Foundation: correct invalid memory usage in callStackSymbols

The recent improvements in string handling in the compiler identified
poor handling of the symbol name.  Correct the logic for extracting the
symbol name from the result.  While in the area, correct the memory
binding for the symbol info pointer.

Author: compnerd

Sources/Foundation/Thread.swift

@@ -391,26 +391,29 @@ open class Thread : NSObject {
         return backtraceAddresses { (addresses, count) in
           var symbols: [String] = []
 
-          var buffer: UnsafeMutablePointer<Int8> =
-              UnsafeMutablePointer<Int8>
-                  .allocate(capacity: MemoryLayout<SYMBOL_INFO>.size + 128)
+          let buffer: UnsafeMutablePointer<UInt8> =
+              .allocate(capacity: MemoryLayout<SYMBOL_INFO>.size + 128)
           defer { buffer.deallocate() }
 
-          buffer.withMemoryRebound(to: SYMBOL_INFO.self, capacity: 1) {
-            $0.pointee.SizeOfStruct = ULONG(MemoryLayout<SYMBOL_INFO>.size)
-            $0.pointee.MaxNameLen = 128
-
-            var address = addresses
-            for _ in 1...count {
-              var dwDisplacement: DWORD64 = 0
-              if !SymFromAddr(hProcess, unsafeBitCast(address.pointee, to: DWORD64.self), &dwDisplacement, $0) {
-                symbols.append("\($0.pointee)")
-              } else {
-                symbols.append(String(cString: &$0.pointee.Name))
+          let pSymbolInfo =
+              UnsafeMutableRawPointer(buffer).assumingMemoryBound(to: SYMBOL_INFO.self)
+          pSymbolInfo.pointee.SizeOfStruct = ULONG(MemoryLayout<SYMBOL_INFO>.size)
+          pSymbolInfo.pointee.MaxNameLen = 128
+
+          let addresses: UnsafeMutableBufferPointer<PVOID?> =
+              UnsafeMutableBufferPointer<PVOID?>(start: addresses, count: count)
+          for address in addresses {
+            var dwDisplacement: DWORD64 = 0
+            if SymFromAddr(hProcess, DWORD64(UInt(bitPattern: address)),
+                           &dwDisplacement, pSymbolInfo) {
+              withUnsafePointer(to: pSymbolInfo.pointee.Name) {
+                symbols.append(String(cString: $0))
               }
-              address = address.successor()
+            } else {
+              symbols.append("\(pSymbolInfo.pointee)")
             }
           }
+
           return symbols
         }
 #else