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Message-ID: <20170814171338.gvtn76awussgxctn@armageddon.cambridge.arm.com>
Date: Mon, 14 Aug 2017 18:13:39 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org, keescook@...omium.org,
ard.biesheuvel@...aro.org, matt@...eblueprint.co.uk,
kernel-hardening@...ts.openwall.com, will.deacon@....com,
linux-kernel@...r.kernel.org, luto@...capital.net,
james.morse@....com, labbott@...hat.com
Subject: Re: [PATCH 10/14] arm64: assembler: allow adr_this_cpu to use the
stack pointer
On Mon, Aug 07, 2017 at 07:36:01PM +0100, Mark Rutland wrote:
> From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>
> Given that adr_this_cpu already requires a temp register in addition
> to the destination register, tweak the instruction sequence so that sp
> may be used as well.
>
> This will simplify switching to per-cpu stacks in subsequent patches. While
> this limits the range of adr_this_cpu, to +/-4GiB, we don't currently use
> adr_this_cpu in modules, and this is not problematic for the main kernel image.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> [Mark: add more commit text]
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: Will Deacon <will.deacon@....com>
> ---
> arch/arm64/include/asm/assembler.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index 610a420..4775af5 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -235,7 +235,8 @@
> * @tmp: scratch register
> */
> .macro adr_this_cpu, dst, sym, tmp
> - adr_l \dst, \sym
> + adrp \tmp, \sym
> + add \dst, \tmp, #:lo12:\sym
> mrs \tmp, tpidr_el1
> add \dst, \dst, \tmp
> .endm
Nitpick: it may be worth adding an #ifndef MODULE around these macros,
together with a comment, just in case. There are other macros in this
file like adr_l which are used in modules (crypto).
--
Catalin
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