On Thu, Dec 13, 2012 at 10:42:28AM -0800, H. Peter Anvin wrote:
> On 12/13/2012 10:37 AM, Borislav Petkov wrote:
> >>
> >> If appropriate, the code could be changed to
> >>
> >> (void *)(unsigned long)m->ip
> >
> > Can we explicitly cast it to what it is so that we can be explicit as to
> > what we're casting it? IOW:
> >
> > (void *)(__u64)m->ip;
> >
> > Does that even work on 32bit?
> >
> > Also, does the compiler bitch about this useless cast when building with
> > W=123?
> >
>
> Uh... no.
>
> The point is that (void *)(unsigned long) casts it to an integer of
> pointer size -- in userspace you would to (void *)(size_t) or (void
> *)(uintptr_t) -- so that the compiler knows "I meant to do that."
Ok, I grok it now. So, in most cases, mce.ip comes from pt_regs.ip which
is unsigned long so we're fine for both 32- and 64-bit. There's only the
case with precise RIP reporting where we get the rip from an MSR but
even then, it should be 4 bytes on 32-bit since our addresses there are
4 bytes.
So, actually struct mce should've had ->ip defined as an unsigned long
from the very beginning. But we can't change that now because this
struct is shared with userspace :(
So yes Joe, make it (void *)(unsigned long).
Thanks guys.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
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