Re: Urgent: x86-32 and GNU ld 2.22.52.0.1

[H. Peter Anvin]

This is a multi-part message in MIME format.On 05/18/2012 08:56 AM, H. Peter Anvin 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.
> 
> 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.
> 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.
> 

For the record, these are the checkins out of the -tip tree.  They are a
little bigger than necessary because they move the tool around to make
it available for reuse, and of course introduce additional functionality.

	-hpa