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

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Date:	Fri, 27 Nov 2015 12:04:58 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	Riku Voipio <riku.voipio@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] uselib: default depending if libc5 was used

On Fri, Nov 27, 2015 at 12:48:29PM +0200, Riku Voipio wrote:
> On 27 November 2015 at 11:33, Josh Triplett <josh@...htriplett.org> wrote:
> > On Fri, Nov 27, 2015 at 11:11:26AM +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
> >>
> >> Signed-off-by: Riku Voipio <riku.voipio@...aro.org>
> >> Cc: Josh Triplett <josh@...htriplett.org>
> >
> > Seems sensible.  Can you also make it only "default y" on 32-bit x86,
> > not 64-bit x86, since the latter never had libc5?
> 
> but running 32bit libc5 apps is possible with X86_64 kernel, so the
> check would become:
> 
> || X86_32 || (X86_64 && IA32_EMULATION)

Fair point.  Seems unlikely that anyone would do so, but certainly possible.

> > With that change:
> > Reviewed-by: Josh Triplett <josh@...htriplett.org>
> >
> >>  init/Kconfig | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/init/Kconfig b/init/Kconfig
> >> index c24b6f7..bef326d 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
> >>       help
> >>         This option enables the uselib syscall, a system call used in the
> >>         dynamic linker from libc5 and earlier.  glibc does not use this
> >> --
> >> 2.6.2
> >>
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