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    SubjectRe: mmap bug?

    On Fri, 29 May 1998, Matthew Kirkwood wrote:

    > On Fri, 29 May 1998, Natarajan Krishnaswami wrote:
    > > [someone] wrote:
    > > >> It seems that attempts to mmap a region of size zero causes
    > > >> mmap to return zero. Is this a bug?
    > > >>
    > > >> Since it doesn't return -1, it looks like success, but of
    > > >> course dereferencing this NULL pointer causes a crash.
    > >
    > > Zero is a multiple of the page size, so there is no partial page mapped:
    > > the map is empty. Returning a pointer which may not be dereferenced
    > > seems reasonable. However, mmap is explicitly forbidden from returning
    > > 0, and SIGBUS would probably be the correct signal to deliver if an
    > > address in a 0-length map were dereferenced.
    > Thank you.
    > I was surprised at the number of people prepared to tell me not to
    > mmap zero length areas. Here's a trivial patch to fix this, although
    > I don't know if this will affect many programs.

    I'm surprised that you never answered the important question: If you're
    mapping 0 bytes then how the hell do you get a SEGV? You shouldn't be
    referencing anything at the address. Your program is at fault as much or
    more than linux. (I can't find a reference which claims that 0 is not a
    valid response.)


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