New approach to disambiguating /disp32 arguments: based on opcodes rather
than metadata.
I interpret /disp32 as PC-relative in a short list of instructions. Otherwise
it's absolute if it gets a label.
There should be no reason to pass labels into /disp8 or /disp16.
Snapshot: this approach of disambiguating /disp32 based on metadata doesn't
work. The `survey` phase runs after `pack`, which gets rid of most metadata.
There's an ambiguity in how x86 interprets disp32 fields:
- For jumps and calls they're displacements from the starting address of
the next instruction. So far so good.
- However, when the ModR/M requires them they can also be absolute addresses.
Ideally I'd take the presence of the ModR/M byte into account in interpreting
them.
However, it's easier to assume relative addressing only for labels in the
code segment.
This commit raises an error if we ever refer to labels in the code segment
in instructions with a ModR/M byte. (I'm assuming that no instruction with
a ModR/M byte will ever use a displacement without the ModR/M byte requiring
it.)
I'm trying to read the status register, but I'm still not seeing the breakpoint
being hit a second time. (And I again ran into the Bochs bug that breakpoints
at the first instruction of an interrupt handler don't work.)
Maybe this is just a debugger issue. Let's keep going, and try to start
using the keyboard events.
I'd missed that VBE call 0x4f01 (get video mode) can write up to 256 bytes.
Unexpected areas were getting clobbered because I wasn't reserving enough
space.
If it's large enough that I have doubts whether my top-of-the-line Mac
is showing the bottom of the screen inside an emulator, it's too large.
This way I also feel more confident that most modern hardware will support
this graphics mode, and that these programs will work for others.
We need a few pages of data for the keyboard mappings.
If I moved them to some later address I'd be able to keep the nice round
starting address unchanged. But that seems like a superficial aesthetic
concern. There's really no value in having an array of hex bytes represented
in SubX rather than just raw hex. And it's better to colocate data near
the handler code which uses it (and which runs instructions SubX doesn't
support).
