Subject: Re: bug: kernel 3.0-rc3 not relocatable on i386?
From: Petr Tesarik <ptesarik@suse.cz>
To: Maarten Lankhorst <m.b.lankhorst@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org
In-Reply-To: <4DF87D2B.7090201@gmail.com>
References: <1308125533.4641.33.camel@nathan.suse.cz>
	 <4DF87D2B.7090201@gmail.com>
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Organization: SUSE LINUX
Date: Wed, 15 Jun 2011 11:58:02 +0200
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Maarten Lankhorst píše v St 15. 06. 2011 v 11:36 +0200:
> Hi Petr,
> 
> Op 15-06-11 10:12, Petr Tesarik schreef:
> > 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.
> 
> Can you try this patch?

Hi Maarten,

thanks for the quick replay, but no, I won't even try. It can't work,
because jiffies is undefined in the final vmlinux link on 32-bit, so I
believe the link will simply fail because of undefined symbols. ;)

Petr

> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 89aed99..49e666e 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -34,12 +34,11 @@ OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT)
>  #ifdef CONFIG_X86_32
>  OUTPUT_ARCH(i386)
>  ENTRY(phys_startup_32)
> -jiffies = jiffies_64;
>  #else
>  OUTPUT_ARCH(i386:x86-64)
>  ENTRY(phys_startup_64)
> -jiffies_64 = jiffies;
>  #endif
> +jiffies_64 = jiffies;
>  
>  #if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
>  /*

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