Implement single stepping

[darkf]

I'd like to construct an x86 emulator+debugger using V86, but it does not support single-stepping, which is quite necessary for it.

[copy]

Here's something to play with:

> cpu = new CPU
CPU {memory_size: 0, segment_is_null: Array[0], segment_offsets: Array[0], segment_limits: Array[0], tlb_data: Int32Array[1048576]…}
> cpu.create_memory(1024 * 1024 * 16)
undefined
> cpu.memory.mem8[0] = 0x40; // inc ax
64
> cpu.instruction_pointer
0
> cpu.reg32s[reg_eax]
0
> cpu.cycle()
undefined
> cpu.reg32s[reg_eax]
1
> cpu.instruction_pointer
1

Use this script to load the required files. None of this is stable now, we'll need to think how to expose internals.

We might need to write some functions similar to this (in order to make sure the names don't get mangled and we can change reg32s at a later point):

/** @export */
CPU.prototype.get_reg32s = function(n)
{
    return this.reg32s[n];
};

[almosnow]

I'm trying to follow your snippet on Node. I can't get it to work.

When doing this:

var CPU = new require('./v86/build/libv86.js').CPU();
CPU.mem8[0] = 0x40;
CPU.cycle();

It throws an exception like:

TypeError: this.memory_map_read8[(a >>> MMAP_BLOCK_BITS)] is not a function
    at CPU.mmap_read8 (libv86.js:254:947)
    at CPU.read8 (libv86.js:256:331)
    at CPU.read_imm8 (502:243)

Any idea on what could I be missing?