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Date: Mon, 4 Sep 2017 12:50:32 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
cc: linux-arm-kernel@...ts.infradead.org, kernel-hardening@...ts.openwall.com, 
    Arnd Bergmann <arnd@...db.de>, Russell King <linux@...linux.org.uk>, 
    Kees Cook <keescook@...omium.org>, Thomas Garnier <thgarnie@...gle.com>, 
    Marc Zyngier <marc.zyngier@....com>, Mark Rutland <mark.rutland@....com>, 
    Tony Lindgren <tony@...mide.com>, Matt Fleming <matt@...eblueprint.co.uk>, 
    Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v2 11/29] ARM: head.S: use PC relative insn sequence to
 calculate PHYS_OFFSET

On Sun, 3 Sep 2017, Ard Biesheuvel wrote:

> Replace the open coded arithmetic with a simple adr_l/sub pair. This
> ensures these quantities are invariant under runtime relocation.
> 
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

Of course there won't be anything to relocate in a XIP kernel. But 
consistency is good and this looks nicer.

Acked-by: Nicolas Pitre <nico@...aro.org>

> ---
>  arch/arm/kernel/head.S | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index f607e290ef4b..62c961849035 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -106,10 +106,8 @@ ENTRY(stext)
>  #endif
>  
>  #ifndef CONFIG_XIP_KERNEL
> -	adr	r3, 2f
> -	ldmia	r3, {r4, r8}
> -	sub	r4, r3, r4			@ (PHYS_OFFSET - PAGE_OFFSET)
> -	add	r8, r8, r4			@ PHYS_OFFSET
> +	adr_l	r8, _text			@ __pa(_text)
> +	sub	r8, r8, #TEXT_OFFSET		@ PHYS_OFFSET
>  #else
>  	ldr	r8, =PLAT_PHYS_OFFSET		@ always constant in this case
>  #endif
> @@ -161,10 +159,6 @@ ENTRY(stext)
>  1:	b	__enable_mmu
>  ENDPROC(stext)
>  	.ltorg
> -#ifndef CONFIG_XIP_KERNEL
> -2:	.long	.
> -	.long	PAGE_OFFSET
> -#endif
>  
>  /*
>   * Setup the initial page tables.  We only setup the barest
> -- 
> 2.11.0
> 
> 

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