Access Errors

When access checking is turned on, runtime checking detects and reports the following types of errors.

Bad Free (baf) Error

Problem: Attempt to free memory that has never been allocated.

Possible causes: Passing a non-heap data pointer to free() or realloc().

Example:

char a[4];
char *b = &a[0];

free(b);                    /* Bad free (baf) */

Duplicate Free (duf) Error

Problem: Attempt to free a heap block that has already been freed.

Possible causes: Calling free() more than once with the same pointer. In C++, using the delete operator more than once on the same pointer.

Example:

char *a = (char *)malloc(1);
free(a);
free(a);                    /* Duplicate free (duf) */

Misaligned Free (maf) Error

Problem: Attempt to free a misaligned heap block.

Possible causes: Passing an improperly aligned pointer to free() or realloc(); changing the pointer returned by malloc.

Example:

char *ptr = (char *)malloc(4);
ptr++;
free(ptr);                    /* Misaligned free */

Misaligned Read (mar) Error

Problem: Attempt to read data from an address without proper alignment.

Possible causes: Reading 2, 4, or 8 bytes from an address that is not half-word-aligned, word-aligned, or double-word-aligned, respectively.

Example:

char *s = “hello world”;
int *i = (int *)&s[1];
int j;

j = *i;                    /* Misaligned read (mar) */

Misaligned Write (maw) Error

Problem: Attempt to write data to an address without proper alignment.

Possible causes: Writing 2, 4, or 8 bytes to an address that is not half-word-aligned, word-aligned, or double-word-aligned, respectively.

Example:

char *s = “hello world”;
int *i = (int *)&s[1];

*i = 0;                    /* Misaligned write (maw) */

Out of Memory (oom) Error

Problem: Attempt to allocate memory beyond physical memory available.

Cause: Program cannot obtain more memory from the system. Useful in locating problems that occur when the return value from malloc() is not checked for NULL, which is a common programming mistake.

Example:

char *ptr = (char *)malloc(0x7fffffff);
/* Out of Memory (oom), ptr == NULL */

Read From Array Out-of-Bounds (rob) Error

Problem: Attempt to read from array out-of-bounds memory.

Possible causes: A stray pointer, overflowing the bounds of a heap block

Example:

char *cp = malloc (10);
char ch = cp[10];

Read From Unallocated Memory (rua) Error

Problem: Attempt to read from nonexistent, unallocated, or unmapped memory.

Possible causes: A stray pointer, overflowing the bounds of a heap block or accessing a heap block that has already been freed.

Example:

char *cp = malloc (10);
free (cp);
cp[0] = 0;

Read From Uninitialized Memory (rui) Error

Problem: Attempt to read from uninitialized memory.

Possible causes: Reading local or heap data that has not been initialized.

Example:

foo()
{   int i, j;
    j = i;    /* Read from uninitialized memory (rui) */
}

Write to Array Out-of-Bounds Memory (wob) Error

Problem: Attempt to write to array out-of-bounds memory.

Possible causes: A stray pointer, overflowing the bounds of a heap block

Example:

char *cp = malloc (10);
cp[10] = 'a';

Write to Read-Only Memory (wro) Error

Problem: Attempt to write to read-only memory.

Possible causes: Writing to a text address, writing to a read-only data section (.rodata), or writing to a page that mmap has made read-only.

Example:

foo()
{   int *foop = (int *) foo;
    *foop = 0;                /* Write to read-only memory (wro) */
}

Write to Unallocated Memory (wua) Error

Problem: Attempt to write to nonexistent, unallocated, or unmapped memory.

Possible causes: A stray pointer, overflowing the bounds of a heap block, or accessing a heap block that has already been freed.

Example:

char *cp = malloc (10);
free (cp);
cp[0] = 0;