Reland "Remove DartSnapshotBuffer and dry up snapshot resolution logi…

…c". (flutter#8645)

This reverts commit 0fcfa0d.
Windows depends on referencing the snapshot symbols directly instead of
via dlsym. Something in the way these symbolsa are generated in
bin_to_assembly.py is causing them to be inaccessible at runtime.

ci/licenses_golden/licenses_flutter

@@ -383,8 +383,6 @@ FILE: ../../../flutter/runtime/dart_service_isolate.h
 FILE: ../../../flutter/runtime/dart_service_isolate_unittests.cc
 FILE: ../../../flutter/runtime/dart_snapshot.cc
 FILE: ../../../flutter/runtime/dart_snapshot.h
-FILE: ../../../flutter/runtime/dart_snapshot_buffer.cc
-FILE: ../../../flutter/runtime/dart_snapshot_buffer.h
 FILE: ../../../flutter/runtime/dart_vm.cc
 FILE: ../../../flutter/runtime/dart_vm.h
 FILE: ../../../flutter/runtime/dart_vm_data.cc

fml/mapping.cc

@@ -4,12 +4,18 @@
 
 #include "flutter/fml/mapping.h"
 
+#include <sstream>
+
 namespace fml {
 
+// FileMapping
+
 uint8_t* FileMapping::GetMutableMapping() {
   return mutable_mapping_;
 }
 
+// Data Mapping
+
 DataMapping::DataMapping(std::vector<uint8_t> data) : data_(std::move(data)) {}
 
 DataMapping::~DataMapping() = default;
@@ -22,6 +28,8 @@ const uint8_t* DataMapping::GetMapping() const {
   return data_.data();
 }
 
+// NonOwnedMapping
+
 size_t NonOwnedMapping::GetSize() const {
   return size_;
 }
@@ -30,4 +38,37 @@ const uint8_t* NonOwnedMapping::GetMapping() const {
   return data_;
 }
 
+// Symbol Mapping
+
+SymbolMapping::SymbolMapping(fml::RefPtr<fml::NativeLibrary> native_library,
+                             const char* symbol_name)
+    : native_library_(std::move(native_library)) {
+  if (native_library_ && symbol_name != nullptr) {
+    mapping_ = native_library_->ResolveSymbol(symbol_name);
+
+    if (mapping_ == nullptr) {
+      // Apparently, dart_bootstrap seems to account for the Mac behavior of
+      // requiring the underscore prefixed symbol name on non-Mac platforms as
+      // well. As a fallback, check the underscore prefixed variant of the
+      // symbol name and allow callers to not have handle this on a per platform
+      // toolchain quirk basis.
+
+      std::stringstream underscore_symbol_name;
+      underscore_symbol_name << "_" << symbol_name;
+      mapping_ =
+          native_library_->ResolveSymbol(underscore_symbol_name.str().c_str());
+    }
+  }
+}
+
+SymbolMapping::~SymbolMapping() = default;
+
+size_t SymbolMapping::GetSize() const {
+  return 0;
+}
+
+const uint8_t* SymbolMapping::GetMapping() const {
+  return mapping_;
+}
+
 }  // namespace fml

fml/mapping.h

@@ -13,6 +13,7 @@
 #include "flutter/fml/build_config.h"
 #include "flutter/fml/file.h"
 #include "flutter/fml/macros.h"
+#include "flutter/fml/native_library.h"
 #include "flutter/fml/unique_fd.h"
 
 namespace fml {
@@ -31,7 +32,7 @@ class Mapping {
   FML_DISALLOW_COPY_AND_ASSIGN(Mapping);
 };
 
-class FileMapping : public Mapping {
+class FileMapping final : public Mapping {
  public:
   enum class Protection {
     kRead,
@@ -45,8 +46,10 @@ class FileMapping : public Mapping {
 
   ~FileMapping() override;
 
+  // |Mapping|
   size_t GetSize() const override;
 
+  // |Mapping|
   const uint8_t* GetMapping() const override;
 
   uint8_t* GetMutableMapping();
@@ -63,14 +66,16 @@ class FileMapping : public Mapping {
   FML_DISALLOW_COPY_AND_ASSIGN(FileMapping);
 };
 
-class DataMapping : public Mapping {
+class DataMapping final : public Mapping {
  public:
   DataMapping(std::vector<uint8_t> data);
 
   ~DataMapping() override;
 
+  // |Mapping|
   size_t GetSize() const override;
 
+  // |Mapping|
   const uint8_t* GetMapping() const override;
 
  private:
@@ -79,13 +84,15 @@ class DataMapping : public Mapping {
   FML_DISALLOW_COPY_AND_ASSIGN(DataMapping);
 };
 
-class NonOwnedMapping : public Mapping {
+class NonOwnedMapping final : public Mapping {
  public:
   NonOwnedMapping(const uint8_t* data, size_t size)
       : data_(data), size_(size) {}
 
+  // |Mapping|
   size_t GetSize() const override;
 
+  // |Mapping|
   const uint8_t* GetMapping() const override;
 
  private:
@@ -95,6 +102,26 @@ class NonOwnedMapping : public Mapping {
   FML_DISALLOW_COPY_AND_ASSIGN(NonOwnedMapping);
 };
 
+class SymbolMapping final : public Mapping {
+ public:
+  SymbolMapping(fml::RefPtr<fml::NativeLibrary> native_library,
+                const char* symbol_name);
+
+  ~SymbolMapping() override;
+
+  // |Mapping|
+  size_t GetSize() const override;
+
+  // |Mapping|
+  const uint8_t* GetMapping() const override;
+
+ private:
+  fml::RefPtr<fml::NativeLibrary> native_library_;
+  const uint8_t* mapping_ = nullptr;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(SymbolMapping);
+};
+
 }  // namespace fml
 
 #endif  // FLUTTER_FML_MAPPING_H_

runtime/BUILD.gn

@@ -46,8 +46,6 @@ source_set("runtime") {
     "dart_service_isolate.h",
     "dart_snapshot.cc",
     "dart_snapshot.h",
-    "dart_snapshot_buffer.cc",
-    "dart_snapshot_buffer.h",
     "dart_vm.cc",
     "dart_vm.h",
     "dart_vm_data.cc",

runtime/dart_isolate.cc

@@ -679,14 +679,11 @@ DartIsolate::CreateDartVMAndEmbedderObjectPair(
   Dart_Isolate isolate = Dart_CreateIsolate(
       advisory_script_uri,         //
       advisory_script_entrypoint,  //
-      (*embedder_isolate)
-          ->GetIsolateSnapshot()
-          ->GetData()
-          ->GetSnapshotPointer(),
-      (*embedder_isolate)->GetIsolateSnapshot()->GetInstructionsIfPresent(),
-      (*embedder_isolate)->GetSharedSnapshot()->GetDataIfPresent(),
-      (*embedder_isolate)->GetSharedSnapshot()->GetInstructionsIfPresent(),
-      flags, embedder_isolate.get(), error);
+      (*embedder_isolate)->GetIsolateSnapshot()->GetDataMapping(),
+      (*embedder_isolate)->GetIsolateSnapshot()->GetInstructionsMapping(),
+      (*embedder_isolate)->GetSharedSnapshot()->GetDataMapping(),
+      (*embedder_isolate)->GetSharedSnapshot()->GetInstructionsMapping(), flags,
+      embedder_isolate.get(), error);
 
   if (isolate == nullptr) {
     FML_DLOG(ERROR) << *error;