[Backtracing] Add ImageMap instead of just using an Array.

We want to be able to efficiently serialise lists of images, and to do so
it makes most sense to create a separate `ImageMap` type.  This also provides
a useful place to put methods to e.g. find an image by address or by build
ID.

rdar://124913332

stdlib/public/RuntimeModule/ImageMap+Darwin.swift

@@ -0,0 +1,91 @@
+//===--- ImageMap+Darwin.swift --------------------------------*- swift -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  Darwin specifics for ImageMap capture.
+//
+//===----------------------------------------------------------------------===//
+
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+
+import Swift
+
+internal import Darwin
+internal import BacktracingImpl.OS.Darwin
+
+extension ImageMap {
+
+  private static func withDyldProcessInfo<T>(for task: task_t,
+                                             fn: (OpaquePointer?) throws -> T)
+    rethrows -> T {
+    var kret = kern_return_t(KERN_SUCCESS)
+    let dyldInfo = _dyld_process_info_create(task, 0, &kret)
+
+    if kret != KERN_SUCCESS {
+      fatalError("error: cannot create dyld process info")
+    }
+
+    defer {
+      _dyld_process_info_release(dyldInfo)
+    }
+
+    return try fn(dyldInfo)
+  }
+
+  @_spi(Internal)
+  public static func capture(for process: Any) -> ImageMap {
+        var images: [Image] = []
+    let task = process as! task_t
+
+    withDyldProcessInfo(for: task) { dyldInfo in
+      _dyld_process_info_for_each_image(dyldInfo) {
+        (machHeaderAddress, uuid, path) in
+
+        if let path = path, let uuid = uuid {
+          let pathString = String(cString: path)
+          let theUUID = Array(UnsafeBufferPointer(start: uuid,
+                                                  count: MemoryLayout<uuid_t>.size))
+          let name: String
+          if let slashIndex = pathString.lastIndex(of: "/") {
+            name = String(pathString.suffix(from:
+                                              pathString.index(after:slashIndex)))
+          } else {
+            name = pathString
+          }
+
+          // Find the end of the __TEXT segment
+          var endOfText = machHeaderAddress + 4096
+
+          _dyld_process_info_for_each_segment(dyldInfo, machHeaderAddress) {
+            address, size, name in
+
+            if let name = String(validatingCString: name!), name == "__TEXT" {
+              endOfText = address + size
+            }
+          }
+
+          images.append(Image(name: name,
+                              path: pathString,
+                              uniqueID: theUUID,
+                              baseAddress: machHeaderAddress,
+                              endOfText: endOfText))
+        }
+      }
+    }
+
+    images.sort(by: { $0.baseAddress < $1.baseAddress })
+
+    return ImageMap(images: images, wordSize: .sixtyFourBit)
+  }
+
+}
+
+#endif // os(macOS) || os(iOS) || os(watchOS) || os(tvOS)