linux-kernel - Re: [PATCH] ARM: head-common.S: Clear lr before jumping to start

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Message-ID: <nycvar.YSQ.7.76.1710031134140.5407@knanqh.ubzr>
Date:   Tue, 3 Oct 2017 11:37:20 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
cc:     Russell King <linux@...linux.org.uk>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Chris Brandt <Chris.Brandt@...esas.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: head-common.S: Clear lr before jumping to
 start_kernel()

On Tue, 3 Oct 2017, Geert Uytterhoeven wrote:

> If CONFIG_DEBUG_LOCK_ALLOC=y, the kernel log is spammed with a few
> hundred identical messages:
> 
>     unwind: Unknown symbol address c0800300
>     unwind: Index not found c0800300
> 
> c0800300 is the return address from the last subroutine call (to
> __memzero()) in __mmap_switched().  Apparently having this address in
> the link register confuses the unwinder.
> 
> To fix this, reset the link register to zero before jumping to
> start_kernel().
> 
> Fixes: 9520b1a1b5f7a348 ("ARM: head-common.S: speed up startup code")
> Suggested-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Good! This fixes another similar case I had but I didn't come around to 
look at closely yet.

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

Please send it to RMK's patch system.


> ---
> Commit 9520b1a1b5f7a348 is in arm/for-next.
> 
>  arch/arm/kernel/head-common.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
> index a25027b87a6024b9..21dde771a7dd8d14 100644
> --- a/arch/arm/kernel/head-common.S
> +++ b/arch/arm/kernel/head-common.S
> @@ -114,6 +114,7 @@ __mmap_switched:
>  	str	r8, [r2]			@ Save atags pointer
>  	cmp	r3, #0
>  	strne	r10, [r3]			@ Save control register values
> +	mov	lr, #0
>  	b	start_kernel
>  ENDPROC(__mmap_switched)
>  
> -- 
> 2.7.4
> 
>