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- From: dswartz@sw.stratus.com (Dan Swartzendruber)
- Newsgroups: comp.arch
- Subject: Re: branch-and-link
- Date: 28 Dec 1992 04:49:40 GMT
- Organization: Stratus Computer, Inc.
- Lines: 15
- Distribution: world
- Message-ID: <1hm114INN6v2@transfer.stratus.com>
- References: <1hkqk3INNsns@transfer.stratus.com> <1hlll9INNe0s@uwm.edu> <1hm0cpINN8nf@darkstar.UCSC.EDU>
- NNTP-Posting-Host: redondo.sw.stratus.com
-
- On a related note (vis-a-vis debugging ease) to the branch-and-link issue, another peeve
- I've always had is that no commercially available processors (that I know of) make NULL
- pointer detection easy withou serious run-time overhead. Various OS's try by unmapping
- the first N pages of memory, which works fine until you run into a chip like the 68030,
- which supports huge displacements. Not to mention if the index register pushes the
- effective address out of your protected window, you're hosed. If you have a standard
- base_reg+index_reg+disp format, it would seem to me that having the processor check the
- base register for NULL and faulting if it is wouldn't be that hard (or inefficient).
- Especially if NULL happens to be zero on that machine.
-
- --
-
- #include <std_disclaimer.h>
-
- Dan S.
-