linux-kernel - Re: [RFC PATCH 0/3] kbuild: generate intermediate C files instead of copying

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Date:   Sat, 19 Aug 2017 10:03:51 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Sam Ravnborg <sam@...nborg.org>, Michal Marek <mmarek@...e.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Richard Purdie <richard.purdie@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Markus Heiser <markus.heiser@...marit.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        SeongJae Park <sj38.park@...il.com>,
        "Yann E. MORIN" <yann.morin.1998@...e.fr>
Subject: Re: [RFC PATCH 0/3] kbuild: generate intermediate C files instead of
 copying _shipped files

On Sat, Aug 19, 2017 at 1:49 AM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
>
> 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.

Yeah, I think we probably should do that.

However, when I just tested, I noticed that we have issues with
re-generating those files. With gperf 3.1 installed, I get

  In file included from scripts/kconfig/zconf.tab.c:213:0:
  scripts/kconfig/zconf.gperf:147:1: error: conflicting types for
‘kconf_id_lookup’
  scripts/kconfig/zconf.gperf:12:31: note: previous declaration of
‘kconf_id_lookup’ was here
   static const struct kconf_id *kconf_id_lookup(register const char
*str, register unsigned int len);
                                 ^~~~~~~~~~~~~~~

because gperf now generates

   const struct kconf_id *
  -kconf_id_lookup (register const char *str, register unsigned int len)
  +kconf_id_lookup (register const char *str, register size_t len)

and I'm not sure how to detect that automatically. It seems to be a
gperf-3.1 change, and gperf doesn't seem to generate any version
markers.

Working around that, I hit:

  In file included from scripts/genksyms/lex.lex.c:1921:0:
  scripts/genksyms/keywords.gperf:54:1: error: conflicting types for
‘is_reserved_word’
   static, STATIC_KEYW
   ^~~~~~~~~~~~~~~~
  In file included from scripts/genksyms/lex.lex.c:1921:0:
  scripts/genksyms/keywords.gperf:6:30: note: previous declaration of
‘is_reserved_word’ was here
   static const struct resword *is_reserved_word(register const char
*str, register unsigned int len);
                              ^~~~~~~~~~~~~~~~

so we have at least two cases of this in the source tree.

So one of the advantages of the pre-shipped files is that we can avoid
that kind of crazy version issues with the tools.

But if we can solve the versioning thing easily, I certainly don't
mind getting rid of the pre-generated files. Having to have
flex/bison/gperf isn't a huge onus on the kernel build system.

              Linus