Updated PE linker, section alignment and cleanup.

Authored by Phyx on Sep 17 2018, 4:06 PM.

Description

Updated PE linker, section alignment and cleanup.

Summary:
This patch is to address a couple of short comings of the PE linker.

The first thing it does is properly honor section alignments, so SSE code
will work reliably.

While doing this I've also changed how it reads and stores ObjectFile
information. Previously the entire object file was read in and treated
as one blob, including headers, symbol tables etc.

Now the ObjectFile is read in but stored in chunks, tables go into a temporary
info struct and code/data into a new private heap. This allows me to free all
meta data once we're done relocating. Which means we can reclaim this memory.

As I've mentioned above I've also moved from using VirtualAlloc to HeapAlloc.
The reason is VirtualAlloc is meant to be used for more low level memory
allocation, it's very fast because it can only allocate whole blocks,
(64k) by default, and the memory must be paged (4k) aligned.

So when you ask for e.g. 30k of memory, you're given a whole block where 34k
will be wasted memory. Nothing else can ever access that untill you free the 30k.

One downside of HeapAlloc is that you're not in control of how the heap grows,
and heap memory is always committed. So it's harder to tell how much we're
actually using now.

Another big upside of splitting off the ObjectCode tables to info structs
is that I can adjust them, so that later addressings can just use array
subscripts to index into them. This simplifies the code a lot and a lot of
complicated casts and indexing can be removed. Leaving less and more simple
code.

This patch doesn't fix the memprotection but it doesn't regress it either.
It does however make the next changes smaller and fixes the alignments.

Test Plan: ./validate , new test T13617

Reviewers: bgamari, erikd, simonmar, hvr, angerman

Reviewed By: angerman

Subscribers: nickkuk, carter, RyanGlScott, rwbarton, thomie

GHC Trac Issues: Trac #13617

Differential Revision: https://phabricator.haskell.org/D3915