diff --git a/third_party/def_parser/def_parser.cc b/third_party/def_parser/def_parser.cc
index 8f78744312..890f33a1ba 100644
--- a/third_party/def_parser/def_parser.cc
+++ b/third_party/def_parser/def_parser.cc
@@ -62,21 +62,14 @@
  * Author:   Valery Fine 16/09/96  (E-mail: fine@vxcern.cern.ch)
  *----------------------------------------------------------------------
  */
-#include "bindexplib.h"
+#include "third_party/def_parser/def_parser.h"
 
-#include <cstddef> // IWYU pragma: keep
+#include <algorithm>
+#include <iostream>
+#include <fstream>
+#include <memory>    // unique_ptr
 #include <sstream>
-#include <vector>
-
-#ifdef _WIN32
-#  include <windows.h>
-
-#  include "cmsys/Encoding.hxx"
-#endif
-
-#include "cmsys/FStream.hxx"
-
-#include "cmSystemTools.h"
+#include <windows.h>
 
 #ifdef _WIN32
 #  ifndef IMAGE_FILE_MACHINE_ARM
@@ -99,6 +92,11 @@
 #    define IMAGE_FILE_MACHINE_ARM64EC 0xa641 // ARM64EC Little-Endian
 #  endif
 
+using std::string;
+using std::wstring;
+using std::stringstream;
+using std::unique_ptr;
+
 typedef struct cmANON_OBJECT_HEADER_BIGOBJ
 {
   /* same as ANON_OBJECT_HEADER_V2 */
@@ -341,77 +339,69 @@ private:
 };
 #endif
 
-static bool DumpFileWithLlvmNm(std::string const& nmPath, const char* filename,
-                               std::set<std::string>& symbols,
-                               std::set<std::string>& dataSymbols)
-{
-  std::string output;
-  // break up command line into a vector
-  std::vector<std::string> command;
-  command.push_back(nmPath);
-  command.emplace_back("--no-weak");
-  command.emplace_back("--defined-only");
-  command.emplace_back("--format=posix");
-  command.emplace_back(filename);
-
-  // run the command
-  int exit_code = 0;
-  cmSystemTools::RunSingleCommand(command, &output, &output, &exit_code,
-                                  nullptr, cmSystemTools::OUTPUT_NONE);
-
-  if (exit_code != 0) {
-    fprintf(stderr, "llvm-nm returned an error: %s\n", output.c_str());
-    return false;
+void PrintLastError() {
+  DWORD last_error = GetLastError();
+  if (last_error == 0) {
+    return;
   }
 
-  std::istringstream ss(output);
-  std::string line;
-  while (std::getline(ss, line)) {
-    if (line.empty()) { // last line
-      continue;
-    }
-    size_t sym_end = line.find(' ');
-    if (sym_end == std::string::npos) {
-      fprintf(stderr, "Couldn't parse llvm-nm output line: %s\n",
-              line.c_str());
-      return false;
-    }
-    if (line.size() < sym_end + 1) {
-      fprintf(stderr, "Couldn't parse llvm-nm output line: %s\n",
-              line.c_str());
-      return false;
-    }
-    const char sym_type = line[sym_end + 1];
-    line.resize(sym_end);
-    switch (sym_type) {
-      case 'D':
-        dataSymbols.insert(line);
-        break;
-      case 'T':
-        symbols.insert(line);
-        break;
-    }
+  char* message_buffer;
+  size_t size = FormatMessageA(
+      FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
+          FORMAT_MESSAGE_IGNORE_INSERTS,
+      NULL, last_error, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+      (LPSTR)&message_buffer, 0, NULL);
+
+  std::cerr << "(error: " << last_error << "): " << message_buffer;
+  LocalFree(message_buffer);
+}
+
+wstring StringToWString(const string& s) {
+  SetLastError(ERROR_SUCCESS);
+  DWORD len = MultiByteToWideChar(CP_ACP, 0, s.c_str(), -1, NULL, 0);
+  if (len == 0 && GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+    PrintLastError();
+    return L"";
   }
+  unique_ptr<WCHAR[]> wstr(new WCHAR[len]);
+  MultiByteToWideChar(CP_ACP, 0, s.c_str(), -1, wstr.get(), len);
+  return wstring(wstr.get());
+}
 
-  return true;
+wstring AsAbsoluteWindowsPath(const string& path) {
+  wstring wpath = StringToWString(path);
+  // Get the buffer length we need for the full path.
+  SetLastError(ERROR_SUCCESS);
+  DWORD len = GetFullPathNameW(wpath.c_str(), 0, NULL, NULL);
+  if (len == 0 && GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+    PrintLastError();
+    return L"";
+  }
+  SetLastError(ERROR_SUCCESS);
+  unique_ptr<WCHAR[]> buffer(new WCHAR[len]);
+  GetFullPathNameW(wpath.c_str(), len, buffer.get(), NULL);
+  if (GetLastError() != ERROR_SUCCESS) {
+    PrintLastError();
+    return L"";
+  }
+  return wstring(L"\\\\?\\") + wstring(buffer.get());
 }
 
-static bool DumpFile(std::string const& nmPath, const char* filename,
+static bool DumpFile(const char* filename,
                      std::set<std::string>& symbols,
                      std::set<std::string>& dataSymbols)
 {
-#ifndef _WIN32
-  return DumpFileWithLlvmNm(nmPath, filename, symbols, dataSymbols);
-#else
   HANDLE hFile;
   HANDLE hFileMapping;
   LPVOID lpFileBase;
 
-  hFile = CreateFileW(cmsys::Encoding::ToWide(filename).c_str(), GENERIC_READ,
+  wstring filenameW = AsAbsoluteWindowsPath(filename);
+  hFile = CreateFileW(filenameW.c_str(), GENERIC_READ,
                       FILE_SHARE_READ, nullptr, OPEN_EXISTING,
                       FILE_ATTRIBUTE_NORMAL, 0);
 
   if (hFile == INVALID_HANDLE_VALUE) {
+    PrintLastError();
     fprintf(stderr, "Couldn't open file '%s' with CreateFile()\n", filename);
     return false;
   }
@@ -419,16 +409,18 @@ static bool DumpFile(std::string const& nmPath, const char* filename,
   hFileMapping =
     CreateFileMapping(hFile, nullptr, PAGE_READONLY, 0, 0, nullptr);
   if (hFileMapping == 0) {
-    CloseHandle(hFile);
+    PrintLastError();
     fprintf(stderr, "Couldn't open file mapping with CreateFileMapping()\n");
+    CloseHandle(hFile);
     return false;
   }
 
   lpFileBase = MapViewOfFile(hFileMapping, FILE_MAP_READ, 0, 0, 0);
   if (lpFileBase == 0) {
+    PrintLastError();
+    fprintf(stderr, "Couldn't map view of file with MapViewOfFile()\n");
     CloseHandle(hFileMapping);
     CloseHandle(hFile);
-    fprintf(stderr, "Couldn't map view of file with MapViewOfFile()\n");
     return false;
   }
 
@@ -474,14 +466,6 @@ static bool DumpFile(std::string const& nmPath, const char* filename,
                : (h->Machine == IMAGE_FILE_MACHINE_ARM64EC ? Arch::ARM64EC
                                                            : Arch::Generic)));
         symbolDumper.DumpObjFile();
-      } else if (
-        // BCexCODE - llvm bitcode
-        (h->Sig1 == 0x4342 && h->Sig2 == 0xDEC0) ||
-        // 0x0B17C0DE - llvm bitcode BC wrapper
-        (h->Sig1 == 0x0B17 && h->Sig2 == 0xC0DE)) {
-
-        return DumpFileWithLlvmNm(nmPath, filename, symbols, dataSymbols);
-
       } else {
         printf("unrecognized file format in '%s, %u'\n", filename,
                imageHeader->Machine);
@@ -493,18 +477,22 @@ static bool DumpFile(std::string const& nmPath, const char* filename,
   CloseHandle(hFileMapping);
   CloseHandle(hFile);
   return true;
-#endif
 }
 
-bool bindexplib::AddObjectFile(const char* filename)
+void DefParser::SetDLLName(const string& dllname) {
+  this->DLLName = dllname;
+}
+
+bool DefParser::AddObjectFile(const char* filename)
 {
-  return DumpFile(this->NmPath, filename, this->Symbols, this->DataSymbols);
+  return DumpFile(filename, this->Symbols, this->DataSymbols);
 }
 
-bool bindexplib::AddDefinitionFile(const char* filename)
+bool DefParser::AddDefinitionFile(const char* filename)
 {
-  cmsys::ifstream infile(filename);
+  std::ifstream infile(filename);
   if (!infile) {
+    PrintLastError();
     fprintf(stderr, "Couldn't open definition file '%s'\n", filename);
     return false;
   }
@@ -529,8 +517,31 @@ bool bindexplib::AddDefinitionFile(const char* filename)
   return true;
 }
 
-void bindexplib::WriteFile(FILE* file)
+bool DefParser::IsDefFile(const string& file) {
+  // Get file extension and convert it to lower case.
+  string ext = file.substr(file.find_last_of(".") + 1);
+  std::transform(ext.begin(), ext.end(), ext.begin(), ::tolower);
+  return ext == "def";
+}
+
+bool DefParser::AddFile(const string& file) {
+  if (IsDefFile(file)) {
+    if (!this->AddDefinitionFile(file.c_str())) {
+      return false;
+    }
+  } else {
+    if (!this->AddObjectFile(file.c_str())) {
+      return false;
+    }
+  }
+  return true;
+}
+
+void DefParser::WriteFile(FILE* file)
 {
+  if (!this->DLLName.empty()) {
+    fprintf(file, "LIBRARY %s\n", this->DLLName.c_str());
+  }
   fprintf(file, "EXPORTS \n");
   for (std::string const& ds : this->DataSymbols) {
     fprintf(file, "\t%s \t DATA\n", ds.c_str());
@@ -539,8 +550,3 @@ void bindexplib::WriteFile(FILE* file)
     fprintf(file, "\t%s\n", s.c_str());
   }
 }
-
-void bindexplib::SetNmPath(std::string const& nm)
-{
-  this->NmPath = nm;
-}
\ No newline at end of file