obj2yaml: Don't crash if the characteristics field is zero

obj2yaml would fail when seeing a Weak External auxiliary record with a
characteristics field holding zero instead of one of
IMAGE_WEAK_EXTERN_SEARCH_NOLIBRARY, IMAGE_WEAK_EXTERN_SEARCH_NOLIBRARY,
or IMAGE_WEAK_EXTERN_SEARCH_NOLIBRARY.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205911 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Object/COFFYAML.cpp

@@ -38,6 +38,7 @@ void ScalarEnumerationTraits<COFFYAML::COMDATType>::enumeration(
 void
 ScalarEnumerationTraits<COFFYAML::WeakExternalCharacteristics>::enumeration(
     IO &IO, COFFYAML::WeakExternalCharacteristics &Value) {
+  IO.enumCase(Value, "0", 0);
   ECase(IMAGE_WEAK_EXTERN_SEARCH_NOLIBRARY);
   ECase(IMAGE_WEAK_EXTERN_SEARCH_LIBRARY);
   ECase(IMAGE_WEAK_EXTERN_SEARCH_ALIAS);

test/Object/Inputs/COFF/weak-external.yaml

@@ -0,0 +1,43 @@
+---
+header:
+  Machine:         IMAGE_FILE_MACHINE_I386
+  Characteristics: [ IMAGE_FILE_LINE_NUMS_STRIPPED, IMAGE_FILE_32BIT_MACHINE ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     5589E583E4F0E800000000B800000000C9C39090
+    Relocations:     
+      - VirtualAddress:  7
+        SymbolName:      ___main
+        Type:            IMAGE_REL_I386_REL32
+symbols:
+  - Name:            .file
+    Value:           0
+    SectionNumber:   65534
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_FILE
+    File:            'file'
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition: 
+      Length:          18
+      NumberOfRelocations: 1
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+  - Name:            ___main
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+    WeakExternal:    
+      TagIndex:        0
+      Characteristics: 0
+...

test/Object/obj2yaml-coff-weak-external.test

@@ -0,0 +1,3 @@
+RUN: yaml2obj %p/Inputs/COFF/weak-external.yaml | obj2yaml | FileCheck %s --check-prefix COFF-I386
+
+COFF-I386: Characteristics: 0