Extend findAddress to provide function parameter names

Summary:
We provide an optional callback that callers can use to save parameter names
where desired.

Differential Revision: D22399275

fbshipit-source-id: 7f9440a46cbcc4085d48a2387ca3d2db51f2fe7e

folly/experimental/symbolizer/Dwarf.cpp

@@ -462,7 +462,8 @@ bool Dwarf::findLocation(
     const LocationInfoMode mode,
     detail::CompilationUnit& cu,
     LocationInfo& locationInfo,
-    folly::Range<SymbolizedFrame*> inlineFrames) const {
+    folly::Range<SymbolizedFrame*> inlineFrames,
+    folly::FunctionRef<void(folly::StringPiece)> eachParameterName) const {
   detail::Die die = getDieAtOffset(cu, cu.firstDie);
   // Partial compilation unit (DW_TAG_partial_unit) is not supported.
   FOLLY_SAFE_CHECK(
@@ -511,8 +512,10 @@ bool Dwarf::findLocation(
       lineVM.findAddress(address, locationInfo.file, locationInfo.line);
 
   // Look up whether inline function.
-  if (mode == LocationInfoMode::FULL_WITH_INLINE && !inlineFrames.empty() &&
-      locationInfo.hasFileAndLine) {
+  bool checkInline =
+      (mode == LocationInfoMode::FULL_WITH_INLINE && !inlineFrames.empty());
+
+  if (locationInfo.hasFileAndLine && (checkInline || eachParameterName)) {
     // Re-get the compilation unit with abbreviation cached.
     std::array<detail::DIEAbbreviation, kMaxAbbreviationEntries> abbrs;
     cu.abbrCache = folly::range(abbrs);
@@ -522,8 +525,23 @@ bool Dwarf::findLocation(
     detail::Die subprogram;
     findSubProgramDieForAddress(cu, die, address, subprogram);
 
+    if (eachParameterName) {
+      forEachChild(cu, subprogram, [&](const detail::Die& child) {
+        if (child.abbr.tag == DW_TAG_formal_parameter) {
+          forEachAttribute(cu, child, [&](const detail::Attribute& attribute) {
+            if (attribute.spec.name == DW_AT_name) {
+              eachParameterName(
+                  boost::get<folly::StringPiece>(attribute.attrValue));
+            }
+            return true;
+          });
+        }
+        return true;
+      });
+    }
+
     // Subprogram is the DIE of caller function.
-    if (subprogram.abbr.hasChildren) {
+    if (checkInline && subprogram.abbr.hasChildren) {
       // Use an extra location and get its call file and call line, so that
       // they can be used for the second last location when we don't have
       // enough inline frames for all inline functions call stack.
@@ -606,7 +624,9 @@ bool Dwarf::findAddress(
     uintptr_t address,
     LocationInfoMode mode,
     LocationInfo& locationInfo,
-    folly::Range<SymbolizedFrame*> inlineFrames) const {
+    folly::Range<SymbolizedFrame*> inlineFrames,
+    folly::FunctionRef<void(const folly::StringPiece name)> eachParameterName)
+    const {
   if (mode == LocationInfoMode::DISABLED) {
     return false;
   }
@@ -622,7 +642,8 @@ bool Dwarf::findAddress(
     if (findDebugInfoOffset(address, debugAranges_, offset)) {
       // Read compilation unit header from .debug_info
       auto unit = getCompilationUnit(debugInfo_, offset);
-      findLocation(address, mode, unit, locationInfo, inlineFrames);
+      findLocation(
+          address, mode, unit, locationInfo, inlineFrames, eachParameterName);
       return locationInfo.hasFileAndLine;
     } else if (mode == LocationInfoMode::FAST) {
       // NOTE: Clang (when using -gdwarf-aranges) doesn't generate entries
@@ -645,7 +666,8 @@ bool Dwarf::findAddress(
   while (offset < debugInfo_.size() && !locationInfo.hasFileAndLine) {
     auto unit = getCompilationUnit(debugInfo_, offset);
     offset += unit.size;
-    findLocation(address, mode, unit, locationInfo, inlineFrames);
+    findLocation(
+        address, mode, unit, locationInfo, inlineFrames, eachParameterName);
   }
   return locationInfo.hasFileAndLine;
 }

folly/experimental/symbolizer/Dwarf.h

@@ -87,12 +87,18 @@ class Dwarf {
    */
   static const uint32_t kMaxInlineLocationInfoPerFrame = 10;
 
-  /** Find the file and line number information corresponding to address. */
+  /**
+   * Find the file and line number information corresponding to address.
+   * If `eachParameterName` is provided, the callback will be invoked once
+   * for each parameter of the function.
+   */
   bool findAddress(
       uintptr_t address,
       LocationInfoMode mode,
       LocationInfo& info,
-      folly::Range<SymbolizedFrame*> inlineFrames = {}) const;
+      folly::Range<SymbolizedFrame*> inlineFrames = {},
+      folly::FunctionRef<void(const folly::StringPiece name)>
+          eachParameterName = {}) const;
 
  private:
   using AttributeValue = boost::variant<uint64_t, folly::StringPiece>;
@@ -110,14 +116,17 @@ class Dwarf {
 
   /**
    * Finds location info (file and line) for a given address in the given
-   * compilation unit.
+   * compilation unit. Invokes `eachParameterName`, if set, for each parameter
+   * of the given function.
    */
   bool findLocation(
       uintptr_t address,
       const LocationInfoMode mode,
       detail::CompilationUnit& cu,
       LocationInfo& info,
-      folly::Range<SymbolizedFrame*> inlineFrames = {}) const;
+      folly::Range<SymbolizedFrame*> inlineFrames = {},
+      folly::FunctionRef<void(folly::StringPiece)> eachParameterName = {})
+      const;
 
   /**
    * Finds a subprogram debugging info entry that contains a given address among

folly/experimental/symbolizer/test/SymbolizerTest.cpp

@@ -432,6 +432,34 @@ TEST(SymbolizerTest, InlineFunctionWithCache) {
   compareFrames(frames, frames2);
 }
 
+int64_t functionWithTwoParameters(size_t a, int32_t b) {
+  return a + b;
+}
+
+TEST(Dwarf, FindParameterNames) {
+  SKIP_IF(!Symbolizer::isAvailable());
+
+  auto address = reinterpret_cast<uintptr_t>(functionWithTwoParameters);
+  Symbolizer symbolizer;
+  SymbolizedFrame frame;
+  ASSERT_TRUE(symbolizer.symbolize(address, frame));
+
+  std::vector<folly::StringPiece> names;
+  Dwarf dwarf(frame.file.get());
+  LocationInfo info;
+  folly::Range<SymbolizedFrame*> extraInlineFrames = {};
+  dwarf.findAddress(
+      address,
+      LocationInfoMode::FAST,
+      info,
+      extraInlineFrames,
+      [&](const folly::StringPiece name) { names.push_back(name); });
+
+  ASSERT_EQ(2, names.size());
+  ASSERT_EQ("a", names[0]);
+  ASSERT_EQ("b", names[1]);
+}
+
 } // namespace test
 } // namespace symbolizer
 } // namespace folly