Fix RawPOSIX exec()

[rennergade]

In lind-nacl we created a new cage on exec, but now with lind-wasm we more correctly just replace the code in the current cage. That makes some of the functionality currently in RawPOSIX exec() unnecessary. Can we clean up this function so it can be patched in to work correctly?

[robinyuan1002]

Is this issue fixed? I implemented dup3 syscall and my testcase need to use exec syscall to test it.

[qianxichen233]

I thought this issue was fixed long time ago, but it turns out it was only fixed on old rawposix repo and haven't been migrated to here: Lind-Project/RawPOSIX#93

[rennergade]

I thought this issue was fixed long time ago, but it turns out it was only fixed on old rawposix repo and haven't been migrated to here: Lind-Project/RawPOSIX#93

We never merged this because theres some unresolved things like things that are going to removed or modified from the cage struct (concurrency stuff that Chinmay is removing, vmmap, signal stuff) and we hadn't implemented closing threads for exit/exec etc.

Porting this for a short term fix to get exec() working probably makes sense but we'll have to go over this stuff again shortly.

[Yaxuan-w]

ok will submit a temporary patch pr after vmmap's pr has been merged

[Yaxuan-w]

Fixed in @ChinmayShringi's newest PR #106 for current rawposix