linux-kernel - Re: [PATCH] Use sed instead of perl to generate x86/kernel/cpu/capflags.c.

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Date:	Sun, 16 Jan 2011 21:39:18 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Rob Landley <rlandley@...allels.com>
cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org,
	"K. Y. Srinivasan" <ksrinivasan@...ell.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH] Use sed instead of perl to generate
 x86/kernel/cpu/capflags.c.

On Sun, 16 Jan 2011, Rob Landley wrote:

> On 01/16/2011 02:05 PM, Jesper Juhl wrote:
> > On Sun, 16 Jan 2011, Rob Landley wrote:
> > 
> >> From: Rob Landley <rlandley@...allels.com>
> >>
> >> Generate capflags.c with sed (POSIX 2008) instead of perl.
> >>
> > 
> > While I'm not personally a great perl fan, this still begs the 
> > question, why?
> 
> 1) In general, simpler is better.  (Why ship autoconf files to build on
> hosts that don't have autoconf?  Why fix make oldconfig so it builds on
> platforms that don't have curses installed?)
> 
> 2) Making reliable cross compile build environments involves creating a
> known build environment on the host, generally removing everything you
> don't actually _need_ so it can't screw things up when you introduce
> another target or upgrade packages on your host.
> 
> I've maintained such a build environment (aboriginal linux) for several
> years.  I've personally encountered literally _dozens_ of others, and
> expect there are at least hundreds if not thousands out in the wild.
> 
> 3) Perl is not a well-defined langauge.  It is a single implementation,
> not a standard.  (Like Microsoft Word and Excel, their file formats are
> just "what this program emits/parses".  Similarly, Perl is what the perl
> binary runs.  Attemts to rewrite it based on Parrot famously collapsed
> into a black hole of corner cases.)
> 
> Meaning, if you have a platform on which the one and only implementation
> of perl doesn't run, you have no alternative implementations to try.
> (Did I mention that Perl's configuration stage is implemented in perl?)
> 
> This moves to an alternative standardized by POSIX, which has well
> understood behavior with multiple independent implementations (gnu, bsd,
> busybox...)
> 
> > We already depend on perl for other stuff, so why replace something that 
> > works with something that may or may not work?
> 
> We have various development scripts that depend on perl, curses, python,
> QT, and so on.  But building a _kernel_ doesn't depend on any of that...
> except perl.  I'm not proposing removing checkstack.pl and such, because
> "development system" != "build machine".  A build machine can be a
> headless box, a development system usually has things like Gnome or KDE
> installed.
> 
> The kernel's dependency on Perl was introduced in 2.6.25.  Before 2008
> the kernel built just fine on a host that didn't have perl installed,
> and I've been patching the kernel to remove the requirement ever since
> in my own build environment.  (And building the resulting kernel for a
> dozen different targets, and submitting those patches here when they
> changed.  They just haven't changed in a while.)
> 
> Perl is used in exactly three places during the kernel build.  I have
> patches to remove the other two instances of perl use, and using them
> have built a kernel on a system that doesn't have perl installed.  I'm
> tweaking them for submission later today.  My prevoius submissions (such
> as http://lkml.indiana.edu/hypermail/linux/kernel/0901.0/00148.html)
> treated them as a series, but since the three issues are really
> orthogonal I'm posting them individually this time, and cc-ing the
> various people get_maintainer.pl says to.
> 

Thanks a lot for spelling out the reasons.
Those are good reasons in my opinion. I'll test your changes once all 3 
are posted and if things still work I'll be sure to reply with a 
Tested-by: to help things along.

-- 
Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

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