Re: [PATCH 5/8] x86/arch_prctl/64: Remove FSBASE/GSBASE < 4G optimization

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH 5/8] x86/arch_prctl/64: Remove FSBASE/GSBASE < 4G optimization
Date	2016-04-27 00:40 +0200
Message-ID	<rsjOa-7f9-23@gated-at.bofh.it> (permalink)
References	<rsgQi-4Hw-9@gated-at.bofh.it> <rsgQi-4Hw-17@gated-at.bofh.it> <rsifn-5Sr-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Tue, Apr 26, 2016 at 1:50 PM, Andi Kleen <andi@firstfloor.org> wrote:
> On Tue, Apr 26, 2016 at 12:23:28PM -0700, Andy Lutomirski wrote:
>> As far as I know, the optimization doesn't work on any modern distro
>> because modern distros use high addresses for ASLR.  Remove it.
>
> I disagree with this patch. For example it will be a regression
> for static executables.  And randomly making old systems slower is a bad
> idea.

That's odd.  statically linked glibc uses low addresses, even in PIE
mode.  I wonder why.

In any event, this isn't actually much of a performance regression, it
has no effect on normal dynamically linked programs, and it's a
considerably simplification, so I still think it's a good idea.  It
also removes some nasty special cases from code that is already way
too full of special cases for comfort.

--Andy

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH 5/8] x86/arch_prctl/64: Remove FSBASE/GSBASE < 4G optimization Andy Lutomirski <luto@kernel.org> - 2016-04-26 21:30 +0200
  Re: [PATCH 5/8] x86/arch_prctl/64: Remove FSBASE/GSBASE < 4G  optimization Andi Kleen <andi@firstfloor.org> - 2016-04-26 23:00 +0200
    Re: [PATCH 5/8] x86/arch_prctl/64: Remove FSBASE/GSBASE < 4G optimization Andy Lutomirski <luto@amacapital.net> - 2016-04-27 00:40 +0200

csiph-web