The current strategy for host allocation is to choose a random address and attempt to allocate there, eventually failing if the allocation cannot be satisfied.
The C standard only guarantees that RAND_MAX >= 32767, so for platforms where this is true allocations will fail with very high probability. On such platforms, you can reproduce this trivially by running lldb, typing "expr (3)" and then hitting enter you see a failure. Failures generally happen with a frequency of about 1 failure every 5 evaluations.
I cannot come up with a good reason that the allocations need to look like "real" pointers, so this patch changes the allocation scheme to simply jump straight to the end and grab a free chunk of memory.