Add a "signature" to AST files to verify that they haven't changed

Since the order of the IDs in the AST file (e.g. DeclIDs, SelectorIDs)
is not stable, it is not safe to load an AST file that depends on
another AST file that has been rebuilt since the importer was built,
even if "nothing changed". We previously used size and modtime to check
this, but I've seen cases where a module rebuilt quickly enough to foil
this check and caused very hard to debug build errors.

To save cycles when we're loading the AST, we just generate a random
nonce value and check that it hasn't changed when we load an imported
module, rather than actually hash the whole file.

This is slightly complicated by the fact that we need to verify the
signature inside addModule, since we might otherwise consider that a
mdoule is "OutOfDate" when really it is the importer that is out of
date. I didn't see any regressions in module load time after this
change.

llvm-svn: 220493

10 files changed, 128 insertions, 4 deletions

diff --git a/clang/include/clang/Serialization/ASTBitCodes.h b/clang/include/clang/Serialization/ASTBitCodes.h
index 26e0ecde15c..241c62e4ced 100644
--- a/clang/include/clang/Serialization/ASTBitCodes.h
+++ b/clang/include/clang/Serialization/ASTBitCodes.h
@@ -288,7 +288,10 @@ namespace clang {
 
       /// \brief Record code for the module map file that was used to build this
       /// AST file.
-      MODULE_MAP_FILE = 14
+      MODULE_MAP_FILE = 14,
+
+      /// \brief Record code for the signature that identifiers this AST file.
+      SIGNATURE = 15
     };
 
     /// \brief Record types that occur within the input-files block
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index 730a257bca8..d967ec8d212 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -1125,6 +1125,7 @@ private:
                             SourceLocation ImportLoc, ModuleFile *ImportedBy,
                             SmallVectorImpl<ImportedModule> &Loaded,
                             off_t ExpectedSize, time_t ExpectedModTime,
+                            serialization::ASTFileSignature ExpectedSignature,
                             unsigned ClientLoadCapabilities);
   ASTReadResult ReadControlBlock(ModuleFile &F,
                                  SmallVectorImpl<ImportedModule> &Loaded,
diff --git a/clang/include/clang/Serialization/Module.h b/clang/include/clang/Serialization/Module.h
index a889e8b6540..f6889cfe8e1 100644
--- a/clang/include/clang/Serialization/Module.h
+++ b/clang/include/clang/Serialization/Module.h
@@ -97,6 +97,8 @@ public:
   bool isNotFound() const { return Val.getInt() == NotFound; }
 };
 
+typedef unsigned ASTFileSignature;
+
 /// \brief Information about a module that has been loaded by the ASTReader.
 ///
 /// Each instance of the Module class corresponds to a single AST file, which
@@ -152,6 +154,10 @@ public:
   /// \brief The file entry for the module file.
   const FileEntry *File;
 
+  /// \brief The signature of the module file, which may be used along with size
+  /// and modification time to identify this particular file.
+  ASTFileSignature Signature;
+
   /// \brief Whether this module has been directly imported by the
   /// user.
   bool DirectlyImported;
diff --git a/clang/include/clang/Serialization/ModuleManager.h b/clang/include/clang/Serialization/ModuleManager.h
index 96c3619510a..3d10fad0a1b 100644
--- a/clang/include/clang/Serialization/ModuleManager.h
+++ b/clang/include/clang/Serialization/ModuleManager.h
@@ -179,6 +179,12 @@ public:
   /// \param ExpectedModTime The expected modification time of the module
   /// file, used for validation. This will be zero if unknown.
   ///
+  /// \param ExpectedSignature The expected signature of the module file, used
+  /// for validation. This will be zero if unknown.
+  ///
+  /// \param ReadSignature Reads the signature from an AST file without actually
+  /// loading it.
+  ///
   /// \param Module A pointer to the module file if the module was successfully
   /// loaded.
   ///
@@ -191,6 +197,9 @@ public:
                             SourceLocation ImportLoc,
                             ModuleFile *ImportedBy, unsigned Generation,
                             off_t ExpectedSize, time_t ExpectedModTime,
+                            ASTFileSignature ExpectedSignature,
+                            std::function<ASTFileSignature(llvm::BitstreamReader &)>
+                                ReadSignature,
                             ModuleFile *&Module,
                             std::string &ErrorStr);
 
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index f3181546320..80b1c2b6bcc 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -2363,6 +2363,11 @@ ASTReader::ReadControlBlock(ModuleFile &F,
       break;
     }
 
+    case SIGNATURE:
+      assert((!F.Signature || F.Signature == Record[0]) && "signature changed");
+      F.Signature = Record[0];
+      break;
+
     case IMPORTS: {
       // Load each of the imported PCH files. 
       unsigned Idx = 0, N = Record.size();
@@ -2376,6 +2381,7 @@ ASTReader::ReadControlBlock(ModuleFile &F,
             SourceLocation::getFromRawEncoding(Record[Idx++]);
         off_t StoredSize = (off_t)Record[Idx++];
         time_t StoredModTime = (time_t)Record[Idx++];
+        ASTFileSignature StoredSignature = Record[Idx++];
         unsigned Length = Record[Idx++];
         SmallString<128> ImportedFile(Record.begin() + Idx,
                                       Record.begin() + Idx + Length);
@@ -2383,7 +2389,7 @@ ASTReader::ReadControlBlock(ModuleFile &F,
 
         // Load the AST file.
         switch(ReadASTCore(ImportedFile, ImportedKind, ImportLoc, &F, Loaded,
-                           StoredSize, StoredModTime,
+                           StoredSize, StoredModTime, StoredSignature,
                            ClientLoadCapabilities)) {
         case Failure: return Failure;
           // If we have to ignore the dependency, we'll have to ignore this too.
@@ -3552,7 +3558,7 @@ ASTReader::ASTReadResult ASTReader::ReadAST(const std::string &FileName,
   SmallVector<ImportedModule, 4> Loaded;
   switch(ASTReadResult ReadResult = ReadASTCore(FileName, Type, ImportLoc,
                                                 /*ImportedBy=*/nullptr, Loaded,
-                                                0, 0,
+                                                0, 0, 0,
                                                 ClientLoadCapabilities)) {
   case Failure:
   case Missing:
@@ -3719,6 +3725,8 @@ ASTReader::ASTReadResult ASTReader::ReadAST(const std::string &FileName,
   return Success;
 }
 
+static ASTFileSignature readASTFileSignature(llvm::BitstreamReader &StreamFile);
+
 ASTReader::ASTReadResult
 ASTReader::ReadASTCore(StringRef FileName,
                        ModuleKind Type,
@@ -3726,12 +3734,14 @@ ASTReader::ReadASTCore(StringRef FileName,
                        ModuleFile *ImportedBy,
                        SmallVectorImpl<ImportedModule> &Loaded,
                        off_t ExpectedSize, time_t ExpectedModTime,
+                       ASTFileSignature ExpectedSignature,
                        unsigned ClientLoadCapabilities) {
   ModuleFile *M;
   std::string ErrorStr;
   ModuleManager::AddModuleResult AddResult
     = ModuleMgr.addModule(FileName, Type, ImportLoc, ImportedBy,
                           getGeneration(), ExpectedSize, ExpectedModTime,
+                          ExpectedSignature, readASTFileSignature,
                           M, ErrorStr);
 
   switch (AddResult) {
@@ -4029,6 +4039,34 @@ static bool SkipCursorToBlock(BitstreamCursor &Cursor, unsigned BlockID) {
   }
 }
 
+static ASTFileSignature readASTFileSignature(llvm::BitstreamReader &StreamFile){
+  BitstreamCursor Stream(StreamFile);
+  if (Stream.Read(8) != 'C' ||
+      Stream.Read(8) != 'P' ||
+      Stream.Read(8) != 'C' ||
+      Stream.Read(8) != 'H') {
+    return 0;
+  }
+
+  // Scan for the CONTROL_BLOCK_ID block.
+  if (SkipCursorToBlock(Stream, CONTROL_BLOCK_ID))
+    return 0;
+
+  // Scan for SIGNATURE inside the control block.
+  ASTReader::RecordData Record;
+  while (1) {
+    llvm::BitstreamEntry Entry = Stream.advanceSkippingSubblocks();
+    if (Entry.Kind == llvm::BitstreamEntry::EndBlock ||
+        Entry.Kind != llvm::BitstreamEntry::Record)
+      return 0;
+
+    Record.clear();
+    StringRef Blob;
+    if (SIGNATURE == Stream.readRecord(Entry.ID, Record, &Blob))
+      return Record[0];
+  }
+}
+
 /// \brief Retrieve the name of the original source file name
 /// directly from the AST file, without actually loading the AST
 /// file.
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 0681e3975d2..e39e5bb0222 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -51,6 +51,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/OnDiskHashTable.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/Process.h"
 #include <algorithm>
 #include <cstdio>
 #include <string.h>
@@ -862,6 +863,7 @@ void ASTWriter::WriteBlockInfoBlock() {
   // Control Block.
   BLOCK(CONTROL_BLOCK);
   RECORD(METADATA);
+  RECORD(SIGNATURE);
   RECORD(MODULE_NAME);
   RECORD(MODULE_MAP_FILE);
   RECORD(IMPORTS);
@@ -1092,6 +1094,14 @@ adjustFilenameForRelocatablePCH(const char *Filename, StringRef isysroot) {
   return Filename + Pos;
 }
 
+static ASTFileSignature getSignature() {
+  while (1) {
+    if (ASTFileSignature S = llvm::sys::Process::GetRandomNumber())
+      return S;
+    // Rely on GetRandomNumber to eventually return non-zero...
+  }
+}
+
 /// \brief Write the control block.
 void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
                                   StringRef isysroot,
@@ -1121,6 +1131,11 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
   Stream.EmitRecordWithBlob(MetadataAbbrevCode, Record,
                             getClangFullRepositoryVersion());
 
+  // Signature
+  Record.clear();
+  Record.push_back(getSignature());
+  Stream.EmitRecord(SIGNATURE, Record);
+
   // Module name
   if (WritingModule) {
     BitCodeAbbrev *Abbrev = new BitCodeAbbrev();
@@ -1173,6 +1188,7 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
       AddSourceLocation((*M)->ImportLoc, Record);
       Record.push_back((*M)->File->getSize());
       Record.push_back((*M)->File->getModificationTime());
+      Record.push_back((*M)->Signature);
       const std::string &FileName = (*M)->FileName;
       Record.push_back(FileName.size());
       Record.append(FileName.begin(), FileName.end());
diff --git a/clang/lib/Serialization/GlobalModuleIndex.cpp b/clang/lib/Serialization/GlobalModuleIndex.cpp
index f43fbaca140..121478ce052 100644
--- a/clang/lib/Serialization/GlobalModuleIndex.cpp
+++ b/clang/lib/Serialization/GlobalModuleIndex.cpp
@@ -591,6 +591,10 @@ bool GlobalModuleIndexBuilder::loadModuleFile(const FileEntry *File) {
         off_t StoredSize = (off_t)Record[Idx++];
         time_t StoredModTime = (time_t)Record[Idx++];
 
+        // Skip the stored signature.
+        // FIXME: we could read the signature out of the import and validate it.
+        Idx++;
+
         // Retrieve the imported file name.
         unsigned Length = Record[Idx++];
         SmallString<128> ImportedFile(Record.begin() + Idx,
diff --git a/clang/lib/Serialization/Module.cpp b/clang/lib/Serialization/Module.cpp
index 6f2a3c22043..6c48a41187c 100644
--- a/clang/lib/Serialization/Module.cpp
+++ b/clang/lib/Serialization/Module.cpp
@@ -21,7 +21,7 @@ using namespace serialization;
 using namespace reader;
 
 ModuleFile::ModuleFile(ModuleKind Kind, unsigned Generation)
-  : Kind(Kind), File(nullptr), DirectlyImported(false),
+  : Kind(Kind), File(nullptr), Signature(0), DirectlyImported(false),
     Generation(Generation), SizeInBits(0),
     LocalNumSLocEntries(0), SLocEntryBaseID(0),
     SLocEntryBaseOffset(0), SLocEntryOffsets(nullptr),
diff --git a/clang/lib/Serialization/ModuleManager.cpp b/clang/lib/Serialization/ModuleManager.cpp
index 20249e0a7bd..300ef31b590 100644
--- a/clang/lib/Serialization/ModuleManager.cpp
+++ b/clang/lib/Serialization/ModuleManager.cpp
@@ -57,6 +57,9 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
                          SourceLocation ImportLoc, ModuleFile *ImportedBy,
                          unsigned Generation,
                          off_t ExpectedSize, time_t ExpectedModTime,
+                         ASTFileSignature ExpectedSignature,
+                         std::function<ASTFileSignature(llvm::BitstreamReader &)>
+                             ReadSignature,
                          ModuleFile *&Module,
                          std::string &ErrorStr) {
   Module = nullptr;
@@ -130,6 +133,21 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
     // Initialize the stream
     New->StreamFile.init((const unsigned char *)New->Buffer->getBufferStart(),
                          (const unsigned char *)New->Buffer->getBufferEnd());
+
+    if (ExpectedSignature) {
+      New->Signature = ReadSignature(New->StreamFile);
+      if (New->Signature != ExpectedSignature) {
+        ErrorStr = New->Signature ? "signature mismatch"
+                                  : "could not read module signature";
+
+        // Remove the module file immediately, since removeModules might try to
+        // invalidate the file cache for Entry, and that is not safe if this
+        // module is *itself* up to date, but has an out-of-date importer.
+        Modules.erase(Entry);
+        Chain.pop_back();
+        return OutOfDate;
+      }
+    }
   }
   
   if (ImportedBy) {
diff --git a/clang/test/Modules/rebuild.m b/clang/test/Modules/rebuild.m
new file mode 100644
index 00000000000..c6e7920339e
--- /dev/null
+++ b/clang/test/Modules/rebuild.m
@@ -0,0 +1,29 @@
+// REQUIRES: shell
+// RUN: rm -rf %t
+
+// Build Module and set its timestamp
+// RUN: echo '@import Module;' | %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash -fsyntax-only -F %S/Inputs -x objective-c -
+// RUN: touch -m -a -t 201101010000 %t/Module.pcm
+// RUN: cp %t/Module.pcm %t/Module.pcm.saved
+// RUN: wc -c %t/Module.pcm > %t/Module.size.saved
+
+// Build DependsOnModule
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash -fsyntax-only -F %S/Inputs %s
+// RUN: diff %t/Module.pcm %t/Module.pcm.saved
+// RUN: cp %t/DependsOnModule.pcm %t/DependsOnModule.pcm.saved
+
+// Rebuild Module, reset its timestamp, and verify its size hasn't changed
+// RUN: rm %t/Module.pcm
+// RUN: echo '@import Module;' | %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash -fsyntax-only -F %S/Inputs -x objective-c -
+// RUN: touch -m -a -t 201101010000 %t/Module.pcm
+// RUN: wc -c %t/Module.pcm > %t/Module.size
+// RUN: diff %t/Module.size %t/Module.size.saved
+// RUN: cp %t/Module.pcm %t/Module.pcm.saved.2
+
+// But the signature at least is expected to change, so we rebuild DependsOnModule.
+// NOTE: if we change how the signature is created, this test may need updating.
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fdisable-module-hash -fsyntax-only -F %S/Inputs %s
+// RUN: diff %t/Module.pcm %t/Module.pcm.saved.2
+// RUN: not diff %t/DependsOnModule.pcm %t/DependsOnModule.pcm.saved
+
+@import DependsOnModule;