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

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Message-ID: <BANLkTi=eGtMpcKaOBH_c_dt3GNQTbZ2fPQ@mail.gmail.com>
Date:	Wed, 15 Jun 2011 07:17:00 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Petr Tesarik <ptesarik@...e.cz>
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?

On Wed, Jun 15, 2011 at 4:12 AM, Petr Tesarik <ptesarik@...e.cz> wrote:
> 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?

This could be a regression in
8c49d9a74bac5ea3f18480307057241b808fcc0c, but I haven't spotted it
yet.  I'm having trouble reproducing this, though: I see the
relocation in the output of relocs --text.

Can you send me your .config?  I'll fiddle with it.

--Andy
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