[vm] Support testing assembly snapshots for ARM.

We have had several bugs propagate to Flutter end-users due to our lack of testing of
AOT Assembly snapshots on ARM (SIMARM_X64 in particular), causing reverts of SDK commits
and disrupting the Dart -> Flutter roll.

This leverages our custom ELF loader to load the generated ELF objects, which cannot be
loaded by dlopen() because they are marked with the ARM ABI.

For example, see:
  - flutter/flutter#40114
  - flutter/flutter#41228

Also do some tree-shaking of the snapshot writers for dart_precompiled_runtime.

Fixes #38433.

Change-Id: I5990769c623b8a13131b1848349af2c0a026272b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/118569
Reviewed-by: Clement Skau <cskau@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Samir Jindel <sjindel@google.com>

pkg/test_runner/lib/src/compiler_configuration.dart

@@ -586,8 +586,12 @@ class PrecompilerCompilerConfiguration extends CompilerConfiguration
 
   bool get _isArm => _configuration.architecture == Architecture.arm;
 
+  bool get _isSimArm => _configuration.architecture == Architecture.simarm;
+
   bool get _isArm64 => _configuration.architecture == Architecture.arm64;
 
+  bool get _isSimArm64 => _configuration.architecture == Architecture.simarm64;
+
   bool get _isX64 => _configuration.architecture == Architecture.x64;
 
   bool get _isIA32 => _configuration.architecture == Architecture.ia32;
@@ -701,12 +705,12 @@ class PrecompilerCompilerConfiguration extends CompilerConfiguration
   Command computeAssembleCommand(String tempDir, List arguments,
       Map<String, String> environmentOverrides) {
     String cc, shared, ldFlags;
-    if (_isAndroid) {
+    if (_isAndroid || _isSimArm || _isSimArm64) {
       var ndk = "third_party/android_tools/ndk";
       String triple;
-      if (_isArm) {
+      if (_isArm || _isSimArm) {
         triple = "arm-linux-androideabi";
-      } else if (_isArm64) {
+      } else if (_isArm64 || _isSimArm64) {
         triple = "aarch64-linux-android";
       }
       String host;

runtime/bin/elf_loader.cc

@@ -53,7 +53,7 @@ class LoadedElf {
   bool ReadSectionStringTable();
   bool ReadSections();
 
-  static uword PageSize();
+  static uword PageSize() { return VirtualMemory::PageSize(); }
 
   // Unlike File::Map, allows non-aligned 'start' and 'length'.
   MappedMemory* MapFilePiece(uword start,
@@ -112,12 +112,9 @@ class LoadedElf {
     return false;                                                              \
   }
 
-uword LoadedElf::PageSize() {
-  static uword page_size_ = VirtualMemory::CalculatePageSize();
-  return page_size_;
-}
-
 bool LoadedElf::Load() {
+  VirtualMemory::Init();
+
   if (error_ != nullptr) {
     return false;
   }

runtime/include/dart_api.h

@@ -1113,7 +1113,8 @@ DART_EXPORT void Dart_ExitIsolate();
  * the vm isolate on startup and fast initialization of an isolate.
  * A Snapshot of the heap is created before any dart code has executed.
  *
- * Requires there to be a current isolate.
+ * Requires there to be a current isolate. Not available in the precompiled
+ * runtime (check Dart_IsPrecompiledRuntime).
  *
  * \param buffer Returns a pointer to a buffer containing the
  *   snapshot. This buffer is scope allocated and is only valid

runtime/vm/clustered_snapshot.cc

@@ -90,6 +90,7 @@ void Deserializer::InitializeHeader(RawObject* raw,
 #endif
 }
 
+#if !defined(DART_PRECOMPILED_RUNTIME)
 void SerializationCluster::WriteAndMeasureAlloc(Serializer* serializer) {
   if (LOG_SECTION_BOUNDARIES) {
     OS::PrintErr("Data + %" Px ": Alloc %s\n", serializer->bytes_written(),
@@ -115,7 +116,6 @@ void SerializationCluster::WriteAndMeasureFill(Serializer* serializer) {
   size_ += (stop - start);
 }
 
-#if !defined(DART_PRECOMPILED_RUNTIME)
 class ClassSerializationCluster : public SerializationCluster {
  public:
   explicit ClassSerializationCluster(intptr_t num_cids)
@@ -4336,6 +4336,10 @@ class FakeSerializationCluster : public SerializationCluster {
 };
 #endif  // !DART_PRECOMPILED_RUNTIME
 
+#if defined(DEBUG)
+static const int32_t kSectionMarker = 0xABAB;
+#endif
+
 Serializer::Serializer(Thread* thread,
                        Snapshot::Kind kind,
                        uint8_t** buffer,
@@ -4551,6 +4555,7 @@ SerializationCluster* Serializer::NewClusterForClass(intptr_t cid) {
 #endif  // !DART_PRECOMPILED_RUNTIME
 }
 
+#if !defined(DART_PRECOMPILED_RUNTIME)
 void Serializer::WriteInstructions(RawInstructions* instr, RawCode* code) {
   ASSERT(code != Code::null());
 
@@ -4740,11 +4745,6 @@ void Serializer::WriteVersionAndFeatures(bool is_vm_snapshot) {
   free(const_cast<char*>(expected_features));
 }
 
-#if defined(DEBUG)
-static const int32_t kSectionMarker = 0xABAB;
-#endif
-
-#if !defined(DART_PRECOMPILED_RUNTIME)
 static int CompareClusters(SerializationCluster* const* a,
                            SerializationCluster* const* b) {
   if ((*a)->size() > (*b)->size()) {
@@ -4755,7 +4755,6 @@ static int CompareClusters(SerializationCluster* const* a,
     return 0;
   }
 }
-#endif  // !defined(DART_PRECOMPILED_RUNTIME)
 
 void Serializer::Serialize() {
   while (stack_.length() > 0) {
@@ -5019,6 +5018,7 @@ void Serializer::WriteIsolateSnapshot(intptr_t num_base_objects,
 
   heap_->ResetObjectIdTable();
 }
+#endif  // !defined(DART_PRECOMPILED_RUNTIME)
 
 Deserializer::Deserializer(Thread* thread,
                            Snapshot::Kind kind,
@@ -5519,6 +5519,7 @@ DEFINE_FLAG(charp,
             "Write a snapshot profile in V8 format to a file.");
 #endif
 
+#if !defined(DART_PRECOMPILED_RUNTIME)
 FullSnapshotWriter::FullSnapshotWriter(Snapshot::Kind kind,
                                        uint8_t** vm_snapshot_data_buffer,
                                        uint8_t** isolate_snapshot_data_buffer,
@@ -5655,6 +5656,7 @@ void FullSnapshotWriter::WriteFullSnapshot() {
   }
 #endif
 }
+#endif  // defined(DART_PRECOMPILED_RUNTIME)
 
 FullSnapshotReader::FullSnapshotReader(const Snapshot* snapshot,
                                        const uint8_t* instructions_buffer,

runtime/vm/dart_api_impl.cc

@@ -1627,19 +1627,24 @@ DART_EXPORT void Dart_ExitIsolate() {
   Thread::ExitIsolate();
 }
 
+#if !defined(DART_PRECOMPILED_RUNTIME)
 static uint8_t* ApiReallocate(uint8_t* ptr,
                               intptr_t old_size,
                               intptr_t new_size) {
   return Api::TopScope(Thread::Current())
       ->zone()
       ->Realloc<uint8_t>(ptr, old_size, new_size);
 }
+#endif
 
 DART_EXPORT Dart_Handle
 Dart_CreateSnapshot(uint8_t** vm_snapshot_data_buffer,
                     intptr_t* vm_snapshot_data_size,
                     uint8_t** isolate_snapshot_data_buffer,
                     intptr_t* isolate_snapshot_data_size) {
+#if defined(DART_PRECOMPILED_RUNTIME)
+  return Api::NewError("Cannot create snapshots on an AOT runtime.");
+#else
   DARTSCOPE(Thread::Current());
   API_TIMELINE_DURATION(T);
   Isolate* I = T->isolate();
@@ -1676,6 +1681,7 @@ Dart_CreateSnapshot(uint8_t** vm_snapshot_data_buffer,
   }
   *isolate_snapshot_data_size = writer.IsolateSnapshotSize();
   return Api::Success();
+#endif
 }
 
 DART_EXPORT bool Dart_IsKernel(const uint8_t* buffer, intptr_t buffer_size) {

runtime/vm/image_snapshot.cc

@@ -6,6 +6,7 @@
 
 #include "platform/assert.h"
 #include "vm/compiler/backend/code_statistics.h"
+#include "vm/compiler/runtime_api.h"
 #include "vm/dwarf.h"
 #include "vm/elf.h"
 #include "vm/hash.h"
@@ -80,6 +81,7 @@ bool ObjectOffsetTrait::IsKeyEqual(Pair pair, Key key) {
                      reinterpret_cast<const void*>(body_b), body_size);
 }
 
+#if !defined(DART_PRECOMPILED_RUNTIME)
 ImageWriter::ImageWriter(Heap* heap,
                          const void* shared_objects,
                          const void* shared_instructions,
@@ -677,7 +679,8 @@ void AssemblyImageWriter::WriteText(WriteStream* clustered_stream, bool vm) {
       text_offset += WriteByteSequence(beginning, entry);
 #endif  // defined(IS_SIMARM_X64)
 
-      ASSERT((text_offset - instr_start) == insns.HeaderSize());
+      ASSERT((text_offset - instr_start) ==
+             compiler::target::Instructions::HeaderSize());
     }
 
     // 2. Write a label at the entry point.
@@ -753,9 +756,9 @@ void AssemblyImageWriter::WriteText(WriteStream* clustered_stream, bool vm) {
 #else
       text_offset += WriteByteSequence(entry, end);
 #endif
+      ASSERT(kWordSize != compiler::target::kWordSize ||
+             (text_offset - instr_start) == insns.raw()->HeapSize());
     }
-
-    ASSERT((text_offset - instr_start) == insns.raw()->HeapSize());
   }
 
   FrameUnwindEpilogue();
@@ -1081,6 +1084,7 @@ void BlobImageWriter::WriteText(WriteStream* clustered_stream, bool vm) {
   }
 #endif
 }
+#endif  // !defined(DART_PRECOMPILED_RUNTIME)
 
 ImageReader::ImageReader(const uint8_t* data_image,
                          const uint8_t* instructions_image,
@@ -1144,6 +1148,7 @@ RawObject* ImageReader::GetSharedObjectAt(uint32_t offset) const {
   return result;
 }
 
+#if !defined(DART_PRECOMPILED_RUNTIME)
 void DropCodeWithoutReusableInstructions(const void* reused_instructions) {
   class DropCodeVisitor : public FunctionVisitor, public ClassVisitor {
    public:
@@ -1243,5 +1248,6 @@ void DropCodeWithoutReusableInstructions(const void* reused_instructions) {
   ProgramVisitor::VisitClasses(&visitor);
   ProgramVisitor::VisitFunctions(&visitor);
 }
+#endif  // !defined(DART_PRECOMPILED_RUNTIME)
 
 }  // namespace dart

runtime/vm/object.h

@@ -4799,11 +4799,9 @@ class Instructions : public Object {
   }
 
   static intptr_t HeaderSize() {
-    intptr_t alignment = OS::PreferredCodeAlignment();
-    intptr_t aligned_size = Utils::RoundUp(sizeof(RawInstructions), alignment);
-#if !defined(IS_SIMARM_X64)
-    ASSERT(aligned_size == alignment);
-#endif  // !defined(IS_SIMARM_X64)
+    const intptr_t alignment = OS::PreferredCodeAlignment();
+    const intptr_t aligned_size =
+        Utils::RoundUp(sizeof(RawInstructions), alignment);
     return aligned_size;
   }
 

runtime/vm/virtual_memory.h

@@ -63,9 +63,6 @@ class VirtualMemory {
     return page_size_;
   }
 
-  // Use only if Init() might not have been called.
-  static intptr_t CalculatePageSize();
-
   static bool InSamePage(uword address0, uword address1);
 
   // Truncate this virtual memory segment.
@@ -79,6 +76,8 @@ class VirtualMemory {
   static VirtualMemory* ForImagePage(void* pointer, uword size);
 
  private:
+  static intptr_t CalculatePageSize();
+
   // Free a sub segment. On operating systems that support it this
   // can give back the virtual memory to the system. Returns true on success.
   static void FreeSubSegment(void* address, intptr_t size);

runtime/vm/virtual_memory_posix.cc

@@ -50,6 +50,11 @@ intptr_t VirtualMemory::CalculatePageSize() {
 }
 
 void VirtualMemory::Init() {
+  if (page_size_ != 0) {
+    // Already initialized.
+    return;
+  }
+
   page_size_ = CalculatePageSize();
 
 #if defined(DUAL_MAPPING_SUPPORTED)

tools/bots/test_matrix.json

@@ -345,7 +345,11 @@
       "options": {
         "use-blobs": true
     }},
-    "dartkp-(linux|win|mac)-(debug|product|release)-(simarm|simarm64)-crossword": {
+    "dartkp-linux-(debug|product|release)-(simarm|simarm64)-crossword": {
+      "options": {
+        "builder-tag": "crossword"
+    }},
+    "dartkp-(win|mac)-(debug|product|release)-(simarm|simarm64)-crossword": {
       "options": {
         "builder-tag": "crossword",
         "use-blobs": true
@@ -2274,7 +2278,7 @@
     },
     {
       "builders": [
-        "vm-kernel-precomp-mac-debug-simarm_x64",
+        "vm-kernel-precomp-linux-debug-simarm_x64",
         "vm-kernel-precomp-mac-release-simarm_x64"
       ],
       "meta": {