linux-kernel - Re: [PPC64/Power7 - 2.6.35-rc5] Bad relocation warnings whileBuilding a CONFIG_RELOCATABLE kernel with CONFIG

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Message-ID: <reloc-2010-07-19@mdm.bga.com>
Date:	Mon, 19 Jul 2010 06:23:32 -0500
From:	Milton Miller <miltonm@....com>
To:	Alexander Graf <agraf@...e.de>
Cc:	Subrata Modak <subrata@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PPC64/Power7 - 2.6.35-rc5] Bad relocation warnings whileBuilding a CONFIG_RELOCATABLE kernel with CONFIG_ISERIES enabled

On Mon Jul 19 2010 at about 03:36:51 EST, Alexander Graf wrote:
> On 19.07.2010, at 03:11, Benjamin Herrenschmidt wrote:
> 
> > On Thu, 2010-07-15 at 17:05 +0530, Subrata Modak wrote:
> > > commit e62cee42e66dcca83aae02748535f62e0f564a0c solved the problem for
> > > 2.6.34-rc6. However some other bad relocation warnings generated against
> > > 2.6.35-rc5 on Power7/ppc64 below:
> > >
> > > MODPOST 2004 modules^M
> > > WARNING: 2 bad relocations^M
> > > c000000000008590 R_PPC64_ADDR32 .text+0x4000000000008460^M
> > > c000000000008594 R_PPC64_ADDR32 .text+0x4000000000008598^M
> >
> > I think this is KVM + CONFIG_RELOCATABLE. Caused by:
> >
> > .global kvmppc_trampoline_lowmem
> > kvmppc_trampoline_lowmem:
> > .long kvmppc_handler_lowmem_trampoline - CONFIG_KERNEL_START
> >
> > .global kvmppc_trampoline_enter
> > kvmppc_trampoline_enter:
> > .long kvmppc_handler_trampoline_enter - CONFIG_KERNEL_START
> >
> > Alex, can you turn these into 64-bit on ppc64 so the relocator
> > can grok them ?
> 
> If I turn them into 64-bit, will the values be > RMA? In that case
> things would break anyways. How does relocation work on PPC? Are the
> first few megs copied over to low memory? Would I have to mask anything
> in the above code to make sure I use the real values? 
>
> Alex
>

You can still do the subtraction, but you have to allocate 64 bits for
storage.  Relocatable ppc64 kernels work by adjusting PPC64_RELOC_RELATIVE
entries during early boot (reloc in reloc_64.S called from head_64.S).

The code purposely only supports 64 bit relative addressing.

milton
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