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From: steele@unc.cs.unc.edu (Oliver Steele)
Newsgroups: comp.sys.mac
Subject: Re: What is wrong with the Sumacc C compiler
Message-ID: <1960@unc.cs.unc.edu>
Date: Mon, 9-Nov-87 18:46:02 EST
Article-I.D.: unc.1960
Posted: Mon Nov  9 18:46:02 1987
Date-Received: Wed, 11-Nov-87 21:24:12 EST
References: <7486@dartvax.UUCP> <7508@dartvax.UUCP> <21522@ucbvax.BERKELEY.EDU> <2283@watcgl.waterloo.edu>
Reply-To: steele@unc.UUCP (Oliver Steele)
Organization: University of North Carolina, Chapel Hill
Lines: 29
Keywords: C compiler gripe

kdmoen@watcgl.waterloo.edu (Doug Moen) writes:
>oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster) writes:
>...concerning why the sumacc compiler is no good...
>>The authors of the compiler seem to be unaware that on a Macintosh
>>executable code can move while the program is running. Unlike all Macintosh
>>compilers, they generate position _dependent_ code, and have a funky
>>loader scheme to resolve non-relocatable references at program load
>>time. Eventually, the code moves, and all that position dependent code
>>points at never-neverland.
>
>Sorry, but this sounds blatantly impossible.

Take a look at UnloadSeg().

>If the code were to move
>while the program is running, then *all of the return addresses and
>function pointers on the stack would become invalid* and the program
>would crash, regardless of what compiler was used to create the program.

That's why it's dangerous to call UnloadSeg() on segments that have live
routines.  The Sumacc compiler just makes it dangerous to call it on
segments that have ever been used, as well.

------------------------------------------------------------------------------
Oliver Steele				  ...!{decvax,ihnp4}!mcnc!unc!steele
							steele%unc@mcnc.org

  "When you believe in a loving God, life appears to be very funny."
							-- Garrison Keillor