On Tue, 23 Aug 2005, Ulrich Drepper wrote:
>
> Linus Torvalds wrote:
> >
> > Especially if you use MAP_SHARED, you don't even need to mprotect
> > anything: you'll get a nice SIGBUS if you ever try to access past the last
> > page that maps the file.
>
> If you guarantee this (and test for this) it's fine with me.
It's how the kernel _should_ work, but very few apps seem to depend on it,
so no guarantees. I looked over the code, and I think we've lost the
SIGBUS thing.
Basically, if you don't ever access past the end, you should always be ok.
If you access past the end, at least some _really_ old kernel versions
will zero-fill the page with an anonymous page and lose coherency, while
more modern kernels should _either_ cause a SIGBUS or alternatively at
least have a coherent zero-filled page.
Linus
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