[lldb] Assert filecache and live memory match on debug under a setting

lldb/include/lldb/Core/Section.h

@@ -236,6 +236,8 @@ public:
 
   void SetIsRelocated(bool b) { m_relocated = b; }
 
+  bool IsReadOnly();
+
 protected:
   ObjectFile *m_obj_file;   // The object file that data for this section should
                             // be read from

lldb/include/lldb/Target/Target.h

@@ -229,6 +229,10 @@ public:
 
   bool GetDebugUtilityExpression() const;
 
+  void SetVerifyFileCacheMemoryReads(bool debug);
+
+  bool GetVerifyFileCacheMemoryReads() const;
+
 private:
   // Callbacks for m_launch_info.
   void Arg0ValueChangedCallback();

lldb/packages/Python/lldbsuite/test/lldbtest.py

@@ -798,6 +798,9 @@ class Base(unittest2.TestCase):
             'settings set symbols.clang-modules-cache-path "{}"'.format(
                 configuration.lldb_module_cache_dir),
             "settings set use-color false",
+            
+            # Verify that file cache and live memory always match.
+            "settings set target.verify-file-cache-memory-reads true",
         ]
 
         # Set any user-overridden settings.

lldb/source/Core/Section.cpp

@@ -599,3 +599,9 @@ size_t SectionList::Slide(addr_t slide_amount, bool slide_children) {
   }
   return count;
 }
+
+bool Section::IsReadOnly() {
+  auto permissions = Flags(GetPermissions());
+  return !permissions.Test(ePermissionsWritable) &&
+         permissions.Test(ePermissionsReadable);
+}

lldb/source/Target/Target.cpp

@@ -1763,21 +1763,34 @@ size_t Target::ReadMemory(const Address &addr, void *dst, size_t dst_len,
   // Read from file cache if read-only section.
   if (!force_live_memory && resolved_addr.IsSectionOffset()) {
     SectionSP section_sp(resolved_addr.GetSection());
-    if (section_sp) {
-      auto permissions = Flags(section_sp->GetPermissions());
-      bool is_readonly = !permissions.Test(ePermissionsWritable) &&
-                         permissions.Test(ePermissionsReadable);
-      if (is_readonly) {
-        file_cache_bytes_read =
-            ReadMemoryFromFileCache(resolved_addr, dst, dst_len, error);
-        if (file_cache_bytes_read == dst_len)
-          return file_cache_bytes_read;
-        else if (file_cache_bytes_read > 0) {
-          file_cache_read_buffer =
-              std::make_unique<uint8_t[]>(file_cache_bytes_read);
-          std::memcpy(file_cache_read_buffer.get(), dst, file_cache_bytes_read);
+    if (section_sp && section_sp->IsReadOnly()) {
+      file_cache_bytes_read =
+          ReadMemoryFromFileCache(resolved_addr, dst, dst_len, error);
+
+      if (GetVerifyFileCacheMemoryReads()) {
+        if (ProcessIsValid() && file_cache_bytes_read == dst_len) {
+          if (load_addr == LLDB_INVALID_ADDRESS)
+            load_addr = resolved_addr.GetLoadAddress(this);
+          if (load_addr != LLDB_INVALID_ADDRESS) {
+            std::unique_ptr<uint8_t[]> live_buf =
+                std::make_unique<uint8_t[]>(dst_len);
+            bytes_read = m_process_sp->ReadMemory(load_addr, live_buf.get(),
+                                                  dst_len, error);
+            if (bytes_read == dst_len) {
+              lldbassert(memcmp(live_buf.get(), dst, dst_len) == 0 &&
+                         "File cache and live memory diverge!");
+            }
+          }
         }
       }
+
+      if (file_cache_bytes_read == dst_len)
+        return file_cache_bytes_read;
+      if (file_cache_bytes_read > 0) {
+        file_cache_read_buffer =
+            std::make_unique<uint8_t[]>(file_cache_bytes_read);
+        std::memcpy(file_cache_read_buffer.get(), dst, file_cache_bytes_read);
+      }
     }
   }
 
@@ -4376,6 +4389,17 @@ void TargetProperties::SetDebugUtilityExpression(bool debug) {
   m_collection_sp->SetPropertyAtIndexAsBoolean(nullptr, idx, debug);
 }
 
+bool TargetProperties::GetVerifyFileCacheMemoryReads() const {
+  const uint32_t idx = ePropertyVerifyFileCacheMemoryReads;
+  return m_collection_sp->GetPropertyAtIndexAsBoolean(
+      nullptr, idx, g_target_properties[idx].default_uint_value != 0);
+}
+
+void TargetProperties::SetVerifyFileCacheMemoryReads(bool verify) {
+  const uint32_t idx = ePropertyVerifyFileCacheMemoryReads;
+  m_collection_sp->SetPropertyAtIndexAsBoolean(nullptr, idx, verify);
+}
+
 // Target::TargetEventData
 
 Target::TargetEventData::TargetEventData(const lldb::TargetSP &target_sp)

lldb/source/Target/TargetProperties.td

@@ -175,6 +175,9 @@ let Definition = "target" in {
   def DebugUtilityExpression: Property<"debug-utility-expression", "Boolean">,
     DefaultFalse,
     Desc<"Enable debugging of LLDB-internal utility expressions.">;
+  def VerifyFileCacheMemoryReads: Property<"verify-file-cache-memory-reads", "Boolean">,
+    DefaultFalse,
+    Desc<"Verify that memory read from the file-cache is identical to the memory read from the process.">;
 }
 
 let Definition = "process_experimental" in {

lldb/test/Shell/lit-lldb-init.in

@@ -6,3 +6,4 @@ settings set symbols.clang-modules-cache-path "@LLDB_TEST_MODULE_CACHE_LLDB@"
 settings set target.auto-apply-fixits false
 settings set target.inherit-tcc true
 settings set target.detach-on-error false
+settings set target.verify-file-cache-memory-reads true