Register Usage: R12 is used as another callee-saved register. It is never used to return the upper 32 bits of a 64-bit result on a 32-bit architecture. All values greater than 32-bits are returned by a pointer.

Although the specification requires stack frames to be double word aligned, the current GCC compiler implements single word alignment.

Integral values more than 32 bits (64 bits on 64-bit architectures), structures and unions are returned as pointers to the location of the result. That location is provided by the calling function, which passes it as a first argument in GPR 3. In other words, where a function returns a result of this type, the first true argument to the function will appear in R4 (or R5/R6 if it is a 64-bit argument on a 32-bit architecture).