[Backtracing] Fix compact image map decoding bug.

If we ended up with a `/` at the beginning of a string segment, we
were erroneously not adding to the expansion dictionary when we
should have been.

rdar://124913332

Author: al45tair

stdlib/public/RuntimeModule/CompactImageMap.swift

@@ -160,7 +160,7 @@ public enum CompactImageMapFormat {
             guard let char = iterator.next() else {
               return nil
             }
-            if n > 0 && char == 0x2f {
+            if base + n > stringBase! && (char == 0x2f || char == 0x5c) {
               let prefix = String(decoding: resultBytes[stringBase!..<base+n],
                                   as: UTF8.self)
               #if DEBUG_COMPACT_IMAGE_MAP
@@ -297,6 +297,10 @@ public enum CompactImageMapFormat {
         let acount = Int(((header >> 3) & 0x7) + 1)
         let ecount = Int((header & 0x7) + 1)
 
+        #if DEBUG_COMPACT_IMAGE_MAP
+        print("r = \(relative), acount = \(acount), ecount = \(ecount)")
+        #endif
+
         // Now the base and end of text addresses
         guard let address = decodeAddress(acount) else {
           return nil
@@ -315,11 +319,20 @@ public enum CompactImageMapFormat {
         }
         let endOfText = baseAddress &+ eotOffset
 
+        #if DEBUG_COMPACT_IMAGE_MAP
+        print("address = \(hex(address)), eotOffset = \(hex(eotOffset))")
+        print("baseAddress = \(hex(baseAddress)), endOfText = \(hex(endOfText))")
+        #endif
+
         // Next, get the build ID byte count
         guard let buildIdBytes = decodeCount() else {
           return nil
         }
 
+        #if DEBUG_COMPACT_IMAGE_MAP
+        print("buildIdBytes = \(buildIdBytes)")
+        #endif
+
         // Read the build ID
         var buildId: [UInt8]? = nil
 
@@ -335,6 +348,10 @@ public enum CompactImageMapFormat {
           }
         }
 
+        #if DEBUG_COMPACT_IMAGE_MAP
+        print("buildId = \(buildId)")
+        #endif
+
         // Decode the path
         let path = decodePath()
         let name: String?
@@ -674,6 +691,9 @@ public enum CompactImageMapFormat {
 
             // Add any new prefixes
             forEachPrefix(of: remainingPath) { prefix in
+              #if DEBUG_COMPACT_IMAGE_MAP
+              print("defining \(nextCode) as \"\(prefix)\"")
+              #endif
               pathPrefixes.append((nextCode, prefix))
               nextCode += 1
             }

stdlib/public/RuntimeModule/ImageMap.swift

@@ -33,7 +33,7 @@ public struct ImageMap: Collection, Sendable, Hashable {
 
   /// Tells us what size of machine words were used when capturing the
   /// image map.
-  enum WordSize {
+  enum WordSize: Sendable {
     case sixteenBit
     case thirtyTwoBit
     case sixtyFourBit