[disassembler] Better support for root-relative values

In particular, recognize builtins' values accesses and direct accesses
to external reference values. For example:

  REX.W leaq rax,[r13+0x47a0]
  REX.W leaq rbx,[r13+0x80b0]

turns into

  REX.W leaq rax,[r13+0x47a0] (builtin (RecordWrite))
  REX.W leaq rbx,[r13+0x80b0] (external value (Isolate::context_address))

Bug: v8:8238
Change-Id: I3b049a1e82de7450bf04135c0c8d76b4dca4ee10
Reviewed-on: https://chromium-review.googlesource.com/c/1256830
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56355}

src/disassembler.cc

@@ -5,6 +5,7 @@
 #include "src/disassembler.h"
 
 #include <memory>
+#include <unordered_map>
 #include <vector>
 
 #include "src/assembler-inl.h"
@@ -38,12 +39,39 @@ class V8NameConverter: public disasm::NameConverter {
   const CodeReference& code() const { return code_; }
 
  private:
+  void InitExternalRefsCache() const;
+
   Isolate* isolate_;
   CodeReference code_;
 
   EmbeddedVector<char, 128> v8_buffer_;
+
+  // Map from root-register relative offset of the external reference value to
+  // the external reference name (stored in the external reference table).
+  // This cache is used to recognize [root_reg + offs] patterns as direct
+  // access to certain external reference's value.
+  mutable std::unordered_map<int, const char*> directly_accessed_external_refs_;
 };
 
+void V8NameConverter::InitExternalRefsCache() const {
+  ExternalReferenceTable* external_reference_table =
+      isolate_->heap()->external_reference_table();
+  if (!external_reference_table->is_initialized()) return;
+
+  base::AddressRegion addressable_region =
+      isolate_->root_register_addressable_region();
+  Address roots_start =
+      reinterpret_cast<Address>(isolate_->heap()->roots_array_start());
+
+  for (uint32_t i = 0; i < external_reference_table->size(); i++) {
+    Address address = external_reference_table->address(i);
+    if (addressable_region.contains(address)) {
+      int offset = static_cast<int>(address - roots_start);
+      const char* name = external_reference_table->name(i);
+      directly_accessed_external_refs_.insert({offset, name});
+    }
+  }
+}
 
 const char* V8NameConverter::NameOfAddress(byte* pc) const {
   if (!code_.is_null()) {
@@ -90,8 +118,11 @@ const char* V8NameConverter::RootRelativeName(int offset) const {
 
   const int kRootsStart = 0;
   const int kRootsEnd = Heap::roots_to_external_reference_table_offset();
-  const int kExtRefsStart = Heap::roots_to_external_reference_table_offset();
+  const int kExtRefsStart = kRootsEnd;
   const int kExtRefsEnd = Heap::roots_to_builtins_offset();
+  const int kBuiltinsStart = kExtRefsEnd;
+  const int kBuiltinsEnd =
+      kBuiltinsStart + Builtins::builtin_count * kPointerSize;
 
   if (kRootsStart <= offset && offset < kRootsEnd) {
     uint32_t offset_in_roots_table = offset - kRootsStart;
@@ -109,6 +140,7 @@ const char* V8NameConverter::RootRelativeName(int offset) const {
 
     SNPrintF(v8_buffer_, "root (%s)", obj_name.get());
     return v8_buffer_.start();
+
   } else if (kExtRefsStart <= offset && offset < kExtRefsEnd) {
     uint32_t offset_in_extref_table = offset - kExtRefsStart;
 
@@ -126,8 +158,29 @@ const char* V8NameConverter::RootRelativeName(int offset) const {
              isolate_->heap()->external_reference_table()->NameFromOffset(
                  offset_in_extref_table));
     return v8_buffer_.start();
+
+  } else if (kBuiltinsStart <= offset && offset < kBuiltinsEnd) {
+    uint32_t offset_in_builtins_table = (offset - kBuiltinsStart);
+
+    Builtins::Name builtin_id =
+        static_cast<Builtins::Name>(offset_in_builtins_table / kPointerSize);
+
+    const char* name = Builtins::name(builtin_id);
+    SNPrintF(v8_buffer_, "builtin (%s)", name);
+    return v8_buffer_.start();
+
   } else {
-    return nullptr;
+    // It must be a direct access to one of the external values.
+    if (directly_accessed_external_refs_.empty()) {
+      InitExternalRefsCache();
+    }
+
+    auto iter = directly_accessed_external_refs_.find(offset);
+    if (iter != directly_accessed_external_refs_.end()) {
+      SNPrintF(v8_buffer_, "external value (%s)", iter->second);
+      return v8_buffer_.start();
+    }
+    return "WAAT??? What are we accessing here???";
   }
 }
 

src/isolate-inl.h

@@ -11,6 +11,12 @@
 namespace v8 {
 namespace internal {
 
+base::AddressRegion Isolate::root_register_addressable_region() {
+  Address start = reinterpret_cast<Address>(this);
+  Address end = heap_.root_register_addressable_end();
+  return base::AddressRegion(start, end - start);
+}
+
 bool Isolate::FromWritableHeapObject(HeapObject* obj, Isolate** isolate) {
   i::MemoryChunk* chunk = i::MemoryChunk::FromHeapObject(obj);
   if (chunk->owner()->identity() == i::RO_SPACE) {

src/isolate.h

@@ -998,6 +998,12 @@ class Isolate : private HiddenFactory {
   }
   StackGuard* stack_guard() { return &stack_guard_; }
   Heap* heap() { return &heap_; }
+
+  // kRootRegister may be used to address any location that falls into this
+  // region. Fields outside this region are not guaranteed to live at a static
+  // offset from kRootRegister.
+  inline base::AddressRegion root_register_addressable_region();
+
   StubCache* load_stub_cache() { return load_stub_cache_; }
   StubCache* store_stub_cache() { return store_stub_cache_; }
   DeoptimizerData* deoptimizer_data() { return deoptimizer_data_; }

src/turbo-assembler.cc

@@ -106,10 +106,8 @@ intptr_t TurboAssemblerBase::RootRegisterOffsetForExternalReference(
 // static
 bool TurboAssemblerBase::IsAddressableThroughRootRegister(
     Isolate* isolate, const ExternalReference& reference) {
-  Address start = reinterpret_cast<Address>(isolate);
-  Address end = isolate->heap()->root_register_addressable_end();
   Address address = reference.address();
-  return start <= address && address < end;
+  return isolate->root_register_addressable_region().contains(address);
 }
 
 // static

src/turbo-assembler.h

@@ -64,7 +64,7 @@ class V8_EXPORT_PRIVATE TurboAssemblerBase : public Assembler {
       Isolate* isolate, const ExternalReference& reference);
 
   // An address is addressable through kRootRegister if it is located within
-  // [isolate, roots_ + root_register_addressable_end_offset[.
+  // isolate->root_register_addressable_region().
   static bool IsAddressableThroughRootRegister(
       Isolate* isolate, const ExternalReference& reference);