Fix poll_oneoff and more I/O syscalls in WASI 0.1 (#187)

Removed following XFAILs:

`pwrite-with-append`,
`renumber`,
`stdio`,
`remove_directory_trailing_slashes`,
`sched_yield`,
`sock_shutdown-invalid_fd`,
`sock_shutdown-not_sock`

Testing Swift Concurrency for WebAssembly requires presence of `poll_oneoff`, which is absent in WasmKit. This change provides an implementation for POSIX hosts according to the ABI specified in WebAssembly System Interface standard https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/docs.md#poll_oneoff


rdar://149935761

Author: MaxDesiatov

Sources/WASI/CMakeLists.txt

@@ -15,6 +15,7 @@ add_wasmkit_library(WASI
   FileSystem.swift
   GuestMemorySupport.swift
   Clock.swift
+  Poll.swift
   RandomBufferGenerator.swift
   WASI.swift
   WASIBridgeToHost.swift

Sources/WASI/Platform/Directory.swift

@@ -111,6 +111,7 @@ extension DirEntry: WASIDir, FdWASIEntry {
         #if os(Windows)
             throw WASIAbi.Errno.ENOSYS
         #else
+            let path = SandboxPrimitives.stripDirSuffix(path)
             let result = try SandboxPrimitives.openParent(start: fd, path: path)
             let dir = result.parentFd
             let basename = result.basename

Sources/WASI/Poll.swift

@@ -0,0 +1,89 @@
+import SystemPackage
+import WasmTypes
+
+#if canImport(Darwin)
+    import Darwin
+#elseif canImport(Glibc)
+    import Glibc
+#elseif canImport(Musl)
+    import Musl
+#elseif canImport(Android)
+    import Android
+#elseif os(Windows)
+    import ucrt
+#elseif os(WASI)
+    import WASILibc
+#else
+    #error("Unsupported Platform")
+#endif
+
+extension FdTable {
+    func fileDescriptor(fd: WASIAbi.Fd) throws -> FileDescriptor {
+        guard case .file(let entry) = self[fd], let fd = (entry as? FdWASIEntry)?.fd else {
+            throw WASIAbi.Errno.EBADF
+        }
+
+        return fd
+    }
+}
+
+func poll(
+    subscriptions: some Sequence<WASIAbi.Subscription>,
+    events: UnsafeGuestBufferPointer<WASIAbi.Event>,
+    _ fdTable: FdTable
+) throws -> WASIAbi.Size {
+    #if os(Windows)
+        throw WASIAbi.Errno.ENOTSUP
+    #else
+        var pollfds = [pollfd]()
+        var fdUserData = [WASIAbi.UserData]()
+        var timeoutMilliseconds = UInt.max
+        var clockUserData: WASIAbi.UserData?
+
+        for subscription in subscriptions {
+            let union = subscription.union
+            switch union {
+            case .clock(let clock):
+                timeoutMilliseconds = min(timeoutMilliseconds, .init(clock.timeout / 1_000_000))
+                clockUserData = subscription.userData
+            case .fdRead(let fd):
+                pollfds.append(.init(fd: try fdTable.fileDescriptor(fd: fd).rawValue, events: .init(POLLIN), revents: 0))
+                fdUserData.append(subscription.userData)
+            case .fdWrite(let fd):
+                pollfds.append(.init(fd: try fdTable.fileDescriptor(fd: fd).rawValue, events: .init(POLLOUT), revents: 0))
+                fdUserData.append(subscription.userData)
+            }
+        }
+
+        let result = poll(&pollfds, .init(pollfds.count), .init(timeoutMilliseconds))
+        let err = errno  // Preserve `errno` global immediately after `poll`
+        var updatedEvents: WASIAbi.Size = 0
+        if result == 0, let clockUserData {
+            updatedEvents += 1
+            events[0] = .init(userData: clockUserData, error: .SUCCESS, eventType: .clock, fdReadWrite: .init(nBytes: 0, flags: .init(rawValue: 0)))
+        } else if result > 0 {
+            for (i, fd) in pollfds.enumerated() {
+                guard fd.revents != 0 else { continue }
+                let eventIndex = updatedEvents
+                updatedEvents += 1
+                let hangup: WASIAbi.Event.FdReadWrite.Flags = fd.revents & Int16(POLLHUP) != 0 ? [.hangup] : []
+                if fd.revents & Int16(POLLIN) != 0 || (fd.events & Int16(POLLIN) != 0 && fd.revents & Int16(POLLHUP) != 0) {
+                    events[.init(eventIndex)] = .init(userData: fdUserData[i], error: .SUCCESS, eventType: .fdRead, fdReadWrite: .init(nBytes: 0, flags: hangup))
+                } else if fd.revents & Int16(POLLOUT) != 0 || (fd.events & Int16(POLLOUT) != 0 && fd.revents & Int16(POLLHUP) != 0) {
+                    events[.init(eventIndex)] = .init(userData: fdUserData[i], error: .SUCCESS, eventType: .fdWrite, fdReadWrite: .init(nBytes: 0, flags: hangup))
+                } else if fd.revents & Int16(POLLERR | POLLNVAL) != 0 {
+                    let eventType: WASIAbi.EventType = fd.events & Int16(POLLIN) != 0 ? .fdRead : .fdWrite
+                    events[.init(eventIndex)] = .init(userData: fdUserData[i], error: .EBADF, eventType: eventType, fdReadWrite: .init(nBytes: 0, flags: []))
+                }
+            }
+        } else {
+            switch err {
+            case ENOMEM: throw WASIAbi.Errno.ENOMEM
+            case EINTR: throw WASIAbi.Errno.EINTR
+            case EINVAL: throw WASIAbi.Errno.EINVAL
+            default: throw WASIAbi.Errno.ENOTSUP
+            }
+        }
+        return updatedEvents
+    #endif
+}