[yaml2obj] - Don't crash on invalid inputs.

[grimar]

Summary

yaml2obj might crash on invalid input when unable to parse the YAML.

The reason for the crash is almost the same to one fixed in D59964,
which fixed it for en empty inputs. But as was mentioned in comments,
fix should have been done in yaml::Input instead.

This patch does that and fixes a crash that I faced
(I updated the test case accordingly).

[compnerd]

Great! Thanks for fixing this. The original change was to mitigate the crashes, and this is definitely the right way to address this. This seems to also be more conforming to the YAML specification.

llvm/trunk/lib/ObjectYAML/ObjectYAML.cpp

if (IO.outputting()) {
     if (ObjectFile.Coff)
       MappingTraits<COFFYAML::Object>::mapping(IO, *ObjectFile.Coff);
     if (ObjectFile.MachO)
       MappingTraits<MachOYAML::Object>::mapping(IO, *ObjectFile.MachO);
     if (ObjectFile.FatMachO)
       MappingTraits<MachOYAML::UniversalBinary>::mapping(IO,
                                                          *ObjectFile.FatMachO);
   } else {
+    Input &In = (Input &)IO;
     if (IO.mapTag("!ELF")) {
       ObjectFile.Elf.reset(new ELFYAML::Object());
       MappingTraits<ELFYAML::Object>::mapping(IO, *ObjectFile.Elf);
     } else if (IO.mapTag("!COFF")) {
       ObjectFile.Coff.reset(new COFFYAML::Object());
       MappingTraits<COFFYAML::Object>::mapping(IO, *ObjectFile.Coff);
     } else if (IO.mapTag("!mach-o")) {
       ObjectFile.MachO.reset(new MachOYAML::Object());
       MappingTraits<MachOYAML::Object>::mapping(IO, *ObjectFile.MachO);
     } else if (IO.mapTag("!fat-mach-o")) {
       ObjectFile.FatMachO.reset(new MachOYAML::UniversalBinary());
       MappingTraits<MachOYAML::UniversalBinary>::mapping(IO,
                                                          *ObjectFile.FatMachO);
     } else if (IO.mapTag("!minidump")) {
       ObjectFile.Minidump.reset(new MinidumpYAML::Object());
       MappingTraits<MinidumpYAML::Object>::mapping(IO, *ObjectFile.Minidump);
     } else if (IO.mapTag("!WASM")) {
       ObjectFile.Wasm.reset(new WasmYAML::Object());
       MappingTraits<WasmYAML::Object>::mapping(IO, *ObjectFile.Wasm);
-    } else {
-      Input &In = (Input &)IO;
-      std::string Tag = In.getCurrentNode()->getRawTag();
-      if (Tag.empty())
+    } else if (const Node *N = In.getCurrentNode()) {
+      if (N->getRawTag().empty())
         IO.setError("YAML Object File missing document type tag!");
       else
-        IO.setError(
-            Twine("YAML Object File unsupported document type tag '") +
-            Twine(Tag) + Twine("'!"));
+        IO.setError("YAML Object File unsupported document type tag '" +
+                    N->getRawTag() + "'!");
     }
   }
 }

llvm/trunk/lib/Support/YAMLTraits.cpp

bool Input::nextDocument() {
   return ++DocIterator != Strm->end();
 }
 
 const Node *Input::getCurrentNode() const {
   return CurrentNode ? CurrentNode->_node : nullptr;
 }
 
 bool Input::mapTag(StringRef Tag, bool Default) {
+  // CurrentNode can be null if setCurrentDocument() was unable to
+  // parse the document because it was invalid or empty.
+  if (!CurrentNode)
+    return false;
+
   std::string foundTag = CurrentNode->_node->getVerbatimTag();
   if (foundTag.empty()) {
     // If no tag found and 'Tag' is the default, say it was found.
     return Default;
   }
   // Return true iff found tag matches supplied tag.
   return Tag.equals(foundTag);
 }

llvm/trunk/test/tools/yaml2obj/empty-or-invalid-doc.yaml

+# RUN: echo "" | not yaml2obj 2>&1 | FileCheck %s
+# RUN: echo -n "" | not yaml2obj 2>&1 | FileCheck %s
+# RUN: echo " " | not yaml2obj 2>&1 | FileCheck %s
+# RUN: echo "  " | not yaml2obj 2>&1 | FileCheck %s
+# CHECK: yaml2obj: Unknown document type!
+
+# RUN: echo -e -n "\xff" | not yaml2obj 2>&1 | FileCheck %s --check-prefix=INVALID
+# INVALID: yaml2obj: Failed to parse YAML file!

llvm/trunk/test/tools/yaml2obj/empty.yaml

-# RUN: echo "" | not yaml2obj 2>&1 | FileCheck %s
-# RUN: echo -n "" | not yaml2obj 2>&1 | FileCheck %s
-# RUN: echo " " | not yaml2obj 2>&1 | FileCheck %s
-# RUN: echo "  " | not yaml2obj 2>&1 | FileCheck %s
-# CHECK: yaml2obj: Error opening '-': Empty File.

llvm/trunk/tools/yaml2obj/yaml2obj.cpp

int main(int argc, char **argv) {
   if (EC)
     error("yaml2obj: Error opening '" + OutputFilename + "': " + EC.message());
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> Buf =
       MemoryBuffer::getFileOrSTDIN(Input);
   if (!Buf)
     return 1;
 
-  StringRef Buffer = Buf.get()->getBuffer();
-  if (Buffer.trim().size() == 0)
-    error("yaml2obj: Error opening '" + Input + "': Empty File.");
-  yaml::Input YIn(Buffer);
-
+  yaml::Input YIn(Buf.get()->getBuffer());
   int Res = convertYAML(YIn, Out->os());
   if (Res == 0)
     Out->keep();
 
   Out->os().flush();
   return Res;
 }