Messages in this thread | | | Date | Thu, 1 Jul 2004 11:37:27 -0500 | From | Matt Mackall <> | Subject | Re: [OT] Testing PROT_NONE and other protections, and a surprise |
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On Thu, Jul 01, 2004 at 11:01:52AM -0400, Kyle Moffett wrote: > On Jul 01, 2004, at 10:50, Jamie Lokier wrote: > >Kyle Moffett wrote: > >>>The error code is -1, aka. MAP_FAILED. > >>Oops! I guess I was just lucky that part didn't fail :-D On the > >>other hand, it couldn't legally return 0 anyway, could it? > > > >Yes it could -- if you request a mapping at address 0 with MAP_FIXED. > >A few OSes won't do that, but Linux and many others will. > > That allows untrapped dereferencing of a NULL pointer. IMHO, that > would be a very unintelligent thing for a program to do, to deny itself > the bug-catching features provided therein, but it's interesting to see > that it is possible.
A typical use is vm86-based emulation of 16-bit DOS where there's data in the immediate vicinity of NULL.
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