Re: arm and patch phys offset

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On Mon, 12 Dec 2011, Russell King - ARM Linux wrote:

> On Mon, Dec 12, 2011 at 04:38:07PM -0500, Nicolas Pitre wrote:
> > You could try instrumenting the patching code, although it is a bit 
> > tricky because of the non-standard register life rules in that file.  
> > But something like this should tell you if the expected amount of fixups 
> > were applied:
> > 
> > diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> > index 08c82fd844..7f43d1fe01 100644
> > --- a/arch/arm/kernel/head.S
> > +++ b/arch/arm/kernel/head.S
> > @@ -530,14 +530,23 @@ __fixup_a_pv_table:
> >  	bcc	1b
> >  	bx	lr
> >  #else
> > +	mov	r0, #0
> >  	b	2f
> >  1:	ldr	ip, [r7, r3]
> >  	bic	ip, ip, #0x000000ff
> >  	orr	ip, ip, r6	@ mask in offset bits 31-24
> >  	str	ip, [r7, r3]
> > +	add	r0, r0, #1
> >  2:	cmp	r4, r5
> >  	ldrcc	r7, [r4], #4	@ use branch for delay slot
> >  	bcc	1b
> 
> If you look at this code, there is _no_ way it can fixup only some entries
> in the table and not others - unless the CPU starts executing something
> which isn't this code.

As you might imagine, I already know that.  But getting the number out 
helps people gain confidence in the code they might not trust otherwise.


Nicolas

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