linux-kernel - Re: bug: kernel 3.0-rc3 not relocatable on i386?

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Message-Id: <1308132448.4641.41.camel@nathan.suse.cz>
Date:	Wed, 15 Jun 2011 12:07:28 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	Maarten Lankhorst <m.b.lankhorst@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: bug: kernel 3.0-rc3 not relocatable on i386?

Petr Tesarik píše v St 15. 06. 2011 v 12:01 +0200:
> Maarten Lankhorst píše v St 15. 06. 2011 v 11:21 +0200:
> > Hi Petr,
> > 
> > 2011/6/15 Petr Tesarik <ptesarik@...e.cz>:
> > > Hi all,
> > >
> > > it seems that the 3.0-rc3 kernel is not relocatable on i386. I get
> > > warnings about jiffies being an absolute symbol, and indeed, when GRUB
> > > loads the kernel at a non-default address, jiffies is not relocated.
> > >
> > > In my example the kernel is configured with
> > > CONFIG_PHYSICAL_START=0x1000000
> > > CONFIG_PHYSICAL_ALIGN=0x200000
> > > CONFIG_RELOCATABLE=y
> > > and loaded at 0x200000 by GRUB.
> > >
> > > Booting fails when checking whether the timer works, because do_timer()
> > > increments jiffies_64, but timer_irq_works() checks jiffies. The code
> > > looks like this:
> > >
> > > c13daab7:       8b 3d 40 7a 39 c1       mov    0xc1397a40,%edi
> > >
> > > but arch/x86/boot/compressed/vmlinux.relocs does not contain c13daaba.
> > > Consequently, timer_irq_works() reads the wrong memory location and
> > > fails, causing a panic:
> > >
> > > kernel panic: IO-APIC + timer doesn't work! Boot with apic=debug and
> > > send a report.  Then try booting with the 'noapic' option.
> > >
> > > Needless to say, the kernel freezes a few initcalls later when booted
> > > with noapic, because IO-APIC worked fine, in fact. I verified that by
> > > inserting a debugging printk() in do_timer(), and I also verified with
> > > that printk() that the address of jiffies_64 and the address of jiffies
> > > differ at run time.
> > >
> > > Any idea how to fix this?
> > Does reverting this commit fix it?
> 
> Isn't this related to VDSO? I've got no troubles with the VDSO. It's
> just that the kernel assumes a fixed location of jiffies (in the kernel
> direct mapping), so it cannot be relocated.
> 
> OTOH this must have worked the other day, so searching for the commit
> that broke it is a good hint. I'll try it here, too.

Ah, it turns out this is in fact reported here:

http://sourceware.org/bugzilla/show_bug.cgi?id=12327

But the patch was reverted by commit
6b35eb9ddcddde7b510726de03fae071178f1ec4, so these binutils have been
broken again since January.

Yes, I've got binutils-2.21 here. :/

Petr


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