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

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Date:   Fri, 8 Sep 2017 15:18:31 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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

Hi Linus,

Very sorry that I had not responded quickly.

When I was digging into tool version dependency,
as you pointed out, gperf is a problem (but seemed one time breakage
for gperf 3.1)
flex seemed very stable for a long time.
bison seemed a bit problem if old version is used.

But, I did not have enough time to take a closer look.
I thought I should respond after I tested more, but I has been pressed
by my daily tasks, then time passed...
Very sorry.

Today, I just noticed gperf usage got dropped from the kernel.

If CONFIG_MODVERSIONS is enabled,
I notice lots of error messages.
WARNING: EXPORT symbol "finish_open" [vmlinux] version generation
failed, symbol will not be

So, I think something was broken in scripts/genksyms/.

Of course, it was a trivial conversion, so it should not be hard to fix...

> gperf is clearly written by clowns that don't understand about
> compatibility issues - it would have been trivial for them to add some
> kind of marker define so that you could test for this directly rather
> than depend on some kind of autoconf "try to build and see if it
> fails" crap.

One idea may be to process the output of "gperf -v"
and embed GPERF_VERSION into the output .c files.

But, if you are unhappy with gperf breakage this time,
we can live without gperf.

> It's likely not even any slower, but who the hell knows.. Do we even
> care? It's almost certainly faster if you compare to generating that
> gperf code.
>

For scripts/kconfig/, I think we do not care at all
because we usually invoke it just once when we configure the build setting.

If we enable CONFIG_MODVERSIONS, scripts/genksyms/ is invoked
over and over again.

Sorry, I have not evaluated if
the perfect hash gives us noticeable advantage or not..

-- 
Best Regards
Masahiro Yamada