linux-kernel - Re: [PATCH] fs, kernel: Support disabling the uselib syscall

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Message-ID: <20140221204144.GA3861@jtriplet-mobl1>
Date:	Fri, 21 Feb 2014 12:44:01 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Mike Frysinger <vapier@...too.org>,
	Kyungsik Lee <kyungsik.lee@....com>,
	Jiri Slaby <jslaby@...e.cz>, Eric Paris <eparis@...hat.com>,
	Dwight Engen <dwight.engen@...cle.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs, kernel: Support disabling the uselib syscall

On Fri, Feb 21, 2014 at 12:16:27PM -0800, Andrew Morton wrote:
> On Fri, 21 Feb 2014 10:11:06 -0800 Josh Triplett <josh@...htriplett.org> wrote:
> > uselib hasn't been used since libc5; glibc does not use it.  Support
> > turning it off.
> > 
> > When disabled, also omit the load_elf_library implementation from
> > binfmt_elf.c, which only uselib invokes.
> > 
> > bloat-o-meter:
> > add/remove: 0/4 grow/shrink: 0/1 up/down: 0/-785 (-785)
> > function                                     old     new   delta
> > padzero                                       39      36      -3
> > uselib_flags                                  20       -     -20
> > sys_uselib                                   168       -    -168
> > SyS_uselib                                   168       -    -168
> > load_elf_library                             426       -    -426
> > 
> 
> The patch disables CONFIG_USELIB by default.  This important decision
> should be mentioned and justified in the changelog, please.

Gah, that was not intentional.  Will fix in v2.  I did very
intentionally not make it require CONFIG_EXPERT or CONFIG_EMBEDDED,
since (like CONFIG_BINFMT_AOUT) almost everyone will want it disabled,
but I had intended to make it "default y".

> > +#ifdef CONFIG_USELIB
> 
> I wonder if CONFIG_SYS_USELIB would be a better identifier.  We haven't
> done anything consistent here.

As far as I can tell, there's no use of CONFIG_SYS_* or any other
consistent prefix for configuring out syscalls; all such symbols appear
unprefixed.  I think it would make sense to have a single common menu
and prefix for configuring out unused syscalls, but given the large
number of existing Kconfig options for that, I think that change ought
to occur as a separate patch series that isn't also trying to add a new
such option.

Perhaps Dave Hansen (CCed) might be interested in incorporating such a
change into his ongoing kconfig consolidation and reorganization?

- Josh Triplett
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