https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63303
--- Comment #6 from mikulas at artax dot karlin.mff.cuni.cz --- "you really can't have an object bigger than half of the address space in C/C++" - where does the standard claim this? If this is true, we should change malloc so that it doesn't allocate 2GiB or larger objects. Regarding pointer difference, the C standard says this: When two pointers are subtracted, both shall point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. The size of the result is implementation-defined, and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. If the result is not representable in an object of that type, the behavior is undefined. In other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of an array object, the expression (P)-(Q) has the value i−j provided the value fits in an object of type ptrdiff_t. So: p points to the beginning, q points one past the last element, so the first condition is valid. The result is the difference of the subscripts of those two array elements: 0x50000000 - 0 = 0x50000000 - this is clearly representable in the type ptrdiff_t, so 0x50000000 result should be returned.
