> What ruins this for C is the existence of pointers. Stacks aren't freely relocatable since pointers into the stack could exist.
I sometimes wonder what computing would be like if the 80286 hadn't sucked, if segmentation had won over flat address spaces, and if we'd been able to do relocation pain-free by changing a segment base register in one spot instead of rewriting linear pointers everywhere. We could have done paging within segments.
Oh well.
That'd only help for one object per address space. Main thing needing relocation - shared libraries - needs arbitrarily-many segment bases.
And when you're not a library, relocation is just a mild probabalistic security improvement (...that'd be massively-more bypassable than it already is if the program was littered full of gadgets of "read register as unrelocated offset and use it with its correct base" instructions).
mmap with MAP_FIXED has allowed you to do this for some time.
Not if you have an address space conflict, e.g. if you want to move a stack within a single process. Linear addresses are relative to a whole address space root.