linux-kernel - Re: [PATCH v2] uselib: default depending if libc5 was used

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Message-Id: <20151130163129.9f29d40b969862d3fdbd8c20@linux-foundation.org>
Date:	Mon, 30 Nov 2015 16:31:29 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Riku Voipio <riku.voipio@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] uselib: default depending if libc5 was used

On Fri, 27 Nov 2015 12:07:10 -0800 Josh Triplett <josh@...htriplett.org> wrote:

> On Fri, Nov 27, 2015 at 01:14:20PM +0200, Riku Voipio wrote:
> > uselib hasn't been used since libc5; glibc does not use it.
> > Deprecate uselib a bit more, by making the default y only
> > if libc5 was widely used on the plaform.
> > 
> > This makes arm64 kernel built with defconfig slighly smaller
> > 
> > bloat-o-meter:
> > add/remove: 0/3 grow/shrink: 0/2 up/down: 0/-1390 (-1390)
> > function                                     old     new   delta
> > kernel_config_data                         18164   18162      -2
> > uselib_flags                                  20       -     -20
> > padzero                                      216     192     -24
> > sys_uselib                                   380       -    -380
> > load_elf_library                             964       -    -964
> 
> One question below.
> 
> > v2: Disable on X86_64 if no 32bit support
> >  init/Kconfig | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/init/Kconfig b/init/Kconfig
> > index c24b6f7..a4bc657 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -285,7 +285,7 @@ config FHANDLE
> >  
> >  config USELIB
> >  	bool "uselib syscall"
> > -	default y
> > +	def_bool ALPHA || M68K || SPARC || X86_32 || (X86_64 && IA32_EMULATION)
> 
> IA32_EMULATION depends on X86_64, so doesn't that reduce to:
> 	def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION

It's a bit old fashioned to add an expression like this at the
definition site anyway.  The cool new thing is to do

	def_bool ARCH_WANT_USELIB

then go off and define ARCH_WANT_USELIB in the appropriate places in
the per-arch Kconfig files.

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