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Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!seismo!mcnc!ethos!ducall!jeff
From: jeff@ducall.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Bug in link - I think there's something to this!
Message-ID: <373@ducall.UUCP>
Date: Thu, 12-Mar-87 20:34:32 EST
Article-I.D.: ducall.373
Posted: Thu Mar 12 20:34:32 1987
Date-Received: Sat, 14-Mar-87 10:02:51 EST
Organization: none
Lines: 56

[]

Someone wrote recently about a problem with static arrays declared in
different modules.  Amazing cooincidence, I just came across the same
type of problem with a static array in one module and malloced memory
in another.  

The code goes something like the following.  The compiler is Microsoft
C.  Procedures foo and bar are in different files.  Both are compiled
using the large memory model.  They are two procedures in a rather large
application, consisting of roughly 20 files and 200 procedures.

struct BAR *first_link;

foo()
{
	char *malloc();
	struct BAR *next_link;

	first_link = (struct BAR *)malloc(sizeof(struct BAR));
	next_link = first_link;
	while (!done) {
		next_link->next = (struct BAR *)malloc(sizeof(struct BAR));
		next_link = next_link->next;
	}
}

bar()
{
	static char my_strings[10][128];
	int i;

	for (i = 0; i < 128; i++)
		strcpy(my_strings[i],"STUNKY FLUFF\n");
}

I am using the large memory model (I don't know if the problem persists
in other models).  The MSC User's Guide implies that the compiler puts
my_strings in a _BSS segment.  When I run the program procedure foo
allocates memory, and runs right over the area that should have been
reserved for my_strings.  When bar executes, of course, the list structure
is destroyed, as well as their contents, and the memory management info
(i.e. program crashes in spectacular flames).

As was the experience with the former observer, when I initialize my_strings
the problem goes away - obviously because the compiler moves the array from
the BSS section to the (initialized) data segment.  This, however, is a
kludge not a solution!  Am I doing something wrong, or is there a bug in
MSC malloc() such that (at least in the large memory model) one cannot
have uninitialized global or static data.


-- 
Jeffrey William Gillette          uucp: mcnc!ethos!ducall!jeff 
Humanities Computing Facility     bitnet: DYBBUK at TUCCVM
Duke University