Only wired up for wow64 and arm64ec. Gives more granular control over
TSO enabling and disabling. Matches arm64ec volatile metadata except
with one more additional feature that whole modules can be disabled at a
time.
Once we know the mapped size of files in Linux then we'll be able to do
the same thing there, but there's not a full mechanism wired up for that
yet.
Taking this very slowly because this is very fickle code. The frontend
needs to manage GDT and LDT, but before we get there, we need to
actually add support for LDT in the backend. Split the segments to two
arrays so the JIT can actually update their cached values correctly.
Still treats GDT and LDT as mirrors like how the JIT previously did (By
it ignoring the selector's TI bit).
While most applications will just create ALL_ACCESS handles which
support the additional operations FEX needs over the regular windows syscall
(usually just QUERY_INFORMATION to lookup the thread object), it is
valid for them to pass in the minimal set required for each operation
and windows/wine will reject any other operations (e.g. querying the TEB
base on a handle with only the SUSPEND right). Windows permits
duplicating handles to extend their permissions given the process itself
has such permissions, so do that as necessary for the operations FEX
needs.
In the terminate case, if we don't return early then we will delete the
FEX thread object but the actual terminate call that follows will
fail, leaving the thread in a bad state.
We don't need to be informed of our own mappings, avoids a deadlock that
occurs if the ThreadCreationMutex lifetime is extended when creating a
thread.
Allocate the stack with uncommited guard pages on either side, if
any faulting accesses to these occur then the call-ret SP value is
reset to the default and execution resumed.
Prevents invalidations being missed under the following circumstances:
Thread A JITs block A into the global codebuffer, adding the guest to host
mapping to its CodePages, thread A is then killed.
Thread B then performs SMC on block A. An exception will be triggered but
as CodePages was stored per-thread, and thread A is now killed when all
threads are iterated over by the frontend to perform invalidations it
will be missed.
The accumulator is introduced to handle the case where multiple threads
have the same code entry in their local caches but share the same codebuffer.
Consider a thread C in the above example that also has block A in its cache,
without an accumulator, when invalidating thread B the entrypoint of A is erased
from the shared guest to host map. So when C is invalidated, the local cache entry
for A is not removed since it was removed from CodePages when invalidating B.
Consider a page with two blocks in it, A and B. Block A performs SMC on B then A.
With the previous logic, the SMC write of B would unprotect the page and then
the inline SMC touching A would not be detected and a single-step would not be forced.
Billy Laws