0xDEADBEEF equivalent for 64-bit development?

Question

For C++ development for 32-bit systems (be it Linux, Mac OS or Windows, PowerPC or x86) I have initialised pointers that would otherwise be undefined (e.g. they can not immedi

Answer 1

Most current 64-bit systems let you use only the lowest 2⁴⁸–2⁵² bits of the address space; higher bits of the address must be all-zero. Some chips (e.g. amd64) also let you use the highest 2⁴⁸–2⁵². Addresses outside these ranges cannot ever be mapped to accessible memory; the hardware simply won't allow it.

I therefore recommend you use a value close to 2⁶³, which is nowhere near either of the possibly-usable spaces. If the leading four hex digits are 7ff8, the value will be a double precision floating-point NaN, which is convenient. So my suggested cute hexadecimal phrase is 0x7FF8BADFBADFBADF.

By the way, you really don't want to use a value close to 0, because that makes it hard to tell an offset dereference of NULL — a structure member access, for instance — from a dereference of the poison pattern.