[PATCH] ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP

[catalin.marinas@arm.com (Catalin Marinas)]

2011/5/23 M?ns Rullg?rd <mans@mansr.com>:
> Catalin Marinas <catalin.marinas@arm.com> writes:
>
>> On Mon, 2011-05-23 at 14:21 +0100, Russell King - ARM Linux wrote:
>>> On Mon, May 23, 2011 at 12:16:48PM +0100, Catalin Marinas wrote:
>>> > Newer versions of gcc generate unaligned accesses by default, causing
>>> > kernel panics when CONFIG_ALIGNMENT_TRAP is enabled. This patch adds the
>>> > -mno-unaligned-access option to gcc.
>>>
>>> This description doesn't make sense. ?If we have alignment traps enabled,
>>> then we _expect_ to fix up unaligned loads and stores.
>>>
>>> Therefore there should be no panic if CONFIG_ALIGNMENT_TRAP is enabled.
>>>
>>> So what's the _actual_ problem that this is trying to address? ?What's
>>> the panic/oops look like? ?And that information should be in the commit
>>> description _anyway_.
>>
>> OK, not clear from my commit log. See below for details (I'll add them
>> to the log):
>>
>> http://www.codesourcery.com/archives/arm-gnu/msg04202.html
>>
>> Basically the fault happens before we call alignment_init(). There are
>> other ways to fix this issue (like initialising the alignment handler
>> earlier).
>
> The reset value of SCTLR.A is 0 on ARMv7. ?Something must be setting it
> to 1 early, before the alignment trap handler is initialised. ?This
> something is what needs to be changed.

It is set to 1 in __enable_mmu in head.S.

-- 
Catalin