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From: conrad@CGL.UCSF.EDU (Conrad Huang)
Newsgroups: mod.computers.vax
Subject: VAX C help needed
Message-ID: <8609060037.AA23826@cgl.ucsf.edu>
Date: Fri, 5-Sep-86 20:37:57 EDT
Article-I.D.: cgl.8609060037.AA23826
Posted: Fri Sep  5 20:37:57 1986
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I've been trying to port ex/vi from 4.3BSD Unix to 4.3VMS (with VAX C
V2.0-003) for the past two weeks.  Ex/vi is a Unix editor written entirely
in C.  One of the problems that I ran into while porting it was getting
access violations at strange places.  Ex/vi uses sbrk() and brk() exclusively
for memory management (there is no reference anywhere to malloc(), free(),
etc).  It also uses two files for temporary storage.  The sequence of event
that lead up to the access violation is as follows:

	open(temp_file_1)
	sbrk(xxx);
	end1 = sbrk(0);
	... lots of processing ...
	open(temp_file_2)
	... more processing with I/O to temp_file_2...
	end2 = sbrk(yyy);
	... copy data to "end1"
	-> ACCESS VIOLATION
		VIRTUAL ADDRESS = end1

If I do not use temp_file_2 (delete the open and I/O), then I do *not*
get the access violation.  I suspect the problem is that opening the
second file somehow allocates memory starting at "end1" and makes it
somehow outside the legal addressing space.  Would anyone who knows
about VAX C innards please let me know whether this is correct?  I'm
completely baffled as to how to fix this problem and would greatly
appreciate any pointers.  Thanks,

Conrad

PS	I've moved the second "open" call around in the code.  It doesn't
matter where it appears.  As long as the second "open" is present, the
program bombs out with an ACCESS VIOLATION sooner or later.