Leafs come from ECX but only some CPUID functions support this.
This adds the initial infrastructure but doesn't yet add support for the CPUID functions to consume the leaf.
Patch moves HandleSIGSEGV in HostFactory.cpp to a non-frontend host signal handler, then registers its own frontend signal handler to catch unhandled segfaults.
Sadly these things can't be split without breaking functionality so it
turns in to a bit of a mess.
SyscallHandler is very much something that is a Linux only construct and
shouldn't be in FEXCore itself. Lets the frontend register a
Syscallhandler with FEXCore. FEXCore itself is then aware of the current
syscall ABI and handles the ABI in an optimal fashion.
So it is not a 100% clean break otherwise we would lose performance.
The SignalDelegator then needs to move to the frontend since the
SyscallHandler requires it for signal based syscalls.
The CPU backend signal handling still needs to happen in FEXCore because
it is a very tight coupling with the CPU backend.
Once we need to support more Signal handling we can give the backends
cleaner support to select which specific OS handler to handle.
This interface is for native host code to be able to call back in to JIT
to execute guest code.
This is mainly for thunks but could be used for other purposes.
This can cross a couple ABI boundaries so one must be careful when
calling in to this
This requires implementing custom ASM dispatchers for the interpreter
side of things so it works correctly.
Allows all of our CPU backends to safely support signaling.
This is a bit of a nightmare change and requires rethinking logic about
debugging in some instances.
Splits out to a jump table approach and loosely classifies and groups
the syscalls.
Also defines syscalls by number of arguments so it can be optimized
Ryan Houdek