Make mmap r+w only during preload for iOS.

While we do not yet enable mmap for ios builds.  If we later do, we must
not try to mmap r+w+x, on iOS as that clearly fails.

This diff also adds a check for the successful mmaping.

I don't think we can blanket change this to r+w for every case, unless
we are absolutely sure that we are going to remap this and set +x where
needed.

This is just one of the pieces for the rts linker support for ios
(aarch64-macho)

---

The following diagram and legend tries to explain the dependencies a
bit:
```
  .- D3240
  v
D3255 <- D3252 <- D3251 <- D3239
  ^
  '- This
```

- In D3238 we started allowing preloading object code with mmap
  in iOS, where we can't have r+w+x.
- In D3239 we introduced a richer extension of the object code
  data type to make working with mach-o files easier.
- In D3240 we set the stage to allow loading archives (.a) on iOS
- In D3251 we added init and deinit functions to populate and
  depopulate the enriched object code data structure for mach-o
  files.
- In D3252 we refactored most of the MachO.c file to use the
  new types and data structure.
- in D3255 we finally introduce the aarch64-mach-o linker.

Reviewers: ezyang, austin, erikd, simonmar, bgamari, rwbarton

Reviewed By: bgamari

Subscribers: rwbarton, ryantrinkle, thomie

Differential Revision: https://phabricator.haskell.org/D3238

0 files changed, 0 insertions, 0 deletions