linux-kernel - Re: Urgent: x86-32 and GNU ld 2.22.52.0.1

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Date:	Fri, 18 May 2012 09:14:05 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <gregkh@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@...el.com>
Subject: Re: Urgent: x86-32 and GNU ld 2.22.52.0.1

On Fri, May 18, 2012 at 8:56 AM, H. Peter Anvin <hpa@...or.com> wrote:
> I need an urgent opinion.  It seems we have an epic mess on our hands.
>
> GNU ld 2.22.52.0.1 silently changed the semantics of section-relative
> symbols that are part of otherwise empty sections, and silently changes
> them to absolute.  We rely on section-relative symbols staying
> section-relative, and actually have several sections in the linker
> script solely for this purpose.

That is I talked to you a couple days ago:

http://sourceware.org/bugzilla/show_bug.cgi?id=14052

> The postprocessor for the x86-32 kernel, relocs.c, currently doesn't
> enforce its audited absolute symbols list.  As part of the
> tip:x86/trampoline rework, however, I made it error out rather that
> silently producing bad output.
>
> Ingo has found that with this particular version of GNU ld, the error
> triggers.  I want to emphasize that this merely catches an error which
> the current version of the tool would have allowed to silently go by,
> which would have (possibly) caused a failure if the kernel was
> subsequently booted in anything but its default location.
>
> There are a few ways we can deal with this, but I think we need to do
> one or the other:
>
> 1. We can blacklist this version of GNU ld.

I think this is the best approach.

> 2. We can uprev the tool to the one from the tip:x86/trampoline work,
>   with error checking, and give it a list of symbols that should
>   be relative but may end up as absolute.  We risk build errors for
>   some people if the list isn't complete.
> 3. We do a minimal forward-port of the error checking into the current
>   tool.
> 4. We add to the list of relative symbols in the current version of
>   the tool without adding the error checking.
>
> However, since it seems clear that we're silently producing corrupt
> kernels out of the current build, I think we need a fix for this for 3.4.
>


-- 
H.J.
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