x86_binary_emitter.ml

(***********************************************************************)
(*                                                                     *)
(*                              OCaml                                  *)
(*                                                                     *)
(*  Copyright 2014, OCamlPro. All rights reserved.                     *)
(*  All rights reserved. This file is distributed under the terms of   *)
(*  the GNU Lesser General Public License version 2.1                  *)
(*                                                                     *)
(***********************************************************************)
(*
  Contributors:
  * Fabrice LE FESSANT (INRIA/OCamlPro)
*)

[@@@ocaml.warning "+A-4-9"]

open X86_ast
open X86_proc
module String = Misc.Stdlib.String

type section = {
  sec_name : string;
  mutable sec_instrs : asm_line array;
}

type data_size = B8 | B16 | B32 | B64

module IntSet = Set.Make (Int)

module StringMap = Map.Make (String)

let print_old_arg ppf = function
  | Imm _ -> Format.fprintf ppf "Imm"
  | Reg8L _ -> Format.fprintf ppf "Reg8L"
  | Reg8H _ -> Format.fprintf ppf "Reg8H"
  | Reg16 _ -> Format.fprintf ppf "Reg16"
  | Reg32 _ -> Format.fprintf ppf "Reg32"
  | Reg64 _ -> Format.fprintf ppf "Reg64"
  | Regf _ -> Format.fprintf ppf "Regf"
  | Mem _ -> Format.fprintf ppf "Mem"
  | Mem64_RIP _ -> Format.fprintf ppf "Mem64_RIP"
  | Sym _ -> Format.fprintf ppf "Sym"

(*
TODO:

If a or-pattern contains both "Reg64 ... | Reg32 ... ", it means that
we didn't discriminate between 32 bit and 64 bit modes for that
instruction. It also means that using this instruction on a 32-bit
register in 64 bit mode will not generate the 32-bit version of the
instruction, but the 64-bit version...

*)

module Relocation = struct
  module Kind = struct
    type t =
      (* 32 bits offset usually in data section *)
      | REL32 of string * int64
      | DIR32 of string * int64
      | DIR64 of string * int64
  end

  type t = { offset_from_section_beginning : int; kind : Kind.t }
end

type symbol = {
  sy_name : string;
  mutable sy_type : string option;
  mutable sy_size : int option;
  mutable sy_global : bool;
  mutable sy_sec : section;
  mutable sy_pos : int option;
  mutable sy_num : int option; (* position in .symtab *)
}

type buffer = {
  sec : section;
  buf : Buffer.t;
  labels : symbol String.Tbl.t;
  mutable patches : (int * data_size * int64) list;
  mutable relocations : Relocation.t list;
}

type local_reloc =
  | RelocCall of string
  | RelocShortJump of string * int (* loc *)
  | RelocLongJump of string
  | RelocConstant of constant * data_size

type result =
  | Rint of int64
  | Rabs of string * int64 (* absolute label + offset *)
  | Rrel of string * int64

(* relative label + offset *)

(*
let string_of_result = function
  Rint n -> Printf.sprintf "Rint %Ld" n
  | Rabs (s, n) -> Printf.sprintf "Rabs (%S, %Ld)" s n
  | Rrel (s, n) -> Printf.sprintf "Rrel (%S, %Ld)" s n
*)

let get_symbol b s =
  try String.Tbl.find b.labels s
  with Not_found ->
    let sy =
      {
        sy_name = s;
        sy_type = None;
        sy_size = None;
        sy_pos = None;
        sy_global = false;
        sy_num = None;
        sy_sec = b.sec;
      }
    in
    String.Tbl.add b.labels s sy ;
    sy

let buf_int8 b i = Buffer.add_char b.buf (char_of_int (i land 0xff))

let buf_int8L b iL = buf_int8 b (Int64.to_int iL)

let buf_int16L b iL =
  buf_int8L b iL;
  buf_int8L b (Int64.shift_right iL 8)

let buf_int32L b iL =
  buf_int16L b iL;
  buf_int16L b (Int64.shift_right iL 16)

let buf_int64L b iL =
  buf_int32L b iL;
  buf_int32L b (Int64.shift_right iL 32)

let str_int8L s pos v = Bytes.set s pos (char_of_int (Int64.to_int v land 0xff))

let str_int16L s pos v =
  str_int8L s pos v;
  str_int8L s (pos + 1) (Int64.shift_right_logical v 8)

let str_int32L s pos v =
  str_int16L s pos v;
  str_int16L s (pos + 2) (Int64.shift_right_logical v 16)

let str_int64L s pos v =
  str_int32L s pos v;
  str_int32L s (pos + 4) (Int64.shift_right_logical v 32)

(* When a jump has to be generated, we compare the offset between the
   source instruction and the target instruction, in number of
   instructions.

   If the offset is less than [short_jump_threshold] instructions,
   we generate a short jump during the first pass. 16 is a "safe"
   value, as most instructions are shorter than 8 bytes: [REX] +
   [OPCODE] + [MODRM] + [SIB] + [IMM32] *)

let local_relocs = ref []

let local_labels = String.Tbl.create 100

let forced_long_jumps = ref IntSet.empty

let instr_size = ref 4

let new_buffer sec =
  {
    sec;
    buf = Buffer.create 10000;
    labels = String.Tbl.create 100;
    relocations = [];
    patches = [];
  }

let label_pos b lbl =
  match (String.Tbl.find b.labels lbl).sy_pos with
  | None -> raise Not_found
  | Some pos -> pos

(* Try to compute some statically computable arithmetic expressions
   in labels, or to simplify them to a form that is encodable by
   relocations. *)
let eval_const b current_pos cst =
  let rec eval = function
    | Const n -> Rint n
    | ConstThis -> Rabs ("", 0L)
    | ConstLabel lbl -> Rabs (lbl, 0L)
    | ConstSub (c1, c2) -> (
        let c1 = eval c1 and c2 = eval c2 in
        match (c1, c2) with
        | Rint n1, Rint n2 -> Rint (Int64.sub n1 n2)
        | Rabs (s, n1), Rint n2 -> Rabs (s, Int64.sub n1 n2)
        | Rrel (s, n1), Rint n2 -> Rrel (s, Int64.sub n1 n2)
        | Rabs ("", n1), Rabs ("", n2) -> Rint (Int64.sub n1 n2)
        | Rabs ("", n1), Rabs (s2, n2) -> (
            try
              let sy2 = String.Tbl.find b.labels s2 in
              match sy2.sy_pos with
              | Some pos2 ->
                  let pos2 = Int64.of_int pos2 in
                  Rint
                    (Int64.sub
                       (Int64.add n1 (Int64.of_int current_pos))
                       (Int64.add pos2 n2))
              | _ -> assert false
            with Not_found -> assert false)
        | Rabs (s, n1), Rabs ("", n2) -> (
            try
              let sy = String.Tbl.find b.labels s in
              match sy.sy_pos with
              | Some pos ->
                  let pos = Int64.of_int pos in
                  Rint
                    (Int64.sub (Int64.add pos n1)
                       (Int64.add n2 (Int64.of_int current_pos)))
              | _ -> assert false
            with Not_found -> Rrel (s, Int64.sub n1 n2))
        | Rabs (s1, n1), Rabs (s2, n2) -> (
            try
              let sy2 = String.Tbl.find b.labels s2 in
              try
                let sy1 = String.Tbl.find b.labels s1 in
                assert (sy1.sy_sec == sy2.sy_sec);
                match (sy1.sy_pos, sy2.sy_pos) with
                | Some pos1, Some pos2 ->
                    let pos1 = Int64.of_int pos1 in
                    let pos2 = Int64.of_int pos2 in
                    Rint (Int64.sub (Int64.add pos1 n1) (Int64.add pos2 n2))
                | _ -> assert false
              with Not_found -> (
                match sy2.sy_pos with
                | Some pos2 ->
                    let pos2 = Int64.of_int pos2 in
                    Rrel
                      ( s1,
                        Int64.sub
                          (Int64.add n1 (Int64.of_int current_pos))
                          (Int64.add pos2 n2) )
                | _ -> assert false)
            with Not_found -> assert false)
        | _ -> assert false)
    | ConstAdd (c1, c2) -> (
        let c1 = eval c1 and c2 = eval c2 in
        match (c1, c2) with
        | Rint n1, Rint n2 -> Rint (Int64.add n1 n2)
        | Rabs (s, n1), Rint n2 | Rint n2, Rabs (s, n1) ->
            Rabs (s, Int64.add n1 n2)
        | Rrel (s, n1), Rint n2 | Rint n2, Rrel (s, n1) ->
            Rrel (s, Int64.add n1 n2)
        (* TODO: we could add another case, easy to solve: adding a
           Rrel to a Rabs where the symbol is local, in which case it
           can be computed. *)
        | Rrel (s, n1), Rabs ("", n2) -> Rabs (s, Int64.add n1 n2)
        | _ -> assert false)
  in
  try
    let r = eval cst in
    (*
    if debug then
      Printf.eprintf "eval_const (%s) = %s at @%d\n%!"
        (X86_gas.string_of_constant cst)
        (string_of_result r) current_pos;
*)
    r
  with e ->
    Printf.eprintf "Error in eval_const: exception %S\n%!"
      (*(X86_gas.string_of_constant cst)*) (Printexc.to_string e);
    raise e

let is_imm32L n = n < 0x8000_0000L && n >= -0x8000_0000L

let is_imm8L x = x < 128L && x >= -128L

let rd_of_regf regf =
  match regf with
  | XMM n -> n
  | TOS -> assert false (* TODO *)
  | ST _st -> assert false

(* TODO *)

let rd_of_reg64 = function
  | RAX -> 0
  | RCX -> 1
  | RDX -> 2
  | RBX -> 3
  | RSP -> 4
  | RBP -> 5
  | RSI -> 6
  | RDI -> 7
  | R8 -> 8
  | R9 -> 9
  | R10 -> 10
  | R11 -> 11
  | R12 -> 12
  | R13 -> 13
  | R14 -> 14
  | R15 -> 15

let rd_of_reg8 = function
  | Reg8L r -> rd_of_reg64 r
  | Reg8H AH -> 4
  | Reg8H CH -> 5
  | Reg8H DH -> 6
  | Reg8H BH -> 7
  | _ -> assert false

let cd_of_condition condition =
  match condition with
  | O -> 0
  | NO -> 1
  | B -> 2
  | AE -> 3
  | E -> 4
  | NE -> 5
  | BE -> 6
  | A -> 7
  | S -> 8
  | NS -> 9
  | P -> 10
  | NP -> 11
  | L -> 12
  | GE -> 13
  | LE -> 14
  | G -> 15

(* We should precompute a position for each label depending on
   the number of instructions: heuristics = offset_in_instrs x 7
*)

let no_rex = 0

let rex = 0b01000000

let rexr = 0b00000100 (* extension of r *)

let rexr_reg reg = if reg > 7 then rexr else 0

let rexw = rex lor 0b00001000

let rexx = 0b00000010

let rexx_index reg = if reg > 7 then rexx else 0

let rexb = 0b00000001

let rexb_opcode reg = if reg > 7 then rexb else 0

let rexb_rm reg = if reg > 7 then rexb else 0

let rexb_base reg = if reg > 7 then rexb else 0

let reg7 reg = reg land 0x07

let rex_of_reg8 = function Reg8L (RSP | RBP | RSI | RDI) -> rex | _ -> 0

(* TODO: we should check conformance with page 3-2, vol 2A of Intel Spec ? *)

let rex_of_reg16 = function
  | RAX | RCX | RDX | RBX | RSP | RBP | RSI | RDI -> 0
  | R8 | R9 | R10 | R11 | R12 | R13 | R14 | R15 -> rex

let mod_rm_reg m rm reg = (m lsl 6) + reg7 rm + (reg7 reg lsl 3)

let sib scale index base =
  let scale =
    match scale with 1 -> 0 | 2 -> 1 | 4 -> 2 | 8 -> 3 | _ -> assert false
  in
  (scale lsl 6) lor (reg7 index lsl 3) lor reg7 base

let record_reloc b offset_from_section_beginning kind =
  b.relocations <-
    { Relocation.offset_from_section_beginning; kind } :: b.relocations

let declare_label b s =
  let sy = get_symbol b s in
  assert (sy.sy_pos = None);
  let pos = Buffer.length b.buf in
  sy.sy_pos <- Some pos

let buf_opcodes b opcodes =
  ListLabels.iter ~f:(fun opcode -> buf_int8 b opcode) opcodes

let arch64 = Config.architecture = "amd64"

let emit_rex b rexcode =
  if arch64 && rexcode <> 0 then buf_int8 b (rexcode lor rex)

let buf_int32_imm b = function
  | Imm n ->
      assert (is_imm32L n);
      buf_int32L b n
  | Sym symbol ->
      record_reloc b (Buffer.length b.buf) (Relocation.Kind.DIR32 (symbol, 0L));
      buf_int32L b 0L
  | _ -> assert false

type offset_exp = OImm8 of int64 | OImm32 of string option * int64

let sym32 b sym =
  record_reloc b (Buffer.length b.buf) (Relocation.Kind.DIR32 (sym, 0L));
  buf_int32L b 0L

let sym64 b sym =
  record_reloc b (Buffer.length b.buf) (Relocation.Kind.DIR64 (sym, 0L));
  buf_int64L b 0L

let buf_sym b sym offset =
  match sym with
  | None -> buf_int32L b offset
  | Some lbl ->
      (* TODO: assert we are in 32 bits ? *)
      record_reloc b (Buffer.length b.buf) (Relocation.Kind.DIR32 (lbl, offset));
      buf_int32L b 0L

let emit_mod_rm_reg b rex opcodes rm reg =
  match rm with
  | Reg32 rm ->
      let rm = rd_of_reg64 rm in
      emit_rex b (rex lor rexr_reg reg lor rexb_rm rm);
      buf_opcodes b opcodes;
      buf_int8 b (mod_rm_reg 0b11 rm reg)
  | Reg64 rm ->
      let rm = rd_of_reg64 rm in
      emit_rex b (rex lor rexr_reg reg lor rexb_rm rm);
      buf_opcodes b opcodes;
      buf_int8 b (mod_rm_reg 0b11 rm reg)
  | (Reg8L _ | Reg8H _) as reg8 ->
      let rm = rd_of_reg8 reg8 in
      emit_rex b (rex lor rex_of_reg8 reg8 lor rexr_reg reg lor rexb_rm rm);
      buf_opcodes b opcodes;
      buf_int8 b (mod_rm_reg 0b11 rm reg)
  | Reg16 reg16 ->
      let rm = rd_of_reg64 reg16 in
      emit_rex b (rex lor rex_of_reg16 reg16 lor rexr_reg reg lor rexb_rm rm);
      buf_opcodes b opcodes;
      buf_int8 b (mod_rm_reg 0b11 rm reg)
  | Regf rm ->
      let rm = rd_of_regf rm in
      emit_rex b (rex lor rexr_reg reg lor rexb_rm rm);
      buf_opcodes b opcodes;
      buf_int8 b (mod_rm_reg 0b11 rm reg)
  (* 64 bits memory access *)
  | Mem64_RIP (_, symbol, offset) ->
      emit_rex b (rex lor rexr_reg reg);
      buf_opcodes b opcodes;
      buf_int8 b (mod_rm_reg 0b00 0b101 reg);
      record_reloc b (Buffer.length b.buf)
        (Relocation.Kind.REL32 (symbol, Int64.of_int offset));
      buf_int32L b 0L
  | Mem { arch; typ = _; idx; scale; base; sym; displ } -> (
      let offset =
        let displ = Int64.of_int displ in
        match sym with
        | None ->
            if is_imm8L displ then OImm8 displ
            else if is_imm32L displ then OImm32 (None, displ)
            else assert false
        | Some s -> OImm32 (Some s, displ)
      in
      let idx_reg = idx in
      let idx = rd_of_reg64 idx in
      if scale = 0 then (
        assert (base = None && arch = X86);
        match offset with
        | OImm8 _ -> assert false
        | OImm32 (sym, offset) ->
            buf_opcodes b opcodes;
            buf_int8 b (mod_rm_reg 0b00 0b101 reg);
            buf_sym b sym offset)
      else
        match base with
        | None -> (
            match (idx_reg, scale, offset) with
            | (RSP | R12), 1, OImm8 0L ->
                emit_rex b (rex lor rexr_reg reg lor rexb_base idx);
                buf_opcodes b opcodes;

                buf_int8 b (mod_rm_reg 0b00 idx reg);
                buf_int8 b (sib 1 0b100 idx)
            | (RSP | R12), 1, OImm8 offset8 ->
                emit_rex b (rex lor rexr_reg reg lor rexb_base idx);
                buf_opcodes b opcodes;

                buf_int8 b (mod_rm_reg 0b01 0b100 reg);
                buf_int8 b (sib 1 0b100 idx);
                buf_int8L b offset8
            | (RSP | R12), 1, OImm32 (sym, offset) ->
                (* to 0x??(%rsp) *)
                emit_rex b (rex lor rexr_reg reg lor rexb_base idx);
                buf_opcodes b opcodes;

                buf_int8 b (mod_rm_reg 0b10 0b100 reg);
                buf_int8 b (sib 1 0b100 idx);
                buf_sym b sym offset
            | (RBP | R13), 1, OImm8 _ -> (
                (* to 0x??(%rbp) *)
                (* TODO check if offset8 = 0 is enough *)
                emit_rex b (rex lor rexr_reg reg lor rexb_base idx);
                buf_opcodes b opcodes;
                buf_int8 b (mod_rm_reg 0b01 idx reg);
                match offset with
                | OImm8 offset8 -> buf_int8L b offset8
                | _ -> assert false)
            | _, 1, OImm8 0L ->
                (* to 0x00(%r??) except %rsp and %rbp *)
                emit_rex b (rex lor rexr_reg reg lor rexb_rm idx);
                buf_opcodes b opcodes;
                buf_int8 b (mod_rm_reg 0b00 idx reg)
            | _, 1, OImm8 offset8 ->
                emit_rex b (rex lor rexr_reg reg lor rexb_rm idx);
                buf_opcodes b opcodes;
                buf_int8 b (mod_rm_reg 0b01 idx reg);
                buf_int8L b offset8
            | _, 1, OImm32 (sym, offset) ->
                emit_rex b (rex lor rexr_reg reg lor rexb_rm idx);
                buf_opcodes b opcodes;
                buf_int8 b (mod_rm_reg 0b10 idx reg);
                buf_sym b sym offset
            | _, _, _ -> (
                emit_rex b (rex lor rexr_reg reg lor rexx_index idx);
                buf_opcodes b opcodes;
                buf_int8 b (mod_rm_reg 0b00 0b100 reg);
                buf_int8 b (sib scale idx 0b101);
                match offset with
                | OImm8 offset8 -> buf_int32L b offset8
                | OImm32 (sym, offset) -> buf_sym b sym offset))
        | Some base_reg -> (
            assert (scale = 1 || scale = 2 || scale = 4 || scale = 8);
            let base = rd_of_reg64 base_reg in
            emit_rex b
              (rex lor rexr_reg reg lor rexx_index idx lor rexb_base base);
            buf_opcodes b opcodes;
            match (base_reg, offset) with
            | (RBP | R13), OImm8 0L ->
                (* to 0x00(%rbp+reg) *)
                buf_int8 b (mod_rm_reg 0b01 0b100 reg);
                buf_int8 b (sib scale idx base);
                buf_int8 b 0
            | _, OImm8 0L ->
                buf_int8 b (mod_rm_reg 0b00 0b100 reg);
                buf_int8 b (sib scale idx base)
            | _, OImm8 offset ->
                buf_int8 b (mod_rm_reg 0b01 0b100 reg);
                buf_int8 b (sib scale idx base);
                buf_int8L b offset
            | _, OImm32 (sym, offset) ->
                buf_int8 b (mod_rm_reg 0b10 0b100 reg);
                buf_int8 b (sib scale idx base);
                buf_sym b sym offset))
  | Imm _ | Sym _ -> assert false

let emit_movlpd b dst src =
  match (dst, src) with
  | Regf reg, ((Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x12 ] rm (rd_of_regf reg)
  | ((Mem _ | Mem64_RIP _) as rm), Regf reg ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x13 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_movapd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x28 ] rm (rd_of_regf reg)
  | ((Mem _ | Mem64_RIP _) as rm), Regf reg ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x29 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_movd b ~dst ~src =
  match (dst, src) with
  | Regf reg, ((Reg32 _ | Mem _ | Mem64_RIP _) as rm) ->
    buf_int8 b 0x66;
    emit_mod_rm_reg b no_rex [ 0x0F; 0x6E ] rm (rd_of_regf reg)
  | ((Reg32 _ | Mem _ | Mem64_RIP _) as rm), Regf reg ->
    buf_int8 b 0x66;
    emit_mod_rm_reg b no_rex [ 0x0F; 0x7E ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_movq b ~dst ~src =
  (* It seems there is a choice to make on how we encode instructions here
     as there are different encoding possible for the same operation.
     See https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf,
     pages 707 and 755.  *)
  match (dst, src) with
  | Regf reg, ((Reg64 _ | Mem _ | Mem64_RIP _) as rm) ->
    buf_int8 b 0x66;
    emit_mod_rm_reg b rexw [ 0x0F; 0x6E ] rm (rd_of_regf reg)
  | ((Reg64 _ | Mem _ | Mem64_RIP _) as rm), Regf reg ->
    buf_int8 b 0x66;
    emit_mod_rm_reg b rexw [ 0x0F; 0x7E ] rm (rd_of_regf reg)
  | Regf reg, ((Regf _) as rm) ->
    buf_int8 b 0xF3;
    emit_mod_rm_reg b no_rex [ 0x0F; 0x7E ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_movsd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x10 ] rm (rd_of_regf reg)
  | ((Mem _ | Mem64_RIP _) as rm), Regf reg ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x11 ] rm (rd_of_regf reg)
  | _ ->
      Format.eprintf "src=%a dst=%a@." print_old_arg src print_old_arg dst;
      assert false

let emit_movss b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF3;
      emit_mod_rm_reg b 0 [ 0x0f; 0x10 ] rm (rd_of_regf reg)
  | ((Mem _ | Mem64_RIP _) as rm), Regf reg ->
      buf_int8 b 0xF3;
      emit_mod_rm_reg b 0 [ 0x0f; 0x11 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_andpd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x54 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_bsf b ~dst ~src =
  match (dst, src) with
  | Reg16 reg, ((Reg16 _ | Mem _ | Mem64_RIP _) as rm)
  | Reg32 reg, ((Reg32 _ | Mem _ | Mem64_RIP _) as rm) ->
    (* BSF r16, r/m16 and BSF r32, r/m32 *)
    emit_mod_rm_reg b 0 [ 0x0F; 0xBC ] rm (rd_of_reg64 reg)
  | Reg64 reg, ((Reg64 _ | Mem _ | Mem64_RIP _) as rm) ->
    (* BSF r64, r/m64 *)
    emit_mod_rm_reg b rexw [ 0x0F; 0xBC ] rm (rd_of_reg64 reg)
  | _ -> assert false

let emit_bsr b ~dst ~src =
  match (dst, src) with
  | Reg16 reg, ((Reg16 _ | Mem _ | Mem64_RIP _) as rm)
  | Reg32 reg, ((Reg32 _ | Mem _ | Mem64_RIP _) as rm) ->
    (* BSR r16, r/m16 and BSR r32, r/m32 *)
    emit_mod_rm_reg b 0 [ 0x0F; 0xBD ] rm (rd_of_reg64 reg)
  | Reg64 reg, ((Reg64 _ | Mem _ | Mem64_RIP _) as rm) ->
    (* BSR r64, r/m64 *)
    emit_mod_rm_reg b rexw [ 0x0F; 0xBD ] rm (rd_of_reg64 reg)
  | _ -> assert false

let imm8_of_rounding rounding =
  (* bits are:
     - 3: Precision Mask (0 = Normal, 1 = Inexact)
     - 2: Rounding Select (0 = Use bits 1 and 0 for Rounding mode, 1 = MXCSR.RC)
     - 1 and 0: Rounding mode *)
  match rounding with
  | RoundNearest -> 0b0000
  | RoundDown -> 0b0001
  | RoundUp -> 0b0010
  | RoundTruncate -> 0b0011
  | RoundCurrent -> 0b0100

let emit_roundsd b dst rounding src =
  let rounding = imm8_of_rounding rounding in
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x3A; 0x0B ] rm (rd_of_regf reg);
      buf_int8 b rounding
  | _ -> assert false

let emit_addsd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x58 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_sqrtsd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x51 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_mulsd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x59 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_divsd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x5E ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_subsd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x5C ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_xorpd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x57 ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_CVTSI2SD b dst src =
  match (dst, src) with
  | Regf reg, ((Reg64 _ | Mem { typ = QWORD }) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b rexw [ 0x0f; 0x2A ] rm (rd_of_regf reg)
  | Regf reg, ((Reg32 _ | Mem { typ = DWORD }) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x2A ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_CVTSD2SI b dst src =
  match (dst, src) with
  | Reg64 reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b rexw [ 0x0f; 0x2D ] rm (rd_of_reg64 reg)
  | Reg32 reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x2D ] rm (rd_of_reg64 reg)
  | _ -> assert false

let emit_CVTTSD2SI b dst src =
  match (dst, src) with
  | Reg64 reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b rexw [ 0x0f; 0x2C ] rm (rd_of_reg64 reg)
  | Reg32 reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x2C ] rm (rd_of_reg64 reg)
  | _ -> assert false

let emit_CVTSD2SS b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF2;
      emit_mod_rm_reg b 0 [ 0x0f; 0x5A ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_CVTSS2SD b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0xF3;
      emit_mod_rm_reg b 0 [ 0x0f; 0x5A ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_comisd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x2F ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_ucomisd b dst src =
  match (dst, src) with
  | Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b 0 [ 0x0f; 0x2E ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_MOV b dst src =
  match (dst, src) with
  (* movb *)
  | ((Reg8L (RAX | RCX | RDX | RBX) | Reg8H _) as r8), Imm n ->
      assert (is_imm8L n);
      buf_opcodes b [ 0xB0 + reg7 (rd_of_reg8 r8) ];
      buf_int8L b n
  | ((Mem _ | Mem64_RIP _) as rm), ((Reg8L _ | Reg8H _) as reg) ->
      emit_mod_rm_reg b (rex_of_reg8 reg) [ 0x88 ] rm (rd_of_reg8 reg)
  (* no REX.W *)
  (* movw *)
  | ((Mem _ | Mem64_RIP _) as rm), Reg16 reg ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b rex [ 0x89 ] rm (rd_of_reg64 reg) (* no REX.W *)
  | Reg16 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      buf_int8 b 0x66;
      emit_mod_rm_reg b rex [ 0x8B ] rm (rd_of_reg64 reg) (* no REX.W *)
  (* movl *)
  | Reg32 reg32, ((Reg32 _ | Mem _ | Mem64_RIP _) as rm) ->
      let reg = rd_of_reg64 reg32 in
      emit_mod_rm_reg b 0 [ 0x8B ] rm reg
  | ((Mem _ | Mem64_RIP _) as rm), Reg32 reg32 ->
      let reg = rd_of_reg64 reg32 in
      emit_mod_rm_reg b 0 [ 0x89 ] rm reg
  | (Mem { typ = DWORD } as rm), ((Imm _ | Sym _) as n) ->
      emit_mod_rm_reg b 0 [ 0xC7 ] rm 0;
      buf_int32_imm b n
  | (Mem { typ = NONE; arch = X86 } as rm), ((Imm _ | Sym _) as n) ->
      let reg = 0 in
      emit_mod_rm_reg b 0 [ 0xC7 ] rm reg;
      buf_int32_imm b n
  | Reg32 r32, ((Imm _ | Sym _) as n) ->
      let n =
        match n with
        | Imm n ->
            (* "Shift" [n] from [0, 0xFFFF_FFFF] to [-0x8000_0000, 0x7FFF_FFFF] *)
            Imm (Int64.of_int32 (Int64.to_int32 n))
        | _ as n -> n
      in
      let reg = rd_of_reg64 r32 in
      emit_rex b (rexb_opcode reg);
      buf_int8 b (0xB8 lor reg7 reg);
      buf_int32_imm b n
  (* movq *)
  | Reg64 reg, ((Reg64 _ | Mem _ | Mem64_RIP _) as rm) ->
      emit_mod_rm_reg b rexw [ 0x8B ] rm (rd_of_reg64 reg)
  | ((Mem _ | Mem64_RIP _) as rm), Reg64 reg ->
      emit_mod_rm_reg b rexw [ 0x89 ] rm (rd_of_reg64 reg)
  | Reg64 r64, Imm n when not (is_imm32L n) ->
      (* MOVNoneQ *)
      let reg = rd_of_reg64 r64 in
      emit_rex b (rexw lor rexb_opcode reg);
      buf_int8 b (0xB8 lor reg7 reg);
      buf_int64L b n
  | Reg64 r64, Sym symbol when windows ->
      let reg = rd_of_reg64 r64 in
      emit_rex b (rexw lor rexb_opcode reg);
      buf_int8 b (0xB8 lor reg7 reg);
      sym64 b symbol
  | ((Mem { arch = X64 } | Reg64 _) as rm), ((Imm _ | Sym _) as n) ->
      emit_mod_rm_reg b rexw [ 0xC7 ] rm 0;
      buf_int32_imm b n
  | _ ->
      Format.printf "dst = %a@." print_old_arg dst;
      Format.printf "src = %a@." print_old_arg src;
      assert false

type simple_encoding = {
  rm8_r8 : int list;
  rm64_r64 : int list;
  r8_rm8 : int list;
  r64_rm64 : int list;
  al_imm8 : int list;
  rax_imm32 : int list;
  rm8_imm8 : int list;
  rm64_imm32 : int list;
  rm64_imm8 : int list;
  reg : int;
}

let emit_simple_encoding enc b dst src =
  match (enc, dst, src) with
  (* 64 bits encodings *)
  | { rm64_r64 = opcodes }, ((Reg64 _ | Mem _ | Mem64_RIP _) as rm), Reg64 reg
    ->
      emit_mod_rm_reg b rexw opcodes rm (rd_of_reg64 reg)
  | { rm64_r64 = opcodes }, ((Reg32 _ | Mem _ | Mem64_RIP _) as rm), Reg32 reg
    ->
      emit_mod_rm_reg b 0 opcodes rm (rd_of_reg64 reg)
  | { r64_rm64 = opcodes }, Reg64 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      emit_mod_rm_reg b rexw opcodes rm (rd_of_reg64 reg)
  | { r64_rm64 = opcodes }, Reg32 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      emit_mod_rm_reg b 0 opcodes rm (rd_of_reg64 reg)
  | ( { rm64_imm8 = opcodes; reg },
      ((Reg64 _ | Mem { typ = NONE | QWORD | REAL8; arch = X64 }) as rm),
      Imm n )
    when is_imm8L n ->
      emit_mod_rm_reg b rexw opcodes rm reg;
      buf_int8L b n
  | ( { rm8_imm8 = opcodes; reg },
      ((Reg8L _ | Reg8H _ | Mem { typ = BYTE; arch = X64 }) as rm),
      Imm n ) ->
      assert (is_imm8L n);
      emit_mod_rm_reg b rexw opcodes rm reg;
      buf_int8L b n
  | ( { rm64_imm8 = opcodes; reg },
      ((Reg32 _ | Mem { typ = DWORD | REAL4 } | Mem { typ = NONE; arch = X86 })
      as rm),
      Imm n )
    when is_imm8L n ->
      emit_mod_rm_reg b 0 opcodes rm reg;
      buf_int8L b n
  | { rax_imm32 = opcodes }, Reg64 RAX, ((Imm _ | Sym _) as n) ->
      emit_rex b rexw;
      buf_opcodes b opcodes;
      buf_int32_imm b n
  | { rax_imm32 = opcodes }, Reg32 RAX, ((Imm _ | Sym _) as n) ->
      buf_opcodes b opcodes;
      buf_int32_imm b n
  | ( { rm64_imm32 = opcodes; reg },
      ((Reg32 _ | Mem { typ = NONE; arch = X86 } | Mem { typ = DWORD | REAL4 })
      as rm),
      ((Imm _ | Sym _) as n) ) ->
      emit_mod_rm_reg b 0 opcodes rm reg;
      buf_int32_imm b n
  | ( { rm64_imm32 = opcodes; reg },
      ((Reg64 _ | Mem _ | Mem64_RIP _) as rm),
      ((Imm _ | Sym _) as n) ) ->
      emit_mod_rm_reg b rexw opcodes rm reg;
      buf_int32_imm b n
  | _ ->
      Format.eprintf "src=%a dst=%a@." print_old_arg src print_old_arg dst;
      assert false

let emit_simple_encoding base reg =
  emit_simple_encoding
    {
      rm8_r8 = [ base ];
      rm64_r64 = [ base + 1 ];
      r8_rm8 = [ base + 2 ];
      r64_rm64 = [ base + 3 ];
      al_imm8 = [ base + 4 ];
      rax_imm32 = [ base + 5 ];
      rm8_imm8 = [ 0x80 ];
      rm64_imm32 = [ 0x81 ];
      rm64_imm8 = [ 0x83 ];
      reg;
    }

let emit_ADD = emit_simple_encoding 0x00 0

let emit_OR = emit_simple_encoding 0x08 1

let emit_AND = emit_simple_encoding 0x20 4

let emit_SUB = emit_simple_encoding 0x28 5

let emit_XOR = emit_simple_encoding 0x30 6

let emit_CMP = emit_simple_encoding 0x38 7

let emit_test b dst src =
  match (dst, src) with
  | ((Reg32 _ | Mem _ | Mem64_RIP _) as rm), Reg32 reg ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b 0 [ 0x85 ] rm reg
  | ((Reg64 _ | Mem _ | Mem64_RIP _) as rm), Reg64 reg ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x85 ] rm reg
  | Reg64 RAX, ((Imm _ | Sym _) as n) ->
      emit_rex b rexw;
      buf_opcodes b [ 0xA9 ];
      buf_int32_imm b n
  | Reg32 RAX, ((Imm _ | Sym _) as n) ->
      buf_opcodes b [ 0xA9 ];
      buf_int32_imm b n
  | ((Reg32 _ | Reg64 _ | Mem _ | Mem64_RIP _) as rm), ((Imm _ | Sym _) as n) ->
      emit_mod_rm_reg b rexw [ 0xF7 ] rm 0;
      buf_int32_imm b n
  | Reg8L RAX, Imm n ->
      assert (is_imm8L n);
      buf_opcodes b [ 0xA8 ];
      buf_int8L b n
  | ((Reg8L _ | Reg8H _) as rm), Imm n ->
      assert (is_imm8L n);
      emit_mod_rm_reg b 0 [ 0xF6 ] rm 0;
      buf_int8L b n
  | _ -> assert false

(* 3-390 -> 452 *)
let emit_imul b dst src =
  match (dst, src) with
  | Some (Reg32 reg), ((Reg32 _ | Mem _ | Mem64_RIP _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b 0 [ 0x0F; 0xAF ] rm reg
  | Some (Reg64 reg), ((Reg64 _ | Mem _ | Mem64_RIP _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x0F; 0xAF ] rm reg
  | Some ((Reg64 reg | Reg32 reg) as rm), Imm n when is_imm8L n ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x6B ] rm reg;
      buf_int8L b n
  | Some ((Reg64 reg | Reg32 reg) as rm), ((Imm _ | Sym _) as n) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x69 ] rm reg;
      buf_int32_imm b n
  | None, ((Reg64 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm) ->
      let reg = 5 in
      emit_mod_rm_reg b rexw [ 0xF7 ] rm reg
  | _ -> assert false

let emit_mul b ~src =
  let opcode_extension = 4 in
  match src with
  | ((Reg8H _ | Reg8L _ | Mem {typ = BYTE; _} | Mem64_RIP (BYTE, _, _)) as rm) ->
    emit_mod_rm_reg b rex [ 0xF6 ] rm opcode_extension
  | ((Reg16 _ | Mem {typ = WORD; _} | Mem64_RIP (WORD, _, _)) as rm)
  | ((Reg32 _ | Mem {typ = DWORD; _} | Mem64_RIP (DWORD, _, _)) as rm) ->
    emit_mod_rm_reg b no_rex [ 0xF7 ] rm opcode_extension
  | ((Reg64 _ | Mem {typ = QWORD; _} | Mem64_RIP (QWORD, _, _)) as rm) ->
    emit_mod_rm_reg b rexw [ 0xF7 ] rm opcode_extension
  | _ -> assert false

let emit_idiv b dst =
  let reg = 7 in
  match dst with
  | (Reg64 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm ->
      emit_mod_rm_reg b rexw [ 0xF7 ] rm reg
  | _ -> assert false

let emit_shift reg b dst src =
  match (dst, src) with
  | ((Reg64 _ | Reg32 _ | Mem _) as rm), Imm 1L ->
      emit_mod_rm_reg b rexw [ 0xD1 ] rm reg
  | ((Reg64 _ | Reg32 _ | Mem _) as rm), Imm n ->
      assert (is_imm8L n);
      emit_mod_rm_reg b rexw [ 0xC1 ] rm reg;
      buf_int8L b n
  | ((Reg64 _ | Reg32 _) as rm), Reg8L RCX ->
      emit_mod_rm_reg b rexw [ 0xD3 ] rm reg
  | _ ->
      Format.eprintf "emit_shift: src=%a dst=%a@." print_old_arg src
        print_old_arg dst;
      assert false

let emit_SAL b dst src = emit_shift 4 b dst src

let emit_SHR b dst src = emit_shift 5 b dst src

let emit_SAR b dst src = emit_shift 7 b dst src

let record_local_reloc b local_reloc =
  local_relocs := (Buffer.length b.buf, local_reloc) :: !local_relocs

let emit_reloc_jump near_opcodes far_opcodes b loc symbol =
  if String.Tbl.mem local_labels symbol then
    (* local_reloc *)
    let target_loc = String.Tbl.find local_labels symbol in
    if target_loc < loc then (
      (* backward *)
      (* The target position is known, and so is the actual offset.  We can
         thus decide locally if a short jump can be used. *)
      let target_pos =
        try label_pos b symbol with Not_found -> assert false
      in
      let source_pos = Buffer.length b.buf in
      assert (target_pos < source_pos);
      let togo = Int64.of_int (target_pos - source_pos) in
      let togo_short =
        Int64.sub togo (Int64.of_int (1 + List.length near_opcodes))
      in

      (*      Printf.printf "%s/%i: backward  togo_short=%Ld\n%!" symbol loc togo_short; *)
      if togo_short >= -128L && togo_short < 128L then (
        buf_opcodes b near_opcodes;
        buf_int8L b togo_short)
      else (
        buf_opcodes b far_opcodes;
        buf_int32L b
          (Int64.sub togo (Int64.of_int (4 + List.length far_opcodes)))))
    else
      (* forward *)
      (* Is the target too far forward (in term of instruction count)
         or have we detected previously that this jump instruction needs
         to be a long one?

         The str_size constant (see below) is chosen to avoid a second
         pass most oftenm while not being overly pessimistic. *)

      (*
      if Int64.of_int ((target_loc - loc) * !instr_size) >= 120L then
        Printf.printf "%s/%i: probably too far (%i)\n%!" symbol loc target_loc
      else if IntSet.mem loc !forced_long_jumps then
        Printf.printf "%s/%i: forced long jump\n%!" symbol loc
      else
        Printf.printf "%s/%i: short\n%!" symbol loc;
*)
      let force_far =
        Int64.of_int ((target_loc - loc) * !instr_size) >= 120L
        || IntSet.mem loc !forced_long_jumps
      in
      if force_far then (
        buf_opcodes b far_opcodes;
        record_local_reloc b (RelocLongJump symbol);
        buf_int32L b 0L)
      else (
        buf_opcodes b near_opcodes;
        record_local_reloc b (RelocShortJump (symbol, loc));
        buf_int8L b 0L)
  else (
    (* external symbol, must reloc *)

    (*    Printf.printf "%s/%i: non local\n%!" symbol loc; *)
    buf_opcodes b far_opcodes;
    record_reloc b (Buffer.length b.buf) (Relocation.Kind.REL32 (symbol, 0L));
    buf_int32L b 0L)

let emit_jmp b loc dst =
  match dst with
  | Sym symbol -> emit_reloc_jump [ 0xEB ] [ 0xE9 ] b loc symbol
  | (Reg64 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm ->
      let reg = 4 in
      emit_mod_rm_reg b 0 [ 0xFF ] rm reg
      (* no REX *)
  | _ -> assert false

let emit_call b dst =
  match dst with
  | Sym symbol ->
      buf_int8 b 0xE8;
      if String.Tbl.mem local_labels symbol then
        record_local_reloc b (RelocCall symbol)
      else
        (* external symbol, must reloc *)
        record_reloc b (Buffer.length b.buf)
          (Relocation.Kind.REL32 (symbol, 0L));
      buf_int32L b 0L
  | (Reg64 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm ->
      emit_mod_rm_reg b no_rex [ 0xFF ] rm 2
  | _ -> assert false

let emit_j b loc condition dst =
  match dst with
  | Sym symbol ->
      let opcode_offset = cd_of_condition condition in
      emit_reloc_jump [ 0x70 + opcode_offset ]
        [ 0x0F; 0x80 + opcode_offset ]
        b loc symbol
  | _ -> assert false

let imm8_of_float_condition = function
  | EQf -> 0x00
  | LTf -> 0x01
  | LEf -> 0x02
  | UNORDf -> 0x03
  | NEQf -> 0x04
  | NLTf -> 0x05
  | NLEf -> 0x06
  | ORDf -> 0x07

let emit_cmpsd b ~condition ~dst ~src =
  match (dst, src) with
  | (Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm)) ->
    (* CMPSD xmm1, xmm2/m64, imm8 *)
    let condition = imm8_of_float_condition condition in
    buf_int8 b 0xF2;
    emit_mod_rm_reg b no_rex [ 0x0F; 0xC2 ] rm (rd_of_regf reg);
    buf_int8 b condition
  | _ -> assert false

let emit_cmov b condition dst src =
  match (dst, src) with
  | (Reg64 reg | Reg32 reg), ((Reg64 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm)
    ->
      emit_mod_rm_reg b rexw
        [ 0x0F; 0x40 + cd_of_condition condition ]
        rm (rd_of_reg64 reg)
  | _ -> assert false

let emit_set b condition dst =
  match dst with
  | (Reg8L _ | Reg8H _) as rm ->
      emit_mod_rm_reg b 0 [ 0x0F; 0x90 + cd_of_condition condition ] rm 0
  | _ -> assert false

let emit_movsx b dst src =
  match (dst, src) with
  | (Reg64 reg | Reg32 reg), ((Mem { typ = BYTE } | Reg8L _ | Reg8H _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rex [ 0x0F; 0xBE ] rm reg
      (* no REX.W *)
  | (Reg64 reg | Reg32 reg), ((Mem { typ = WORD } | Reg16 _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x0F; 0xBF ] rm reg
  | _ -> assert false

let emit_movsxd b dst src =
  match (dst, src) with
  | (Reg64 reg | Reg32 reg), ((Mem _ | Mem64_RIP _ | Reg32 _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x63 ] rm reg
  | _ -> assert false

let emit_MOVZX b dst src =
  match (dst, src) with
  | (Reg64 reg | Reg32 reg), ((Mem { typ = BYTE } | Reg8L _ | Reg8H _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x0F; 0xB6 ] rm reg
  | Reg64 reg, ((Mem { typ = WORD } | Reg16 _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x0F; 0xB7 ] rm reg
  | Reg32 reg, ((Mem { typ = WORD } | Reg16 _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b 0 [ 0x0F; 0xB7 ] rm reg
  | _ -> assert false

let emit_FSTP b dst =
  match dst with
  | Mem { typ = REAL8 | QWORD } as rm -> emit_mod_rm_reg b 0 [ 0xDD ] rm 3
  | Mem { typ = REAL4 } as rm -> emit_mod_rm_reg b 0 [ 0xD9 ] rm 3
  | Regf (ST i) ->
      (*      assert (i >= 0 && i < float_stack_size); *)
      buf_opcodes b [ 0xDD; 0xD8 + i ]
  | _ -> assert false

let emit_neg b dst =
  match dst with
  | (Reg64 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm ->
      emit_mod_rm_reg b rexw [ 0xF7 ] rm 3
  | _ -> assert false

let emit_LEA b dst src =
  match (dst, src) with
  | Reg64 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b rexw [ 0x8D ] rm reg
  | Reg32 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      let reg = rd_of_reg64 reg in
      emit_mod_rm_reg b 0 [ 0x8D ] rm reg
  (*
        | Reg16 reg, (Mem _ | Mem64_RIP _ as rm) ->
        let reg = rd_of_reg64 reg in
        emit_mod_rm_reg b 0 [ 0x8D ] rm reg
    *)
  | _ ->
      Format.eprintf "lea src=%a dst=%a@." print_old_arg src print_old_arg dst;
      assert false

let emit_stack_reg b opcode dst =
  match dst with
  | Reg64 reg ->
      let reg = rd_of_reg64 reg in
      if reg > 7 then emit_rex b (rex lor rexb_opcode reg);
      buf_int8 b (opcode + reg7 reg)
  | Reg32 reg ->
      let reg = rd_of_reg64 reg in
      buf_int8 b (opcode + reg7 reg)
  | _ -> assert false

let emit_push b dst =
  match dst with
  | Reg32 _ | Reg64 _ -> emit_stack_reg b 0x50 dst
  | (Mem _ | Mem64_RIP _) as rm -> emit_mod_rm_reg b no_rex [ 0xFF ] rm 6
  | Imm n ->
      if is_imm8L n then (
        buf_int8 b 0x6A;
        buf_int8L b n)
      else (
        assert (is_imm32L n);
        buf_int8 b 0x68;
        buf_int32L b n)
  | Sym sym ->
      buf_int8 b 0x68;
      sym32 b sym
  | _ -> assert false

let emit_pop b dst =
  match dst with
  | Reg32 _ | Reg64 _ -> emit_stack_reg b 0x58 dst
  | (Mem _ | Mem64_RIP _) as rm -> emit_mod_rm_reg b no_rex [ 0x8F ] rm 0
  | _ -> assert false

let emit_popcnt b ~dst ~src =
  match (dst, src) with
  | (Reg16 reg, ((Reg16 _ | Mem _ | Mem64_RIP _) as rm))
  | (Reg32 reg, ((Reg32 _ | Mem _ | Mem64_RIP _) as rm)) ->
    (* POPCNT r16, r/m16 and POPCNT r32, r/m32 *)
    buf_int8 b 0xF3;
    emit_mod_rm_reg b no_rex [ 0x0F; 0xB8 ] rm (rd_of_reg64 reg);
  | (Reg64 reg, ((Reg64 _ | Mem _ | Mem64_RIP _) as rm)) ->
    (* POPCNT r64, r/m64 *)
    buf_int8 b 0xF3;
    emit_mod_rm_reg b rexw [ 0x0F; 0xB8 ] rm (rd_of_reg64 reg);
  | _ -> assert false

let rd_of_prefetch_hint = function
  | Nta -> 0
  | T0 -> 1
  | T1 -> 2
  | T2 -> 3

let emit_prefetch b ~is_write ~hint rm =
  match (is_write, hint, rm) with
  | (false, _, (Mem _ | Mem64_RIP _)) ->
    (* PREFETCHT0 m8, PREFETCHT1 m8, PREFETCHT1 m8 and PREFETCHNTA m8 *)
    emit_mod_rm_reg b no_rex [ 0x0F; 0x18 ] rm (rd_of_prefetch_hint hint)
  | (true, T0, (Mem _ | Mem64_RIP _)) ->
    (* PREFETCHW m8 *)
    emit_mod_rm_reg b no_rex [ 0x0F; 0x0D ] rm (rd_of_prefetch_hint hint)
  | (true, (T1 | T2 | Nta), (Mem _ | Mem64_RIP _)) ->
    (* PREFETCHWT1 m8 *)
    (* This sticks to X86_gas' behaviour which emit prefetchwt1 if hint is
       [T2 | Nta] *)
    emit_mod_rm_reg b no_rex [ 0x0F; 0x0D ] rm (rd_of_prefetch_hint T1)
  | _ -> assert false

let emit_pause b = buf_opcodes b [ 0xF3; 0x90 ]

let emit_rdtsc b = buf_opcodes b [ 0x0F; 0x31 ]

let emit_rdpmc b = buf_opcodes b [ 0x0F; 0x33 ]

let emit_leave b = buf_int8 b 0xC9

let emit_maxsd b ~dst ~src =
  match (dst, src) with
  | (Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm)) ->
    buf_int8 b 0xF2;
    emit_mod_rm_reg b no_rex [ 0x0F; 0x5F ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_minsd b ~dst ~src =
  match (dst, src) with
  | (Regf reg, ((Regf _ | Mem _ | Mem64_RIP _) as rm)) ->
    buf_int8 b 0xF2;
    emit_mod_rm_reg b no_rex [ 0x0F; 0x5D ] rm (rd_of_regf reg)
  | _ -> assert false

let emit_inc b = function
  | (Reg64 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm ->
      emit_mod_rm_reg b rexw [ 0xFF ] rm 0
  | _ -> assert false

let emit_DEC b = function
  (* FE /1 DEC r/m8 M Valid Valid *)
  | [ ((Reg8L _ | Reg8H _ | Mem { typ = BYTE }) as rm) ] ->
      emit_mod_rm_reg b no_rex [ 0xFE ] rm 1
  (* FF /1 DEC r/m16 M Valid Valid *)
  | [ ((Reg16 _ | Mem { typ = WORD }) as rm) ] ->
      emit_mod_rm_reg b no_rex [ 0x66; 0xFF ] rm 1
  (* FF /1 DEC r/m32 M Valid Valid *)
  | [ ((Reg32 _ | Mem { typ = DWORD }) as rm) ] ->
      emit_mod_rm_reg b no_rex [ 0xFF ] rm 1
  (* REX.W + FF /1 DEC r/m64 M Valid N.E. *)
  | [ ((Reg64 _ | Mem { typ = QWORD }) as rm) ] ->
      emit_mod_rm_reg b rexw [ 0xFF ] rm 1
  | _ -> assert false

let emit_ret b = buf_int8 b 0xC3

let emit_cqto b =
  emit_rex b rexw;
  buf_int8 b 0x99

let emit_crc32 b ~dst ~src =
  match (dst, src) with
  | (Reg32 reg, ((Reg8L _ | Reg8H _ | Mem {typ = BYTE; _} | Mem64_RIP (BYTE, _, _)) as rm)) ->
    (* CRC32 r32, r/m8 *)
    buf_int8 b 0xF2;
    emit_mod_rm_reg b rex [ 0x0F; 0x38; 0xF0 ] rm (rd_of_reg64 reg)
  | (Reg64 reg, ((Reg8L _ | Reg8H _ | Mem {typ = BYTE; _} | Mem64_RIP (BYTE, _, _)) as rm)) ->
    (* CRC32 r64, r/m8 *)
    buf_int8 b 0xF2;
    emit_mod_rm_reg b rexw [ 0x0F; 0x38; 0xF0 ] rm (rd_of_reg64 reg)
  | (Reg32 reg, ((Reg16 _ | Reg32 _ | Mem _ | Mem64_RIP _) as rm)) ->
    (* CRC32 r32, r/m16 and CRC32 r32, r/m32 *)
    buf_int8 b 0xF2;
    emit_mod_rm_reg b no_rex [ 0x0F; 0x38; 0xF1 ] rm (rd_of_reg64 reg)
  | (Reg64 reg, ((Reg64 _ | Mem _ | Mem64_RIP _) as rm)) ->
     (* CRC32 r64, r/m64 *)
    buf_int8 b 0xF2;
    emit_mod_rm_reg b rexw [ 0x0F; 0x38; 0xF1 ] rm (rd_of_reg64 reg)
  | _ -> assert false

let emit_BSWAP b = function
  | Reg32 reg -> buf_opcodes b [ 0x0F; 0xC8 + reg7 (rd_of_reg64 reg) ]
  | Reg64 reg ->
      let reg = rd_of_reg64 reg in
      emit_rex b (rexw lor rexb_opcode reg);
      buf_opcodes b [ 0x0F; 0xC8 + reg7 reg ]
  | _ -> assert false

let emit_FLDCW b = function
  | (Mem _ | Mem64_RIP _) as rm -> emit_mod_rm_reg b no_rex [ 0xD9 ] rm 5
  | _ -> assert false

let emit_FXCH b = function
  | Regf (ST i) -> buf_opcodes b [ 0xD9; 0xC8 + i ]
  | _ -> assert false

let emit_FLD b = function
  | Mem { typ = REAL4 | DWORD } as rm -> emit_mod_rm_reg b 0 [ 0xD9 ] rm 0
  | Mem { typ = REAL8 | QWORD } as rm -> emit_mod_rm_reg b 0 [ 0xDD ] rm 0
  | Regf (ST i) -> buf_opcodes b [ 0xD9; 0xC0 + i ]
  | _ -> assert false

let emit_FCOMP b = function
  | Mem { typ = REAL4 | DWORD } as rm -> emit_mod_rm_reg b no_rex [ 0xD8 ] rm 3
  | Mem { typ = REAL8 | QWORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDC ] rm 3
  | Regf (ST i) -> buf_opcodes b [ 0xD8; 0xD8 + i ]
  | _ -> assert false

let emit_FXXX reg b rm =
  match rm with
  | Mem { typ = REAL4 | DWORD } -> emit_mod_rm_reg b no_rex [ 0xD8 ] rm reg
  | Mem { typ = REAL8 | QWORD } -> emit_mod_rm_reg b no_rex [ 0xDC ] rm reg
  | _ -> assert false

let emit_FADD = emit_FXXX 0

let emit_FMUL = emit_FXXX 1

(* let emit_FCOM = emit_FXXX 2 *)
(* let emit_FCOMP = emit_FXXX 3 *)
let emit_FSUB = emit_FXXX 4

let emit_FSUBR = emit_FXXX 5

let emit_FDIV = emit_FXXX 6

let emit_FDIVR = emit_FXXX 7

let emit_FILD b = function
  | Mem { typ = QWORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDF ] rm 5
  | Mem { typ = DWORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDB ] rm 0
  | Mem { typ = WORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDF ] rm 0
  | _ -> assert false

let emit_FISTP b = function
  | Mem { typ = WORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDF ] rm 3
  | Mem { typ = DWORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDB ] rm 3
  | Mem { typ = QWORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDF ] rm 7
  | _ -> assert false

let emit_FNSTCW b = function
  | Mem { typ = NONE | WORD } as rm ->
      emit_mod_rm_reg b no_rex [ 0x9B; 0xD9 ] rm 7
  | _ -> assert false

let emit_FNSTSW b = function
  | Reg16 RAX -> buf_opcodes b [ 0xDF; 0xE0 ]
  | Mem { typ = NONE | WORD } as rm -> emit_mod_rm_reg b no_rex [ 0xDD ] rm 7
  | _ -> assert false

let emit_FXXXP opcode b a1 a2 =
  match (a1, a2) with
  | Regf (ST i), Regf (ST 0) -> buf_opcodes b [ 0xDE; opcode + i ]
  | _ -> assert false

let emit_FADDP b = emit_FXXXP 0xC0 b

let emit_FMULP b = emit_FXXXP 0xC8 b

let emit_FSUBRP b = emit_FXXXP 0xE0 b

let emit_FSUBP b = emit_FXXXP 0xE8 b

let emit_FDIVRP b = emit_FXXXP 0xF0 b

let emit_FDIVP b = emit_FXXXP 0xF8 b

let emit_XCHG b src dst =
  (* TODO: test ! *)
  match (dst, src) with
  | ((Reg64 _ | Mem _ | Mem64_RIP _) as rm), Reg64 reg
  | Reg64 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      (* r64, r/m64 *)
      emit_mod_rm_reg b rexw [ 0x87 ] rm (rd_of_reg64 reg)
  | ((Reg32 _ | Mem _ | Mem64_RIP _) as rm), Reg32 reg
  | Reg32 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      (* r32, r/m32 *)
      emit_mod_rm_reg b no_rex [ 0x87 ] rm (rd_of_reg64 reg)
  | ((Reg16 _ | Mem _ | Mem64_RIP _) as rm), Reg16 reg
  | Reg16 reg, ((Mem _ | Mem64_RIP _) as rm) ->
      (* r16, r/m16 *)
      emit_mod_rm_reg b rex [ 0x66; 0x87 ] rm (rd_of_reg64 reg)
  | ( ((Reg8L _ | Reg8H _ | Mem _ | Mem64_RIP _) as rm),
      ((Reg8L _ | Reg8H _) as reg) )
  | ((Reg8L _ | Reg8H _) as reg), ((Mem _ | Mem64_RIP _) as rm) ->
      (* r8, r/m8 *)
      emit_mod_rm_reg b no_rex [ 0x86 ] rm (rd_of_reg8 reg)
  | _ -> assert false

let assemble_instr b loc = function
  | ADD (src, dst) -> emit_ADD b dst src
  | ADDSD (src, dst) -> emit_addsd b dst src
  | AND (src, dst) -> emit_AND b dst src
  | ANDPD (src, dst) -> emit_andpd b dst src
  | BSF (src, dst) -> emit_bsf b ~dst ~src
  | BSR (src, dst) -> emit_bsr b ~dst ~src
  | BSWAP arg -> emit_BSWAP b arg
  | CALL dst -> emit_call b dst
  | CVTSI2SD (src, dst) -> emit_CVTSI2SD b dst src
  | CVTSD2SI (src, dst) -> emit_CVTSD2SI b dst src
  | CVTTSD2SI (src, dst) -> emit_CVTTSD2SI b dst src
  | CVTSD2SS (src, dst) -> emit_CVTSD2SS b dst src
  | CVTSS2SD (src, dst) -> emit_CVTSS2SD b dst src
  | COMISD (src, dst) -> emit_comisd b dst src
  | CQO -> emit_cqto b
  | CRC32 (src, dst) -> emit_crc32 b ~dst ~src
  | CMP (src, dst) -> emit_CMP b dst src
  | CMPSD (condition, src, dst) -> emit_cmpsd b ~condition ~dst ~src
  | CMOV (condition, src, dst) -> emit_cmov b condition dst src
  | CDQ -> buf_int8 b 0x99
  | DIVSD (src, dst) -> emit_divsd b dst src
  | DEC dst -> emit_DEC b [ dst ]
  | FCOMPP -> buf_opcodes b [ 0xDE; 0xD9 ]
  | FLD1 -> buf_opcodes b [ 0xD9; 0xE8 ]
  | FLDLG2 -> buf_opcodes b [ 0xD9; 0xEC ]
  | FLDLN2 -> buf_opcodes b [ 0xD9; 0xED ]
  | FLDZ -> buf_opcodes b [ 0xD9; 0xEE ]
  | FPATAN -> buf_opcodes b [ 0xD9; 0xF3 ]
  | FCOS -> buf_opcodes b [ 0xD9; 0xFF ]
  | FYL2X -> buf_opcodes b [ 0xD9; 0xF1 ]
  | FSIN -> buf_opcodes b [ 0xD9; 0xFE ]
  | FSQRT -> buf_opcodes b [ 0xD9; 0xFA ]
  | FPTAN -> buf_opcodes b [ 0xD9; 0xF2 ]
  | FSTP dst -> emit_FSTP b dst
  | FXCH arg -> emit_FXCH b arg
  | FCOMP arg -> emit_FCOMP b arg
  | FNSTSW arg -> emit_FNSTSW b arg
  | FNSTCW arg -> emit_FNSTCW b arg
  | FCHS -> buf_opcodes b [ 0xD9; 0xE0 ]
  | FABS -> buf_opcodes b [ 0xD9; 0xE1 ]
  | FADD arg -> emit_FADD b arg
  | FSUB arg -> emit_FSUB b arg
  | FMUL arg -> emit_FMUL b arg
  | FDIV arg -> emit_FDIV b arg
  | FDIVR arg -> emit_FDIVR b arg
  | FSUBR arg -> emit_FSUBR b arg
  | FILD arg -> emit_FILD b arg
  | FISTP arg -> emit_FISTP b arg
  | FLD arg -> emit_FLD b arg
  | FLDCW arg -> emit_FLDCW b arg
  | FADDP (src, dst) -> emit_FADDP b dst src
  | FSUBP (src, dst) -> emit_FSUBP b dst src
  | FMULP (src, dst) -> emit_FMULP b dst src
  | FDIVP (src, dst) -> emit_FDIVP b dst src
  | FSUBRP (src, dst) -> emit_FSUBRP b dst src
  | FDIVRP (src, dst) -> emit_FDIVRP b dst src
  | HLT -> buf_int8 b 0xF4
  | INC dst -> emit_inc b dst
  | IMUL (src, dst) -> emit_imul b dst src
  | MUL src -> emit_mul b ~src
  | IDIV dst -> emit_idiv b dst
  | J (condition, dst) -> emit_j b !loc condition dst
  | JMP dst -> emit_jmp b !loc dst
  | LEAVE -> emit_leave b
  | LEA (src, dst) -> emit_LEA b dst src
  | MAXSD (src, dst) -> emit_maxsd b ~dst ~src
  | MINSD (src, dst) -> emit_minsd b ~dst ~src
  | MOV (src, dst) -> emit_MOV b dst src
  | MOVAPD (src, dst) -> emit_movapd b dst src
  | MOVD (src, dst) -> emit_movd b ~dst ~src
  | MOVQ (src, dst) -> emit_movq b ~dst ~src
  | MOVLPD (src, dst) -> emit_movlpd b dst src
  | MOVSD (src, dst) -> emit_movsd b dst src
  | MOVSS (src, dst) -> emit_movss b dst src
  | MULSD (src, dst) -> emit_mulsd b dst src
  | MOVSX (src, dst) -> emit_movsx b dst src
  | MOVZX (src, dst) -> emit_MOVZX b dst src
  | MOVSXD (src, dst) -> emit_movsxd b dst src
  | NEG dst -> emit_neg b dst
  | NOP -> buf_int8 b 0x90
  | OR (src, dst) -> emit_OR b dst src
  | PAUSE -> emit_pause b
  | PUSH dst -> emit_push b dst
  | POP dst -> emit_pop b dst
  | POPCNT (src, dst) -> emit_popcnt b ~dst ~src
  | PREFETCH (is_write, hint, rm) -> emit_prefetch b ~is_write ~hint rm
  | RDTSC -> emit_rdtsc b
  | RDPMC -> emit_rdpmc b
  | RET -> emit_ret b
  | ROUNDSD (rounding, src, dst) -> emit_roundsd b dst rounding src
  | SAL (src, dst) -> emit_SAL b dst src
  | SAR (src, dst) -> emit_SAR b dst src
  | SHR (src, dst) -> emit_SHR b dst src
  | SUBSD (src, dst) -> emit_subsd b dst src
  | SQRTSD (src, dst) -> emit_sqrtsd b dst src
  | SUB (src, dst) -> emit_SUB b dst src
  | SET (condition, dst) -> emit_set b condition dst
  | TEST (src, dst) -> emit_test b dst src
  | UCOMISD (src, dst) -> emit_ucomisd b dst src
  | XCHG (src, dst) -> emit_XCHG b dst src
  | XOR (src, dst) -> emit_XOR b dst src
  | XORPD (src, dst) -> emit_xorpd b dst src

let assemble_line b loc ins =
  try
    match ins with
    | Ins instr ->
        assemble_instr b loc instr;
        incr loc
    | Comment _ -> ()
    | Global s -> (get_symbol b s).sy_global <- true
    | Quad (Const n) -> buf_int64L b n
    | Quad cst ->
        record_local_reloc b (RelocConstant (cst, B64));
        buf_int64L b 0L
    | Long (Const n) -> buf_int32L b n
    | Long cst ->
        record_local_reloc b (RelocConstant (cst, B32));
        buf_int32L b 0L
    | Word (Const n) -> buf_int16L b n
    | Word cst ->
        record_local_reloc b (RelocConstant (cst, B16));
        buf_int16L b 0L
    | Byte (Const n) -> buf_int8L b n
    | Byte cst ->
        record_local_reloc b (RelocConstant (cst, B8));
        buf_int8L b 0L
    | NewLabel (s, _) -> declare_label b s
    | Bytes s -> Buffer.add_string b.buf s
    | External (_, _) -> ()
    | Set (_, _) -> assert false
    | Section _ -> assert false
    | Mode386 -> assert (system = S_win32)
    | Model _ -> assert (system = S_win32)
    | Cfi_startproc -> ()
    | Cfi_endproc -> ()
    | Cfi_adjust_cfa_offset _ -> ()
    | File _ -> ()
    | Loc _ -> ()
    | Private_extern _ -> assert false
    | Indirect_symbol _ -> assert false
    | Type (lbl, kind) -> (get_symbol b lbl).sy_type <- Some kind
    | Size (lbl, cst) -> (
        match eval_const b (Buffer.length b.buf) cst with
        | Rint n -> (get_symbol b lbl).sy_size <- Some (Int64.to_int n)
        | _ -> assert false)
    | Align (data, n) -> (
        (* TODO: Buffer.length = 0 => set section align *)
        let pos = Buffer.length b.buf in
        let current = pos mod n in
        if current > 0 then
          let n = n - current in
          if data then
            for _ = 1 to n do
              buf_int8 b 0x00
            done
          else
            match n with
            | 0 -> ()
            | 1 -> buf_int8 b 0x90
            | 2 -> buf_opcodes b [ 0x66; 0x90 ]
            | 3 -> buf_opcodes b [ 0x0f; 0x1f; 0x00 ]
            | 4 -> buf_opcodes b [ 0x0f; 0x1f; 0x40; 0x00 ]
            | 5 -> buf_opcodes b [ 0x0f; 0x1f; 0x44; 0x00; 0x00 ]
            | 6 ->
                buf_opcodes b [ 0x66; 0x0f; 0x1f; 0x44 ];
                buf_int16L b 0L
            | 7 ->
                buf_opcodes b [ 0x0f; 0x1f; 0x80 ];
                buf_int32L b 0L
            | _ ->
                for _ = 9 to n do
                  buf_int8 b 0x66
                done;
                buf_opcodes b [ 0x0f; 0x1f; 0x84; 0x00 ];
                buf_int32L b 0L)
    | Space n ->
        (* TODO: in text section, should be NOP *)
        for _ = 1 to n do
          buf_int8 b 0
        done
    | Hidden _ | Weak _ | Reloc _ | NewLine | Sleb128 _ | Uleb128 _ | Direct_assignment _ -> ()
  with e ->
    Printf.eprintf "Exception %s:\n%!" (Printexc.to_string e);
    (*
    Printf.eprintf "   masm: %s%!"
      (string_of_buffer X86_masm.bprint_instr !arch64 ins);
    Printf.eprintf "   gas : %s%!"
      (string_of_buffer X86_gas.bprint_instr !arch64 ins);
*)
    raise e

let add_patch b pos size v = b.patches <- (pos, size, v) :: b.patches

let assemble_section arch section =
  (match arch with X86 -> instr_size := 5 | X64 -> instr_size := 6);
  forced_long_jumps := IntSet.empty;
  String.Tbl.clear local_labels;

  let icount = ref 0 in
  ArrayLabels.iter section.sec_instrs ~f:(function
    | NewLabel (lbl, _) ->
        String.Tbl.add local_labels lbl !icount 
    | Ins _ -> incr icount
    | _ -> ());

  let passes = ref 0 in

  let rec iter_assemble () =
    incr passes;

    (*     if !passes >= 2 then Printf.eprintf "[binary backend] pass %i\n%!" !passes; *)
    let b = new_buffer section in
    local_relocs := [];

    let loc = ref 0 in
    ArrayLabels.iter ~f:(assemble_line b loc) section.sec_instrs;

    let retry = ref false in

    let do_local_reloc pos = function
      | RelocShortJump (label, loc) ->
          let source_pos = pos + 1 in
          let target_pos = label_pos b label in
          let n = target_pos - source_pos in
          if n >= -128 && n < 128 then add_patch b pos B8 (Int64.of_int n)
          else (
            (* We thought this could be a short jump, but actually, this is
               not the case.  Force another pass and remember to use
               a long jump for this instruction. *)
            forced_long_jumps := IntSet.add loc !forced_long_jumps;
            retry := true)
      | RelocCall label | RelocLongJump label ->
          let source_pos = pos + 4 in
          let target_pos = label_pos b label in
          let n = target_pos - source_pos in
          add_patch b pos B32 (Int64.of_int n)
      (* TODO: here, we resolve all computations in each section, i.e. we can only
         allow one external symbol per expression. We could tolerate more complex
         expressions if we delay resolution later, i.e. after all sections have
         been generated and all symbol positions are known. *)
      | RelocConstant (cst, data_size) -> (
          (* Printf.eprintf "RelocConstant (%s, %s)\n%!"
             (X86_gas.string_of_constant cst)
             (string_of_data_size data_size); *)
          let v = eval_const b pos cst in
          match (v, data_size) with
          | Rint n, _ -> add_patch b pos data_size n
          | Rabs (lbl, offset), B32 ->
              record_reloc b pos (Relocation.Kind.DIR32 (lbl, offset))
          | Rabs (lbl, offset), B64 ->
              record_reloc b pos (Relocation.Kind.DIR64 (lbl, offset))
          (* Relative relocation in data segment. We add an offset of 4 because
              REL32 relocations are computed with a PC at the end, while here, it
              is at the beginning. *)
          | Rrel (lbl, offset), B32 ->
              record_reloc b pos
                (Relocation.Kind.REL32 (lbl, Int64.add offset 4L))
          | Rrel _, _ -> assert false
          | Rabs _, _ -> assert false)
    in

    ListLabels.iter !local_relocs ~f:(fun (pos, local_reloc) ->
        do_local_reloc pos local_reloc);

    if !retry then iter_assemble () else b
  in
  iter_assemble ()

(* Relocations: we should compute all non-local relocations completely at the
   end. We should keep the last string/bytes couple to avoid duplication.
   All external labels should be absolute (ConstLabelAbs), while internal
   labels should be replaced by a relative computation. The goal is to make
   all computations either absolute, or relative to the current offset.
*)

let size b = Buffer.length b.buf

let add_patch ~offset ~size ~data t = add_patch t offset size data

let contents_mut b =
  let buf = Buffer.to_bytes b.buf in
  ListLabels.iter b.patches ~f:(fun (pos, nbits, v) ->
      (*    Printf.eprintf "Apply patch %s @%d\n%!" (string_of_data_size nbits) pos; *)
      match nbits with
      | B64 -> str_int64L buf pos v
      | B32 -> str_int32L buf pos v
      | B16 -> str_int16L buf pos v
      | B8 -> str_int8L buf pos v);
  buf

let contents b =
  Bytes.to_string (contents_mut b)

let relocations b = b.relocations

let labels b = b.labels