This avoids a bunch of sharp edges for RA at a small cost when obscure
segment registers are used.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
doesn't matter for left shifts (we mask off the garbage), or 32-bit shifts, or
shifts where we explicitly sbfe after.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
undefined instructions are expected to return SIGILL, while implemented
instructions that aren't available in CPL-3 are expected to SIGSEGV.
Noticed this while testing out CPU-Z, it installs a kernel module and
does a bunch of `RDMSR` and `OUTS` instructions. Decided to walk through
the rest of the instructions in the `System Instruction Reference`
section.
Turns out there's a bunch of oddities in there that we don't support.
First step is to go through all the explicitl SIGILL and SIGSEGV and
implement a test for them.
Next step will be implementing the remaining operations that are
considered "System" operations but are still available in CPL-3.
This list includes:
- lar
- lgdt
- lsl
- sidt
- sldt
- stac
- clac
- verr
- verw
SRA is fundamentally about hardware registers, not stores into a
software-defined context. So, it should take a register instead of an offset.
This makes all the unaligned special cases unrepresentable (by design).
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Found out that Far Cry uses this instruction and it is viable to use in
CPL-3. This only returns constant data but its behaviour is a little
quirky.
This instruction has a weird behaviour that the 32-bit operation does an
insert in to the 64-bit destination, which might be an Intel versus AMD
behaviour. I don't have an Intel machine available to test if that
theory is true although. This assumption would match similar behaviour
where segment registers are inserted instead of zext.
Gets the game farther but then it crashes in a `___ascii_strnicmp`
function where the arguments end up being `___ascii_strnicmp(nullptr, "Color", 5);`.
There's quite a few places where the segment offset appending is open-coded
throughout the opcode dispatcher, but we can pull these out into a few
helpers to make the sites a little more compact and declarative.
1. pull flag calculation out of the loop body for perf
2. fully rotate the inner loop to save an instruction per iteration
3. hoist the rcx=0 jump to avoid computing df when rcx=0
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
single unified implementation for ROL & ROR (instead of 4 cases). no more
deferred flags because it's easy to shoot ourselves in the foot with deferred
flags w.r.t the new RA design, and rotates are rare enough with very efficient
flag calculations such that the extra JIT overhead should be minimal to DCE the
resulting calculations later.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Alyssa Rosenzweig