[PDB] Don't write uninitialized bytes to a PDB file.

There were certain fields that we didn't know how to write, as
well as various padding bytes that we would ignore.  This leads
to garbage data in the PDB.  While not strictly necessary, we
should initialize these bytes to something meaningful, as it
makes for easier binary comparison between PDBs.

llvm-svn: 305819

llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp

@@ -51,6 +51,7 @@ DbiModuleDescriptorBuilder::DbiModuleDescriptorBuilder(StringRef ModuleName,
                                                        uint32_t ModIndex,
                                                        msf::MSFBuilder &Msf)
     : MSF(Msf), ModuleName(ModuleName) {
+  ::memset(&Layout, 0, sizeof(Layout));
   Layout.Mod = ModIndex;
 }
 
@@ -102,6 +103,7 @@ template <typename T> struct Foo {
 template <typename T> Foo<T> makeFoo(T &&t) { return Foo<T>(std::move(t)); }
 
 void DbiModuleDescriptorBuilder::finalize() {
+  Layout.SC.ModuleIndex = Layout.Mod;
   Layout.FileNameOffs = 0; // TODO: Fix this
   Layout.Flags = 0;        // TODO: Fix this
   Layout.C11Bytes = 0;

llvm/lib/DebugInfo/PDB/Native/DbiStreamBuilder.cpp

@@ -237,6 +237,7 @@ Error DbiStreamBuilder::finalize() {
     return EC;
 
   DbiStreamHeader *H = Allocator.Allocate<DbiStreamHeader>();
+  ::memset(H, 0, sizeof(DbiStreamHeader));
   H->VersionHeader = *VerHeader;
   H->VersionSignature = -1;
   H->Age = Age;