1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
(*
This module originated as a copy of interpreter/binary/decode.ml in the
reference implementation.
With adjustments from memory64.

The changes are:
 * Support for additional custom sections
 * Manual selective support for bulk-memory operations `memory_copy` and `memory_fill` (WebAssembly/spec@7fa2f20).
 * Support for passive data segments (incl. `MemoryInit`).
 * Support for table index in `call_indirect` (reference-types proposal).

The code is otherwise as untouched as possible, so that we can relatively
easily apply diffs from the original code (possibly manually).

TODO:
 The treatment of known custom sections is suboptimal and assumes
 they appear once, in a fixed relative order.
 It would be better to just rescan the whole binary for each such section,
 re-using the original custom section decoder from the reference implementation.
*)

module Error = Wasm.Error
module Source = Wasm.Source
module F32 = Wasm.F32
module F64 = Wasm.F64
module I32_convert = Wasm.I32_convert
module I64_convert = Wasm.I64_convert
module Utf8 = Lib.Utf8
open CustomModule
open Types

(* Decoding stream *)

type stream =
{
  name : string;
  bytes : string;
  pos : int ref;
}

exception EOS

let stream name bs = {name; bytes = bs; pos = ref 0}

let len s = String.length s.bytes
let pos s = !(s.pos)
let eos s = (pos s = len s)

let check n s = if pos s + n > len s then raise EOS
let skip n s = if n < 0 then raise EOS else check n s; s.pos := !(s.pos) + n

let read s = Char.code (s.bytes.[!(s.pos)])
let peek s = if eos s then None else Some (read s)
let get s = check 1 s; let b = read s in skip 1 s; b
let get_string n s = let i = pos s in skip n s; String.sub s.bytes i n

let checkpoint s = let p = !(s.pos) in fun () -> s.pos := p


(* Errors *)

module Code = Error.Make ()
exception Code = Code.Error

let string_of_byte b = Printf.sprintf "%02x" b

let position (s : stream) pos = Source.({file = s.name; line = -1; column = pos})
let region s left right =
  Source.({left = position s left; right = position s right})

let error s pos msg = raise (Code (region s pos pos, msg))
let require b s pos msg = if not b then error s pos msg

let guard f s =
  try f s with EOS -> error s (len s) "unexpected end of section or function"

let get = guard get
let get_string n = guard (get_string n)
let skip n = guard (skip n)

let expect b s msg = require (guard get s = b) s (pos s - 1) msg
let illegal s pos b = error s pos ("illegal opcode " ^ string_of_byte b)

let at f s =
  let left = pos s in
  let x = f s in
  let right = pos s in
  Source.(x @@ region s left right)



(* Generic values *)

let u8 s =
  get s

let u16 s =
  let lo = u8 s in
  let hi = u8 s in
  hi lsl 8 + lo

let u32 s =
  let lo = Int32.of_int (u16 s) in
  let hi = Int32.of_int (u16 s) in
  Int32.(add lo (shift_left hi 16))

let u64 s =
  let lo = I64_convert.extend_i32_u (u32 s) in
  let hi = I64_convert.extend_i32_u (u32 s) in
  Int64.(add lo (shift_left hi 32))

let rec vuN n s =
  require (n > 0) s (pos s) "integer representation too long";
  let b = u8 s in
  require (n >= 7 || b land 0x7f < 1 lsl n) s (pos s - 1) "integer too large";
  let x = Int64.of_int (b land 0x7f) in
  if b land 0x80 = 0 then x else Int64.(logor x (shift_left (vuN (n - 7) s) 7))

let rec vsN n s =
  require (n > 0) s (pos s) "integer representation too long";
  let b = u8 s in
  let mask = (-1 lsl (n - 1)) land 0x7f in
  require (n >= 7 || b land mask = 0 || b land mask = mask) s (pos s - 1)
    "integer too large";
  let x = Int64.of_int (b land 0x7f) in
  if b land 0x80 = 0
  then (if b land 0x40 = 0 then x else Int64.(logor x (logxor (-1L) 0x7fL)))
  else Int64.(logor x (shift_left (vsN (n - 7) s) 7))

let vu8 s = Int64.to_int32 (vuN 8 s)
let vu32 s = Int64.to_int32 (vuN 32 s)
let vu64 s = vuN 64 s
let vs7 s = Int64.to_int (vsN 7 s)
let vs32 s = Int64.to_int32 (vsN 32 s)
let vs33 s = I32_convert.wrap_i64 (vsN 33 s)
let vs64 s = vsN 64 s
let f32 s = F32.of_bits (u32 s)
let f64 s = F64.of_bits (u64 s)

let len32 s =
  let pos = pos s in
  let n = vu32 s in
  if I32.le_u n (Int32.of_int (len s)) then Int32.to_int n else
    error s pos "length out of bounds"

let string s = let n = len32 s in get_string n s
let rec list f n s = if n = 0 then [] else let x = f s in x :: list f (n - 1) s
let opt f b s = if b then Some (f s) else None
let vec f s = let n = len32 s in list f n s

let name s =
  let pos = pos s in
  try Utf8.decode (string s) with Utf8.Utf8 ->
    error s pos "malformed UTF-8 encoding"

let sized (f : int -> stream -> 'a) (s : stream) =
  let size = len32 s in
  let start = pos s in
  let x = f size s in
  require (pos s = start + size) s start "section size mismatch";
  x


(* Types *)

open Types

let value_type s =
  match vs7 s with
  | -0x01 -> I32Type
  | -0x02 -> I64Type
  | -0x03 -> F32Type
  | -0x04 -> F64Type
  | _ -> error s (pos s - 1) "malformed value type"

let elem_type s =
  match vs7 s with
  | -0x10 -> FuncRefType
  | _ -> error s (pos s - 1) "malformed element type"

let stack_type s = vec value_type s
let func_type s =
  match vs7 s with
  | -0x20 ->
    let ins = stack_type s in
    let out = stack_type s in
    FuncType (ins, out)
  | _ -> error s (pos s - 1) "malformed function type"

let limits vu s =
  let flags = u8 s in
  require (flags land 0xfa = 0) s (pos s - 1) "malformed limits flags";
  let has_max = (flags land 1 = 1) in
  let is64 = (flags land 4 = 4) in
  let min = vu s in
  let max = opt vu has_max s in
  {min; max}, is64

let table_type s =
  let t = elem_type s in
  let lim, is64 = limits vu32 s in
  require (not is64) s (pos s - 1) "tables cannot have 64-bit indices";
  TableType (lim, t)

let memory_type s =
  let lim, is64 = limits vu64 s in
  MemoryType (lim, if is64 then I64IndexType else I32IndexType)

let mutability s =
  match u8 s with
  | 0 -> Immutable
  | 1 -> Mutable
  | _ -> error s (pos s - 1) "malformed mutability"

let global_type s =
  let t = value_type s in
  let mut = mutability s in
  GlobalType (t, mut)


(* Decode instructions *)

open Ast
open Operators

let var s = vu32 s

let op s = u8 s
let end_ s = expect 0x0b s "END opcode expected"
let zero s = expect 0x00 s "zero byte expected"

let memop s =
  let align = vu32 s in
  require (I32.le_u align 32l) s (pos s - 1) "malformed memop flags";
  let offset = vu64 s in
  Int32.to_int align, offset

let block_type s =
  match peek s with
  | Some 0x40 -> skip 1 s; ValBlockType None
  | Some b when b land 0xc0 = 0x40 -> ValBlockType (Some (value_type s))
  | _ -> VarBlockType (at vs33 s)

let math_prefix s =
  let pos = pos s in
  match op s with
  | 0x00 -> i32_trunc_sat_f32_s
  | 0x01 -> i32_trunc_sat_f32_u
  | 0x02 -> i32_trunc_sat_f64_s
  | 0x03 -> i32_trunc_sat_f64_u
  | 0x04 -> i64_trunc_sat_f32_s
  | 0x05 -> i64_trunc_sat_f32_u
  | 0x06 -> i64_trunc_sat_f64_s
  | 0x07 -> i64_trunc_sat_f64_u
  (* Manual extension for specific bulk-memory operations *)
  | 0x0a -> zero s; zero s; memory_copy
  | 0x0b -> zero s; memory_fill
  (* End of manual extension *)
  (* Manual extension for passive data segments *)
  | 0x08 ->
    let x = at var s in
    zero s; memory_init x
  (* End of manual extension *)
  | b -> illegal s pos b

let rec instr s =
  let pos = pos s in
  match op s with
  | 0x00 -> unreachable
  | 0x01 -> nop

  | 0x02 ->
    let bt = block_type s in
    let es' = instr_block s in
    end_ s;
    block bt es'
  | 0x03 ->
    let bt = block_type s in
    let es' = instr_block s in
    end_ s;
    loop bt es'
  | 0x04 ->
    let bt = block_type s in
    let es1 = instr_block s in
    if peek s = Some 0x05 then begin
      expect 0x05 s "ELSE or END opcode expected";
      let es2 = instr_block s in
      end_ s;
      if_ bt es1 es2
    end else begin
      end_ s;
      if_ bt es1 []
    end

  | 0x05 -> error s pos "misplaced ELSE opcode"
  | 0x06| 0x07 | 0x08 | 0x09 | 0x0a as b -> illegal s pos b
  | 0x0b -> error s pos "misplaced END opcode"

  | 0x0c -> br (at var s)
  | 0x0d -> br_if (at var s)
  | 0x0e ->
    let xs = vec (at var) s in
    let x = at var s in
    br_table xs x
  | 0x0f -> return

  | 0x10 -> call (at var s)
  | 0x11 ->
    let y = at var s in
    let x = at var s in
    call_indirect x y

  | 0x12 | 0x13 | 0x14 | 0x15 | 0x16 | 0x17 | 0x18 | 0x19 as b -> illegal s pos b

  | 0x1a -> drop
  | 0x1b -> select

  | 0x1c | 0x1d | 0x1e | 0x1f as b -> illegal s pos b

  | 0x20 -> local_get (at var s)
  | 0x21 -> local_set (at var s)
  | 0x22 -> local_tee (at var s)
  | 0x23 -> global_get (at var s)
  | 0x24 -> global_set (at var s)

  | 0x25 | 0x26 | 0x27 as b -> illegal s pos b

  | 0x28 -> let a, o = memop s in i32_load a o
  | 0x29 -> let a, o = memop s in i64_load a o
  | 0x2a -> let a, o = memop s in f32_load a o
  | 0x2b -> let a, o = memop s in f64_load a o
  | 0x2c -> let a, o = memop s in i32_load8_s a o
  | 0x2d -> let a, o = memop s in i32_load8_u a o
  | 0x2e -> let a, o = memop s in i32_load16_s a o
  | 0x2f -> let a, o = memop s in i32_load16_u a o
  | 0x30 -> let a, o = memop s in i64_load8_s a o
  | 0x31 -> let a, o = memop s in i64_load8_u a o
  | 0x32 -> let a, o = memop s in i64_load16_s a o
  | 0x33 -> let a, o = memop s in i64_load16_u a o
  | 0x34 -> let a, o = memop s in i64_load32_s a o
  | 0x35 -> let a, o = memop s in i64_load32_u a o

  | 0x36 -> let a, o = memop s in i32_store a o
  | 0x37 -> let a, o = memop s in i64_store a o
  | 0x38 -> let a, o = memop s in f32_store a o
  | 0x39 -> let a, o = memop s in f64_store a o
  | 0x3a -> let a, o = memop s in i32_store8 a o
  | 0x3b -> let a, o = memop s in i32_store16 a o
  | 0x3c -> let a, o = memop s in i64_store8 a o
  | 0x3d -> let a, o = memop s in i64_store16 a o
  | 0x3e -> let a, o = memop s in i64_store32 a o

  | 0x3f ->
    expect 0x00 s "zero flag expected";
    memory_size
  | 0x40 ->
    expect 0x00 s "zero flag expected";
    memory_grow

  | 0x41 -> i32_const (at vs32 s)
  | 0x42 -> i64_const (at vs64 s)
  | 0x43 -> f32_const (at f32 s)
  | 0x44 -> f64_const (at f64 s)

  | 0x45 -> i32_eqz
  | 0x46 -> i32_eq
  | 0x47 -> i32_ne
  | 0x48 -> i32_lt_s
  | 0x49 -> i32_lt_u
  | 0x4a -> i32_gt_s
  | 0x4b -> i32_gt_u
  | 0x4c -> i32_le_s
  | 0x4d -> i32_le_u
  | 0x4e -> i32_ge_s
  | 0x4f -> i32_ge_u

  | 0x50 -> i64_eqz
  | 0x51 -> i64_eq
  | 0x52 -> i64_ne
  | 0x53 -> i64_lt_s
  | 0x54 -> i64_lt_u
  | 0x55 -> i64_gt_s
  | 0x56 -> i64_gt_u
  | 0x57 -> i64_le_s
  | 0x58 -> i64_le_u
  | 0x59 -> i64_ge_s
  | 0x5a -> i64_ge_u

  | 0x5b -> f32_eq
  | 0x5c -> f32_ne
  | 0x5d -> f32_lt
  | 0x5e -> f32_gt
  | 0x5f -> f32_le
  | 0x60 -> f32_ge

  | 0x61 -> f64_eq
  | 0x62 -> f64_ne
  | 0x63 -> f64_lt
  | 0x64 -> f64_gt
  | 0x65 -> f64_le
  | 0x66 -> f64_ge

  | 0x67 -> i32_clz
  | 0x68 -> i32_ctz
  | 0x69 -> i32_popcnt
  | 0x6a -> i32_add
  | 0x6b -> i32_sub
  | 0x6c -> i32_mul
  | 0x6d -> i32_div_s
  | 0x6e -> i32_div_u
  | 0x6f -> i32_rem_s
  | 0x70 -> i32_rem_u
  | 0x71 -> i32_and
  | 0x72 -> i32_or
  | 0x73 -> i32_xor
  | 0x74 -> i32_shl
  | 0x75 -> i32_shr_s
  | 0x76 -> i32_shr_u
  | 0x77 -> i32_rotl
  | 0x78 -> i32_rotr

  | 0x79 -> i64_clz
  | 0x7a -> i64_ctz
  | 0x7b -> i64_popcnt
  | 0x7c -> i64_add
  | 0x7d -> i64_sub
  | 0x7e -> i64_mul
  | 0x7f -> i64_div_s
  | 0x80 -> i64_div_u
  | 0x81 -> i64_rem_s
  | 0x82 -> i64_rem_u
  | 0x83 -> i64_and
  | 0x84 -> i64_or
  | 0x85 -> i64_xor
  | 0x86 -> i64_shl
  | 0x87 -> i64_shr_s
  | 0x88 -> i64_shr_u
  | 0x89 -> i64_rotl
  | 0x8a -> i64_rotr

  | 0x8b -> f32_abs
  | 0x8c -> f32_neg
  | 0x8d -> f32_ceil
  | 0x8e -> f32_floor
  | 0x8f -> f32_trunc
  | 0x90 -> f32_nearest
  | 0x91 -> f32_sqrt
  | 0x92 -> f32_add
  | 0x93 -> f32_sub
  | 0x94 -> f32_mul
  | 0x95 -> f32_div
  | 0x96 -> f32_min
  | 0x97 -> f32_max
  | 0x98 -> f32_copysign

  | 0x99 -> f64_abs
  | 0x9a -> f64_neg
  | 0x9b -> f64_ceil
  | 0x9c -> f64_floor
  | 0x9d -> f64_trunc
  | 0x9e -> f64_nearest
  | 0x9f -> f64_sqrt
  | 0xa0 -> f64_add
  | 0xa1 -> f64_sub
  | 0xa2 -> f64_mul
  | 0xa3 -> f64_div
  | 0xa4 -> f64_min
  | 0xa5 -> f64_max
  | 0xa6 -> f64_copysign

  | 0xa7 -> i32_wrap_i64
  | 0xa8 -> i32_trunc_f32_s
  | 0xa9 -> i32_trunc_f32_u
  | 0xaa -> i32_trunc_f64_s
  | 0xab -> i32_trunc_f64_u
  | 0xac -> i64_extend_i32_s
  | 0xad -> i64_extend_i32_u
  | 0xae -> i64_trunc_f32_s
  | 0xaf -> i64_trunc_f32_u
  | 0xb0 -> i64_trunc_f64_s
  | 0xb1 -> i64_trunc_f64_u
  | 0xb2 -> f32_convert_i32_s
  | 0xb3 -> f32_convert_i32_u
  | 0xb4 -> f32_convert_i64_s
  | 0xb5 -> f32_convert_i64_u
  | 0xb6 -> f32_demote_f64
  | 0xb7 -> f64_convert_i32_s
  | 0xb8 -> f64_convert_i32_u
  | 0xb9 -> f64_convert_i64_s
  | 0xba -> f64_convert_i64_u
  | 0xbb -> f64_promote_f32

  | 0xbc -> i32_reinterpret_f32
  | 0xbd -> i64_reinterpret_f64
  | 0xbe -> f32_reinterpret_i32
  | 0xbf -> f64_reinterpret_i64

  | 0xc0 -> i32_extend8_s
  | 0xc1 -> i32_extend16_s
  | 0xc2 -> i64_extend8_s
  | 0xc3 -> i64_extend16_s
  | 0xc4 -> i64_extend32_s

  | 0xfc -> math_prefix s

  | b -> illegal s pos b

and instr_block s = List.rev (instr_block' s [])
and instr_block' s es =
  match peek s with
  | None | Some (0x05 | 0x0b) -> es
  | _ ->
    let pos = pos s in
    let e' = instr s in
    instr_block' s (Source.(e' @@ region s pos pos) :: es)

let const s =
  let c = at instr_block s in
  end_ s;
  c


(* Sections *)

let id s =
  let bo = peek s in
  Option.map
    (function
    | 0 -> `CustomSection
    | 1 -> `TypeSection
    | 2 -> `ImportSection
    | 3 -> `FuncSection
    | 4 -> `TableSection
    | 5 -> `MemorySection
    | 6 -> `GlobalSection
    | 7 -> `ExportSection
    | 8 -> `StartSection
    | 9 -> `ElemSection
    | 10 -> `CodeSection
    | 11 -> `DataSection
    | 12 -> `DataCountSection
    | _ -> error s (pos s) "malformed section id"
    ) bo

let section_with_size tag f default s =
  match id s with
  | Some tag' when tag' = tag -> ignore (u8 s); sized f s
  | _ -> default

let section tag f default s =
  section_with_size tag (fun _ -> f) default s


(* Type section *)

let type_ s = at func_type s

let type_section s =
  section `TypeSection (vec type_) [] s


(* Import section *)

let import_desc s =
  match u8 s with
  | 0x00 -> FuncImport (at var s)
  | 0x01 -> TableImport (table_type s)
  | 0x02 -> MemoryImport (memory_type s)
  | 0x03 -> GlobalImport (global_type s)
  | _ -> error s (pos s - 1) "malformed import kind"

let import s =
  let module_name = name s in
  let item_name = name s in
  let idesc = at import_desc s in
  {module_name; item_name; idesc}

let import_section s =
  section `ImportSection (vec (at import)) [] s


(* Function section *)

let func_section s =
  section `FuncSection (vec (at var)) [] s


(* Table section *)

let table s =
  let ttype = table_type s in
  {ttype}

let table_section s =
  section `TableSection (vec (at table)) [] s


(* Memory section *)

let memory s =
  let mtype = memory_type s in
  {mtype}

let memory_section s =
  section `MemorySection (vec (at memory)) [] s


(* Global section *)

let global s =
  let gtype = global_type s in
  let value = const s in
  {gtype; value}

let global_section s =
  section `GlobalSection (vec (at global)) [] s


(* Export section *)

let export_desc s =
  match u8 s with
  | 0x00 -> FuncExport (at var s)
  | 0x01 -> TableExport (at var s)
  | 0x02 -> MemoryExport (at var s)
  | 0x03 -> GlobalExport (at var s)
  | _ -> error s (pos s - 1) "malformed export kind"

let export s =
  let name = name s in
  let edesc = at export_desc s in
  {name; edesc}

let export_section s =
  section `ExportSection (vec (at export)) [] s


(* Start section *)

let start_section s =
  section `StartSection (opt (at var) true) None s


(* Code section *)

let local s =
  let n = vu32 s in
  let t = value_type s in
  n, t

let code _ s =
  let pos = pos s in
  let nts = vec local s in
  let ns = List.map (fun (n, _) -> I64_convert.extend_i32_u n) nts in
  require (I64.lt_u (List.fold_left I64.add 0L ns) 0x1_0000_0000L)
    s pos "too many locals";
  let locals = List.flatten (List.map (Lib.Fun.uncurry Lib.List32.make) nts) in
  let body = instr_block s in
  end_ s;
  {locals; body; ftype = Source.((-1l) @@ Source.no_region)}

let code_section s =
  section `CodeSection (vec (at (sized code))) [] s


(* Element section *)

(* Manual extension for passive data segments *)
let passive s =
  Passive

let active s =
  let index = at var s in
  let offset = const s in
  Active {index; offset}

let active_zero s =
  let index = Source.(0l @@ no_region) in
  let offset = const s in
  Active {index; offset}
(* End of manual extension *)

let segment dat s =
  let index = at var s in
  let offset = const s in
  let init = dat s in
  {index; offset; init}

let table_segment s =
  segment (vec (at var)) s

let elem_section s =
  section `ElemSection (vec (at table_segment)) [] s


(* Manual extension for passive data segments *)
(* Data section *)

let data s =
  match vu32 s with
  | 0x00l ->
    let dmode = at active_zero s in
    let dinit = string s in
    {dinit; dmode}
  | 0x01l ->
    let dmode = at passive s in
    let dinit = string s in
    {dinit; dmode}
  | 0x02l ->
    let dmode = at active s in
    let dinit = string s in
    {dinit; dmode}
  | _ -> error s (pos s - 1) "malformed data segment kind"

let data_section s =
  section `DataSection (vec (at data)) [] s


(* DataCount section *)

let data_count s =
  Some (vu32 s)

let data_count_section s =
  section `DataCountSection data_count None s
(* End of manual extension *)

(* Custom sections *)

let custom_section (name_pred : int list -> bool) (f : int -> stream -> 'a) (default : 'a) (s : stream) =
  let rewind = checkpoint s in
  match id s with
  | Some `CustomSection ->
    ignore (u8 s);
    let sec_size = len32 s in
    let sec_start = pos s in
    let sec_end = sec_start + sec_size in
    if name_pred (name s)
    then (* this is the right custom section *)
      let x = f sec_end s in
      require (pos s = sec_end) s sec_start "custom section size mismatch";
      x
    else begin (* wrong custom section, rewind *)
      rewind ();
      default
    end
  | Some _ -> default
  | _ -> default


let icp_name suffix =
  let public_name = Utf8.decode ("icp:public " ^ suffix) in
  let private_name = Utf8.decode ("icp:private " ^ suffix) in
  fun name ->
    if public_name = name then
      Some true
    else if private_name = name then
      Some false
    else None

let icp_custom_section n (f : int -> stream -> 'a) (default : (bool * 'a) option) (s : stream) =
  let rewind = checkpoint s in
  match id s with
  | Some `CustomSection ->
    ignore (u8 s);
    let sec_size = len32 s in
    let sec_start = pos s in
    let sec_end = sec_start + sec_size in
    let name = name s in
    let opt = icp_name n name in
    begin
    match opt with
    | Some b ->
      (* this is the right custom section *)
      let x = f sec_end s in
      require (pos s = sec_end) s sec_start "custom section size mismatch";
      Some (b, x)
    | None -> begin (* wrong custom section, rewind *)
      rewind ();
      default
      end
    end
  | Some _ -> default
  | _ -> default

(* Dylink section *)

(* Cf. https://llvm.org/doxygen/WasmObjectFile_8cpp_source.html and 
   https://github.com/WebAssembly/tool-conventions/blob/main/DynamicLinking.md *)
let rec dylink0 sec_end s =
  let dylink0_subsection s =
    let subsection_type = vu8 s in
    let subsection_size = Int32.to_int (vu32 s) in
    let subsection_end = pos s + subsection_size in
    match subsection_type with
    | 0x01l -> (* mem_info *)
      let memory_size = vu32 s in
      let memory_alignment = vu32 s in
      let table_size = vu32 s in
      let table_alignment = vu32 s in
      assert (pos s = subsection_end);
      MemInfo { memory_size; memory_alignment; table_size; table_alignment }
    | 0x02l -> (* needed *)
      let dynlibs = vec string s in
      assert (pos s = subsection_end);
      Needed dynlibs
    | _ -> error s (pos s - 1) "unsupported dylink.0 subsection"
  in
  assert (pos s <= sec_end);
  if pos s = sec_end then []
  else
    let subsection = dylink0_subsection s in
    subsection :: (dylink0 sec_end s)

let is_dylink0 n = (n = Utf8.decode "dylink.0")

let dylink0_section s =
  custom_section is_dylink0 dylink0 [] s

(* Name custom section *)

let repeat_until p_end s x0 f =
  let rec go x =
    require (pos s <= p_end) s (pos s) "repeat_until overshot";
    if pos s = p_end then x else go (f x s)
  in go x0

let assoc_list f = vec (fun s ->
    let i = var s in
    let x = f s in
    (i, x)
  )
let name_map = assoc_list string
let indirect_name_map = assoc_list name_map

let name_section_subsection (ns : name_section) (s : stream) : name_section =
  match u8 s with
  | 0 -> (* module name *)
    let mod_name = sized (fun _ -> string) s in
    { ns with module_ = Some mod_name }
  | 1 -> (* function names *)
    let func_names = sized (fun _ -> name_map) s in
    { ns with function_names = ns.function_names @ func_names }
  | 2 -> (* local names *)
    let loc_names = sized (fun _ -> indirect_name_map) s in
    { ns with locals_names = ns.locals_names @ loc_names }
  (* The following subsections are not in the standard yet, but from the extended-name-section proposal
     https://github.com/WebAssembly/extended-name-section/blob/master/proposals/extended-name-section/Overview.md
  *)
  | 3 -> (* label names *)
    let label_names = sized (fun _ -> indirect_name_map) s in
    { ns with label_names = ns.label_names @ label_names }
  | 4 -> (* type names *)
    let type_names = sized (fun _ -> name_map) s in
    { ns with type_names = ns.type_names @ type_names }
  | 5 -> (* table names *)
    let table_names = sized (fun _ -> name_map) s in
    { ns with table_names = ns.table_names @ table_names }
  | 6 -> (* memory names *)
    let memory_names = sized (fun _ -> name_map) s in
    { ns with memory_names = ns.memory_names @ memory_names }
  | 7 -> (* global names *)
    let global_names = sized (fun _ -> name_map) s in
    { ns with global_names = ns.global_names @ global_names }
  | 8 -> (* elem segment names *)
    let elem_segment_names = sized (fun _ -> name_map) s in
    { ns with elem_segment_names = ns.elem_segment_names @ elem_segment_names }
  | 9 -> (* data segment names *)
    let data_segment_names = sized (fun _ -> name_map) s in
    { ns with data_segment_names = ns.data_segment_names @ data_segment_names }
  | i -> error s (pos s) (Printf.sprintf "unknown name section subsection id %d" i)

let name_section_content p_end s =
  repeat_until p_end s empty_name_section name_section_subsection

let is_name n = (n = Utf8.decode "name")

let name_section s =
  custom_section is_name name_section_content empty_name_section s

(* Motoko sections *)

let motoko_section_subsection (ms : motoko_sections) s =
  match u8 s with
  | 0 ->
    let labels = sized (fun _ -> vec string) s in
    { ms with labels = ms.labels @ labels }
  | i -> error s (pos s) (Printf.sprintf "unknown motoko section subsection id %d" i)

let motoko_section_content p_end s =
  repeat_until p_end s empty_motoko_sections motoko_section_subsection

let is_motoko n = (n = Utf8.decode "motoko")

let utf8 sec_end s =
  let pos = pos s in
  let bytes = get_string (sec_end - pos) s in
  try
    let _ = Utf8.decode (string s) in
    bytes
  with Utf8.Utf8 ->
    error s pos "malformed UTF-8 encoding"

let motoko_sections s =
  let stable_types = icp_custom_section "motoko:stable-types" utf8 None s in
  let compiler = icp_custom_section "motoko:compiler" utf8 None s in
  custom_section is_motoko motoko_section_content { empty_motoko_sections with stable_types; compiler; } s

(* Enhanced orthogonal persistence section *)
let enhanced_orthogonal_persistence_section s =
  icp_custom_section "enhanced-orthogonal-persistence" utf8 None s

(* Candid sections *)

let candid_sections s =
  let service = icp_custom_section "candid:service" utf8 None s in
  let args = icp_custom_section "candid:args" utf8 None s in
  { service; args }

(* Other custom sections *)

let candid_service_name = icp_name "candid:service"
let candid_args_name = icp_name "candid:args"
let motoko_stable_types_name = icp_name "motoko:stable-types"

let is_icp icp_name n = icp_name n <> None

let is_wasm_features n = (n = Utf8.decode "wasm_features")
let wasm_features_section s =
  custom_section is_wasm_features
    (fun sec_end s -> let t = utf8 sec_end s in String.split_on_char ',' t) [] s

let is_unknown n = not (
  is_dylink0 n ||
  is_name n ||
  is_motoko n ||
  is_icp candid_service_name n ||
  is_icp candid_args_name n ||
  is_icp motoko_stable_types_name n ||
  is_wasm_features n)

let skip_custom sec_end s =
  skip (sec_end - pos s) s;
  true

let skip_custom_section s =
  custom_section is_unknown skip_custom false s

(* Modules *)

let rec iterate f s = if f s then iterate f s

let module_ s =
  let magic = u32 s in
  require (magic = 0x6d736100l) s 0 "magic header not detected";
  let version = u32 s in
  require (version = Wasm.Encode.version) s 4 "unknown binary version";
  let dylink0 = dylink0_section s in
  iterate skip_custom_section s;
  let types = type_section s in
  iterate skip_custom_section s;
  let imports = import_section s in
  iterate skip_custom_section s;
  let func_types = func_section s in
  iterate skip_custom_section s;
  let tables = table_section s in
  iterate skip_custom_section s;
  let memories = memory_section s in
  iterate skip_custom_section s;
  let globals = global_section s in
  iterate skip_custom_section s;
  let exports = export_section s in
  iterate skip_custom_section s;
  let start = start_section s in
  iterate skip_custom_section s;
  let elems = elem_section s in
  iterate skip_custom_section s;
  let data_count = data_count_section s in
  iterate skip_custom_section s;
  let func_bodies = code_section s in
  iterate skip_custom_section s;
  let datas = data_section s in
  iterate skip_custom_section s;
  let name = name_section s in
  iterate skip_custom_section s;
  (* TODO: allow candid/motoko sections anywhere, not just here, in this order *)
  let candid = candid_sections s in
  iterate skip_custom_section s;
  let motoko = motoko_sections s in
  iterate skip_custom_section s;
  let enhanced_orthogonal_persistence = enhanced_orthogonal_persistence_section s in
  iterate skip_custom_section s;
  let wasm_features = wasm_features_section s in
  iterate skip_custom_section s;
  require (pos s = len s) s (len s) "junk after last section";
  require (List.length func_types = List.length func_bodies)
    s (len s) "function and code section have inconsistent lengths";
  require (data_count = None || data_count = Some (Lib.List32.length datas))
  s (len s) "data count and data section have inconsistent lengths";
  let funcs =
    List.map2 Source.(fun t f -> {f.it with ftype = t} @@ f.at)
      func_types func_bodies
  in
  { module_ =
     {types; tables; memories; globals; funcs; imports; exports; elems; datas; start};
    dylink0;
    name;
    motoko;
    enhanced_orthogonal_persistence;
    candid;
    source_mapping_url = None;
    wasm_features = wasm_features;
  }


let decode name bs = module_ (stream name bs)