SpiderMonkey stores objects in 64 bits JSvals using punboxing, which means 17 bits are used to indicate the type and 47 bits to store a pointer to the actual value.

This is fine when the pointer have no more than 47 significant bits, which is the case on x86-64, but not on Power under AIX, where mmap returns pointers in the range 0x07000000_00000000-0x07FFFFFF_FFFFFFFF (58 significant bits).

This is compromising the port of MongoDB to AIX.

Issue as also been reported to Mozilla (Bug 1263543).