[RemoteMirrors] Add hook for resolving indirect addresses

include/swift/Remote/MemoryReader.h

@@ -192,6 +192,20 @@ class MemoryReader {
     return ReadObjResult<T>(reinterpret_cast<const T *>(ptr), deleter);
   }
 
+  /// Resolves an indirect address at the given relative offset.
+  ///
+  /// \param address The base address which contains the relative offset.
+  /// \param offset The offset read.
+  /// \param directnessEncodedInOffset Whether the relative offset encodes the
+  /// directness as the last bit. Note that this is not the offset passed in as
+  /// a parameter, but whether the offset read at address would have the last
+  /// bit set.
+  virtual RemoteAddress
+  resolveIndirectAddressAtOffset(RemoteAddress address, uint64_t offset,
+                                 bool directnessEncodedInOffset) {
+    return address + offset;
+  }
+
   /// Attempts to read 'size' bytes from the given address in the remote process.
   ///
   /// Returns a pointer to the requested data and a function that must be called to

include/swift/Remote/MetadataReader.h

@@ -457,18 +457,20 @@ class MetadataReader {
         swift::Demangle::NodePointer {
       // Resolve the reference to a remote address.
       auto offsetInMangledName =
-            (const char *)base - mangledName.getLocalBuffer();
-      auto remoteAddress =
-          mangledName.getRemoteAddress() + offsetInMangledName + offset;
+          (const char *)base - mangledName.getLocalBuffer();
+      auto offsetAddress = mangledName.getRemoteAddress() + offsetInMangledName;
 
       RemoteAbsolutePointer resolved;
       if (directness == Directness::Indirect) {
+        auto remoteAddress = Reader->resolveIndirectAddressAtOffset(
+            offsetAddress, offset, /*directnessEncodedInOffset=*/false);
         if (auto indirectAddress = readPointer(remoteAddress)) {
           resolved = stripSignedPointer(*indirectAddress);
         } else {
           return nullptr;
         }
       } else {
+        auto remoteAddress = offsetAddress + offset;
         resolved = Reader->getSymbol(remoteAddress);
       }
 
@@ -2084,17 +2086,19 @@ class MetadataReader {
 
     using SignedPointer = typename std::make_signed<StoredPointer>::type;
 
-    RemoteAddress resultAddress = getAddress(fieldRef) + (SignedPointer)offset;
-
     // Low bit set in the offset indicates that the offset leads to the absolute
     // address in memory.
     if (indirect) {
+      RemoteAddress resultAddress = Reader->resolveIndirectAddressAtOffset(
+          getAddress(fieldRef), (SignedPointer)offset,
+          /*directnessEncodedInOffset=*/true);
       if (auto ptr = readPointer(resultAddress)) {
         return stripSignedPointer(*ptr);
       }
       return std::nullopt;
     }
 
+    RemoteAddress resultAddress = getAddress(fieldRef) + (SignedPointer)offset;
     return RemoteAbsolutePointer(resultAddress);
   }