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/* klaar@ida
Create a buffer that spans invalid pages. Used to check memory
verification.
*/
#include <stdio.h>
#include <stdlib.h>
#include <syscall.h>
/* global variables are placed by the compiler in the process image,
* among the initialized variables
* the process image is loaded at the bottom of the virtual memory space
*/
char global = 0;
int main (int argc, char *argv[])
{
/* local variables are allocated on the proces stack during runtime
* the stack is at top of the virtual memory space
*/
char local = 0;
int fd;
int count;
unsigned l, g;
/* both adresses will of course be valid */
printf("global: %p\n", &global);
printf("local : %p\n", &local);
/* and a pointer starting at the global variable adress, and ending
* at the local variable addres will have valid start and end
* but will all addresses (about 3 GB) inbetween be valid?
*/
l = (unsigned)&local;
g = (unsigned)&global;
printf("size : %u MiB\n", (l - g)/1024/1024);
create("somefile", 1000);
fd = open("somefile");
/* this tries to use the buffer (it should fail verification) */
count = read(fd, &global, (l - g + 1));
printf("read %i out of %u bytes\n", count, (l - g + 1));
/* this tries to use a buffer probably ending before the stack */
count = read(fd, &global, (l - g + 1) - 4096);
printf("read %i out of %u bytes\n", count, (l - g + 1) - 4096);
close(fd);
return 0;
}
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