Message-ID: <4C97BD6B.8090900@budcat.com>
Date: Mon, 20 Sep 2010 15:00:43 -0500
From: Heath Kehoe <hkehoe@budcat.com>
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To: "cygwin@cygwin.com" <cygwin@cygwin.com>
Subject: Problem with mmap in latest snapshot
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  My application uses mmap on a 16MB file. On released 1.7.7, there's no 
problem. But with the 20100919 snapshot, it crashes when it tries to 
access the mmap space past the first 32KB or so. Attached is a simple 
test program that illustrates the problem.

***** With 1.7.7 *****

$ uname -a
CYGWIN_NT-6.1-WOW64 hkehoe1 1.7.7(0.230/5/3) 2010-08-31 09:58 i686 Cygwin

$ ./a
creating mmap-test-file
Writing zeros
mmap-ing
writing ones to mmap region
done!

$ ls -l mmap*
-rw-r--r--+ 1 hkehoe Domain Users 16777216 2010-09-20 14:51 mmap-test-file

$ od -tc mmap-test-file
0000000 001 001 001 001 001 001 001 001 001 001 001 001 001 001 001 001
*
100000000

***** With snapshot *****

$ uname -a
CYGWIN_NT-6.1-WOW64 hkehoe1 1.7.8s(0.231/5/3) 20100919 16:19:37 i686 Cygwin

$ ./a
creating mmap-test-file
Writing zeros
mmap-ing
writing ones to mmap region
Segmentation fault (core dumped)

$ od -tc mmap-test-file
0000000 001 001 001 001 001 001 001 001 001 001 001 001 001 001 001 001
*
0100000  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
100000000


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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/mman.h>

#define MMAP_FILE "mmap-test-file"
#define MMAP_SIZE 16384*1024

main()
{
	int fd;
	char* maddr;

	printf("creating " MMAP_FILE "\n");
	fd = open(MMAP_FILE, O_CREAT|O_TRUNC|O_RDWR, 0666);
	if(fd < 0)
	{
		perror("Could not open " MMAP_FILE);
		exit(1);
	}

	printf("Writing zeros\n");
	{
		int n = MMAP_SIZE;
		char buf[1024];
		memset(buf, 0, 1024);
		while(n > 0)
		{
			write(fd, buf, 1024);
			n -= 1024;
		}
	}
	
	printf("mmap-ing\n");
	maddr = mmap(NULL, MMAP_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
	if(maddr == NULL || maddr == MAP_FAILED)
	{
		perror("mmap");
		exit(1);
	}

	printf("writing ones to mmap region\n");
	{
		int n;
		for(n = 0; n < MMAP_SIZE; n++)	
			maddr[n] = 1;
	}

	printf("done!\n");
}


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