Noticed this while debugging Proton Experimental hanging and thought
this could be related. Didn't solve that issue but this should be merged
anyway.
vfork doesn't fork the host's process space in to the child process.
Saving Copy-On-Write overhead problems. It also puts the parent process
to sleep until the fork terminates or executes.
This is a major issue under FEX where we can't emulate vfork correctly
because we need to do other work before this process terminates or
executes a new process. We have been treating `vfork` as a `fork` this
entire time.
This can likely cause problems for applications that actually use vfork
to wait for a process to complete. So let's actually emulate that
feature by using a pipe with poll to determine when that FD gets
removed.
FEX can't use waitpid to wait for this process to terminate since we
would affect the guest also wanted to use a waitpid.
This is a very OS specific operation and it living in FEXCore doesn't
make much sense. This still requires some strong collaboration between
FEXCore and the frontend but it is now split between the locations.
There's still a bit more cleanup work that can be done after this is
merged, but we need to get this burning fire out of the way.
This is necessary for llvm-mingw, this requires all previous PRs to be
merged first.
After this is merged, most of the llvm-mingw work is complete, just some
minor cleanups.
To be merged first:
- #2602
- #2604
- #2605
- #2607
- #2610
- #2615
- #2619
- #2621
- #2622
- #2624
- #2625
- #2626
- #2627
- #2628
- #2629
FEX might not ever make it to its cleanup routines when exit is used. So
make sure to disable the fault checking if exit is used.
Opened #2594 to track this investigation.
Ryan Houdek