linux-kernel - Re: [RFC PATCH 1/3] arm64: entry: Remove unnecessary calculation for S

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Message-ID: <20150907145646.GB13786@leverpostej>
Date:	Mon, 7 Sep 2015 15:56:47 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Jungseok Lee <jungseoklee85@...il.com>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave P Martin <Dave.Martin@....com>,
	James Morse <James.Morse@....com>
Subject: Re: [RFC PATCH 1/3] arm64: entry: Remove unnecessary calculation for
 S_SP in EL1h

On Fri, Sep 04, 2015 at 03:23:05PM +0100, Jungseok Lee wrote:
> Under EL1h, S_SP data is not seen in kernel_exit. Thus, x21 calculation
> is not needed in kernel_entry. Currently, S_SP information is vaild only
> when sp_el0 is used.

I don't think this is true. The generic BUG implementation will grab the
saved SP from the pt_regs, and with this change we'll report whatever
happened to be in x21 instead.

> Signed-off-by: Jungseok Lee <jungseoklee85@...il.com>
> ---
>  arch/arm64/kernel/entry.S | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index e163518..d23ca0d 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -91,8 +91,6 @@
>  	get_thread_info tsk			// Ensure MDSCR_EL1.SS is clear,
>  	ldr	x19, [tsk, #TI_FLAGS]		// since we can unmask debug
>  	disable_step_tsk x19, x20		// exceptions when scheduling.
> -	.else
> -	add	x21, sp, #S_FRAME_SIZE
>  	.endif
>  	mrs	x22, elr_el1
>  	mrs	x23, spsr_el1

Immediately after this we do:

	stp     lr, x21, [sp, #S_LR]

To store the LR and SP to the pt_regs which bug_handler would use.

Am I missing smoething?

Thanks,
Mark.
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