Fix errno to use UInt16 per the WASI p1 spec

Per the WebAssembly System Interface (WASI) standard specification, size of `errno` variant is 2 bytes, which is equivalent to `UInt16` in Swift. In WasmKit it's currently specified incorrectly to `UInt32`, which leads to bugs when reading and writing `errno` values in guest memory. Corresponding uses of `WASIAbi.Errno` zero-extend value of 2 bytes to 4 bytes when returning 32-bit integers, since WebAssembly doesn't have a separate 16-bit integer type and zero-extension of narrower integers is the expected behavior.

Additionally `ClockId` type specifies a fixed number of cases, disallowing unknown raw values, which could be specified in the future. This edge case is exercised in the WASI specification test suite. The change relaxes this restriction, making the implementation compliant with the test.

Author: MaxDesiatov

Sources/WASI/WASI.swift

@@ -220,7 +220,7 @@ protocol WASI {
 }
 
 enum WASIAbi {
-    enum Errno: UInt32, Error, GuestPointee {
+    enum Errno: UInt16, Error, GuestPointee {
         /// No error occurred. System call completed successfully.
         case SUCCESS = 0
         /// Argument list too long.
@@ -579,19 +579,20 @@ enum WASIAbi {
         }
     }
 
-    enum ClockId: UInt32, GuestPointee {
+    struct ClockId: Equatable, RawRepresentable, GuestPointee {
+        let rawValue: UInt32
         /// The clock measuring real time. Time value zero corresponds with
         /// 1970-01-01T00:00:00Z.
-        case REALTIME = 0
+        static let REALTIME = Self(rawValue: 0)
         /// The store-wide monotonic clock, which is defined as a clock measuring
         /// real time, whose value cannot be adjusted and which cannot have negative
         /// clock jumps. The epoch of this clock is undefined. The absolute time
         /// value of this clock therefore has no meaning.
-        case MONOTONIC = 1
+        static let MONOTONIC = Self(rawValue: 1)
         /// The CPU-time clock associated with the current process.
-        case PROCESS_CPUTIME_ID = 2
+        static let PROCESS_CPUTIME_ID = Self(rawValue: 2)
         /// The CPU-time clock associated with the current thread.
-        case THREAD_CPUTIME_ID = 3
+        static let THREAD_CPUTIME_ID = Self(rawValue: 3)
     }
 
     typealias Timestamp = UInt64
@@ -980,7 +981,7 @@ extension WASI {
             let (name, type) = entry
             functions[name] = WASIHostFunction(type: type) { _, _ in
                 print("\"\(name)\" not implemented yet")
-                return [.i32(WASIAbi.Errno.ENOSYS.rawValue)]
+                return [.i32(.init(WASIAbi.Errno.ENOSYS.rawValue))]
             }
         }
 
@@ -1013,7 +1014,7 @@ extension WASI {
                 do {
                     return try implementation(caller, arguments)
                 } catch let errno as WASIAbi.Errno {
-                    return [.i32(errno.rawValue)]
+                    return [.i32(.init(errno.rawValue))]
                 }
             }
         }
@@ -1026,7 +1027,7 @@ extension WASI {
                     argv: .init(memorySpace: buffer, offset: arguments[0].i32),
                     argvBuffer: .init(memorySpace: buffer, offset: arguments[1].i32)
                 )
-                return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+                return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
             }
         }
 
@@ -1039,7 +1040,7 @@ extension WASI {
                 argcPointer.pointee = argc
                 let bufferSizePointer = UnsafeGuestPointer<WASIAbi.Size>(memorySpace: buffer, offset: arguments[1].i32)
                 bufferSizePointer.pointee = bufferSize
-                return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+                return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
             }
         }
 
@@ -1051,7 +1052,7 @@ extension WASI {
                     environ: .init(memorySpace: buffer, offset: arguments[0].i32),
                     environBuffer: .init(memorySpace: buffer, offset: arguments[1].i32)
                 )
-                return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+                return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
             }
         }
 
@@ -1064,40 +1065,36 @@ extension WASI {
                 environSizePointer.pointee = environSize
                 let bufferSizePointer = UnsafeGuestPointer<WASIAbi.Size>(memorySpace: buffer, offset: arguments[1].i32)
                 bufferSizePointer.pointee = bufferSize
-                return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+                return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
             }
         }
 
         preview1["clock_res_get"] = wasiFunction(
             type: .init(parameters: [.i32, .i32], results: [.i32])
         ) { caller, arguments in
-            guard let id = WASIAbi.ClockId(rawValue: arguments[0].i32) else {
-                throw WASIAbi.Errno.EBADF
-            }
+            let id = WASIAbi.ClockId(rawValue: arguments[0].i32)
             let res = try self.clock_res_get(id: id)
             try withMemoryBuffer(caller: caller) { buffer in
                 let resPointer = UnsafeGuestPointer<WASIAbi.Timestamp>(
                     memorySpace: buffer, offset: arguments[1].i32
                 )
                 resPointer.pointee = res
             }
-            return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+            return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
         }
 
         preview1["clock_time_get"] = wasiFunction(
             type: .init(parameters: [.i32, .i64, .i32], results: [.i32])
         ) { caller, arguments in
-            guard let id = WASIAbi.ClockId(rawValue: arguments[0].i32) else {
-                throw WASIAbi.Errno.EBADF
-            }
+            let id = WASIAbi.ClockId(rawValue: arguments[0].i32)
             let time = try self.clock_time_get(id: id, precision: WASIAbi.Timestamp(arguments[1].i64))
             try withMemoryBuffer(caller: caller) { buffer in
                 let resPointer = UnsafeGuestPointer<WASIAbi.Timestamp>(
                     memorySpace: buffer, offset: arguments[2].i32
                 )
                 resPointer.pointee = time
             }
-            return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+            return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
         }
 
         preview1["fd_advise"] = wasiFunction(
@@ -1112,7 +1109,7 @@ extension WASI {
                 fd: arguments[0].i32, offset: arguments[1].i64,
                 length: arguments[2].i64, advice: advice
             )
-            return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+            return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
         }
 
         preview1["fd_allocate"] = wasiFunction(
@@ -1121,21 +1118,21 @@ extension WASI {
             try self.fd_allocate(
                 fd: arguments[0].i32, offset: arguments[1].i64, length: arguments[2].i64
             )
-            return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+            return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
         }
 
         preview1["fd_close"] = wasiFunction(
             type: .init(parameters: [.i32], results: [.i32])
         ) { caller, arguments in
             try self.fd_close(fd: arguments[0].i32)
-            return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+            return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
         }
 
         preview1["fd_datasync"] = wasiFunction(
             type: .init(parameters: [.i32], results: [.i32])
         ) { caller, arguments in
             try self.fd_datasync(fd: arguments[0].i32)
-            return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+            return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
         }
 
         preview1["fd_fdstat_get"] = wasiFunction(
@@ -1145,7 +1142,7 @@ extension WASI {
                 let stat = try self.fd_fdstat_get(fileDescriptor: arguments[0].i32)
                 let statPointer = UnsafeGuestPointer<WASIAbi.FdStat>(memorySpace: buffer, offset: arguments[1].i32)
                 statPointer.pointee = stat
-                return [.i32(WASIAbi.Errno.SUCCESS.rawValue)]
+                return [.i32(.init(WASIAbi.Errno.SUCCESS.rawValue))]
             }
         }