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Article View: comp.std.c
Article #771

Re: Out-of-bounds pointers

#771
From: Doug Gwyn
Date: Tue, 17 Oct 1989 05:11
21 lines
1829 bytes
In article <252@bbxsda.UUCP> scott@bbxsda.UUCP (Scott Amspoker) writes:
>While I fully agree that a pointer to "expired" stack data is to
>be considered "invalid" I am not aware of any implementation that
>actually removes stack memory from the memory map upon exit from
>a procedure.  That would probably slow things down considerably.
>Dereferencing such a pointer would be meaningless but would probably
>not cause a trap (although such a program is certainly headed for a
>trap :-)

Again, the question is NOT about dereferencing the pointer value,
but rather about accessing the now-invalid pointer value at all.

On the same general class of architectures for which it would be a
problem for free()d pointers, it could easily be a problem for
expired activation records (what you would probably call a "stack
frame", but in a true segmented architecture an activation record
is a separate system-controlled object in its own right, normally
reclaimed by the system immediately upon expiration of its
dynamic scope).  I don't know of any C compilers for the B[56]x00
family of computers, but of there are any I would expect them to
exhibit this behavior.
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References: <1009@mtxinu.UUCP> <12570028@hpclwjm.HP.COM> <868@crdos1.crd.ge.COM> <217@bbxsda.UUCP> <1989Oct7.131404.656@jarvis.csri.toronto.edu> <220@bbxsda.UUCP> <1989Oct10.163732.3241@jarvis.csri.toronto.edu> <240@bbxsda.UUCP> <MEISSNER.89Oct14124500@tiktok.rtp.dg.

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uakari.primate.wisc.edu!aplcen!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.std.c
Subject: Re: Out-of-bounds pointers
Message-ID: <11319@smoke.BRL.MIL>
Date: 17 Oct 89 05:11:18 GMT
References: <1009@mtxinu.UUCP> <12570028@hpclwjm.HP.COM> <868@crdos1.crd.ge.COM> <217@bbxsda.UUCP> <1989Oct7.131404.656@jarvis.csri.toronto.edu> <220@bbxsda.UUCP> <1989Oct10.163732.3241@jarvis.csri.toronto.edu> <240@bbxsda.UUCP> <MEISSNER.89Oct14124500@tiktok.rtp.dg.
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 21