[vm] Add Dart_SetDwarfStackTraceFootnoteCallback

This API allows embedder to append arbitrary footers to DWARF stack
traces. For example, embedder can append a link to a symbolizer
service, which could be used to symbolize the stack-trace.

TEST=manually tested, hard to create automatic tests because vm/cc tests  only support JIT, not AOT.

Bug: b/255741575
Change-Id: Id034b9b3194f7b91a8405574ea771c4a06fda2c2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/275700
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>

runtime/include/dart_api.h

@@ -4104,4 +4104,29 @@ DART_EXPORT void Dart_DumpNativeStackTrace(void* context);
  */
 DART_EXPORT void Dart_PrepareToAbort(void);
 
+/**
+ * Callback provided by the embedder that is used by the VM to
+ * produce footnotes appended to DWARF stack traces.
+ *
+ * Whenever VM formats a stack trace as a string it would call this callback
+ * passing raw program counters for each frame in the stack trace.
+ *
+ * Embedder can then return a string which if not-null will be appended to the
+ * formatted stack trace.
+ *
+ * Returned string is expected to be `malloc()` allocated. VM takes ownership
+ * of the returned string and will `free()` it.
+ *
+ * \param addresses raw program counter addresses for each frame
+ * \param count number of elements in the addresses array
+ */
+typedef char* (*Dart_DwarfStackTraceFootnoteCallback)(void* addresses[],
+                                                      intptr_t count);
+
+/**
+ *  Configure DWARF stack trace footnote callback.
+ */
+DART_EXPORT void Dart_SetDwarfStackTraceFootnoteCallback(
+    Dart_DwarfStackTraceFootnoteCallback callback);
+
 #endif /* INCLUDE_DART_API_H_ */ /* NOLINT */

runtime/vm/dart.cc

@@ -69,6 +69,8 @@ Dart_FileWriteCallback Dart::file_write_callback_ = NULL;
 Dart_FileCloseCallback Dart::file_close_callback_ = NULL;
 Dart_EntropySource Dart::entropy_source_callback_ = NULL;
 Dart_GCEventCallback Dart::gc_event_callback_ = nullptr;
+Dart_DwarfStackTraceFootnoteCallback Dart::dwarf_stacktrace_footnote_callback_ =
+    nullptr;
 
 // Structure for managing read-only global handles allocation used for
 // creating global read-only handles that are pre created and initialized

runtime/vm/dart.h

@@ -141,6 +141,16 @@ class Dart : public AllStatic {
   }
   static Dart_GCEventCallback gc_event_callback() { return gc_event_callback_; }
 
+  static void set_dwarf_stacktrace_footnote_callback(
+      Dart_DwarfStackTraceFootnoteCallback cb) {
+    dwarf_stacktrace_footnote_callback_ = cb;
+  }
+
+  static Dart_DwarfStackTraceFootnoteCallback
+  dwarf_stacktrace_footnote_callback() {
+    return dwarf_stacktrace_footnote_callback_;
+  }
+
  private:
   static char* DartInit(const Dart_InitializeParams* params);
 
@@ -163,6 +173,8 @@ class Dart : public AllStatic {
   static Dart_FileCloseCallback file_close_callback_;
   static Dart_EntropySource entropy_source_callback_;
   static Dart_GCEventCallback gc_event_callback_;
+  static Dart_DwarfStackTraceFootnoteCallback
+      dwarf_stacktrace_footnote_callback_;
 };
 
 }  // namespace dart

runtime/vm/dart_api_impl.cc

@@ -6310,6 +6310,11 @@ DART_EXPORT void Dart_SetGCEventCallback(Dart_GCEventCallback callback) {
   Dart::set_gc_event_callback(callback);
 }
 
+DART_EXPORT void Dart_SetDwarfStackTraceFootnoteCallback(
+    Dart_DwarfStackTraceFootnoteCallback callback) {
+  Dart::set_dwarf_stacktrace_footnote_callback(callback);
+}
+
 DART_EXPORT char* Dart_SetFileModifiedCallback(
     Dart_FileModifiedCallback file_modified_callback) {
 #if !defined(PRODUCT)

runtime/vm/object.cc

@@ -26508,6 +26508,14 @@ const char* StackTrace::ToCString() const {
   NoSafepointScope no_allocation;
   GrowableArray<const Function*> inlined_functions;
   GrowableArray<TokenPosition> inlined_token_positions;
+
+#if defined(DART_PRECOMPILED_RUNTIME)
+  GrowableArray<void*> addresses(10);
+  const bool have_footnote_callback =
+      FLAG_dwarf_stack_traces_mode &&
+      Dart::dwarf_stacktrace_footnote_callback() != nullptr;
+#endif
+
   ZoneTextBuffer buffer(zone, 1024);
 
 #if defined(DART_PRECOMPILED_RUNTIME)
@@ -26635,6 +26643,10 @@ const char* StackTrace::ToCString() const {
       const uword call_addr = is_future_listener ? pc : pc - 1;
 
       if (FLAG_dwarf_stack_traces_mode) {
+        if (have_footnote_callback) {
+          addresses.Add(reinterpret_cast<void*>(call_addr));
+        }
+
         // This output is formatted like Android's debuggerd. Note debuggerd
         // prints call addresses instead of return addresses.
         buffer.Printf("    #%02" Pd " abs %" Pp "", frame_index, call_addr);
@@ -26690,6 +26702,17 @@ const char* StackTrace::ToCString() const {
     stack_trace = stack_trace.async_link();
   } while (!stack_trace.IsNull());
 
+#if defined(DART_PRECOMPILED_RUNTIME)
+  if (have_footnote_callback) {
+    char* footnote = Dart::dwarf_stacktrace_footnote_callback()(
+        &addresses[0], addresses.length());
+    if (footnote != nullptr) {
+      buffer.AddString(footnote);
+      free(footnote);
+    }
+  }
+#endif
+
   return buffer.buffer();
 }