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Message-ID: <20140528112738.GE15222@arm.com>
Date: Wed, 28 May 2014 12:27:38 +0100
From: Will Deacon <will.deacon@....com>
To: Larry Bassel <larry.bassel@...aro.org>
Cc: Catalin Marinas <Catalin.Marinas@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
"khilman@...aro.org" <khilman@...aro.org>
Subject: Re: [PATCH v5 1/2] arm64: adjust el0_sync so that a function can be
called
Hi Larry,
On Mon, May 26, 2014 at 07:56:12PM +0100, Larry Bassel wrote:
> To implement the context tracker properly on arm64,
> a function call needs to be made after debugging and
> interrupts are turned on, but before the lr is changed
> to point to ret_to_user(). If the function call
> is made after the lr is changed the function will not
> return to the correct place.
>
> For similar reasons, defer the setting of x0 so that
> it doesn't need to be saved around the function call
> (save far_el1 in x26 temporarily instead).
>
> Signed-off-by: Larry Bassel <larry.bassel@...aro.org>
[...]
> @@ -476,23 +481,27 @@ el0_undef:
> // enable interrupts before calling the main handler
> enable_dbg_and_irq
> mov x0, sp
> + adr lr, ret_to_user
> b do_undefinstr
> el0_dbg:
> /*
> * Debug exception handling
> */
> tbnz x24, #0, el0_inv // EL0 only
> - mrs x0, far_el1
> + mrs x26, far_el1
> + mov x0, x26
> mov x1, x25
> mov x2, sp
> bl do_debug_exception
> enable_dbg
> + mov x0, x26
> b ret_to_user
Why have you added this mov instruction?
Will
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