This matches kernel behaviour for how brk works. I initially implemented
this as a way to speed up some early applications that relied heavily on
brk. We're long past that time and we should match Linux behaviour
instead.
This fixes issues where applications (FEXLoader really) can see we've
allocated a larger granule and breaks self-hosting. There's no reason to
be smarter around this, if applications want more perf then they'll
switch to a better allocator than brk.
Also need to make sure that after the brk region has been reserved, to
unmap its initial mapping to allow future mmap syscalls to overwrite it.
We need to reserve it early to ensure the region initially exists and we
don't accidentally map other things in that space. Then it is up to the
guest if they don't want to overwrite it.
Implied the maximum size that brk could grow to. Which isn't correct, it
is the current maximum size mapped which is page size, versus the
current brk offset which is byte ranged.
A prevalent pattern in the FEX codebase is to compute some data and store it
in a maybe_unused variable that's only ever passed to LOGMAN_THROW_A_FMT.
Besides few exceptions, we never compute expensive data in the macro
arguments themselves, so we can remove a lot of code noise by unconditionally
evaluating the condition even in assertion-disabled builds.
When loading an ELF file (usually PT_EXEC), we would have BSS regions
that ended up in the high pages of the address space. We would then
attempt mapping BRK after whatever the highest address ending up being.
This was problematic because we used `MAP_FIXED` which means that the
BRK region could cross in to 64-bit address space, overwrite VDSO,
overwrite the stack, vsyscall, maybe a couple of other things.
Instead of letting that happen, reorder some of the logic so that in
`LoadElfFile` will ensure the full `BRK_SIZE` is allocated (or return
zero) and then we can ensure we're never overwriting other various
memory regions.
This doesn't fix two fundamental issues that FEX has with brk:
* If BRK gets mapped below the ELF, that should mean it isn't mapped at all
* Linux-isms, doubt this breaks new software
* We still map the full 8MB, which isn't correct
* I'm working on fixing this issue, which is why I encountered this.
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.
This nearly gets FEX's TestHarnessRunner to be self-hosting inside of
FEX. The only thing blocking it currently is that our SBRK emulation
reserves the whole region, when it should be "soft-reserved" and mmap
with MAP_FIXED_NOREPLACE can override it. Plus an assert in
OpcodeDispatcher preventing any 32-bit code from running from a 64-bit
process.
In the most simple terms, gdt and ldt are setup to be unique per thread,
and modify_ldt then modifies that thread's ldt entry. On thread
creation, these values get inherited as a copy.
This allows installation of 32-bit code entries, which with the previous
PRs merged allows the code to attempt jumping to that 32-bit code entry.
It then will immediately explode with an assert in our OpcodeDispatcher.
We can't allow 32-bit code jumping yet until our OpDispatcher/X86Tables
allows runtime selection of 64-bit and 32-bit code entries which is
still a ways away.
With the assert removed and the SBRK code handling hacked out,
/technically/ the TestHarnessRunner can run some code, albeit anything
that changes behaviour between bitness is completely incorrect.
Effectively NFC today while we don't allow installing LDT entries, but
is required to have signal handlers execute in the correct bitness if
32-bit code segments are enabled.
Nothing too crazy, just that four segments are stuffed in to the
`REG_CSGSFS` data value, and then CS/SS gets restored on restore.
FS and GS are ignored in this instance because edge case behaviour where
those don't get reset on signal entry, so if they get changed then it is
on the userspace application to fix it.
Gets another change out of my stashes.
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.
Lioncache