ELF: print out a verbose error when a windows emulation is used

llvm-svn: 253985
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 22297f5..015ac30 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -52,6 +52,12 @@
     return {ELF64LEKind, EM_X86_64};
   if (S == "aarch64linux")
     return {ELF64LEKind, EM_AARCH64};
+  if (S == "i386pe")
+    return {ELFNoneKind, EM_386};
+  if (S == "i386pep")
+    return {ELFNoneKind, EM_X86_64};
+  if (S == "thumb2pe")
+    return {ELFNoneKind, EM_ARM};
   error("Unknown emulation: " + S);
 }
 
@@ -104,9 +110,21 @@
 }
 
 void LinkerDriver::main(ArrayRef<const char *> ArgsArr) {
-  initSymbols();
 
   opt::InputArgList Args = parseArgs(&Alloc, ArgsArr);
+
+  if (auto *Arg = Args.getLastArg(OPT_m)) {
+    StringRef S = Arg->getValue();
+    std::pair<ELFKind, uint16_t> P = parseEmulation(S);
+    Config->EKind = P.first;
+    Config->EMachine = P.second;
+    Config->Emulation = S;
+  }
+
+  if((Config->EKind == ELFNoneKind) && (Config->EMachine !=  EM_NONE))
+    error("windows coff targets aren't supported on the gnu frontend.");
+
+  initSymbols();
   createFiles(Args);
 
   // Traditional linkers can generate re-linkable object files instead
@@ -143,14 +161,6 @@
   if (!RPaths.empty())
     Config->RPath = llvm::join(RPaths.begin(), RPaths.end(), ":");
 
-  if (auto *Arg = Args.getLastArg(OPT_m)) {
-    StringRef S = Arg->getValue();
-    std::pair<ELFKind, uint16_t> P = parseEmulation(S);
-    Config->EKind = P.first;
-    Config->EMachine = P.second;
-    Config->Emulation = S;
-  }
-
   Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
   Config->DiscardAll = Args.hasArg(OPT_discard_all);