Fixes#2136
This is a fairly tricky edge case to support with FEX.
If execveat is used with AT_EMPTY_PATH then the application can pass an
FD to execve instead of a filename. This includes FDs that have been
deleted from the disk so the child process can't open it by filename
anymore.
To work around this limitation, we need to pass the FD to the new FEX
process and open it directly, similar to how binfmt_misc works with FDs.
The FD will get passed through environment variables, which the new
process will check for and then remove the variable from the
environment.
Lots of prickly edge cases to support here.
Without binfmt_misc:
- Passes the FD to FEXLoader directly.
- Requires duplicating the FD if it has O_CLOEXEC on the FD.
With binfmt_misc:
- Shebang file, pass directly to FEXLoader, just like without binfmt.
- x86 ELF Files, rely on the kernel's binfmt_misc support here.
- Unsupported ELF files, let kernel handle it through binfmt_misc
Argument handling:
- The application can pass in no arguments.
- Means our application configurations were failing to find a config
- Also various checks in the frontend were failing.
- If opened through an FD, find the symlink for that FD for the
application configuration instead.
Side note:
Fixed a performance issue in execve where when we were checking for file
format support. Either ELF or Shebang files, we were reading the /whole/
file upfront. We only need to read a header worth of ELF files, and only
257 bytes if it is potentially a shebang file. Should dramatically
reduce some application's execve times.
Segment registers are indexed significantly more than they are changed.
Pay the cost of indexing during the set and store rather than the per
register index.
Should be a fairly significant performance improvement for 32-bit
applications. At least on hardware that doesn't have a data dependent
prefetcher.
Breaks Steam atm and isn't clean.
We weren't adjusting the guest stack size when using clone3.
If the clone comes from CLONE3 then we need to offset the RSP by the
provided stack size.
This also translates to fork/vfork through clone, so make sure to adjust
stack in that case as well.
Fixes Ender Lilies crashing with Ubuntu 22.04 rootfs
On Set, we have four options that need to be converted.
On Get, we have two options that need to be converted.
This fixes a crash that Tomb Raider 2013 was having on launch.
The main one that we can't implement is readdir. Falls in to the same
problem space as getdents.
With this, we have the full entry tables filled out for both 64-bit and
32-bit. With some holes in the implementation, we have almost all
coverage now.
Most of these were already marked for passthrough, just needed to be
enabled.
Some syscalls can be passed through but need to be renamed for 32-bit.
This adds another define which does that for us.
This isn't quite a 100% clean sweep of IWYU.
There are some false positives where clang fails.
Additionally there are still a few missed in the frontend side of things
that I didn't get to
Due to an incorrect pointer check, we were never setting the sigaltstack
on 32-bit applications.
Additionally the stack_t type didn't have the members in the correct
order.
This fixes wine 32-bit applications where wine sends an application
SIGUSR1 and expects the altstack to be used. This is because the
altstack has the thread's TEB region at the start of the stack.
Without this when the application was getting sent a SIGUSR1, it would
remain in the application stack, thus getting an invalid TEB and loading
an FS register with zero.
This is very tricky to handle and it has a bunch of rough edges.
One of the major problems that we can't workaround is that if we receive a
clone flag that pthreads can't support with THREAD, then we are required to fall down
the pthreads code path.
This is because threads going down the clone path will break TLS and we don't have
a way to work around it currently.
So this adds a clone path, a clone3 path, and keeps the legacy path as well.
Which makes this fairly convoluted but it gets pressure-vessel working on x86-64 host.
It's a bit tricky to setup but it does work.
Still some work necessary to get pressure-vessel working on AArch64 host, but I'm working on that.
Currently our 32-bit code only gave one TLS slot and crashed
if you needed more.
First switch over to the same initial slot as the Linux kernel.
Then allow searching the slots for a free spot.
This allows us to more closely match the behaviour of the Linux kernel just in case
anything has hardcoded the TLS slots
This makes it so Saints Row: The Third stops crashing at boot, plays a few intro videos, then hangs instead.
Syscall entry points still have different argument orders,
Moves the arguments to the clone3 argument structure and passes to generic handler.
Also implements clone3 while doing this
C++ no-op functions can't optimize out the predicate arguments in all cases.
This was causing a problem where zero cost assertions weren't actually zero cost.
The only way to resolve this is to actually use macros sadly enough.
This will give a fairly hefty performance uplift with anything operating on IR.
Notably this allows applications to work that don't require the namespace but check up front if they are able to clone with it.
Civ 6's launcher checks this as an example
The vast majoirty of syscalls don't need anything in thread or frame.
So lets save an indirection for all those syscalls.
Most of the syscalls which do need Thread (or CTX via
Thread are in Thread.cpp or Memory.cpp
These have all been modifiy to fetch Thread from Frame
We need to check to see if the application wanting to be executed is in
the rootfs first. Otherwise we end up in a case where we either lose
tracking of applications in FEX, or applications fail to launch since
they don't exist in the global filesystem
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.
Ryan Houdek