[dsymutil] Ignore absolute symbols in the debug map

Quoting from the comment added to the code:

    // Objective-C on i386 uses artificial absolute symbols to
    // perform some link time checks. Those symbols have a fixed 0
    // address that might conflict with real symbols in the object
    // file. As I cannot see a way for absolute symbols to find
    // their way into the debug information, let's just ignore those.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255350 91177308-0d34-0410-b5e6-96231b3b80d8

test/tools/dsymutil/absolute_symbol.test

@@ -0,0 +1,16 @@
+RUN: llvm-dsymutil -dump-debug-map -oso-prepend-path %p %p/Inputs/absolute_sym.macho.i386 | FileCheck %s
+
+The tested object file has been created by the dummy Objective-C code:
+@interface Foo
+@end
+
+@implementation Foo
+@end
+
+int main() { return 0; }
+
+compiled for i386. This create an absolute symbol .objc_class_name_Foo
+We must not consider this symbol for debug info linking as its address
+might conflict with other real symbols in the same file.
+
+CHECK-NOT: objc_class_name_Foo

tools/dsymutil/MachODebugMapParser.cpp

@@ -10,6 +10,7 @@
 #include "BinaryHolder.h"
 #include "DebugMap.h"
 #include "dsymutil.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/Object/MachO.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
@@ -53,7 +54,7 @@ class MachODebugMapParser {
   /// Owns the MemoryBuffer for the currently handled object file.
   BinaryHolder CurrentObjectHolder;
   /// Map of the currently processed object file symbol addresses.
-  StringMap<uint64_t> CurrentObjectAddresses;
+  StringMap<Optional<uint64_t>> CurrentObjectAddresses;
   /// Element of the debug map corresponfing to the current object file.
   DebugMapObject *CurrentDebugMapObject;
 
@@ -388,7 +389,9 @@ void MachODebugMapParser::handleStabSymbolTableEntry(uint32_t StringIndex,
   if (ObjectSymIt == CurrentObjectAddresses.end())
     return Warning("could not find object file symbol for symbol " +
                    Twine(Name));
-  if (!CurrentDebugMapObject->addSymbol(Name, ObjectSymIt->getValue(), Value,
+  if (!ObjectSymIt->getValue())
+    return;
+  if (!CurrentDebugMapObject->addSymbol(Name, *ObjectSymIt->getValue(), Value,
                                         Size))
     return Warning(Twine("failed to insert symbol '") + Name +
                    "' in the debug map.");
@@ -404,7 +407,15 @@ void MachODebugMapParser::loadCurrentObjectFileSymbols(
     ErrorOr<StringRef> Name = Sym.getName();
     if (!Name)
       continue;
-    CurrentObjectAddresses[*Name] = Addr;
+    // Objective-C on i386 uses artificial absolute symbols to
+    // perform some link time checks. Those symbols have a fixed 0
+    // address that might conflict with real symbols in the object
+    // file. As I cannot see a way for absolute symbols to find
+    // their way into the debug information, let's just ignore those.
+    if (Sym.getFlags() & SymbolRef::SF_Absolute)
+      CurrentObjectAddresses[*Name] = None;
+    else
+      CurrentObjectAddresses[*Name] = Addr;
   }
 }