Add C symbol support to name mangling Ghida script

ghidra/ghidra_scripts/MSVC7Mangle.java

@@ -11,6 +11,9 @@
 // appear in objdiff, replacing spaces with underscores, e.g. "operator_new"
 // and "`scalar_deleting_destructor'" (notice the ` and ').
 //
+// MSVC also applies minor name mangling to C symbols.  This can be enabled for
+// a given symbol by placing it in a top-level namespace named extern_"C".
+//
 // This script can be called in headless mode with the address ranges to mangle
 // as arguments, e.g. 0x1234-0x5678.  Any symbols referenced by functions being
 // mangled will also be mangled in this mode (so that the references are
@@ -135,21 +138,56 @@ public class MSVC7Mangle extends GhidraScript{
 	/* Generate a mangled name for a function */
 		final String nameRaw = f.getName(true);
 
-		// Internal symbols like intrinsics aren't mangled
+		// main() and extern "C" symbols get C name mangling
-		if (nameRaw.startsWith("_")) return nameRaw;
+		// (some other things, do, too, but just use extern "C" instead
+		// of making me find and list them all...)
+		return nameRaw == "main" ||
+		       nameRaw.startsWith("extern_\"C\"::") ? mangleCFn  (f)
+		                                            : mangleCppFn(f);
+	}
 
-		// Other special cases
+	private static String mangleCFn(final Function f) throws Exception {
-		switch (nameRaw) {
+	/* Produce a C function mangled name
-			case "atexit": return "_atexit";
+	(MSVC does indeed do this despite the folk wisdom that only C++ gets
-			case "main"  : return "_main"  ;
+	name mangling; it is certainly simpler than the C++ sort, at least)
-			default      : {}
+	*/
-		}
+		return switch (f.getCallingConventionName()) {
+			case "__cdecl"    -> "_" + f.getName(false);
+			case "__stdcall"  -> "_" + f.getName(false) + argSize(f);
+			case "__fastcall" -> "@" + f.getName(false) + argSize(f);
+			case "__thiscall" -> throw new Exception(
+				f.getName() +
+				"(): __thiscall not allowed for C symbols"
+			);
+			default           -> throw new Exception(
+				f.getName() +
+				"(): Need to specify calling convention"
+			);
+		};
+	}
+
+	private static String argSize(final Function f) {
+	/* Produce the argument size suffix for a C function
+	The format is "@123" where "123" is however many bytes the arguments
+	occupy (each argument occupies at least four bytes).
+	*/
+		return "@" + Arrays.stream(f.getSignature(true).getArguments())
+		                   .map(ParameterDefinition::getDataType)
+		                   .map(t -> Math.max(t.getLength(), 4))
+		                   .reduce(0, Integer::sum)
+		                   .toString();
+	}
+
+	private String mangleCppFn(final Function f) throws Exception {
+	/* Produce a C++ function mangled name */
+		final String nameRaw = f.getName(true);
 
 		final ArrayList<String> dict = new ArrayList<>();
 
 		final List<String> nameParts   = Arrays.asList(nameRaw.split("::"));
 		Collections.reverse(nameParts);
-		final boolean      isMethod    = f.getCallingConventionName().equals("__thiscall") &&
+		final boolean      isMethod    = f.getCallingConventionName()
+		                                  .equals("__thiscall")       &&
 		                                 nameParts.size() >= 2;
 		final String       name        = mangleIdentifier(nameRaw, isMethod, f.getReturnType(), dict);
 
@@ -500,6 +538,11 @@ public class MSVC7Mangle extends GhidraScript{
 			);
 
 		// Other data
+		if (name.startsWith("extern_\"C\"::")) {
+			final String[] nameParts = name.split("::");
+			return "_" + nameParts[nameParts.length - 1];
+		}
+
 		final ArrayList<String> dict  = new ArrayList<>();
 		final String            ident = mangleIdentifier(name, false, null, dict);