On Tuesday, 12 July 2016 at 13:28:33 UTC, jmh530 wrote:
On Monday, 11 July 2016 at 17:23:49 UTC, Ola Fosheim Grøstad
wrote:
You can, but OSes usually give you randomized memory layout as
a security measure.
What if the memory allocation scheme were something like:
randomly pick memory locations below some threshold from the
32bit segment and then above the threshold pick from elsewhere?
One possible technique is to use contiguous "unmapped" memory
areas that cover your worst case number of elements with a
specific base and just use indexes instead of absolute
addressing. That way you often can just use 16 bits typed
addressing (assuming max 65535 objects of a given type + a null
index).
The base address may then be injected (during linking or by using
self-modifying code if the OS allows it) into the code segments.
Or you could use TLS + indexing, or whatever the OS supports.
Using global 64 bit pointers is just for generality and to keep
language-implementation simple. It is not strictly hardware
related if you have a MMU, nor directly related to machine
language as such. For a statically typed language you could
probably get away with 16 or 32 bits for typed pointers most of
the time if the OS and language doesn't make it difficult (like
the conservative D GC scan).
