[Reflection] Try to read only the reflection sections.

(instead of the whole object).

Author: Davide Italiano

include/swift/Reflection/ReflectionContext.h

@@ -140,9 +140,49 @@ class ReflectionContext
       return false;
 
     // Read everything including the __TEXT segment.
-    Buf = this->getReader().readBytes(ImageStart, Command->vmsize);
+    // Buf = this->getReader().readBytes(ImageStart, Command->vmsize);
     auto Start = reinterpret_cast<const char *>(Buf.get());
 
+    // Find the load command offset.
+    auto loadCmdOffset = Start + Offset + sizeof(typename T::Header);
+
+    // Read the load command.
+    auto LoadCmdAddress = reinterpret_cast<const char *>(loadCmdOffset);
+    auto LoadCmdBuf = this->getReader().readBytes(
+        RemoteAddress(LoadCmdAddress), sizeof(typename T::SegmentCmd));
+    auto LoadCmd = reinterpret_cast<typename T::SegmentCmd *>(LoadCmdBuf.get());
+
+    // The sections start immediately after the load command.
+    unsigned NumSect = LoadCmd->nsects;
+    auto SectAddress = reinterpret_cast<const char *>(loadCmdOffset) +
+                       sizeof(typename T::SegmentCmd);
+    auto Sections = this->getReader().readBytes(
+        RemoteAddress(SectAddress), NumSect * sizeof(typename T::Section));
+
+    std::string Prefix = "__swift5";
+    uint64_t RangeStart = UINT64_MAX;
+    uint64_t RangeEnd = UINT64_MAX;
+    for (unsigned I = 0; I < NumSect; ++I) {
+      auto S = reinterpret_cast<typename T::Section *>(
+          SectAddress + (I * sizeof(typename T::Section)));
+      if (strncmp(S->sectname, Prefix.c_str(), strlen(Prefix.c_str())) != 0)
+        continue;
+      if (RangeStart == UINT64_MAX && RangeEnd == UINT64_MAX) {
+        RangeStart = S->addr;
+        RangeEnd = S->addr + S->size;
+        continue;
+      }
+      RangeStart = std::min(RangeStart, (uint64_t)S->addr);
+      RangeEnd = std::max(RangeEnd, (uint64_t)(S->addr + S->size));
+    }
+
+    if (RangeStart == UINT64_MAX && RangeEnd == UINT64_MAX)
+      return false;
+
+    auto Slide = ImageStart.getAddressData() - Command->vmaddr;
+    auto SectBuf = this->getReader().readBytes(RemoteAddress(RangeStart),
+                                               RangeEnd - RangeStart);
+
     auto findMachOSectionByName = [&](std::string Name)
         -> std::pair<std::pair<const char *, const char *>, uint32_t> {
       auto cmdOffset = Start + Offset + sizeof(typename T::Header);
@@ -156,9 +196,13 @@ class ReflectionContext
           continue;
         auto Slide = ImageStart.getAddressData() - Command->vmaddr;
         auto RemoteSecStart = S->addr + Slide;
-        auto LocalSecStart = RemoteSecStart - ImageStart.getAddressData() + Start;
-        auto SecSize = S->size;
-        return {{LocalSecStart, LocalSecStart + SecSize}, 0};
+        auto LocalSectBuf =
+            this->getReader().readBytes(RemoteAddress(RemoteSecStart), S->size);
+        auto LocalSectStart =
+            reinterpret_cast<const char *>(LocalSectBuf.get());
+        auto LocalSectEnd =
+            reinterpret_cast<const char *>(LocalSectBuf.get()) + S->size;
+        return {{LocalSectStart, LocalSectEnd}, 0};
       }
       return {{nullptr, nullptr}, 0};
     };