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

[Mike Frysinger]

On Tuesday 17 March 2009 14:13:39 Kumar Gala wrote:
> >>> 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.

i never said Scott's proposed change was wrong
-mike
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