The PowerPC ABI expects the caller to allocate space for the return
address on the stack, above the current stack pointer, even if the
address is passed in the link register (usually the address is stored at
SP+4 by the callee).

The address calculation was wrong, as the addition of the lower 16 bits
is a signed addition, so if bit 15 is set, the upper 16 bits need to be
incremented by one (so the hi portion of the symbol always references
the symbol + 0x8000).

Thanks to Marek Mahut for the translation.