[U-Boot] [PATCH] arm: fix exception vectors

[Luca Ellero <luca.ellero@brickedbrain.com>]

Hi Albert,

On 19/01/2015 11:28, Albert ARIBAUD wrote:
> Hello Luca,
>
> On Mon, 19 Jan 2015 11:11:34 +0100, Luca Ellero
> <luca.ellero@brickedbrain.com> wrote:
>> Hi Albert,
>>
>> On 17/01/2015 07:40, Albert ARIBAUD wrote:
>>> Hello Luca,
>>>
>>> On Mon, 29 Dec 2014 16:10:53 +0100, Luca Ellero
>>> <luca.ellero@brickedbrain.com> wrote:
>>>> After relocation, exception vectors still point to the old code (not relocated).
>>>> This patch fixes them.
>>>>
>>>> Signed-off-by: Luca Ellero <luca.ellero@brickedbrain.com>
>>>> ---
>>>>    arch/arm/lib/relocate.S |   15 +++++++++++++++
>>>>    1 file changed, 15 insertions(+)
>>>>
>>>> diff --git a/arch/arm/lib/relocate.S b/arch/arm/lib/relocate.S
>>>> index 92f5314..4186344 100644
>>>> --- a/arch/arm/lib/relocate.S
>>>> +++ b/arch/arm/lib/relocate.S
>>>> @@ -76,6 +76,21 @@ copy_loop:
>>>>    	blo	copy_loop
>>>>
>>>>    	/*
>>>> +	 * fix exception vectors
>>>> +	 */
>>>> +	ldr r2, =_undefined_instruction
>>>> +	ldr r3, =_fiq
>>>> +	add	r2, r2, r4
>>>> +	add	r3, r3, r4
>>>> +fix_exceptions:
>>>> +	ldr r0, [r2]
>>>> +	add	r0, r0, r4
>>>> +	str	r0, [r2]
>>>> +	cmp r2,r3
>>>> +	add r2, #4
>>>> +	blo fix_exceptions
>>>> +
>>>> +	/*
>>>>    	 * fix .rel.dyn relocations
>>>>    	 */
>>>>    	ldr	r2, =__rel_dyn_start	/* r2 <- SRC &__rel_dyn_start */
>>>> --
>>>> 1.7.10.4
>>>>
>>>
>>> There is already a mechanism to relocate vectors (do a git grep for
>>> 'relocate_vectors' which takes into account various ISA and SoC cases.
>>>
>>> Can you describe the use case which you are encountering?
>>
>> As far as I can see the mechanism to relocate vectors is implemented
>> only on iMX25/27 and involves high vectors address (0xFFFFxxxx).
>
> You are correct that the mechanism is /used/ only by mx25 and mx27.
>
> However, it has been introduced to support /all/ SoCs (or even boards),
> not only mx25, mx27, and /all/ exception vector handling scenarios, not
> only high vectors addresses.
>
> Actually, the standard high and low address is handled by default,
> and mx25 and mx27 are cases where this default is overriden /because/
> high or low vector addresses are *unapplicable* for them due to their
> memory mapping.
>
>> The problem is that, after relocation, U-Boot doesn't fix the vector
>> table addresses, they still point to the old addresses (before relocation).
>> This is wrong and this patch fixes them to point to the new addresses.
>
> You are right about the problem, and this problem is exactly what the
> relocate_vectors mechanism is here to fix -- exactly the same problem
> mx25 and mx27 had before we fixed it (quite recently actually, as it
> was done mid-November, between 2015.01-rc1 and 2015.01-rc1 rc2).
>
>> I had to use this patch trying to implement IRQ support for a Freescale
>> iMX6 board. iMX6 does not provide RAM at the high vectors address and
>> trying to access them leads to errors, so I couldn't use them.
>
> This is *exactly* the case where you should define your own version of
> relocate_vectors (probably at SoC level).
>

Ok, I will try to implement it as you suggested.
Thank you
regards
Luca


-- 
Luca Ellero

E-mail: luca.ellero at brickedbrain.com
Internet: www.brickedbrain.com