How the Compiler Defines Bounds Information for Pointers

Intel® C++ Compiler Classic Developer Guide and Reference

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ID 767249

Date 12/16/2022

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How the Compiler Defines Bounds Information for Pointers

The pointer checker is not supported on macOS systems.

The following defines how the compiler determines the bound information for pointers.

NOTE:

In each section, lower_bound(p) refers to the lower bound associated with p and upper_bound(p) refers to the upper bound associated with p.

Pointers created by the alloca() function
p = alloca(size); // lower_bound (p) is (char *)p // upper_bound (p) is lower_bound(p) + size - 1

Pointers created by the calloc() function
p = calloc(num, size); // lower_bound(p) is (char )p // upper_bound(p) is lower_bound(p) + size num - 1

Pointers created by the malloc() function
p = malloc(size); // lower_bound(p) is (char *)p // upper_bound(p) is lower_bound(p) + size - 1

Pointers created by casting
p = (T *)q; // lower_bound(p) is lower_bound(q) // upper_bound(p) is upper_bound(q)

Casting a pointer does not affect the bounds of a pointer. If you cast a pointer to a new type that is larger than the bounds associated with the original pointer, you will get an out-of-bounds error when you try to access any member or element outside the original bounds. If you cast a pointer to a smaller type than the original pointer, you can still access the original data.

Pointers created for a variable length array in a structure
typedef struct { int num; int a[]; } T; q = malloc(sizeof(T) + sizeof(int) * num); p = &q->a; // lower_bound(p) is (char *)&q->a // upper_bound(p) is upper_bound(q)

When you define an array as the last member of a structure, the upper bound is not narrowed and is allowed to access all of the array elements allocated by the malloc() function.

Pointers defined by the address (&) operator
p = &v; // lower_bound(p) is (char )&v // upper_bound(p) is (char )&v + sizeof(v) - 1 p = &v.m; // lower_bound(p) is (char )&v + offsetof(typeof(v), m) // upper_bound(p) is lower_bound(p) + sizeof(v.m) – 1 p = &q->m; // lower_bound(p) is (char )q + offsetof(typeof(*q), m) // upper_bound(p) is lower_bound(p) + sizeof(q->m) – 1

Pointers defined by the address (&) operator

p = &v;
    // lower_bound(p) is (char *)&v
    // upper_bound(p) is (char *)&v + sizeof(v) - 1

p = &v.m;
    // lower_bound(p) is (char *)&v + offsetof(typeof(v),  m)
    // upper_bound(p) is lower_bound(p) + sizeof(v.m) – 1

p = &q->m;
    // lower_bound(p) is (char *)q + offsetof(typeof(*q),  m)
    // upper_bound(p) is lower_bound(p) + sizeof(q->m) – 1

NOTE:

The bounds information is narrowed to the size of the member when you point to a member of a structure, union, or class.

Pointers defined by the new operator
p = new T; // lower_bound(p) is (char *)p // upper_bound(p) is lower_bound(p) + sizeof(T) - 1

Pointers defined by the addresses in an array
T a[X][Y]; p = a; p = &a[x]; p = &a[x][y]; // lower_bound(p) is (char *)a // upper_bound(p) is lower_bound(p) + sizeof(a) - 1

When you take the address of an element of an array or the address of a single row of a multi-dimensioned array, the bounds are not narrowed to the size of the element. You can increment or decrement the pointer throughout the array.

Incrementing and Decrementing Pointers
p = &a[x][y].m; // lower_bound(p) is (char *)&a[n][m] + offsetof(T, m) // upper_bound(p) is lower_bound(p) + sizeof(T.m) – 1

When you take the address of a member of an element, the bounds are narrowed to the size of the member.

Pointers defined by pointer copies
p = q; p = q + expr; p = q – expr; // lower_bound(p) is lower_bound(q) // upper_bound(p) is upper_bound(q)

The bounds are copied from q. Offsetting the pointer on the right does not affect the bounds.

Pointers defined by incrementing or decrementing a pointer
p++; p--; ++p; --p; p += expr; p -= expr;

The bounds do not change when you increment or decrement a pointer.

Parent topic: Using the Pointer Checker

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Intel® C++ Compiler Classic Developer Guide and Reference

How the Compiler Defines Bounds Information for Pointers