Re: [Xen-devel] [PATCH] xen/arm: Correctly support WARN_ON

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 07/03/2014 11:30 AM, Ian Campbell wrote:
> On Tue, 2014-07-01 at 19:51 +0100, Julien Grall wrote:
> 
>> TODO:
>> I haven't yet hook the code on ARM64 as I'm not sure how undefined
>> instruction are handled. It looks like there is multiple way to get it
>> via HSR.
> 
> I think EC==0x00 (the catchall) is where it will end up "The attempted
> execution of an instruction bit patterns that has no allocated
> instruction at the current Exception level".

So if EC==0x00 I can safely assume this is a undefined instruction
exception, right?

>> +/* ARM doesn't provide any undefined instruction, make our own based on
>> + * a combination of bits which is not used by the instruction set
>> + */
>> +#define BUG_INSTR 0xe7f000f0
> 
> Linux uses 0xe7f001f2. I'm not sure what the difference is but it seems
> safer to follow suit.

Linux uses multiple different undefined opcode (bug, debugger,...). This
value is already used in Xen by dump_execution_state (see
include/asm-arm/processor.h).

I don't see why we should change it.

Regards,

-- 
Julien Grall

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