[llvm] [llvm-dlltool] Implement the --identify option (PR #127465)

[Jacek Caban via llvm-commits]

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@@ -158,6 +159,169 @@ bool parseModuleDefinition(StringRef DefFileName, MachineTypes Machine,
   return true;
 }
 
+int printError(llvm::Error E, Twine File) {
+  if (!E)
+    return 0;
+  handleAllErrors(std::move(E), [&](const llvm::ErrorInfoBase &EIB) {
+    llvm::errs() << "error opening " << File << ": " << EIB.message() << "\n";
+  });
+  return 1;
+}
+
+template <typename Callable>
+int forEachCoff(object::Archive &Archive, StringRef Name, Callable Callback) {
+  Error Err = Error::success();
+  for (auto &C : Archive.children(Err)) {
+    Expected<StringRef> NameOrErr = C.getName();
+    if (!NameOrErr)
+      return printError(NameOrErr.takeError(), Name);
+    StringRef Name = *NameOrErr;
+
+    Expected<MemoryBufferRef> ChildMB = C.getMemoryBufferRef();
+    if (!ChildMB)
+      return printError(ChildMB.takeError(), Name);
+
+    if (identify_magic(ChildMB->getBuffer()) == file_magic::coff_object) {
+      auto Obj = object::COFFObjectFile::create(*ChildMB);
+      if (!Obj)
+        return printError(Obj.takeError(), Name);
+      if (!Callback(*Obj->get(), Name))
+        return 1;
+    }
+  }
+  if (Err)
+    return printError(std::move(Err), Name);
+  return 0;
+}
+
+// To find the named of the imported DLL from an import library, we can either
+// inspect the object files that form the import table entries, or we could
+// just look at the archive member names, for MSVC style import libraries.
+// Looking at the archive member names doesn't work for GNU style import
+// libraries though, while inspecting the import table entries works for
+// both. (MSVC style import libraries contain a couple regular object files
+// for the header/trailers.)
+//
+// This implementation does the same as GNU dlltool does; look at the
+// content of ".idata$7" sections, or for MSVC style libraries, look
+// at ".idata$6$" sections.
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cjacek wrote:

Typo: `".idata$6"`.

https://github.com/llvm/llvm-project/pull/127465