[PATCH v2] ARM: proc-v7.S: Adjust stack address when XIP_KERNEL

[Nicolas Pitre]

On Tue, 16 Feb 2016, Russell King - ARM Linux wrote:

> > > index 0f92d57..1595fb2 100644
> > > --- a/arch/arm/mm/proc-v7.S
> > > +++ b/arch/arm/mm/proc-v7.S
> > > @@ -487,7 +487,7 @@ __errata_finish:
> > >  
> > >  	.align	2
> > >  __v7_setup_stack_ptr:
> > > -	.word	__v7_setup_stack - .
> > > +	.word	__v7_setup_stack - . + PHYS_OFFSET_FIXUP
> 
> I keep looking at this patch, and I really find that I detest this
> PHYS_OFFSET_FIXUP thing - it's really not obvious what's going on
> here.  It's taken a _long_ time to work this out, which _really_
> isn't good going forward.
> 
> Let's instead change things to make it much more obvious - see the
> patch below.
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index ebdaaf7dd19f..593e5613184d 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -135,11 +135,18 @@
>  #define PLAT_PHYS_OFFSET	UL(CONFIG_PHYS_OFFSET)
>  
>  #ifdef CONFIG_XIP_KERNEL
> -#define PHYS_OFFSET_FIXUP \
> -	( XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR) - PAGE_OFFSET + \
> -	  PLAT_PHYS_OFFSET - CONFIG_XIP_PHYS_ADDR )
> +/*
> + * When referencing data in RAM from the XIP region in a relative manner
> + * with the MMU off, we need the relative offset between the two physical
> + * addresses.  The macro below achieves this, which is:
> + *    __pa(v_data) - __xip_pa(v_text)
> + */
> +#define PHYS_RELATIVE(v_data, v_text) \
> +	(((v_data) - PAGE_OFFSET + PLAT_PHYS_OFFSET) - \
> +	 ((v_text) - XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR) + \
> +          CONFIG_XIP_PHYS_ADDR))

Sure, this is less opaque.

>  #else
> -#define PHYS_OFFSET_FIXUP 0
> +#define PHYS_RELATIVE(v_data, v_text) (v_data) - (v_text)

You should probably surround the whole thing with parents in case this 
gets used in some other computations.


Nicolas