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
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
use crate::store::{StoreData, StoreOpaque, Stored};
use crate::{
    AsContext, AsContextMut, CallHook, Engine, Extern, FuncType, Instance, InterruptHandle,
    StoreContext, StoreContextMut, Trap, Val, ValRaw, ValType,
};
use anyhow::{bail, Context as _, Result};
use std::error::Error;
use std::fmt;
use std::future::Future;
use std::mem;
use std::panic::{self, AssertUnwindSafe};
use std::pin::Pin;
use std::ptr::NonNull;
use std::sync::atomic::Ordering::Relaxed;
use std::sync::Arc;
use wasmtime_environ::{EntityIndex, FuncIndex};
use wasmtime_runtime::{
    raise_user_trap, ExportFunction, InstanceAllocator, InstanceHandle, OnDemandInstanceAllocator,
    VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport, VMSharedSignatureIndex,
    VMTrampoline,
};

/// A WebAssembly function which can be called.
///
/// This type can represent either an exported function from a WebAssembly
/// module or a host-defined function which can be used to satisfy an import of
/// a module. [`Func`] and can be used to both instantiate an [`Instance`] as
/// well as be extracted from an [`Instance`].
///
/// [`Instance`]: crate::Instance
///
/// A [`Func`] "belongs" to the store that it was originally created within.
/// Operations on a [`Func`] only work with the store it belongs to, and if
/// another store is passed in by accident then methods will panic.
///
/// # `Func` and `async`
///
/// Functions from the perspective of WebAssembly are always synchronous. You
/// might have an `async` function in Rust, however, which you'd like to make
/// available from WebAssembly. Wasmtime supports asynchronously calling
/// WebAssembly through native stack switching. You can get some more
/// information about [asynchronous configs](crate::Config::async_support), but
/// from the perspective of `Func` it's important to know that whether or not
/// your [`Store`](crate::Store) is asynchronous will dictate whether you call
/// functions through [`Func::call`] or [`Func::call_async`] (or the typed
/// wrappers such as [`TypedFunc::call`] vs [`TypedFunc::call_async`]).
///
/// # To `Func::call` or to `Func::typed().call()`
///
/// There's a 2x2 matrix of methods to call [`Func`]. Invocations can either be
/// asynchronous or synchronous. They can also be statically typed or not.
/// Whether or not an invocation is asynchronous is indicated via the method
/// being `async` and [`call_async`](Func::call_async) being the entry point.
/// Otherwise for statically typed or not your options are:
///
/// * Dynamically typed - if you don't statically know the signature of the
///   function that you're calling you'll be using [`Func::call`] or
///   [`Func::call_async`]. These functions take a variable-length slice of
///   "boxed" arguments in their [`Val`] representation. Additionally the
///   results are returned as an owned slice of [`Val`]. These methods are not
///   optimized due to the dynamic type checks that must occur, in addition to
///   some dynamic allocations for where to put all the arguments. While this
///   allows you to call all possible wasm function signatures, if you're
///   looking for a speedier alternative you can also use...
///
/// * Statically typed - if you statically know the type signature of the wasm
///   function you're calling, then you'll want to use the [`Func::typed`]
///   method to acquire an instance of [`TypedFunc`]. This structure is static proof
///   that the underlying wasm function has the ascripted type, and type
///   validation is only done once up-front. The [`TypedFunc::call`] and
///   [`TypedFunc::call_async`] methods are much more efficient than [`Func::call`]
///   and [`Func::call_async`] because the type signature is statically known.
///   This eschews runtime checks as much as possible to get into wasm as fast
///   as possible.
///
/// # Examples
///
/// One way to get a `Func` is from an [`Instance`] after you've instantiated
/// it:
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> anyhow::Result<()> {
/// let engine = Engine::default();
/// let module = Module::new(&engine, r#"(module (func (export "foo")))"#)?;
/// let mut store = Store::new(&engine, ());
/// let instance = Instance::new(&mut store, &module, &[])?;
/// let foo = instance.get_func(&mut store, "foo").expect("export wasn't a function");
///
/// // Work with `foo` as a `Func` at this point, such as calling it
/// // dynamically...
/// match foo.call(&mut store, &[], &mut []) {
///     Ok(()) => { /* ... */ }
///     Err(trap) => {
///         panic!("execution of `foo` resulted in a wasm trap: {}", trap);
///     }
/// }
/// foo.call(&mut store, &[], &mut [])?;
///
/// // ... or we can make a static assertion about its signature and call it.
/// // Our first call here can fail if the signatures don't match, and then the
/// // second call can fail if the function traps (like the `match` above).
/// let foo = foo.typed::<(), (), _>(&store)?;
/// foo.call(&mut store, ())?;
/// # Ok(())
/// # }
/// ```
///
/// You can also use the [`wrap` function](Func::wrap) to create a
/// `Func`
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> anyhow::Result<()> {
/// let mut store = Store::<()>::default();
///
/// // Create a custom `Func` which can execute arbitrary code inside of the
/// // closure.
/// let add = Func::wrap(&mut store, |a: i32, b: i32| -> i32 { a + b });
///
/// // Next we can hook that up to a wasm module which uses it.
/// let module = Module::new(
///     store.engine(),
///     r#"
///         (module
///             (import "" "" (func $add (param i32 i32) (result i32)))
///             (func (export "call_add_twice") (result i32)
///                 i32.const 1
///                 i32.const 2
///                 call $add
///                 i32.const 3
///                 i32.const 4
///                 call $add
///                 i32.add))
///     "#,
/// )?;
/// let instance = Instance::new(&mut store, &module, &[add.into()])?;
/// let call_add_twice = instance.get_typed_func::<(), i32, _>(&mut store, "call_add_twice")?;
///
/// assert_eq!(call_add_twice.call(&mut store, ())?, 10);
/// # Ok(())
/// # }
/// ```
///
/// Or you could also create an entirely dynamic `Func`!
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> anyhow::Result<()> {
/// let mut store = Store::<()>::default();
///
/// // Here we need to define the type signature of our `Double` function and
/// // then wrap it up in a `Func`
/// let double_type = wasmtime::FuncType::new(
///     [wasmtime::ValType::I32].iter().cloned(),
///     [wasmtime::ValType::I32].iter().cloned(),
/// );
/// let double = Func::new(&mut store, double_type, |_, params, results| {
///     let mut value = params[0].unwrap_i32();
///     value *= 2;
///     results[0] = value.into();
///     Ok(())
/// });
///
/// let module = Module::new(
///     store.engine(),
///     r#"
///         (module
///             (import "" "" (func $double (param i32) (result i32)))
///             (func $start
///                 i32.const 1
///                 call $double
///                 drop)
///             (start $start))
///     "#,
/// )?;
/// let instance = Instance::new(&mut store, &module, &[double.into()])?;
/// // .. work with `instance` if necessary
/// # Ok(())
/// # }
/// ```
#[derive(Copy, Clone, Debug)]
#[repr(transparent)] // here for the C API
pub struct Func(Stored<FuncData>);

pub(crate) struct FuncData {
    kind: FuncKind,
    ty: FuncType,
}

/// The three ways that a function can be created and referenced from within a
/// store.
enum FuncKind {
    /// A function already owned by the store via some other means. This is
    /// used, for example, when creating a `Func` from an instance's exported
    /// function. The instance's `InstanceHandle` is already owned by the store
    /// and we just have some pointers into that which represent how to call the
    /// function.
    StoreOwned {
        trampoline: VMTrampoline,
        export: ExportFunction,
    },

    /// A function is shared across possibly other stores, hence the `Arc`. This
    /// variant happens when a `Linker`-defined function is instantiated within
    /// a `Store` (e.g. via `Linker::get` or similar APIs). The `Arc` here
    /// indicates that there's some number of other stores holding this function
    /// too, so dropping this may not deallocate the underlying
    /// `InstanceHandle`.
    SharedHost(Arc<HostFunc>),

    /// A uniquely-owned host function within a `Store`. This comes about with
    /// `Func::new` or similar APIs. The `HostFunc` internally owns the
    /// `InstanceHandle` and that will get dropped when this `HostFunc` itself
    /// is dropped.
    Host(HostFunc),
}

macro_rules! for_each_function_signature {
    ($mac:ident) => {
        $mac!(0);
        $mac!(1 A1);
        $mac!(2 A1 A2);
        $mac!(3 A1 A2 A3);
        $mac!(4 A1 A2 A3 A4);
        $mac!(5 A1 A2 A3 A4 A5);
        $mac!(6 A1 A2 A3 A4 A5 A6);
        $mac!(7 A1 A2 A3 A4 A5 A6 A7);
        $mac!(8 A1 A2 A3 A4 A5 A6 A7 A8);
        $mac!(9 A1 A2 A3 A4 A5 A6 A7 A8 A9);
        $mac!(10 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10);
        $mac!(11 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11);
        $mac!(12 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12);
        $mac!(13 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13);
        $mac!(14 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14);
        $mac!(15 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15);
        $mac!(16 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16);
    };
}

mod typed;
pub use typed::*;

macro_rules! generate_wrap_async_func {
    ($num:tt $($args:ident)*) => (paste::paste!{
        /// Same as [`Func::wrap`], except the closure asynchronously produces
        /// its result. For more information see the [`Func`] documentation.
        ///
        /// # Panics
        ///
        /// This function will panic if called with a non-asynchronous store.
        #[allow(non_snake_case)]
        #[cfg(feature = "async")]
        #[cfg_attr(nightlydoc, doc(cfg(feature = "async")))]
        pub fn [<wrap $num _async>]<T, $($args,)* R>(
            store: impl AsContextMut<Data = T>,
            func: impl for<'a> Fn(Caller<'a, T>, $($args),*) -> Box<dyn Future<Output = R> + Send + 'a> + Send + Sync + 'static,
        ) -> Func
        where
            $($args: WasmTy,)*
            R: WasmRet,
        {
            assert!(store.as_context().async_support(), concat!("cannot use `wrap", $num, "_async` without enabling async support on the config"));
            Func::wrap(store, move |mut caller: Caller<'_, T>, $($args: $args),*| {
                let async_cx = caller.store.as_context_mut().0.async_cx();
                let mut future = Pin::from(func(caller, $($args),*));
                match unsafe { async_cx.block_on(future.as_mut()) } {
                    Ok(ret) => ret.into_fallible(),
                    Err(e) => R::fallible_from_trap(e),
                }
            })
        }
    })
}

impl Func {
    /// Creates a new `Func` with the given arguments, typically to create a
    /// host-defined function to pass as an import to a module.
    ///
    /// * `store` - the store in which to create this [`Func`], which will own
    ///   the return value.
    ///
    /// * `ty` - the signature of this function, used to indicate what the
    ///   inputs and outputs are.
    ///
    /// * `func` - the native code invoked whenever this `Func` will be called.
    ///   This closure is provided a [`Caller`] as its first argument to learn
    ///   information about the caller, and then it's passed a list of
    ///   parameters as a slice along with a mutable slice of where to write
    ///   results.
    ///
    /// Note that the implementation of `func` must adhere to the `ty` signature
    /// given, error or traps may occur if it does not respect the `ty`
    /// signature. For example if the function type declares that it returns one
    /// i32 but the `func` closures does not write anything into the results
    /// slice then a trap may be generated.
    ///
    /// Additionally note that this is quite a dynamic function since signatures
    /// are not statically known. For a more performant and ergonomic `Func`
    /// it's recommended to use [`Func::wrap`] if you can because with
    /// statically known signatures Wasmtime can optimize the implementation
    /// much more.
    ///
    /// For more information about `Send + Sync + 'static` requirements on the
    /// `func`, see [`Func::wrap`](#why-send--sync--static).
    #[cfg(compiler)]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "cranelift")))] // see build.rs
    pub fn new<T>(
        store: impl AsContextMut<Data = T>,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, &[Val], &mut [Val]) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let ty_clone = ty.clone();
        unsafe {
            Func::new_unchecked(store, ty, move |caller, values| {
                Func::invoke(caller, &ty_clone, values, &func)
            })
        }
    }

    /// Creates a new [`Func`] with the given arguments, although has fewer
    /// runtime checks than [`Func::new`].
    ///
    /// This function takes a callback of a different signature than
    /// [`Func::new`], instead receiving a raw pointer with a list of [`ValRaw`]
    /// structures. These values have no type information associated with them
    /// so it's up to the caller to provide a function that will correctly
    /// interpret the list of values as those coming from the `ty` specified.
    ///
    /// If you're calling this from Rust it's recommended to either instead use
    /// [`Func::new`] or [`Func::wrap`]. The [`Func::wrap`] API, in particular,
    /// is both safer and faster than this API.
    ///
    /// # Unsafety
    ///
    /// This function is not safe because it's not known at compile time that
    /// the `func` provided correctly interprets the argument types provided to
    /// it, or that the results it produces will be of the correct type.
    #[cfg(compiler)]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "cranelift")))] // see build.rs
    pub unsafe fn new_unchecked<T>(
        mut store: impl AsContextMut<Data = T>,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, *mut ValRaw) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let store = store.as_context_mut().0;
        let host = HostFunc::new_unchecked(store.engine(), ty, func);
        host.into_func(store)
    }

    /// Creates a new host-defined WebAssembly function which, when called,
    /// will run the asynchronous computation defined by `func` to completion
    /// and then return the result to WebAssembly.
    ///
    /// This function is the asynchronous analogue of [`Func::new`] and much of
    /// that documentation applies to this as well. The key difference is that
    /// `func` returns a future instead of simply a `Result`. Note that the
    /// returned future can close over any of the arguments, but it cannot close
    /// over the state of the closure itself. It's recommended to store any
    /// necessary async state in the `T` of the [`Store<T>`](crate::Store) which
    /// can be accessed through [`Caller::data`] or [`Caller::data_mut`].
    ///
    /// For more information on `Send + Sync + 'static`, see
    /// [`Func::wrap`](#why-send--sync--static).
    ///
    /// # Panics
    ///
    /// This function will panic if `store` is not associated with an [async
    /// config](crate::Config::async_support).
    ///
    /// # Examples
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// // Simulate some application-specific state as well as asynchronous
    /// // functions to query that state.
    /// struct MyDatabase {
    ///     // ...
    /// }
    ///
    /// impl MyDatabase {
    ///     async fn get_row_count(&self) -> u32 {
    ///         // ...
    /// #       100
    ///     }
    /// }
    ///
    /// let my_database = MyDatabase {
    ///     // ...
    /// };
    ///
    /// // Using `new_async` we can hook up into calling our async
    /// // `get_row_count` function.
    /// let engine = Engine::new(Config::new().async_support(true))?;
    /// let mut store = Store::new(&engine, MyDatabase {
    ///     // ...
    /// });
    /// let get_row_count_type = wasmtime::FuncType::new(
    ///     None,
    ///     Some(wasmtime::ValType::I32),
    /// );
    /// let get = Func::new_async(&mut store, get_row_count_type, |caller, _params, results| {
    ///     Box::new(async move {
    ///         let count = caller.data().get_row_count().await;
    ///         results[0] = Val::I32(count as i32);
    ///         Ok(())
    ///     })
    /// });
    /// // ...
    /// # Ok(())
    /// # }
    /// ```
    #[cfg(all(feature = "async", feature = "cranelift"))]
    #[cfg_attr(nightlydoc, doc(cfg(all(feature = "async", feature = "cranelift"))))]
    pub fn new_async<T, F>(store: impl AsContextMut<Data = T>, ty: FuncType, func: F) -> Func
    where
        F: for<'a> Fn(
                Caller<'a, T>,
                &'a [Val],
                &'a mut [Val],
            ) -> Box<dyn Future<Output = Result<(), Trap>> + Send + 'a>
            + Send
            + Sync
            + 'static,
    {
        assert!(
            store.as_context().async_support(),
            "cannot use `new_async` without enabling async support in the config"
        );
        Func::new(store, ty, move |mut caller, params, results| {
            let async_cx = caller.store.as_context_mut().0.async_cx();
            let mut future = Pin::from(func(caller, params, results));
            match unsafe { async_cx.block_on(future.as_mut()) } {
                Ok(Ok(())) => Ok(()),
                Ok(Err(trap)) | Err(trap) => Err(trap),
            }
        })
    }

    pub(crate) unsafe fn from_caller_checked_anyfunc(
        store: &mut StoreOpaque,
        raw: *mut VMCallerCheckedAnyfunc,
    ) -> Option<Func> {
        let anyfunc = NonNull::new(raw)?;
        debug_assert!(anyfunc.as_ref().type_index != VMSharedSignatureIndex::default());
        let export = ExportFunction { anyfunc };
        Some(Func::from_wasmtime_function(export, store))
    }

    /// Creates a new `Func` from the given Rust closure.
    ///
    /// This function will create a new `Func` which, when called, will
    /// execute the given Rust closure. Unlike [`Func::new`] the target
    /// function being called is known statically so the type signature can
    /// be inferred. Rust types will map to WebAssembly types as follows:
    ///
    /// | Rust Argument Type  | WebAssembly Type |
    /// |---------------------|------------------|
    /// | `i32`               | `i32`            |
    /// | `u32`               | `i32`            |
    /// | `i64`               | `i64`            |
    /// | `u64`               | `i64`            |
    /// | `f32`               | `f32`            |
    /// | `f64`               | `f64`            |
    /// | (not supported)     | `v128`           |
    /// | `Option<Func>`      | `funcref`        |
    /// | `Option<ExternRef>` | `externref`      |
    ///
    /// Any of the Rust types can be returned from the closure as well, in
    /// addition to some extra types
    ///
    /// | Rust Return Type  | WebAssembly Return Type | Meaning               |
    /// |-------------------|-------------------------|-----------------------|
    /// | `()`              | nothing                 | no return value       |
    /// | `T`               | `T`                     | a single return value |
    /// | `(T1, T2, ...)`   | `T1 T2 ...`             | multiple returns      |
    ///
    /// Note that all return types can also be wrapped in `Result<_, Trap>` to
    /// indicate that the host function can generate a trap as well as possibly
    /// returning a value.
    ///
    /// Finally you can also optionally take [`Caller`] as the first argument of
    /// your closure. If inserted then you're able to inspect the caller's
    /// state, for example the [`Memory`](crate::Memory) it has exported so you
    /// can read what pointers point to.
    ///
    /// Note that when using this API, the intention is to create as thin of a
    /// layer as possible for when WebAssembly calls the function provided. With
    /// sufficient inlining and optimization the WebAssembly will call straight
    /// into `func` provided, with no extra fluff entailed.
    ///
    /// # Why `Send + Sync + 'static`?
    ///
    /// All host functions defined in a [`Store`](crate::Store) (including
    /// those from [`Func::new`] and other constructors) require that the
    /// `func` provided is `Send + Sync + 'static`. Additionally host functions
    /// always are `Fn` as opposed to `FnMut` or `FnOnce`. This can at-a-glance
    /// feel restrictive since the closure cannot close over as many types as
    /// before. The reason for this, though, is to ensure that
    /// [`Store<T>`](crate::Store) can implement both the `Send` and `Sync`
    /// traits.
    ///
    /// Fear not, however, because this isn't as restrictive as it seems! Host
    /// functions are provided a [`Caller<'_, T>`](crate::Caller) argument which
    /// allows access to the host-defined data within the
    /// [`Store`](crate::Store). The `T` type is not required to be any of
    /// `Send`, `Sync`, or `'static`! This means that you can store whatever
    /// you'd like in `T` and have it accessible by all host functions.
    /// Additionally mutable access to `T` is allowed through
    /// [`Caller::data_mut`].
    ///
    /// Most host-defined [`Func`] values provide closures that end up not
    /// actually closing over any values. These zero-sized types will use the
    /// context from [`Caller`] for host-defined information.
    ///
    /// # Examples
    ///
    /// First up we can see how simple wasm imports can be implemented, such
    /// as a function that adds its two arguments and returns the result.
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::<()>::default();
    /// let add = Func::wrap(&mut store, |a: i32, b: i32| a + b);
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $add (param i32 i32) (result i32)))
    ///             (func (export "foo") (param i32 i32) (result i32)
    ///                 local.get 0
    ///                 local.get 1
    ///                 call $add))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[add.into()])?;
    /// let foo = instance.get_typed_func::<(i32, i32), i32, _>(&mut store, "foo")?;
    /// assert_eq!(foo.call(&mut store, (1, 2))?, 3);
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// We can also do the same thing, but generate a trap if the addition
    /// overflows:
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::<()>::default();
    /// let add = Func::wrap(&mut store, |a: i32, b: i32| {
    ///     match a.checked_add(b) {
    ///         Some(i) => Ok(i),
    ///         None => Err(Trap::new("overflow")),
    ///     }
    /// });
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $add (param i32 i32) (result i32)))
    ///             (func (export "foo") (param i32 i32) (result i32)
    ///                 local.get 0
    ///                 local.get 1
    ///                 call $add))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[add.into()])?;
    /// let foo = instance.get_typed_func::<(i32, i32), i32, _>(&mut store, "foo")?;
    /// assert_eq!(foo.call(&mut store, (1, 2))?, 3);
    /// assert!(foo.call(&mut store, (i32::max_value(), 1)).is_err());
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// And don't forget all the wasm types are supported!
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::<()>::default();
    /// let debug = Func::wrap(&mut store, |a: i32, b: u32, c: f32, d: i64, e: u64, f: f64| {
    ///
    ///     println!("a={}", a);
    ///     println!("b={}", b);
    ///     println!("c={}", c);
    ///     println!("d={}", d);
    ///     println!("e={}", e);
    ///     println!("f={}", f);
    /// });
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $debug (param i32 i32 f32 i64 i64 f64)))
    ///             (func (export "foo")
    ///                 i32.const -1
    ///                 i32.const 1
    ///                 f32.const 2
    ///                 i64.const -3
    ///                 i64.const 3
    ///                 f64.const 4
    ///                 call $debug))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[debug.into()])?;
    /// let foo = instance.get_typed_func::<(), (), _>(&mut store, "foo")?;
    /// foo.call(&mut store, ())?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Finally if you want to get really fancy you can also implement
    /// imports that read/write wasm module's memory
    ///
    /// ```
    /// use std::str;
    ///
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::default();
    /// let log_str = Func::wrap(&mut store, |mut caller: Caller<'_, ()>, ptr: i32, len: i32| {
    ///     let mem = match caller.get_export("memory") {
    ///         Some(Extern::Memory(mem)) => mem,
    ///         _ => return Err(Trap::new("failed to find host memory")),
    ///     };
    ///     let data = mem.data(&caller)
    ///         .get(ptr as u32 as usize..)
    ///         .and_then(|arr| arr.get(..len as u32 as usize));
    ///     let string = match data {
    ///         Some(data) => match str::from_utf8(data) {
    ///             Ok(s) => s,
    ///             Err(_) => return Err(Trap::new("invalid utf-8")),
    ///         },
    ///         None => return Err(Trap::new("pointer/length out of bounds")),
    ///     };
    ///     assert_eq!(string, "Hello, world!");
    ///     println!("{}", string);
    ///     Ok(())
    /// });
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $log_str (param i32 i32)))
    ///             (func (export "foo")
    ///                 i32.const 4   ;; ptr
    ///                 i32.const 13  ;; len
    ///                 call $log_str)
    ///             (memory (export "memory") 1)
    ///             (data (i32.const 4) "Hello, world!"))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[log_str.into()])?;
    /// let foo = instance.get_typed_func::<(), (), _>(&mut store, "foo")?;
    /// foo.call(&mut store, ())?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn wrap<T, Params, Results>(
        mut store: impl AsContextMut<Data = T>,
        func: impl IntoFunc<T, Params, Results>,
    ) -> Func {
        let store = store.as_context_mut().0;
        // part of this unsafety is about matching the `T` to a `Store<T>`,
        // which is done through the `AsContextMut` bound above.
        unsafe {
            let host = HostFunc::wrap(store.engine(), func);
            host.into_func(store)
        }
    }

    for_each_function_signature!(generate_wrap_async_func);

    /// Returns the underlying wasm type that this `Func` has.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this function.
    pub fn ty(&self, store: impl AsContext) -> FuncType {
        store.as_context()[self.0].ty.clone()
    }

    pub(crate) fn sig_index(&self, data: &StoreData) -> VMSharedSignatureIndex {
        unsafe { data[self.0].export().anyfunc.as_ref().type_index }
    }

    /// Invokes this function with the `params` given and writes returned values
    /// to `results`.
    ///
    /// The `params` here must match the type signature of this `Func`, or a
    /// trap will occur. If a trap occurs while executing this function, then a
    /// trap will also be returned. Additionally `results` must have the same
    /// length as the number of results for this function.
    ///
    /// # Panics
    ///
    /// This function will panic if called on a function belonging to an async
    /// store. Asynchronous stores must always use `call_async`.
    /// initiates a panic. Also panics if `store` does not own this function.
    pub fn call(
        &self,
        mut store: impl AsContextMut,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        assert!(
            !store.as_context().async_support(),
            "must use `call_async` when async support is enabled on the config",
        );
        self.call_impl(&mut store.as_context_mut(), params, results)
    }

    /// Invokes this function in an "unchecked" fashion, reading parameters and
    /// writing results to `params_and_returns`.
    ///
    /// This function is the same as [`Func::call`] except that the arguments
    /// and results both use a different representation. If possible it's
    /// recommended to use [`Func::call`] if safety isn't necessary or to use
    /// [`Func::typed`] in conjunction with [`TypedFunc::call`] since that's
    /// both safer and faster than this method of invoking a function.
    ///
    /// Note that if this function takes `externref` arguments then it will
    /// **not** automatically GC unlike the [`Func::call`] and
    /// [`TypedFunc::call`] functions. This means that if this function is
    /// invoked many times with new `ExternRef` values and no other GC happens
    /// via any other means then no values will get collected.
    ///
    /// # Unsafety
    ///
    /// This function is unsafe because the `params_and_returns` argument is not
    /// validated at all. It must uphold invariants such as:
    ///
    /// * It's a valid pointer to an array
    /// * It has enough space to store all parameters
    /// * It has enough space to store all results (not at the same time as
    ///   parameters)
    /// * Parameters are initially written to the array and have the correct
    ///   types and such.
    /// * Reference types like `externref` and `funcref` are valid at the
    ///   time of this call and for the `store` specified.
    ///
    /// These invariants are all upheld for you with [`Func::call`] and
    /// [`TypedFunc::call`].
    pub unsafe fn call_unchecked(
        &self,
        mut store: impl AsContextMut,
        params_and_returns: *mut ValRaw,
    ) -> Result<(), Trap> {
        let mut store = store.as_context_mut();
        let data = &store.0.store_data()[self.0];
        let trampoline = data.trampoline();
        let anyfunc = data.export().anyfunc;
        invoke_wasm_and_catch_traps(&mut store, |callee| {
            trampoline(
                (*anyfunc.as_ptr()).vmctx,
                callee,
                (*anyfunc.as_ptr()).func_ptr.as_ptr(),
                params_and_returns,
            )
        })
    }

    /// Converts the raw representation of a `funcref` into an `Option<Func>`
    ///
    /// This is intended to be used in conjunction with [`Func::new_unchecked`],
    /// [`Func::call_unchecked`], and [`ValRaw`] with its `funcref` field.
    ///
    /// # Unsafety
    ///
    /// This function is not safe because `raw` is not validated at all. The
    /// caller must guarantee that `raw` is owned by the `store` provided and is
    /// valid within the `store`.
    pub unsafe fn from_raw(mut store: impl AsContextMut, raw: usize) -> Option<Func> {
        Func::from_caller_checked_anyfunc(store.as_context_mut().0, raw as *mut _)
    }

    /// Extracts the raw value of this `Func`, which is owned by `store`.
    ///
    /// This function returns a value that's suitable for writing into the
    /// `funcref` field of the [`ValRaw`] structure.
    ///
    /// # Unsafety
    ///
    /// The returned value is only valid for as long as the store is alive and
    /// this function is properly rooted within it. Additionally this function
    /// should not be liberally used since it's a very low-level knob.
    pub unsafe fn to_raw(&self, store: impl AsContext) -> usize {
        self.caller_checked_anyfunc(store.as_context().0).as_ptr() as usize
    }

    /// Invokes this function with the `params` given, returning the results
    /// asynchronously.
    ///
    /// This function is the same as [`Func::call`] except that it is
    /// asynchronous. This is only compatible with stores associated with an
    /// [asynchronous config](crate::Config::async_support).
    ///
    /// It's important to note that the execution of WebAssembly will happen
    /// synchronously in the `poll` method of the future returned from this
    /// function. Wasmtime does not manage its own thread pool or similar to
    /// execute WebAssembly in. Future `poll` methods are generally expected to
    /// resolve quickly, so it's recommended that you run or poll this future
    /// in a "blocking context".
    ///
    /// For more information see the documentation on [asynchronous
    /// configs](crate::Config::async_support).
    ///
    /// # Panics
    ///
    /// Panics if this is called on a function in a synchronous store. This
    /// only works with functions defined within an asynchronous store. Also
    /// panics if `store` does not own this function.
    #[cfg(feature = "async")]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "async")))]
    pub async fn call_async<T>(
        &self,
        mut store: impl AsContextMut<Data = T>,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()>
    where
        T: Send,
    {
        let mut store = store.as_context_mut();
        assert!(
            store.0.async_support(),
            "cannot use `call_async` without enabling async support in the config",
        );
        let result = store
            .on_fiber(|store| self.call_impl(store, params, results))
            .await??;
        Ok(result)
    }

    fn call_impl<T>(
        &self,
        store: &mut StoreContextMut<'_, T>,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        // We need to perform a dynamic check that the arguments given to us
        // match the signature of this function and are appropriate to pass to
        // this function. This involves checking to make sure we have the right
        // number and types of arguments as well as making sure everything is
        // from the same `Store`.
        let ty = &store[self.0].ty;
        if ty.params().len() != params.len() {
            bail!(
                "expected {} arguments, got {}",
                ty.params().len(),
                params.len()
            );
        }
        if ty.results().len() != results.len() {
            bail!(
                "expected {} results, got {}",
                ty.results().len(),
                results.len()
            );
        }
        for (ty, arg) in ty.params().zip(params) {
            if arg.ty() != ty {
                bail!(
                    "argument type mismatch: found {} but expected {}",
                    arg.ty(),
                    ty
                );
            }
            if !arg.comes_from_same_store(store.0) {
                bail!("cross-`Store` values are not currently supported");
            }
        }

        let values_vec_size = params.len().max(ty.results().len());

        // Whenever we pass `externref`s from host code to Wasm code, they
        // go into the `VMExternRefActivationsTable`. But the table might be
        // at capacity already, so check for that. If it is at capacity
        // (unlikely) then do a GC to free up space. This is necessary
        // because otherwise we would either keep filling up the bump chunk
        // and making it larger and larger or we would always take the slow
        // path when inserting references into the table.
        if ty.as_wasm_func_type().externref_params_count()
            > store
                .0
                .externref_activations_table()
                .bump_capacity_remaining()
        {
            store.gc();
        }

        // Store the argument values into `values_vec`.
        let mut values_vec = store.0.take_wasm_val_raw_storage();
        debug_assert!(values_vec.is_empty());
        values_vec.resize_with(values_vec_size, || ValRaw { i32: 0 });
        for (arg, slot) in params.iter().cloned().zip(&mut values_vec) {
            unsafe {
                *slot = arg.to_raw(&mut *store);
            }
        }

        unsafe {
            self.call_unchecked(&mut *store, values_vec.as_mut_ptr())?;
        }

        for ((i, slot), val) in results.iter_mut().enumerate().zip(&values_vec) {
            let ty = store[self.0].ty.results().nth(i).unwrap();
            *slot = unsafe { Val::from_raw(&mut *store, *val, ty) };
        }
        values_vec.truncate(0);
        store.0.save_wasm_val_raw_storage(values_vec);
        Ok(())
    }

    #[inline]
    pub(crate) fn caller_checked_anyfunc(
        &self,
        store: &StoreOpaque,
    ) -> NonNull<VMCallerCheckedAnyfunc> {
        store.store_data()[self.0].export().anyfunc
    }

    pub(crate) unsafe fn from_wasmtime_function(
        export: ExportFunction,
        store: &mut StoreOpaque,
    ) -> Self {
        let anyfunc = export.anyfunc.as_ref();
        let trampoline = store.lookup_trampoline(&*anyfunc);
        Func::from_func_kind(FuncKind::StoreOwned { trampoline, export }, store)
    }

    fn from_func_kind(kind: FuncKind, store: &mut StoreOpaque) -> Self {
        // Signatures should always be registered in the engine's registry of
        // shared signatures, so we should be able to unwrap safely here.
        let ty = unsafe { kind.export().anyfunc.as_ref().type_index };
        let ty = FuncType::from_wasm_func_type(
            store
                .engine()
                .signatures()
                .lookup_type(ty)
                .expect("signature should be registered"),
        );
        Func(store.store_data_mut().insert(FuncData { kind, ty }))
    }

    pub(crate) fn vmimport(&self, store: &mut StoreOpaque) -> VMFunctionImport {
        unsafe {
            let f = self.caller_checked_anyfunc(store);
            VMFunctionImport {
                body: f.as_ref().func_ptr,
                vmctx: f.as_ref().vmctx,
            }
        }
    }

    pub(crate) fn comes_from_same_store(&self, store: &StoreOpaque) -> bool {
        store.store_data().contains(self.0)
    }

    fn invoke<T>(
        mut caller: Caller<'_, T>,
        ty: &FuncType,
        values_vec: *mut ValRaw,
        func: &dyn Fn(Caller<'_, T>, &[Val], &mut [Val]) -> Result<(), Trap>,
    ) -> Result<(), Trap> {
        caller.store.0.call_hook(CallHook::CallingHost)?;

        // Translate the raw JIT arguments in `values_vec` into a `Val` which
        // we'll be passing as a slice. The storage for our slice-of-`Val` we'll
        // be taking from the `Store`. We preserve our slice back into the
        // `Store` after the hostcall, ideally amortizing the cost of allocating
        // the storage across wasm->host calls.
        //
        // Note that we have a dynamic guarantee that `values_vec` is the
        // appropriate length to both read all arguments from as well as store
        // all results into.
        let mut val_vec = caller.store.0.take_hostcall_val_storage();
        debug_assert!(val_vec.is_empty());
        let nparams = ty.params().len();
        val_vec.reserve(nparams + ty.results().len());
        for (i, ty) in ty.params().enumerate() {
            val_vec.push(unsafe { Val::from_raw(&mut caller.store, *values_vec.add(i), ty) })
        }

        val_vec.extend((0..ty.results().len()).map(|_| Val::null()));
        let (params, results) = val_vec.split_at_mut(nparams);
        func(caller.sub_caller(), params, results)?;

        // See the comment in `Func::call_impl`'s `write_params` function.
        if ty.as_wasm_func_type().externref_returns_count()
            > caller
                .store
                .0
                .externref_activations_table()
                .bump_capacity_remaining()
        {
            caller.store.gc();
        }

        // Unlike our arguments we need to dynamically check that the return
        // values produced are correct. There could be a bug in `func` that
        // produces the wrong number, wrong types, or wrong stores of
        // values, and we need to catch that here.
        for (i, (ret, ty)) in results.iter().zip(ty.results()).enumerate() {
            if ret.ty() != ty {
                return Err(Trap::new(
                    "function attempted to return an incompatible value",
                ));
            }
            if !ret.comes_from_same_store(caller.store.0) {
                return Err(Trap::new(
                    "cross-`Store` values are not currently supported",
                ));
            }
            unsafe {
                *values_vec.add(i) = ret.to_raw(&mut caller.store);
            }
        }

        // Restore our `val_vec` back into the store so it's usable for the next
        // hostcall to reuse our own storage.
        val_vec.truncate(0);
        caller.store.0.save_hostcall_val_storage(val_vec);
        caller.store.0.call_hook(CallHook::ReturningFromHost)?;
        Ok(())
    }

    /// Attempts to extract a typed object from this `Func` through which the
    /// function can be called.
    ///
    /// This function serves as an alternative to [`Func::call`] and
    /// [`Func::call_async`]. This method performs a static type check (using
    /// the `Params` and `Results` type parameters on the underlying wasm
    /// function. If the type check passes then a `TypedFunc` object is returned,
    /// otherwise an error is returned describing the typecheck failure.
    ///
    /// The purpose of this relative to [`Func::call`] is that it's much more
    /// efficient when used to invoke WebAssembly functions. With the types
    /// statically known far less setup/teardown is required when invoking
    /// WebAssembly. If speed is desired then this function is recommended to be
    /// used instead of [`Func::call`] (which is more general, hence its
    /// slowdown).
    ///
    /// The `Params` type parameter is used to describe the parameters of the
    /// WebAssembly function. This can either be a single type (like `i32`), or
    /// a tuple of types representing the list of parameters (like `(i32, f32,
    /// f64)`). Additionally you can use `()` to represent that the function has
    /// no parameters.
    ///
    /// The `Results` type parameter is used to describe the results of the
    /// function. This behaves the same way as `Params`, but just for the
    /// results of the function.
    ///
    /// The `S` type parameter represents the method of passing in the store
    /// context, and can typically be specified as simply `_` when calling this
    /// function.
    ///
    /// Translation between Rust types and WebAssembly types looks like:
    ///
    /// | WebAssembly | Rust                |
    /// |-------------|---------------------|
    /// | `i32`       | `i32` or `u32`      |
    /// | `i64`       | `i64` or `u64`      |
    /// | `f32`       | `f32`               |
    /// | `f64`       | `f64`               |
    /// | `externref` | `Option<ExternRef>` |
    /// | `funcref`   | `Option<Func>`      |
    /// | `v128`      | not supported       |
    ///
    /// (note that this mapping is the same as that of [`Func::wrap`]).
    ///
    /// Note that once the [`TypedFunc`] return value is acquired you'll use either
    /// [`TypedFunc::call`] or [`TypedFunc::call_async`] as necessary to actually invoke
    /// the function. This method does not invoke any WebAssembly code, it
    /// simply performs a typecheck before returning the [`TypedFunc`] value.
    ///
    /// This method also has a convenience wrapper as
    /// [`Instance::get_typed_func`](crate::Instance::get_typed_func) to
    /// directly get a typed function value from an
    /// [`Instance`](crate::Instance).
    ///
    /// # Errors
    ///
    /// This function will return an error if `Params` or `Results` does not
    /// match the native type of this WebAssembly function.
    ///
    /// # Panics
    ///
    /// This method will panic if `store` does not own this function.
    ///
    /// # Examples
    ///
    /// An end-to-end example of calling a function which takes no parameters
    /// and has no results:
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// let engine = Engine::default();
    /// let mut store = Store::new(&engine, ());
    /// let module = Module::new(&engine, r#"(module (func (export "foo")))"#)?;
    /// let instance = Instance::new(&mut store, &module, &[])?;
    /// let foo = instance.get_func(&mut store, "foo").expect("export wasn't a function");
    ///
    /// // Note that this call can fail due to the typecheck not passing, but
    /// // in our case we statically know the module so we know this should
    /// // pass.
    /// let typed = foo.typed::<(), (), _>(&store)?;
    ///
    /// // Note that this can fail if the wasm traps at runtime.
    /// typed.call(&mut store, ())?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// You can also pass in multiple parameters and get a result back
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn foo(add: &Func, mut store: Store<()>) -> anyhow::Result<()> {
    /// let typed = add.typed::<(i32, i64), f32, _>(&store)?;
    /// assert_eq!(typed.call(&mut store, (1, 2))?, 3.0);
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// and similarly if a function has multiple results you can bind that too
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn foo(add_with_overflow: &Func, mut store: Store<()>) -> anyhow::Result<()> {
    /// let typed = add_with_overflow.typed::<(u32, u32), (u32, i32), _>(&store)?;
    /// let (result, overflow) = typed.call(&mut store, (u32::max_value(), 2))?;
    /// assert_eq!(result, 1);
    /// assert_eq!(overflow, 1);
    /// # Ok(())
    /// # }
    /// ```
    pub fn typed<Params, Results, S>(&self, store: S) -> Result<TypedFunc<Params, Results>>
    where
        Params: WasmParams,
        Results: WasmResults,
        S: AsContext,
    {
        // Type-check that the params/results are all valid
        let ty = self.ty(store);
        Params::typecheck(ty.params()).context("type mismatch with parameters")?;
        Results::typecheck(ty.results()).context("type mismatch with results")?;

        // and then we can construct the typed version of this function
        // (unsafely), which should be safe since we just did the type check above.
        unsafe { Ok(TypedFunc::new_unchecked(*self)) }
    }
}

/// Prepares for entrance into WebAssembly.
///
/// This function will set up context such that `closure` is allowed to call a
/// raw trampoline or a raw WebAssembly function. This *must* be called to do
/// things like catch traps and set up GC properly.
///
/// The `closure` provided receives a default "callee" `VMContext` parameter it
/// can pass to the called wasm function, if desired.
pub(crate) fn invoke_wasm_and_catch_traps<T>(
    store: &mut StoreContextMut<'_, T>,
    closure: impl FnMut(*mut VMContext),
) -> Result<(), Trap> {
    unsafe {
        let exit = enter_wasm(store)?;

        if let Err(trap) = store.0.call_hook(CallHook::CallingWasm) {
            exit_wasm(store, exit);
            return Err(trap);
        }
        let result = wasmtime_runtime::catch_traps(
            store.0.vminterrupts(),
            store.0.signal_handler(),
            store.0.default_callee(),
            closure,
        );
        exit_wasm(store, exit);
        store.0.call_hook(CallHook::ReturningFromWasm)?;
        result.map_err(Trap::from_runtime_box)
    }
}

/// This function is called to register state within `Store` whenever
/// WebAssembly is entered within the `Store`.
///
/// This function sets up various limits such as:
///
/// * The stack limit. This is what ensures that we limit the stack space
///   allocated by WebAssembly code and it's relative to the initial stack
///   pointer that called into wasm.
///
/// * Stack canaries for externref gc tracing. Currently the implementation
///   relies on walking frames but the stack walker isn't always 100% reliable,
///   so a canary is used to ensure that if the canary is seen then it's
///   guaranteed all wasm frames have been walked.
///
/// This function may fail if the the stack limit can't be set because an
/// interrupt already happened.
fn enter_wasm<T>(store: &mut StoreContextMut<'_, T>) -> Result<Option<usize>, Trap> {
    // If this is a recursive call, e.g. our stack canary is already set, then
    // we may be able to skip this function.
    //
    // For synchronous stores there's nothing else to do because all wasm calls
    // happen synchronously and on the same stack. This means that the previous
    // stack limit will suffice for the next recursive call.
    //
    // For asynchronous stores then each call happens on a separate native
    // stack. This means that the previous stack limit is no longer relevant
    // because we're on a separate stack. In this situation we need to
    // update the stack limit, but we don't need to update the gc stack canary
    // in this situation.
    if store
        .0
        .externref_activations_table()
        .stack_canary()
        .is_some()
        && !store.0.async_support()
    {
        return Ok(None);
    }

    let stack_pointer = psm::stack_pointer() as usize;

    // Determine the stack pointer where, after which, any wasm code will
    // immediately trap. This is checked on the entry to all wasm functions.
    //
    // Note that this isn't 100% precise. We are requested to give wasm
    // `max_wasm_stack` bytes, but what we're actually doing is giving wasm
    // probably a little less than `max_wasm_stack` because we're
    // calculating the limit relative to this function's approximate stack
    // pointer. Wasm will be executed on a frame beneath this one (or next
    // to it). In any case it's expected to be at most a few hundred bytes
    // of slop one way or another. When wasm is typically given a MB or so
    // (a million bytes) the slop shouldn't matter too much.
    //
    // After we've got the stack limit then we store it into the `stack_limit`
    // variable. Note that the store is an atomic swap to ensure that we can
    // consume any previously-sent interrupt requests. If we found that wasm was
    // previously interrupted then we immediately return a trap (after resetting
    // the stack limit). Otherwise we're good to keep on going.
    //
    // Note the usage of `Relaxed` memory orderings here. This is specifically
    // an optimization in the `Drop` below where a `Relaxed` store is speedier
    // than a `SeqCst` store. The rationale for `Relaxed` here is that the
    // atomic orderings here aren't actually protecting any memory, we're just
    // trying to be atomic with respect to this one location in memory (for when
    // `InterruptHandle` sends us a signal). Due to the lack of needing to
    // synchronize with any other memory it's hoped that the choice of `Relaxed`
    // here should be correct for our use case.
    let wasm_stack_limit = stack_pointer - store.engine().config().max_wasm_stack;
    let interrupts = store.0.interrupts();
    let prev_stack = match interrupts.stack_limit.swap(wasm_stack_limit, Relaxed) {
        wasmtime_environ::INTERRUPTED => {
            // This means that an interrupt happened before we actually
            // called this function, which means that we're now
            // considered interrupted.
            interrupts.stack_limit.store(usize::max_value(), Relaxed);
            return Err(Trap::new_wasm(
                None,
                wasmtime_environ::TrapCode::Interrupt,
                backtrace::Backtrace::new_unresolved(),
            ));
        }
        n => n,
    };

    // The `usize::max_value()` sentinel is present on recursive calls to
    // asynchronous stores here. In that situation we don't want to keep
    // updating the stack canary, so only execute this once at the top.
    if prev_stack == usize::max_value() {
        debug_assert!(store
            .0
            .externref_activations_table()
            .stack_canary()
            .is_none());
        store
            .0
            .externref_activations_table()
            .set_stack_canary(Some(stack_pointer));
    }

    Ok(Some(prev_stack))
}

fn exit_wasm<T>(store: &mut StoreContextMut<'_, T>, prev_stack: Option<usize>) {
    // If we don't have a previous stack pointer to restore, then there's no
    // cleanup we need to perform here.
    let prev_stack = match prev_stack {
        Some(stack) => stack,
        None => return,
    };

    // Only if we're restoring a top-level value do we clear the stack canary
    // value. Otherwise our purpose here might be restoring a recursive stack
    // limit but leaving the active canary in place.
    if prev_stack == usize::max_value() {
        store.0.externref_activations_table().set_stack_canary(None);
    }

    // see docs above for why this uses `Relaxed`
    store.0.interrupts().stack_limit.store(prev_stack, Relaxed);
}

/// A trait implemented for types which can be returned from closures passed to
/// [`Func::wrap`] and friends.
///
/// This trait should not be implemented by user types. This trait may change at
/// any time internally. The types which implement this trait, however, are
/// stable over time.
///
/// For more information see [`Func::wrap`]
pub unsafe trait WasmRet {
    // Same as `WasmTy::Abi`.
    #[doc(hidden)]
    type Abi: Copy;
    #[doc(hidden)]
    type Retptr: Copy;

    // Same as `WasmTy::compatible_with_store`.
    #[doc(hidden)]
    fn compatible_with_store(&self, store: &StoreOpaque) -> bool;

    // Similar to `WasmTy::into_abi_for_arg` but used when host code is
    // returning a value into Wasm, rather than host code passing an argument to
    // a Wasm call. Unlike `into_abi_for_arg`, implementors of this method can
    // raise traps, which means that callers must ensure that
    // `invoke_wasm_and_catch_traps` is on the stack, and therefore this method
    // is unsafe.
    #[doc(hidden)]
    unsafe fn into_abi_for_ret(
        self,
        store: &mut StoreOpaque,
        ptr: Self::Retptr,
    ) -> Result<Self::Abi, Trap>;

    #[doc(hidden)]
    fn func_type(params: impl Iterator<Item = ValType>) -> FuncType;

    #[doc(hidden)]
    unsafe fn wrap_trampoline(ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi);

    // Utilities used to convert an instance of this type to a `Result`
    // explicitly, used when wrapping async functions which always bottom-out
    // in a function that returns a trap because futures can be cancelled.
    #[doc(hidden)]
    type Fallible: WasmRet<Abi = Self::Abi, Retptr = Self::Retptr>;
    #[doc(hidden)]
    fn into_fallible(self) -> Self::Fallible;
    #[doc(hidden)]
    fn fallible_from_trap(trap: Trap) -> Self::Fallible;
}

unsafe impl<T> WasmRet for T
where
    T: WasmTy,
{
    type Abi = <T as WasmTy>::Abi;
    type Retptr = ();
    type Fallible = Result<T, Trap>;

    fn compatible_with_store(&self, store: &StoreOpaque) -> bool {
        <Self as WasmTy>::compatible_with_store(self, store)
    }

    unsafe fn into_abi_for_ret(
        self,
        store: &mut StoreOpaque,
        _retptr: (),
    ) -> Result<Self::Abi, Trap> {
        Ok(<Self as WasmTy>::into_abi(self, store))
    }

    fn func_type(params: impl Iterator<Item = ValType>) -> FuncType {
        FuncType::new(params, Some(<Self as WasmTy>::valtype()))
    }

    unsafe fn wrap_trampoline(ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi) {
        *ptr.cast::<Self::Abi>() = f(());
    }

    fn into_fallible(self) -> Result<T, Trap> {
        Ok(self)
    }

    fn fallible_from_trap(trap: Trap) -> Result<T, Trap> {
        Err(trap)
    }
}

unsafe impl<T> WasmRet for Result<T, Trap>
where
    T: WasmRet,
{
    type Abi = <T as WasmRet>::Abi;
    type Retptr = <T as WasmRet>::Retptr;
    type Fallible = Self;

    fn compatible_with_store(&self, store: &StoreOpaque) -> bool {
        match self {
            Ok(x) => <T as WasmRet>::compatible_with_store(x, store),
            Err(_) => true,
        }
    }

    unsafe fn into_abi_for_ret(
        self,
        store: &mut StoreOpaque,
        retptr: Self::Retptr,
    ) -> Result<Self::Abi, Trap> {
        self.and_then(|val| val.into_abi_for_ret(store, retptr))
    }

    fn func_type(params: impl Iterator<Item = ValType>) -> FuncType {
        T::func_type(params)
    }

    unsafe fn wrap_trampoline(ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi) {
        T::wrap_trampoline(ptr, f)
    }

    fn into_fallible(self) -> Result<T, Trap> {
        self
    }

    fn fallible_from_trap(trap: Trap) -> Result<T, Trap> {
        Err(trap)
    }
}

macro_rules! impl_wasm_host_results {
    ($n:tt $($t:ident)*) => (
        #[allow(non_snake_case)]
        unsafe impl<$($t),*> WasmRet for ($($t,)*)
        where
            $($t: WasmTy,)*
            ($($t::Abi,)*): HostAbi,
        {
            type Abi = <($($t::Abi,)*) as HostAbi>::Abi;
            type Retptr = <($($t::Abi,)*) as HostAbi>::Retptr;
            type Fallible = Result<Self, Trap>;

            #[inline]
            fn compatible_with_store(&self, _store: &StoreOpaque) -> bool {
                let ($($t,)*) = self;
                $( $t.compatible_with_store(_store) && )* true
            }

            #[inline]
            unsafe fn into_abi_for_ret(self, _store: &mut StoreOpaque, ptr: Self::Retptr) -> Result<Self::Abi, Trap> {
                let ($($t,)*) = self;
                let abi = ($($t.into_abi(_store),)*);
                Ok(<($($t::Abi,)*) as HostAbi>::into_abi(abi, ptr))
            }

            fn func_type(params: impl Iterator<Item = ValType>) -> FuncType {
                FuncType::new(
                    params,
                    std::array::IntoIter::new([$($t::valtype(),)*]),
                )
            }

            #[allow(unused_assignments)]
            unsafe fn wrap_trampoline(mut _ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi) {
                let ($($t,)*) = <($($t::Abi,)*) as HostAbi>::call(f);
                $(
                    *_ptr.cast() = $t;
                    _ptr = _ptr.add(1);
                )*
            }

            #[inline]
            fn into_fallible(self) -> Result<Self, Trap> {
                Ok(self)
            }

            #[inline]
            fn fallible_from_trap(trap: Trap) -> Result<Self, Trap> {
                Err(trap)
            }
        }
    )
}

for_each_function_signature!(impl_wasm_host_results);

// Internal trait representing how to communicate tuples of return values across
// an ABI boundary. This internally corresponds to the "wasmtime" ABI inside of
// cranelift itself. Notably the first element of each tuple is returned via the
// typical system ABI (e.g. systemv or fastcall depending on platform) and all
// other values are returned packed via the stack.
//
// This trait helps to encapsulate all the details of that.
#[doc(hidden)]
pub trait HostAbi {
    // A value returned from native functions which return `Self`
    type Abi: Copy;
    // A return pointer, added to the end of the argument list, for native
    // functions that return `Self`. Note that a 0-sized type here should get
    // elided at the ABI level.
    type Retptr: Copy;

    // Converts a value of `self` into its components. Stores necessary values
    // into `ptr` and then returns whatever needs to be returned from the
    // function.
    unsafe fn into_abi(self, ptr: Self::Retptr) -> Self::Abi;

    // Calls `f` with a suitably sized return area and requires `f` to return
    // the raw abi value of the first element of our tuple. This will then
    // unpack the `Retptr` and assemble it with `Self::Abi` to return an
    // instance of the whole tuple.
    unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self;
}

macro_rules! impl_host_abi {
    // Base case, everything is `()`
    (0) => {
        impl HostAbi for () {
            type Abi = ();
            type Retptr = ();

            #[inline]
            unsafe fn into_abi(self, _ptr: Self::Retptr) -> Self::Abi {}

            #[inline]
            unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self {
                f(())
            }
        }
    };

    // In the 1-case the retptr is not present, so it's a 0-sized value.
    (1 $a:ident) => {
        impl<$a: Copy> HostAbi for ($a,) {
            type Abi = $a;
            type Retptr = ();

            unsafe fn into_abi(self, _ptr: Self::Retptr) -> Self::Abi {
                self.0
            }

            unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self {
                (f(()),)
            }
        }
    };

    // This is where the more interesting case happens. The first element of the
    // tuple is returned via `Abi` and all other elements are returned via
    // `Retptr`. We create a `TupleRetNN` structure to represent all of the
    // return values here.
    //
    // Also note that this isn't implemented for the old backend right now due
    // to the original author not really being sure how to implement this in the
    // old backend.
    ($n:tt $t:ident $($u:ident)*) => {paste::paste!{
        #[doc(hidden)]
        #[allow(non_snake_case)]
        #[repr(C)]
        pub struct [<TupleRet $n>]<$($u,)*> {
            $($u: $u,)*
        }

        #[allow(non_snake_case, unused_assignments)]
        impl<$t: Copy, $($u: Copy,)*> HostAbi for ($t, $($u,)*) {
            type Abi = $t;
            type Retptr = *mut [<TupleRet $n>]<$($u,)*>;

            unsafe fn into_abi(self, ptr: Self::Retptr) -> Self::Abi {
                let ($t, $($u,)*) = self;
                // Store the tail of our tuple into the return pointer...
                $((*ptr).$u = $u;)*
                // ... and return the head raw.
                $t
            }

            unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self {
                // Create space to store all the return values and then invoke
                // the function.
                let mut space = std::mem::MaybeUninit::uninit();
                let t = f(space.as_mut_ptr());
                let space = space.assume_init();

                // Use the return value as the head of the tuple and unpack our
                // return area to get the rest of the tuple.
                (t, $(space.$u,)*)
            }
        }
    }};
}

for_each_function_signature!(impl_host_abi);

/// Internal trait implemented for all arguments that can be passed to
/// [`Func::wrap`] and [`Linker::func_wrap`](crate::Linker::func_wrap).
///
/// This trait should not be implemented by external users, it's only intended
/// as an implementation detail of this crate.
pub trait IntoFunc<T, Params, Results>: Send + Sync + 'static {
    #[doc(hidden)]
    fn into_func(self, engine: &Engine) -> (InstanceHandle, VMTrampoline);
}

/// A structure representing the caller's context when creating a function
/// via [`Func::wrap`].
///
/// This structure can be taken as the first parameter of a closure passed to
/// [`Func::wrap`] or other constructors, and serves two purposes:
///
/// * First consumers can use [`Caller<'_, T>`](crate::Caller) to get access to
///   [`StoreContextMut<'_, T>`](crate::StoreContextMut) and/or get access to
///   `T` itself. This means that the [`Caller`] type can serve as a proxy to
///   the original [`Store`](crate::Store) itself and is used to satisfy
///   [`AsContext`] and [`AsContextMut`] bounds.
///
/// * Second a [`Caller`] can be used as the name implies, learning about the
///   caller's context, namely it's exported memory and exported functions. This
///   allows functions which take pointers as arguments to easily read the
///   memory the pointers point into, or if a function is expected to call
///   malloc in the wasm module to reserve space for the output you can do that.
///
/// Host functions which want access to [`Store`](crate::Store)-level state are
/// recommended to use this type.
pub struct Caller<'a, T> {
    pub(crate) store: StoreContextMut<'a, T>,
    caller: &'a InstanceHandle,
}

impl<T> Caller<'_, T> {
    unsafe fn with<R>(caller: *mut VMContext, f: impl FnOnce(Caller<'_, T>) -> R) -> R {
        assert!(!caller.is_null());
        let instance = InstanceHandle::from_vmctx(caller);
        let store = StoreContextMut::from_raw(instance.store());
        f(Caller {
            store,
            caller: &instance,
        })
    }

    fn sub_caller(&mut self) -> Caller<'_, T> {
        Caller {
            store: self.store.as_context_mut(),
            caller: self.caller,
        }
    }

    /// Looks up an export from the caller's module by the `name` given.
    ///
    /// Note that this function is only implemented for the `Extern::Memory`
    /// and the `Extern::Func` types currently. No other exported structures
    /// can be acquired through this method.
    ///
    /// Note that when accessing and calling exported functions, one should
    /// adhere to the guidelines of the interface types proposal.  This method
    /// is a temporary mechanism for accessing the caller's information until
    /// interface types has been fully standardized and implemented. The
    /// interface types proposal will obsolete this type and this will be
    /// removed in the future at some point after interface types is
    /// implemented. If you're relying on this method type it's recommended to
    /// become familiar with interface types to ensure that your use case is
    /// covered by the proposal.
    ///
    /// # Return
    ///
    /// If a memory or function export with the `name` provided was found, then it is
    /// returned as a `Memory`. There are a number of situations, however, where
    /// the memory or function may not be available:
    ///
    /// * The caller instance may not have an export named `name`
    /// * The export named `name` may not be an exported memory
    /// * There may not be a caller available, for example if `Func` was called
    ///   directly from host code.
    ///
    /// It's recommended to take care when calling this API and gracefully
    /// handling a `None` return value.
    pub fn get_export(&mut self, name: &str) -> Option<Extern> {
        // All instances created have a `host_state` with a pointer pointing
        // back to themselves. If this caller doesn't have that `host_state`
        // then it probably means it was a host-created object like `Func::new`
        // which doesn't have any exports we want to return anyway.
        match self
            .caller
            .host_state()
            .downcast_ref::<Instance>()?
            .get_export(&mut self.store, name)?
        {
            Extern::Func(f) => Some(Extern::Func(f)),
            Extern::Memory(f) => Some(Extern::Memory(f)),
            // Intentionally ignore other Extern items here since this API is
            // supposed to be a temporary stop-gap until interface types.
            _ => None,
        }
    }

    /// Access the underlying data owned by this `Store`.
    ///
    /// Same as [`Store::data`](crate::Store::data)
    pub fn data(&self) -> &T {
        self.store.data()
    }

    /// Access the underlying data owned by this `Store`.
    ///
    /// Same as [`Store::data_mut`](crate::Store::data_mut)
    pub fn data_mut(&mut self) -> &mut T {
        self.store.data_mut()
    }

    /// Returns the underlying [`Engine`] this store is connected to.
    pub fn engine(&self) -> &Engine {
        self.store.engine()
    }

    /// Returns an [`InterruptHandle`] to interrupt wasm execution.
    ///
    /// See [`Store::interrupt_handle`](crate::Store::interrupt_handle) for more
    /// information.
    pub fn interrupt_handle(&self) -> Result<InterruptHandle> {
        self.store.interrupt_handle()
    }

    /// Perform garbage collection of `ExternRef`s.
    ///
    /// Same as [`Store::gc`](crate::Store::gc).
    pub fn gc(&mut self) {
        self.store.gc()
    }

    /// Returns the fuel consumed by this store.
    ///
    /// For more information see [`Store::fuel_consumed`](crate::Store::fuel_consumed)
    pub fn fuel_consumed(&self) -> Option<u64> {
        self.store.fuel_consumed()
    }

    /// Inject more fuel into this store to be consumed when executing wasm code.
    ///
    /// For more information see [`Store::add_fuel`](crate::Store::add_fuel)
    pub fn add_fuel(&mut self, fuel: u64) -> Result<()> {
        self.store.add_fuel(fuel)
    }

    /// Synthetically consumes fuel from the store.
    ///
    /// For more information see [`Store::consume_fuel`](crate::Store::consume_fuel)
    pub fn consume_fuel(&mut self, fuel: u64) -> Result<u64> {
        self.store.consume_fuel(fuel)
    }

    /// Configures this `Store` to trap whenever fuel runs out.
    ///
    /// For more information see
    /// [`Store::out_of_fuel_trap`](crate::Store::out_of_fuel_trap)
    pub fn out_of_fuel_trap(&mut self) {
        self.store.out_of_fuel_trap()
    }

    /// Configures this `Store` to yield while executing futures whenever fuel
    /// runs out.
    ///
    /// For more information see
    /// [`Store::out_of_fuel_async_yield`](crate::Store::out_of_fuel_async_yield)
    pub fn out_of_fuel_async_yield(&mut self, injection_count: u64, fuel_to_inject: u64) {
        self.store
            .out_of_fuel_async_yield(injection_count, fuel_to_inject)
    }
}

impl<T> AsContext for Caller<'_, T> {
    type Data = T;
    fn as_context(&self) -> StoreContext<'_, T> {
        self.store.as_context()
    }
}

impl<T> AsContextMut for Caller<'_, T> {
    fn as_context_mut(&mut self) -> StoreContextMut<'_, T> {
        self.store.as_context_mut()
    }
}

fn cross_store_trap() -> Box<dyn Error + Send + Sync> {
    #[derive(Debug)]
    struct CrossStoreError;

    impl Error for CrossStoreError {}

    impl fmt::Display for CrossStoreError {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(
                f,
                "host function attempted to return cross-`Store` \
                 value to Wasm",
            )
        }
    }

    Box::new(CrossStoreError)
}

macro_rules! impl_into_func {
    ($num:tt $($args:ident)*) => {
        // Implement for functions without a leading `&Caller` parameter,
        // delegating to the implementation below which does have the leading
        // `Caller` parameter.
        #[allow(non_snake_case)]
        impl<T, F, $($args,)* R> IntoFunc<T, ($($args,)*), R> for F
        where
            F: Fn($($args),*) -> R + Send + Sync + 'static,
            $($args: WasmTy,)*
            R: WasmRet,
        {
            fn into_func(self, engine: &Engine) -> (InstanceHandle, VMTrampoline) {
                let f = move |_: Caller<'_, T>, $($args:$args),*| {
                    self($($args),*)
                };

                f.into_func(engine)
            }
        }

        #[allow(non_snake_case)]
        impl<T, F, $($args,)* R> IntoFunc<T, (Caller<'_, T>, $($args,)*), R> for F
        where
            F: Fn(Caller<'_, T>, $($args),*) -> R + Send + Sync + 'static,
            $($args: WasmTy,)*
            R: WasmRet,
        {
            fn into_func(self, engine: &Engine) -> (InstanceHandle, VMTrampoline) {
                /// This shim is called by Wasm code, constructs a `Caller`,
                /// calls the wrapped host function, and returns the translated
                /// result back to Wasm.
                ///
                /// Note that this shim's ABI must *exactly* match that expected
                /// by Cranelift, since Cranelift is generating raw function
                /// calls directly to this function.
                unsafe extern "C" fn wasm_to_host_shim<T, F, $($args,)* R>(
                    vmctx: *mut VMContext,
                    caller_vmctx: *mut VMContext,
                    $( $args: $args::Abi, )*
                    retptr: R::Retptr,
                ) -> R::Abi
                where
                    F: Fn(Caller<'_, T>, $( $args ),*) -> R + 'static,
                    $( $args: WasmTy, )*
                    R: WasmRet,
                {
                    enum CallResult<U> {
                        Ok(U),
                        Trap(Box<dyn Error + Send + Sync>),
                        Panic(Box<dyn std::any::Any + Send>),
                    }

                    // Note that this `result` is intentionally scoped into a
                    // separate block. Handling traps and panics will involve
                    // longjmp-ing from this function which means we won't run
                    // destructors. As a result anything requiring a destructor
                    // should be part of this block, and the long-jmp-ing
                    // happens after the block in handling `CallResult`.
                    let result = Caller::with(caller_vmctx, |mut caller| {
                        let state = (*vmctx).host_state();
                        // Double-check ourselves in debug mode, but we control
                        // the `Any` here so an unsafe downcast should also
                        // work.
                        debug_assert!(state.is::<F>());
                        let func = &*(state as *const _ as *const F);

                        let ret = {
                            panic::catch_unwind(AssertUnwindSafe(|| {
                                if let Err(trap) = caller.store.0.call_hook(CallHook::CallingHost) {
                                    return R::fallible_from_trap(trap);
                                }
                                $(let $args = $args::from_abi($args, caller.store.0);)*
                                let r = func(
                                    caller.sub_caller(),
                                    $( $args, )*
                                );
                                if let Err(trap) = caller.store.0.call_hook(CallHook::ReturningFromHost) {
                                    return R::fallible_from_trap(trap);
                                }
                                r.into_fallible()
                            }))
                        };

                        // Note that we need to be careful when dealing with traps
                        // here. Traps are implemented with longjmp/setjmp meaning
                        // that it's not unwinding and consequently no Rust
                        // destructors are run. We need to be careful to ensure that
                        // nothing on the stack needs a destructor when we exit
                        // abnormally from this `match`, e.g. on `Err`, on
                        // cross-store-issues, or if `Ok(Err)` is raised.
                        match ret {
                            Err(panic) => CallResult::Panic(panic),
                            Ok(ret) => {
                                // Because the wrapped function is not `unsafe`, we
                                // can't assume it returned a value that is
                                // compatible with this store.
                                if !ret.compatible_with_store(caller.store.0) {
                                    CallResult::Trap(cross_store_trap())
                                } else {
                                    match ret.into_abi_for_ret(caller.store.0, retptr) {
                                        Ok(val) => CallResult::Ok(val),
                                        Err(trap) => CallResult::Trap(trap.into()),
                                    }
                                }

                            }
                        }
                    });

                    match result {
                        CallResult::Ok(val) => val,
                        CallResult::Trap(trap) => raise_user_trap(trap),
                        CallResult::Panic(panic) => wasmtime_runtime::resume_panic(panic),
                    }
                }

                /// This trampoline allows host code to indirectly call the
                /// wrapped function (e.g. via `Func::call` on a `funcref` that
                /// happens to reference our wrapped function).
                ///
                /// It reads the arguments out of the incoming `args` array,
                /// calls the given function pointer, and then stores the result
                /// back into the `args` array.
                unsafe extern "C" fn host_trampoline<$($args,)* R>(
                    callee_vmctx: *mut VMContext,
                    caller_vmctx: *mut VMContext,
                    ptr: *const VMFunctionBody,
                    args: *mut ValRaw,
                )
                where
                    $($args: WasmTy,)*
                    R: WasmRet,
                {
                    let ptr = mem::transmute::<
                        *const VMFunctionBody,
                        unsafe extern "C" fn(
                            *mut VMContext,
                            *mut VMContext,
                            $( $args::Abi, )*
                            R::Retptr,
                        ) -> R::Abi,
                    >(ptr);

                    let mut _n = 0;
                    $(
                        let $args = *args.add(_n).cast::<$args::Abi>();
                        _n += 1;
                    )*
                    R::wrap_trampoline(args, |retptr| {
                        ptr(callee_vmctx, caller_vmctx, $( $args, )* retptr)
                    });
                }

                let ty = R::func_type(
                    None::<ValType>.into_iter()
                        $(.chain(Some($args::valtype())))*
                );

                let shared_signature_id = engine.signatures().register(ty.as_wasm_func_type());

                let trampoline = host_trampoline::<$($args,)* R>;


                let instance = unsafe {
                    crate::trampoline::create_raw_function(
                        std::slice::from_raw_parts_mut(
                            wasm_to_host_shim::<T, F, $($args,)* R> as *mut _,
                            0,
                        ),
                        shared_signature_id,
                        Box::new(self),
                    )
                    .expect("failed to create raw function")
                };

                (instance, trampoline)
            }
        }
    }
}

for_each_function_signature!(impl_into_func);

/// Representation of a host-defined function.
///
/// This is used for `Func::new` but also for `Linker`-defined functions. For
/// `Func::new` this is stored within a `Store`, and for `Linker`-defined
/// functions they wrap this up in `Arc` to enable shared ownership of this
/// across many stores.
///
/// Technically this structure needs a `<T>` type parameter to connect to the
/// `Store<T>` itself, but that's an unsafe contract of using this for now
/// rather than part of the struct type (to avoid `Func<T>` in the API).
pub(crate) struct HostFunc {
    // Owned `*mut VMContext` allocation. Deallocated when this `HostFunc` is
    // dropped.
    instance: InstanceHandle,
    // Trampoline to enter this function from Rust.
    trampoline: VMTrampoline,
    // The loaded `ExportFunction` from the above `InstanceHandle` which has raw
    // pointers and information about how to actually call this function (e.g.
    // the actual address in JIT code and the vm shared function index).
    export: ExportFunction,
    // Stored to unregister this function's signature with the engine when this
    // is dropped.
    engine: Engine,
}

impl HostFunc {
    /// Analog of [`Func::new`]
    #[cfg(compiler)]
    pub fn new<T>(
        engine: &Engine,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, &[Val], &mut [Val]) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let ty_clone = ty.clone();
        unsafe {
            HostFunc::new_unchecked(engine, ty, move |caller, values| {
                Func::invoke(caller, &ty_clone, values, &func)
            })
        }
    }

    /// Analog of [`Func::new_unchecked`]
    #[cfg(compiler)]
    pub unsafe fn new_unchecked<T>(
        engine: &Engine,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, *mut ValRaw) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let func = move |caller_vmctx, values: *mut ValRaw| unsafe {
            Caller::<T>::with(caller_vmctx, |caller| func(caller, values))
        };
        let (instance, trampoline) = crate::trampoline::create_function(&ty, func, engine)
            .expect("failed to create function");
        HostFunc::_new(engine, instance, trampoline)
    }

    /// Analog of [`Func::wrap`]
    pub fn wrap<T, Params, Results>(
        engine: &Engine,
        func: impl IntoFunc<T, Params, Results>,
    ) -> Self {
        let (instance, trampoline) = func.into_func(engine);
        HostFunc::_new(engine, instance, trampoline)
    }

    /// Requires that this function's signature is already registered within
    /// `Engine`. This happens automatically during the above two constructors.
    fn _new(engine: &Engine, instance: InstanceHandle, trampoline: VMTrampoline) -> Self {
        let idx = EntityIndex::Function(FuncIndex::from_u32(0));
        let export = match instance.lookup_by_declaration(&idx) {
            wasmtime_runtime::Export::Function(f) => f,
            _ => unreachable!(),
        };

        HostFunc {
            instance,
            trampoline,
            export,
            engine: engine.clone(),
        }
    }

    /// Inserts this `HostFunc` into a `Store`, returning the `Func` pointing to
    /// it.
    ///
    /// # Unsafety
    ///
    /// Can only be inserted into stores with a matching `T` relative to when
    /// this `HostFunc` was first created.
    pub unsafe fn to_func(self: &Arc<Self>, store: &mut StoreOpaque) -> Func {
        self.register_trampoline(store);
        let me = self.clone();
        Func::from_func_kind(FuncKind::SharedHost(me), store)
    }

    /// Same as [`HostFunc::to_func`], different ownership.
    unsafe fn into_func(self, store: &mut StoreOpaque) -> Func {
        self.register_trampoline(store);
        Func::from_func_kind(FuncKind::Host(self), store)
    }

    unsafe fn register_trampoline(&self, store: &mut StoreOpaque) {
        // This assert is required to ensure that we can indeed safely insert
        // `self` into the `store` provided, otherwise the type information we
        // have listed won't be correct. This is possible to hit with the public
        // API of Wasmtime, and should be documented in relevant functions.
        assert!(
            Engine::same(&self.engine, store.engine()),
            "cannot use a store with a different engine than a linker was created with",
        );
        let idx = self.export.anyfunc.as_ref().type_index;
        store.register_host_trampoline(idx, self.trampoline);
    }

    pub(crate) fn sig_index(&self) -> VMSharedSignatureIndex {
        unsafe { self.export.anyfunc.as_ref().type_index }
    }
}

impl Drop for HostFunc {
    fn drop(&mut self) {
        unsafe {
            self.engine
                .signatures()
                .unregister(self.export.anyfunc.as_ref().type_index);

            // Host functions are always allocated with the default (on-demand)
            // allocator
            OnDemandInstanceAllocator::default().deallocate(&self.instance);
        }
    }
}

impl FuncData {
    #[inline]
    fn trampoline(&self) -> VMTrampoline {
        match &self.kind {
            FuncKind::StoreOwned { trampoline, .. } => *trampoline,
            FuncKind::SharedHost(host) => host.trampoline,
            FuncKind::Host(host) => host.trampoline,
        }
    }

    #[inline]
    fn export(&self) -> &ExportFunction {
        self.kind.export()
    }
}

impl FuncKind {
    #[inline]
    fn export(&self) -> &ExportFunction {
        match self {
            FuncKind::StoreOwned { export, .. } => export,
            FuncKind::SharedHost(host) => &host.export,
            FuncKind::Host(host) => &host.export,
        }
    }
}