[U-Boot] [PATCH] 8313erdb: Set guarded bit on BAT that covers the end of the address space.

[Kumar Gala]

>>> if C code is doing ptr checks, the compiler should make sure that
>>> pointer is not dereferenced at all if the hardware cannot suffer the
>>> consequences, even speculatively.
>>
>> There is no reasonable way for the compiler to prevent such  
>> speculative
>> accesses.  Non-memory-like mappings must have the guarded bit set.   
>> That
>> is what the bit is there for.
>
> if the hardware doesnt have a way of preventing it, then the  
> compiler must nop
> bad accesses that are unknown.
>
> i'm not sure your example proves your position.  if you have a  
> region that
> cannot stand speculative access, how do you handle bad pointer  
> checking if the
> compiler may generate code that'll speculatively hit it at any time ?

This has nothing to do w/the compiler but how HW speculation actually  
works.

If you don't understand that say so and ask about it.. Dont try and  
claim Scott's example and patch aren't valid because they are.

- k