lex.c
    SHIPPED scripts/kconfig/zconf.hash.c
    HOSTCC  scripts/kconfig/zconf.tab.o
    HOSTLD  scripts/kconfig/conf
  *** Default configuration is based on 'x86_64_defconfig'
  #
  # configuration written to .config
  #

With this series, they are created from *real* sources
(*.y, *.l, *.gperf files).

  $ make mrproper; make defconfig
    HOSTCC  scripts/basic/fixdep
    HOSTCC  scripts/kconfig/conf.o
    YACC    scripts/kconfig/zconf.tab.c
    LEX     scripts/kconfig/zconf.lex.c
    GPERF   scripts/kconfig/zconf.hash.c
    HOSTCC  scripts/kconfig/zconf.tab.o
    HOSTLD  scripts/kconfig/conf
  *** Default configuration is based on 'x86_64_defconfig'
  #
  # configuration written to .config
  #

Note:
The tool versions in Documentation/process/changes.rst are just
place-holders for now.  We need to figure out the minimal versions
if we like to switch to this approach.



Masahiro Yamada (3):
  kbuild: generate *.hash.c during build
  kbuild: generate *.lex.c during build
  kbuild: generate *.tab.c and *.tab.h during build

 Documentation/process/changes.rst        |   36 +
 scripts/Makefile.lib                     |   26 +-
 scripts/dtc/Makefile                     |    6 +-
 scripts/dtc/dtc-lexer.lex.c_shipped      | 2259 ---------------------------
 scripts/dtc/dtc-parser.tab.c_shipped     | 2303 ----------------------------
 scripts/dtc/dtc-parser.tab.h_shipped     |  125 --
 scripts/genksyms/Makefile                |    4 +-
 scripts/genksyms/keywords.hash.c_shipped |  230 ---
 scripts/genksyms/lex.lex.c_shipped       | 2291 ---------------------------
 scripts/genksyms/parse.tab.c_shipped     | 2394 -----------------------------
 scripts/genksyms/parse.tab.h_shipped     |  119 --
 scripts/kconfig/Makefile                 |    1 +
 scripts/kconfig/zconf.hash.c_shipped     |  297 ----
 scripts/kconfig/zconf.lex.c_shipped      | 2473 ------------------------------
 scripts/kconfig/zconf.tab.c_shipped      | 2471 -----------------------------
 15 files changed, 53 insertions(+), 14982 deletions(-)
 delete mode 100644 scripts/dtc/dtc-lexer.lex.c_shipped
 delete mode 100644 scripts/dtc/dtc-parser.tab.c_shipped
 delete mode 100644 scripts/dtc/dtc-parser.tab.h_shipped
 delete mode 100644 scripts/genksyms/keywords.hash.c_shipped
 delete mode 100644 scripts/genksyms/lex.lex.c_shipped
 delete mode 100644 scripts/genksyms/parse.tab.c_shipped
 delete mode 100644 scripts/genksyms/parse.tab.h_shipped
 delete mode 100644 scripts/kconfig/zconf.hash.c_shipped
 delete mode 100644 scripts/kconfig/zconf.lex.c_shipped
 delete mode 100644 scripts/kconfig/zconf.tab.c_shipped

-- 
2.7.4