Check snapshots for feature compatibility.

runtime/vm/snapshot.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
@@ skipping 585 matching lines @@
   Isolate* isolate = thread->isolate();
   ASSERT(isolate != NULL);
   ObjectStore* object_store = isolate->object_store();
   ASSERT(object_store != NULL);
 
   // First read the version string, and check that it matches.
   RawApiError* error = VerifyVersion();
   if (error != ApiError::null()) {
     return error;
   }
+  error = VerifyFeatures();
+  if (error != ApiError::null()) {
+    return error;
+  }
 
   // The version string matches. Read the rest of the snapshot.
 
   // TODO(asiva): Add a check here to ensure we have the right heap
   // size for the full snapshot being read.
   {
     NoSafepointScope no_safepoint;
     HeapLocker hl(thread, old_space());
 
     // Read in all the objects stored in the object store.
@@ skipping 51 matching lines @@
 
 
 RawObject* SnapshotReader::ReadScriptSnapshot() {
   ASSERT(kind_ == Snapshot::kScript);
 
   // First read the version string, and check that it matches.
   RawApiError* error = VerifyVersion();
   if (error != ApiError::null()) {
     return error;
   }
+  error = VerifyFeatures();
+  if (error != ApiError::null()) {
+    return error;
+  }
 
   // The version string matches. Read the rest of the snapshot.
   obj_ = ReadObject();
   if (!obj_.IsLibrary()) {
     if (!obj_.IsError()) {
       const intptr_t kMessageBufferSize = 128;
       char message_buffer[kMessageBufferSize];
       OS::SNPrint(message_buffer,
                   kMessageBufferSize,
                   "Invalid object %s found in script snapshot",
@@ skipping 12 matching lines @@
 
   const char* expected_version = Version::SnapshotString();
   ASSERT(expected_version != NULL);
   const intptr_t version_len = strlen(expected_version);
   if (PendingBytes() < version_len) {
     const intptr_t kMessageBufferSize = 128;
     char message_buffer[kMessageBufferSize];
     OS::SNPrint(message_buffer,
                 kMessageBufferSize,
                 "No full snapshot version found, expected '%s'",
-                Version::SnapshotString());
+                expected_version);
     // This can also fail while bringing up the VM isolate, so make sure to
     // allocate the error message in old space.
     const String& msg = String::Handle(String::New(message_buffer, Heap::kOld));
     return ApiError::New(msg, Heap::kOld);
   }
 
   const char* version = reinterpret_cast<const char*>(CurrentBufferAddress());
   ASSERT(version != NULL);
   if (strncmp(version, expected_version, version_len)) {
     const intptr_t kMessageBufferSize = 256;
     char message_buffer[kMessageBufferSize];
     char* actual_version = OS::StrNDup(version, version_len);
     OS::SNPrint(message_buffer,
                 kMessageBufferSize,
                 "Wrong %s snapshot version, expected '%s' found '%s'",
                 (Snapshot::IsFull(kind_)) ? "full" : "script",
-                Version::SnapshotString(),
+                expected_version,
                 actual_version);
     free(actual_version);
     // This can also fail while bringing up the VM isolate, so make sure to
     // allocate the error message in old space.
     const String& msg = String::Handle(String::New(message_buffer, Heap::kOld));
     return ApiError::New(msg, Heap::kOld);
   }
   Advance(version_len);
   return ApiError::null();
 }
 
 
+RawApiError* SnapshotReader::VerifyFeatures() {
+  // If the features string doesn't match, return an error.
+  // Note: New things are allocated only if we're going to return an error.
+
+  const char* expected_features = Dart::FeaturesString(kind_);
+  ASSERT(expected_features != NULL);
+  const intptr_t expected_len = strlen(expected_features);
+
+  const char* features = reinterpret_cast<const char*>(CurrentBufferAddress());
+  ASSERT(features != NULL);
+  intptr_t buffer_len = strnlen(features, PendingBytes());
+  if (strncmp(features, expected_features,
+              expected_len < buffer_len ? expected_len : buffer_len)) {

[siva, 2016/05/16 16:48:00]

why not write this as 
if ((expected_len > buffer_len) ||
    strncmp(features, expected_features, expected_len)) {
  .....
  .....
}

[rmacnak, 2016/05/16 20:59:56]

Done.

+    const intptr_t kMessageBufferSize = 256;
+    char message_buffer[kMessageBufferSize];
+    char* actual_features = OS::StrNDup(features, buffer_len < 128 ? buffer_len
+                                                                   : 128);
+    OS::SNPrint(message_buffer,
+                kMessageBufferSize,
+                "Wrong features in snapshot, expected '%s' found '%s'",
+                expected_features,
+                actual_features);
+    free(const_cast<char*>(expected_features));
+    free(actual_features);
+    // This can also fail while bringing up the VM isolate, so make sure to
+    // allocate the error message in old space.
+    const String& msg = String::Handle(String::New(message_buffer, Heap::kOld));
+    return ApiError::New(msg, Heap::kOld);
+  }
+  free(const_cast<char*>(expected_features));
+  Advance(expected_len + 1);
+  return ApiError::null();
+}
+
+
 #define ALLOC_NEW_OBJECT_WITH_LEN(type, length)                                \
   ASSERT(Snapshot::IsFull(kind_));                                            \
   ASSERT_NO_SAFEPOINT_SCOPE();                                                 \
   Raw##type* obj = reinterpret_cast<Raw##type*>(                               \
       AllocateUninitialized(k##type##Cid, type::InstanceSize(length)));        \
   obj->StoreSmi(&(obj->ptr()->length_), Smi::New(length));                     \
   return obj;                                                                  \
 
 
 RawArray* SnapshotReader::NewArray(intptr_t len) {
@@ skipping 963 matching lines @@
   ASSERT(isolate != NULL);
   ASSERT(isolate == Dart::vm_isolate());
   ObjectStore* object_store = isolate->object_store();
   ASSERT(object_store != NULL);
 
   // First read the version string, and check that it matches.
   RawApiError* error = VerifyVersion();
   if (error != ApiError::null()) {
     return error;
   }
+  error = VerifyFeatures();
+  if (error != ApiError::null()) {
+    return error;
+  }
 
   // The version string matches. Read the rest of the snapshot.
 
   {
     NoSafepointScope no_safepoint;
     HeapLocker hl(thread, old_space());
 
     // Read in the symbol table.
     object_store->symbol_table_ = reinterpret_cast<RawArray*>(ReadObject());
 
@@ skipping 375 matching lines @@
   // Write full snapshot for the VM isolate.
   // Setup for long jump in case there is an exception while writing
   // the snapshot.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     // Reserve space in the output buffer for a snapshot header.
     writer.ReserveHeader();
 
     // Write out the version string.
     writer.WriteVersion();
+    writer.WriteFeatures();
 
     /*
      * Now Write out the following
      * - the symbol table
      * - all the scripts and token streams for these scripts
      * - the stub code (precompiled snapshots only)
      **/
     // Write out the symbol table.
     writer.WriteObject(new_vm_symbol_table_.raw());
 
@@ skipping 31 matching lines @@
   // Write full snapshot for a regular isolate.
   // Setup for long jump in case there is an exception while writing
   // the snapshot.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     // Reserve space in the output buffer for a snapshot header.
     writer.ReserveHeader();
 
     // Write out the version string.
     writer.WriteVersion();
+    writer.WriteFeatures();
 
     // Write out the full snapshot.
 
     // Write out all the objects in the object store of the isolate which
     // is the root set for all dart allocated objects at this point.
     SnapshotWriterVisitor visitor(&writer, false);
     visitor.VisitPointers(object_store->from(),
                           object_store->to_snapshot(kind_));
 
     // Write out all forwarded objects.
@@ skipping 511 matching lines @@
 
 
 void SnapshotWriter::WriteVersion() {
   const char* expected_version = Version::SnapshotString();
   ASSERT(expected_version != NULL);
   const intptr_t version_len = strlen(expected_version);
   WriteBytes(reinterpret_cast<const uint8_t*>(expected_version), version_len);
 }
 
 
+void SnapshotWriter::WriteFeatures() {
+  const char* expected_features = Dart::FeaturesString(kind_);
+  ASSERT(expected_features != NULL);
+  const intptr_t features_len = strlen(expected_features);
+  WriteBytes(reinterpret_cast<const uint8_t*>(expected_features),
+             features_len + 1);
+  free(const_cast<char*>(expected_features));
+}
+
+
 ScriptSnapshotWriter::ScriptSnapshotWriter(uint8_t** buffer,
                                            ReAlloc alloc)
     : SnapshotWriter(Thread::Current(),
                      Snapshot::kScript,
                      buffer,
                      alloc,
                      kInitialSize,
                      &forward_list_,
                      NULL, /* instructions_writer */
                      true, /* can_send_any_object */
@@ skipping 11 matching lines @@
 
   // Setup for long jump in case there is an exception while writing
   // the snapshot.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     // Reserve space in the output buffer for a snapshot header.
     ReserveHeader();
 
     // Write out the version string.
     WriteVersion();
+    WriteFeatures();
 
     // Write out the library object.
     {
       NoSafepointScope no_safepoint;
 
       // Write out the library object.
       WriteObject(lib.raw());
 
       FillHeader(kind());
     }
@@ skipping 39 matching lines @@
   if (setjmp(*jump.Set()) == 0) {
     NoSafepointScope no_safepoint;
     WriteObject(obj.raw());
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart