We were failing to save the entire 64-bit register, cutting off the top
32-bits which contain SS and CS. This ...happened to not cause issues
but is a bug that I encountered with far jump handling.
This patch does cover up all v4l2 syscalls in i386. It just works
well with the poor v4l2 driver of wine32.
Signed-off-by: Changwei Miao <chanthmiao@outlook.com>
Previously we were only storing the 32-bit base address which isn't
actually how segment descriptors work.
In reality segment descriptors are 64-bit descriptors that are laid out
in a particular layout depending on the 4-bit type value. In reality we
only care about code and data segment layouts since the rest are
bonkers.
Describe these descriptors correctly and setup a default code descriptor
for the operating mode that FEX is starting in.
This matches the systemd path, no more _32 and _64 versions, just
binfmt_misc.
Having a mixed install where one program does one architecture and
another is weird and unsupported anyway.
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