memcheck/tests/pointer-trace.c

/* 
   Make sure that leak-check's pointer tracing avoids traps, i.e. tricky
   memory areas where it could crash if not careful.
 */

#include <stdio.h>
#include "memcheck/memcheck.h"
#include "tests/sys_mman.h"
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>

#if !defined(MAP_NORESERVE)
#  define MAP_NORESERVE 0
#endif

int main()
{
	char **volatile ptrs;
	int i;
	int fd;
	char *map;

	/* I _think_ the point of this is to fill ptrs with a pointer
	   to every 4th page in the entire address space, hence
	   guaranteeing that at least one of them points into one of
	   the below traps, and so checks that the leak checker
	   doesn't bomb when following them.  That's fine on 32-bit
	   platforms, but hopeless for a 64-bit system.  So the
	   following settings do achieve that on a 32-bit target but
	   merely make a 64-bit target give the same output without
	   properly testing it. */
        int ptrbits, stepbits, stepsize, nptrs;
	if (sizeof(void*) == 8) {
           /* 64-bit machine */
	   ptrbits = 32;   //bogus
           stepbits = 14+1;  //bogus
	   stepsize = (1 << stepbits);
	   nptrs = 1 << (ptrbits - stepbits);
	} else {
           /* 32-bit machine */
	   ptrbits = 32;
           stepbits = 14;
	   stepsize = (1 << stepbits);
	   nptrs = 1 << (ptrbits - stepbits);
	}

	ptrs = malloc(nptrs * sizeof(char *));
	for (i = 0; i < nptrs; i++)
		ptrs[i] = (char *)((long)i << stepbits);

	/* lay some traps */
        /* non-RWX memory, and MAP_NORESERVE if present */
	map = mmap(0, stepsize * 2, PROT_NONE, MAP_PRIVATE|MAP_NORESERVE|MAP_ANONYMOUS, -1, 0);
	if (map == (char *)-1)
		perror("trap 1 failed");

        /* write-only memory, and MAP_NORESERVE if supported */
	map = mmap(0, stepsize * 2, PROT_WRITE, MAP_PRIVATE|MAP_NORESERVE|MAP_ANONYMOUS, -1, 0);
	if (map == (char *)-1)
		perror("trap 2 failed");

	/* non-zero mmap of a zero-length file -> SIGBUS */
	fd = open("./pointer-trace-test-file", O_RDWR | O_CREAT | O_EXCL, 0600);
	unlink("./pointer-trace-test-file");
	map = mmap(0, stepsize * 2, PROT_WRITE|PROT_READ, MAP_PRIVATE, fd, 0);
	if (map == (char *)-1)
		perror("trap 3 failed");
	//printf("trap 3 = %p-%p\n", map, map+stepsize*2);

        /* unmapped memory that's marked as defined */
	map = mmap(0, 256*1024, PROT_NONE, MAP_PRIVATE|MAP_NORESERVE|MAP_ANONYMOUS, -1, 0);
	if (map == (char *)-1)
		perror("trap 4 failed");
	else {
		munmap(map, 256*1024);
		(void)VALGRIND_MAKE_MEM_DEFINED(map, 256*1024); /* great big fat lie */
	}

	VALGRIND_DO_LEAK_CHECK;

	free(ptrs);

        // We deliberately make a leak, it'll be obvious if something went
        // wrong because the message won't be printed.
        ptrs = malloc(1000);

	return 0;
}