GDB RP: support qWasmCallStack and debugger breakpoints

.github/workflows/main.yml

@@ -137,19 +137,21 @@ jobs:
             wasi-swift-sdk-checksum: "b64dfad9e1c9ccdf06f35cf9b1a00317e000df0c0de0b3eb9f49d6db0fcba4d9"
             test-args: "--traits WasmDebuggingSupport --enable-code-coverage"
             build-dev-dashboard: true
-          - swift: "swiftlang/swift:nightly-main-noble"
-            development-toolchain-download: "https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a-ubuntu24.04.tar.gz"
-            wasi-swift-sdk-download: "https://download.swift.org/development/wasm-sdk/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm.artifactbundle.tar.gz"
-            wasi-swift-sdk-id: swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm
-            wasi-swift-sdk-checksum: "b64dfad9e1c9ccdf06f35cf9b1a00317e000df0c0de0b3eb9f49d6db0fcba4d9"
-            test-args: "--traits WasmDebuggingSupport -Xswiftc -DWASMKIT_CI_TOOLCHAIN_NIGHTLY"
-          - swift: "swiftlang/swift:nightly-main-noble"
-            development-toolchain-download: "https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a-ubuntu24.04.tar.gz"
-            wasi-swift-sdk-download: "https://download.swift.org/development/wasm-sdk/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm.artifactbundle.tar.gz"
-            wasi-swift-sdk-id: swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm
-            wasi-swift-sdk-checksum: "b64dfad9e1c9ccdf06f35cf9b1a00317e000df0c0de0b3eb9f49d6db0fcba4d9"
-            test-args: "--traits WasmDebuggingSupport -Xswiftc -DWASMKIT_CI_TOOLCHAIN_NIGHTLY --build-system swiftbuild"
-            label: " --build-system swiftbuild"
+            # Disabled until a toolchain containing https://github.com/swiftlang/swift/commit/b219d4089c922ceb8b700424236ca97f6087a9a1
+            # is tagged.
+          # - swift: "swiftlang/swift:nightly-main-noble"
+          #   development-toolchain-download: "https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a-ubuntu24.04.tar.gz"
+          #   wasi-swift-sdk-download: "https://download.swift.org/development/wasm-sdk/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm.artifactbundle.tar.gz"
+          #   wasi-swift-sdk-id: swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm
+          #   wasi-swift-sdk-checksum: "b64dfad9e1c9ccdf06f35cf9b1a00317e000df0c0de0b3eb9f49d6db0fcba4d9"
+          #   test-args: "--traits WasmDebuggingSupport -Xswiftc -DWASMKIT_CI_TOOLCHAIN_NIGHTLY"
+#           - swift: "swiftlang/swift:nightly-main-noble"
+#             development-toolchain-download: "https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a-ubuntu24.04.tar.gz"
+#             wasi-swift-sdk-download: "https://download.swift.org/development/wasm-sdk/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm.artifactbundle.tar.gz"
+#             wasi-swift-sdk-id: swift-DEVELOPMENT-SNAPSHOT-2025-10-02-a_wasm
+#             wasi-swift-sdk-checksum: "b64dfad9e1c9ccdf06f35cf9b1a00317e000df0c0de0b3eb9f49d6db0fcba4d9"
+#             test-args: "--traits WasmDebuggingSupport -Xswiftc -DWASMKIT_CI_TOOLCHAIN_NIGHTLY --build-system swiftbuild"
+#             label: " --build-system swiftbuild"
 
     runs-on: ubuntu-24.04
     name: "build-linux (${{ matrix.swift }}${{ matrix.label }})"

Package@swift-6.1.swift

@@ -21,7 +21,7 @@ let package = Package(
     ],
     traits: [
         .default(enabledTraits: []),
-        "WasmDebuggingSupport"
+        "WasmDebuggingSupport",
     ],
     targets: [
         .executableTarget(
@@ -123,7 +123,8 @@ let package = Package(
         .target(name: "WITExtractor"),
         .testTarget(name: "WITExtractorTests", dependencies: ["WITExtractor", "WIT"]),
 
-        .target(name: "GDBRemoteProtocol",
+        .target(
+            name: "GDBRemoteProtocol",
             dependencies: [
                 .product(name: "Logging", package: "swift-log"),
                 .product(name: "NIOCore", package: "swift-nio"),

Sources/GDBRemoteProtocol/GDBHostCommand.swift

@@ -38,6 +38,7 @@ package struct GDBHostCommand: Equatable {
         case readMemoryBinaryData
         case readMemory
         case wasmCallStack
+        case threadStopInfo
 
         case generalRegisters
 
@@ -97,6 +98,7 @@ package struct GDBHostCommand: Equatable {
     ///   - arguments: raw arguments that immediately follow kind of the command.
     package init(kindString: String, arguments: String) throws(GDBHostCommandDecoder.Error) {
         let registerInfoPrefix = "qRegisterInfo"
+        let threadStopInfoPrefix = "qThreadStopInfo"
 
         if kindString.starts(with: "x") {
             self.kind = .readMemoryBinaryData
@@ -109,6 +111,14 @@ package struct GDBHostCommand: Equatable {
         } else if kindString.starts(with: registerInfoPrefix) {
             self.kind = .registerInfo
 
+            guard arguments.isEmpty else {
+                throw GDBHostCommandDecoder.Error.unexpectedArgumentsValue
+            }
+            self.arguments = String(kindString.dropFirst(registerInfoPrefix.count))
+            return
+        } else if kindString.starts(with: threadStopInfoPrefix) {
+            self.kind = .threadStopInfo
+
             guard arguments.isEmpty else {
                 throw GDBHostCommandDecoder.Error.unexpectedArgumentsValue
             }

Sources/GDBRemoteProtocol/GDBTargetResponseEncoder.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
+import Logging
 import NIOCore
 
 extension String {
@@ -27,7 +28,12 @@ extension String {
 package class GDBTargetResponseEncoder: MessageToByteEncoder {
     private var isNoAckModeActive = false
 
-    package init() {}
+    private let logger: Logger
+
+    package init(logger: Logger) {
+        self.logger = logger
+    }
+
     package func encode(data: GDBTargetResponse, out: inout ByteBuffer) {
         if !isNoAckModeActive {
             out.writeInteger(UInt8(ascii: "+"))
@@ -51,8 +57,9 @@ package class GDBTargetResponseEncoder: MessageToByteEncoder {
             out.writeString(str.appendedChecksum)
 
         case .hexEncodedBinary(let binary):
-            let hexDump = ByteBuffer(bytes: binary).hexDump(format: .compact)
-            out.writeString(hexDump.appendedChecksum)
+            let hexDumpResponse = ByteBuffer(bytes: binary).hexDump(format: .compact).appendedChecksum
+            self.logger.trace("GDBTargetResponseEncoder encoded a response", metadata: ["RawResponse": .string(hexDumpResponse)])
+            out.writeString(hexDumpResponse)
 
         case .empty:
             out.writeString("".appendedChecksum)

Sources/WAT/Encoder.swift

@@ -158,6 +158,7 @@ extension TableType: WasmEncodable {
 struct ElementExprCollector: AnyInstructionVisitor {
     typealias Output = Void
 
+    var binaryOffset: Int = 0
     var isAllRefFunc: Bool = true
     var instructions: [Instruction] = []
 
@@ -443,6 +444,7 @@ extension WatParser.DataSegmentDecl {
 }
 
 struct ExpressionEncoder: BinaryInstructionEncoder {
+    var binaryOffset: Int = 0
     var encoder = Encoder()
     var hasDataSegmentInstruction: Bool = false
 

Sources/WAT/Parser/WastParser.swift

@@ -54,6 +54,7 @@ struct WastParser {
     }
 
     struct ConstExpressionCollector: WastConstInstructionVisitor {
+        var binaryOffset: Int = 0
         let addValue: (Value) -> Void
 
         mutating func visitI32Const(value: Int32) throws { addValue(.i32(UInt32(bitPattern: value))) }

Sources/WasmKit/DebuggerInstructionMapping.swift

@@ -0,0 +1,86 @@
+
+/// Two-way mapping between Wasm and internal iseq bytecode instructions. The implementation of the mapping
+/// is private and is empty when `WasmDebuggingSupport` package trait is disabled.
+struct DebuggerInstructionMapping {
+#if WasmDebuggingSupport
+
+    /// Mapping from iseq Pc to instruction addresses in the original binary.
+    /// Used for handling current call stack requests issued by a ``Debugger`` instance.
+    private var iseqToWasm = [Pc: Int]()
+
+    /// Mapping from Wasm instruction addresses in the original binary to iseq instruction addresses.
+    /// Used for handling breakpoint requests issued by a ``Debugger`` instance.
+    private var wasmToIseq = [Int: Pc]()
+
+    /// Wasm addresses sorted in ascending order for binary search when of the next closest mapped
+    /// instruction, when no key is found in `wasmToIseqMapping`.
+    private var wasmMappings = [Int]()
+
+    mutating func add(wasm: Int, iseq: Pc) {
+        // Don't override the existing mapping, only store a new pair if there's no mapping for a given key.
+        if self.iseqToWasm[iseq] == nil {
+            self.iseqToWasm[iseq] = wasm
+        }
+        if self.wasmToIseq[wasm] == nil {
+            self.wasmToIseq[wasm] = iseq
+        }
+        self.wasmMappings.append(wasm)
+    }
+
+    /// Computes an address of WasmKit's iseq bytecode instruction that matches a given Wasm instruction address.
+    /// - Parameter address: the Wasm instruction to find a mapping for.
+    /// - Returns: A tuple with an address of found iseq instruction and the original Wasm instruction or next
+    /// closest match if no direct match was found.
+    func findIseq(forWasmAddress address: Int) -> (iseq: Pc, wasm: Int)? {
+        // Look in the main mapping
+        if let iseq = self.wasmToIseq[address] {
+            return (iseq, address)
+        }
+
+        // If nothing found, find the closest Wasm address using binary search
+        guard let nextAddress = self.wasmMappings.binarySearch(nextClosestTo: address),
+            // Look in the main mapping again with the next closest address if binary search produced anything
+            let iseq = self.wasmToIseq[nextAddress]
+        else {
+            return nil
+        }
+
+        return (iseq, nextAddress)
+    }
+
+    func findWasm(forIseqAddress pc: Pc) -> Int? {
+        self.iseqToWasm[pc]
+    }
+#endif
+}
+
+
+#if WasmDebuggingSupport
+    extension [Int] {
+        /// Uses binary search to find an element in `self` that's next closest to a given value.
+        /// - Parameter value: the array element to search for or to use as a baseline when searching.
+        /// - Returns: array element `result`, where `result - value` is the smallest possible, while
+        /// `result > value` also holds.
+        package func binarySearch(nextClosestTo value: Int) -> Int? {
+            switch self.count {
+            case 0:
+                return nil
+            default:
+                var slice = self[0..<self.count]
+                while slice.count > 1 {
+                    let middle = (slice.endIndex - slice.startIndex) / 2
+                    if slice[middle] < value {
+                        // Not found anything in the lower half, assigning higher half to `slice`.
+                        slice = slice[(middle + 1)..<slice.endIndex]
+                    } else {
+                        // Not found anything in the higher half, assigning lower half to `slice`.
+                        slice = slice[slice.startIndex..<middle]
+                    }
+                }
+
+                return self[slice.startIndex]
+            }
+        }
+    }
+
+#endif