linux-kernel - Re: [PATCH 01/25] asm-generic: Change time_t and clock

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Message-ID: <alpine.DEB.2.02.1405131625520.6261@ionos.tec.linutronix.de>
Date:	Tue, 13 May 2014 16:37:04 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arnd Bergmann <arnd@...db.de>
cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Ley Foon Tan <lftan@...era.com>,
	James Hogan <james.hogan@...tec.com>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Chung-Lin Tang <cltang@...esourcery.com>
Subject: Re: [PATCH 01/25] asm-generic: Change time_t and clock_t to 64 bit

On Tue, 13 May 2014, Arnd Bergmann wrote:
> On Tuesday 13 May 2014 15:11:33 Geert Uytterhoeven wrote:
> > On Tue, May 13, 2014 at 2:07 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > > On Tue, 13 May 2014, Arnd Bergmann wrote:
> > >> On Tuesday 13 May 2014 18:17:40 Ley Foon Tan wrote:
> > >> > When we export this posix_types.h file for user software, they need to
> > >> > define this config, eg: CONFIG_32BIT_TIME to use 32 bit time. Is this
> > >> > what we want to do?
> > >>
> > >> No, this doesn't really work: You can't use CONFIG_* symbols in
> > >> user-visible header files.
> > >
> > > Then make the config symbol generate the header from a template.
> > 
> > Indeed. I think it's worthwhile to add CONFIG_* expansion for such "hard"
> > CONFIG symbols to make headers_install, cfr. the existing unifdef support.
> > 
> > We do such a hard work to improve asm-generic, so new architectures can
> > just use that, only to see early adaptors now having to migrate away from it
> > (e.g. OpenRISC suddenly gaining uapi/asm/posix_types.h).
> 
> This was always the idea: New architectures should use the default ABI
> as it is defined at the time when they get added. When we later change
> the ABI, everything that is already there is no longer using the default,
> so they now have to change.
>  
> > Or is there another solution?
> 
> We could in theory have a versioned ABI, and define for instance that
> openrisc uses the 3.1 version while nios2 uses the 3.16 version.
> 
> Doing that would introduce other problems I guess, but it would
> avoid the use of changing lots of architectures when the default
> ABI changes.

The most simple solution is to use the existing unifdef machinery for
the export version and make the #ifdef maze use CONFIG_ARCH_XXX. For
the simple architectures you just need the CONFIG_ARCH_NAME, for such
which support 32 and 64 or some more ABI versions you need to look for
a matching one or a combination of several config options.

You even can combine that with versioning:

#ifdef CONFIG_ARCH_OPENRISC
# include <asm-generic/hdr-v31.h>
#endif

That gives you a nice history in a single place and avoids updating
the world and some when you change stuff.

Hmm?

	tglx
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