[llvm-lib][llvm-dlltool] Fix handling of invalid ARM64EC function names (#116250)

This is a follow-up to #115567. Emit an error for invalid function
names, similar to MSVC's `lib.exe` behavior.

Returning an error from `writeImportLibrary` exposed bugs in error
handling by its callers, which have been addressed in this patch.

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/Object/COFFImportFile.cpp b/llvm/lib/Object/COFFImportFile.cpp
index cc0a5da..ff3dcf9 100644
--- a/llvm/lib/Object/COFFImportFile.cpp
+++ b/llvm/lib/Object/COFFImportFile.cpp
@@ -756,8 +756,15 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
           }
           Name = std::move(*MangledName);
         } else if (!E.Noname && ExportName.empty()) {
+          std::optional<std::string> DemangledName =
+              getArm64ECDemangledFunctionName(Name);
+          if (!DemangledName)
+            return make_error<StringError>(
+                StringRef(Twine("Invalid ARM64EC function name '" + Name + "'")
+                              .str()),
+                object_error::parse_failed);
           NameType = IMPORT_NAME_EXPORTAS;
-          ExportName = std::move(*getArm64ECDemangledFunctionName(Name));
+          ExportName = std::move(*DemangledName);
         }
       }