linux-kernel - Re: [RFC, PATCH] Fixup COMPAT_VDSO to work with CONFIG

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Date:	Fri, 16 Mar 2007 08:08:11 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	"Zachary Amsden" <zach@...are.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Virtualization Mailing List" <virtualization@...ts.osdl.org>,
	"Andrew Morton" <akpm@...l.org>,
	"Linus Torvalds" <torvalds@...l.org>,
	"Rusty Russell" <rusty@...tcorp.com.au>,
	"Chris Wright" <chrisw@...s-sol.org>, "Andi Kleen" <ak@...e.de>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC, PATCH] Fixup COMPAT_VDSO to work with
	CONFIG_PARAVIRT

>>> Jeremy Fitzhardinge <jeremy@...p.org> 16.03.07 06:10 >>>
>Zachary Amsden wrote:
>> Well testing that is not so fun.  I installed SUSE Pro 9.0, and
>> strings on ld.so contains the magic at_sysinfo assert!  But it doesn't
>> install TLS libraries, so I'll have to install them by hand.
>>
>> In works - in theory.  Look, a puppy!
>>
>> Scratchbox is rumored to produce the fabled assertion even on modern
>> distros by installing its own toolchain which includes the dreaded glibc.
>
>I think Andi and Andrew have boxes which are afflicted.

I have one, too (which is one reasone why I created the original Xen patch).

>> I'm playing safe.  Binary identical relocation to 0xffffe000 was my goal.
>
>Yeah, fair enough.  But as Eric likes to keep pointing out, an
>executable ELF file need not have any sections at all, so the only safe
>course for anything "real" is via the section headers.

Program headers you mean.

>So I guess the right thing to do is relocate the dynamic stuff via
>PT_DYNAMIC, and relocate the symtab if its present.

Symtab should also be deduced from program headers.

I'm actually surprised this got re-implemented from scratch, when my patch
already had both variants (one just #ifdef-ed out), and was tested in both
forms (actually, I first implemented the ELF form, and only after seeing the
bloat it added to the sources I came up with the second variant, which in
the end unfortunately didn't add significantly less bloat to the Makefile.

Jan
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