Re: [PATCH] xen/arm: Init traps very early

[Julien Grall <julien.grall@linaro.org>]

Hi Andrew,

On 05/28/2014 02:49 PM, Andrew Cooper wrote:
> On 28/05/14 14:33, Julien Grall wrote:
>> The function init_traps setups the handler taken when Xen hits a BUG_ON/ASSERT.
>>
>> If an error happen before init_traps is called, we loose the backtrace.
>>
>> As the function doesn't require any specific setup, we can call it just
>> after Xen has jumped in C code.
>>
>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>> ---
>>  xen/arch/arm/setup.c |    3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
>> index b9ce7a9..5bf8686 100644
>> --- a/xen/arch/arm/setup.c
>> +++ b/xen/arch/arm/setup.c
>> @@ -666,6 +666,7 @@ void __init start_xen(unsigned long boot_phys_offset,
>>      struct domain *dom0;
>>  
>>      setup_cache();
>> +    init_traps();
> 
> Having recently redone this in x86, it must be after
> set_processor_id(0), set_current() for debug sanity, and after
> percpu_init_areas() for future proofing.

Even though it doesn't harm to call before (the stack will be
corrupted), I agree to call init_traps after set_processor_id(0), and
therefore percpu_init_areas.

But we don't need to have set_current correctly set up. The trap entries
won't save anything about the guest if the exception are taken from HYP
mode.

-- 
Julien Grall