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

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Date:	Mon, 30 Nov 2015 17:06:28 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	Andrew Morton <akpm@...ux-foundation.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 Mon, Nov 30, 2015 at 04:31:29PM -0800, Andrew Morton wrote:
> 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.

Good point; that does seem cleaner.

- Josh Triplett
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