[PECOFF] Add comments for symbols.

llvm-svn: 183700

lld/include/lld/Core/DefinedAtom.h

@@ -196,6 +196,11 @@ public:
   ///
   /// This is used by the linker to order the layout of Atoms so that the
   /// resulting image is stable and reproducible.
+  ///
+  /// Note that this should not be confused with ordinals of exported symbols in
+  /// Windows DLLs. In Windows terminology, ordinals are symbols' export table
+  /// indices (small integers) which can be used instead of symbol names to
+  /// refer items in a DLL.
   virtual uint64_t ordinal() const = 0;
 
   /// \brief the number of bytes of space this atom's content will occupy in the

lld/include/lld/Core/SharedLibraryAtom.h

@@ -25,6 +25,7 @@ public:
   /// Returns shared library name used to load it at runtime.
   /// On linux that is the DT_NEEDED name.
   /// On Darwin it is the LC_DYLIB_LOAD dylib name.
+  /// On Windows it is the DLL name that to be referred from .idata section.
   virtual StringRef loadName() const = 0;
 
   /// Returns if shared library symbol can be missing at runtime and if

lld/include/lld/Core/UndefinedAtom.h

@@ -35,15 +35,15 @@ public:
     /// __attribute__((weak_import)).
     /// On linux this is generated using a function prototype with
     ///  __attribute__((weak)).
+    /// On Windows this feature is not supported.
     canBeNullAtRuntime,
 
-
     /// This symbol can be missing at build time.
     /// That is, the static linker will not error if a definition for
     /// this symbol is not found at build time. Instead, the linker
     /// will build an executable that lets the dynamic loader find the
     /// symbol at runtime.
-    /// This feature is not supported on Darwin.
+    /// This feature is not supported on Darwin nor Windows.
     /// On linux this is generated using a function prototype with
     ///  __attribute__((weak)).
     canBeNullAtBuildtime