When a fork occurs FEX needs to be incredibly careful as any thread
(that isn't forking) that holds a lock will vanish when the fork occurs.
At this point if the newly forked process tries to use these mutexes
then the process hangs indefinitely.
The three major mutexes that need to be held during a fork:
- Code Invalidation mutex
- This is the highest priority and causes us to hang frequently.
- This is highly likely to occur when one thread is loading shared
libraries and another thread is forking.
- Happens frequently with Wine and steam.
- VMA tracking mutex
- This one happens when one thread is allocating memory while a fork
occurs.
- This closely relates to the code invalidation mutex, just happens at
the syscall layer instead of the FEXCore layer.
- Happens as frequently as the code invalidation mutex.
- Allocation mutex
- This mutex is used for FEX's 64-bit Allocator, this happens when FEX
is allocating memory on one thread and a fork occurs.
- Fairly infrequent because jemalloc doesn't allocate VMA regions that
often.
While this likely doesn't hit all of the FEX mutexes, this hits the ones
that are burning fires and are happening frequently.
- FEXCore: Adds forkable mutex/locks
Necessary since we have a few locations in FEX that need to be locked
before and after a fork.
When a fork occurs the locks must be locked prior to the fork. Then
afterwards they either need to unlock or be set to default
initialization state.
- Parent
- Does an unlock
- Child
- Sets the lock to default initialization state
- This is because it pthreads does TID based ownership checking on
unique locks and refcount based waiting for shared locks.
- No way to "unlock" after fork in this case other than default
initializing.
This has been around since the initial commit. Bad idea that wasn't ever
thought through. Something about remapping guest virtual and host
virtual memory which will never be a thing.
This returns the `XFEATURE_ENABLED_MASK` register which reports what
features are enabled on the CPU.
This behaves similarly to CPUID where it uses an index register in ecx.
This is a prerequisite to enabling XSAVE/XRSTOR and AVX since
applications will expect this to exist.
xsetbv is a privileged instruction and doesn't need to be implemented.
Currently WINE's longjump doesn't work, so instead set a flag that if
HLT is attempted, just exit the JIT.
This will get our unittests executing at least.
From https://github.com/AsahiLinux/linux/commits/bits/220-tso
This fails gracefully in the case the upstream kernel doesn't support
this feature, so can go in early.
This feature allows FEX to use hardware's TSO emulation capability to
reduce emulation overhead from our atomic/lrcpc implementation.
In the case that the TSO emulation feature is enabled in FEX, we will
check if the hardware supports this feature and then enable it.
If the hardware feature is supported it will then use regular memory
accesses with the expectation that these are x86-TSO in strength.
The only hardware that anyone cares about that supports this is Apple's
M class SoCs. Theoretically NVIDIA Denver/Carmel supports sequentially
consistent, which isn't quite the same thing. I haven't cared to check
if multithreaded SC has as strong of guarantees. But also since
Carmel/Denver hardware is fairly rare, it's hard to care about for our
use case.
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
This lets all the path generation for the config to be in the frontend.
This then informs FEXCore where things should live.
This is for llvm-mingw. While paths aren't quite generated correctly,
this gets the code closer to compiling.
The dispatcher was saving AVX state even though FEX doesn't support it
currently. This is due to it checking for the config option rather than
the HostFeatures option.
The `EnableAVX` config option is supposed to be used to inform FEXCore
if we want AVX disabled or not when the host supports the feature. In
this case it is universally enabled because we haven't encountered any
games that have issues with AVX state being saved with signals. (We know
they exist, we just don't have configurations for them).
The HostFeatures option `SupportsAVX` is the option that is supposed to
be getting used for determining if the runtime AVX feature is enabled.
This also had an issue though that this was **also** always enabled if
running on an x86 host with AVX, or an ARM host with SVE2-256bit.
It was then disabled if the config option was disabled; But, since
FEX-Emu doesn't support AVX fully yet, we need to ensure this isn't yet
enabled.
But this only solves half the problem. In order for our CI to test AVX
features before fully supporting AVX, it needs to be able to enable AVX
so that the CPU state is correctly saved.
So we need to change the default configuration option to be false, and
have CI enable it for the tests that matter before AVX is fully
implemented.
This has been a long time coming. The C interface has been a thorn in
our side for no reason for a long time.
The purpose of this step is to remove the C interface without changing
behaviour as much as possible. This means that with this commit there
are still some bad practices but the remaining issues will be solved
with followup PRs.
Primarily, we still have a `DestroyContext(CTX)` static function which calls
the Context implementation's `DestroyContext` and does a raw C++ delete.
Follow up PR will remove that, but I didn't want to touch it yet since
it'll require checking to ensure the unique_ptr changes play nice with
our allocator hooking. Which this is already a huge PR without trying to
change behaviour.
For the case that the 32-bit VDSO thunk library isn't available, have a
fallback that can work as well.
Otherwise 32-bit applications will just straight up crash on signal
return.
glibc lazily initializes the SETXID signal handler until first thread
creation.
Once we create our first pthread, steal it back from GLIBC after the
fact.
Fixes SOMA again.
If we have SVE2 support and a vector length of at least 256, then we can
adequately handle AVX.
However we also add in the ability for application profiles to disable
AVX if necessary for any reason.
Not currently used, but will be in subsequent changes.
If an application is doing long jumps on exceptions then we need to
ensure that RIP is synchronized at least to block entry for some amount
of safety.
Due to our block linking which doesn't ensure that RIP is synchronized
on block entry, our exception handling wouldn't see a RIP change, thus
not going down the path that we jump to Dispatcher loop top on RIP
change.
Burn a couple of instructions on block entry to ensure that RIP
synchronized but only on config.
Ryan Houdek