disasm.fsx

let bin = System.IO.File.ReadAllBytes "../../test"
let mutable i = 0
let show len asm =
    printf "%08X  " i
    for j = 0 to len - 1 do
        printf "%02X" bin.[i + j]
    for j = len to 5 do
        printf "  "
    printfn "%s" asm
    i <- i + len
let reg16 = [| "ax"; "cx"; "dx"; "bx"; "sp"; "bp"; "si"; "di" |]
let reg8  = [| "al"; "cl"; "dl"; "bl"; "ah"; "ch"; "dh"; "bh" |]
let sreg  = [| "es"; "cs"; "ss"; "ds" |]
let regm  = [| "bx+si"; "bx+di"; "bp+si"; "bp+di"
               "si"; "di"; "bp"; "bx" |]
let dispstr d =
    if d < 0 then
        sprintf "-0x%x" (abs d)
    else
        sprintf "+0x%x" d
let modrm() =
    let mode = int bin.[i+1] >>> 6
    let rm   = int bin.[i+1] &&& 0b111
    match mode, rm with
    | 0b00, 0b110 ->
        2, sprintf "[0x%02x%02x]" bin.[i+3] bin.[i+2]
    | 0b00, _ ->
        0, sprintf "[%s]" regm.[rm]
    | 0b01, _ ->
        let d = bin.[i+2] |> sbyte
        1, sprintf "[%s%s]" regm.[rm] (dispstr (int d))
    | 0b10, _ ->
        let d = (int16 bin.[i+2]) ||| ((int16 bin.[i+3]) <<< 8)
        2, sprintf "[%s%s]" regm.[rm] (dispstr (int d))
    | 0b11, _ ->
        0, reg16.[rm]
    | _ ->
        0, "???"
while i < bin.Length do
    match int bin.[i] with
    | 0b10001101 ->
        let reg = (int bin.[i+1] >>> 3) &&& 0b111
        let len, opr = modrm()
        show (2 + len) <| sprintf "lea %s, %s"
                                  reg16.[reg] opr
    | 0b10001110 ->
        let reg = (int bin.[i+1] >>> 3) &&& 0b11
        let len, opr = modrm()
        show (2 + len) <| sprintf "mov %s, %s"
                                  sreg.[reg] opr
    | 0b10001100 ->
        let reg = (int bin.[i+1] >>> 3) &&& 0b11
        let len, opr = modrm()
        show (2 + len) <| sprintf "mov %s, %s"
                                  opr sreg.[reg]
    | b when b &&& 0b11111000 = 0b10110000 ->
        show 2 <| sprintf "mov %s, 0x%02x"
            reg8.[b &&& 0b111] bin.[i+1]
    | b when b &&& 0b11111000 = 0b10111000 ->
        show 3 <| sprintf "mov %s, 0x%02x%02x"
            reg16.[b &&& 0b111] bin.[i+2] bin.[i+1]
    | _ ->
        show 1 <| sprintf "db 0x%02x" bin.[i]