[dsymutil] Better support for symbol aliases

This patch adds logic to follow a symbol's aliases when the symbol name
cannot be found in the current object file. It checks the main binary
for the symbol's address and queries the current object for its aliases
(symbols with the same address) before printing out a warning.

Differential revision: https://reviews.llvm.org/D38230

llvm-svn: 314198

llvm/test/tools/dsymutil/X86/alias.test

@@ -0,0 +1,19 @@
+# RUN: llvm-dsymutil -f -oso-prepend-path=%p/../Inputs/alias \
+# RUN: %p/../Inputs/alias/foobar -o - 2>&1 | llvm-dwarfdump - | FileCheck %s
+# CHECK-NOT: could not find object file symbol for symbol
+# CHECK: DW_AT_name ("foo.c")
+# CHECK: DW_AT_name ("bar.c")
+
+# Source:
+#   $ cat foo.c
+#   int foo = 1;
+#   $ cat bar.c
+#   extern int bar;
+#   int main() {
+#     return bar;
+#   }
+
+# Compile with:
+#   $ clang -g -O0 bar.c -c -o bar.o
+#   $ clang -g -O0 foo.c -c -o foo.o
+#   $ ld -arch x86_64 -macosx_version_min 10.13.0 foo.o bar.o -lSystem -alias _foo _bar -o foobar

llvm/tools/dsymutil/MachODebugMapParser.cpp

@@ -70,6 +70,7 @@ private:
                             sys::TimePoint<std::chrono::seconds> Timestamp);
   void resetParserState();
   uint64_t getMainBinarySymbolAddress(StringRef Name);
+  std::vector<StringRef> getMainBinarySymbolNames(uint64_t Value);
   void loadMainBinarySymbols(const MachOObjectFile &MainBinary);
   void loadCurrentObjectFileSymbols(const object::MachOObjectFile &Obj);
   void handleStabSymbolTableEntry(uint32_t StringIndex, uint8_t Type,
@@ -382,9 +383,21 @@ void MachODebugMapParser::handleStabSymbolTableEntry(uint32_t StringIndex,
   }
 
   auto ObjectSymIt = CurrentObjectAddresses.find(Name);
+
+  // If the name of a (non-static) symbol is not in the current object, we
+  // check all its aliases from the main binary.
+  if (ObjectSymIt == CurrentObjectAddresses.end() && Type != MachO::N_STSYM) {
+    for (const auto &Alias : getMainBinarySymbolNames(Value)) {
+      ObjectSymIt = CurrentObjectAddresses.find(Alias);
+      if (ObjectSymIt != CurrentObjectAddresses.end())
+        break;
+    }
+  }
+
   if (ObjectSymIt == CurrentObjectAddresses.end())
     return Warning("could not find object file symbol for symbol " +
                    Twine(Name));
+
   if (!CurrentDebugMapObject->addSymbol(Name, ObjectSymIt->getValue(), Value,
                                         Size))
     return Warning(Twine("failed to insert symbol '") + Name +
@@ -429,6 +442,17 @@ uint64_t MachODebugMapParser::getMainBinarySymbolAddress(StringRef Name) {
   return Sym->second;
 }
 
+/// Get all symbol names in the main binary for the given value.
+std::vector<StringRef>
+MachODebugMapParser::getMainBinarySymbolNames(uint64_t Value) {
+  std::vector<StringRef> Names;
+  for (const auto &Entry : MainBinarySymbolAddresses) {
+    if (Entry.second == Value)
+      Names.push_back(Entry.first());
+  }
+  return Names;
+}
+
 /// Load the interesting main binary symbols' addresses into
 /// MainBinarySymbolAddresses.
 void MachODebugMapParser::loadMainBinarySymbols(