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Date: Sat, 23 Jun 2001 16:17:36 -0400 (EDT)
From: Zhihui Zhang <zzhang@cs.binghamton.edu>
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To: freebsd-questions@freebsd.org
Subject: sbrk() and segment fault
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Out of curiosity, I tried the following program on FreeBSD 4.3-Release:

#include <stdio.h>
#include <unistd.h>
main()
{
	char * ret, * endpt;

	endpt = sbrk(0);
	printf("endpt = %x after sbrk\n", (int)endpt);

#if 1
	ret = brk(endpt);
	if (ret == (char *) -1) {
		printf("brk of %x failed\n", endpt);
		exit(0);
	}

#endif
	printf("brk of %x succeed\n", (int)endpt);
}
dell# cc sbrk2.c; a.out
endpt = 8049708 after sbrk
Segmentation fault (core dumped)

If I change #if 1 to #if 0, then it runs OK. So why brk() to the SAME
address can cause problem?  Is it some roundup done in obreak() in
vm_unix.c?  Or maybe my understanding of break is not complete. Thanks for
any help.

-Zhihui


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