[LLD][COFF] Add support for the -defArm64Native argument (#123850)

MSVC ignores the `/defArm64Native` argument on non-ARM64X targets.
It is also ignored if the `/def` option is not specified.

Author: cjacek

lld/COFF/Driver.cpp

@@ -1795,6 +1795,9 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
       setMachine(machine);
     }
   }
+
+  // Most of main arguments apply either to both or only to EC symbol table on
+  // ARM64X target.
   SymbolTable &mainSymtab = ctx.hybridSymtab ? *ctx.hybridSymtab : ctx.symtab;
 
   // Handle /nodefaultlib:<filename>
@@ -2291,6 +2294,12 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   if (auto *arg = args.getLastArg(OPT_deffile)) {
     // parseModuleDefs mutates Config object.
     mainSymtab.parseModuleDefs(arg->getValue());
+    if (ctx.hybridSymtab) {
+      // MSVC ignores the /defArm64Native argument on non-ARM64X targets.
+      // It is also ignored if the /def option is not specified.
+      if (auto *arg = args.getLastArg(OPT_defarm64native))
+        ctx.symtab.parseModuleDefs(arg->getValue());
+    }
   }
 
   // Handle generation of import library from a def file.

lld/COFF/Options.td

@@ -140,6 +140,9 @@ def incl : Joined<["/", "-", "/?", "-?"], "include:">,
 def deffile : Joined<["/", "-", "/?", "-?"], "def:">,
     HelpText<"Use module-definition file">;
 
+def defarm64native
+    : P<"defarm64native",
+        "Use a module-definition file for the native view in a hybrid image.">;
 def debug : F<"debug">, HelpText<"Embed a symbol table in the image">;
 def debug_opt : P<"debug", "Embed a symbol table in the image with option">;
 def debugtype : P<"debugtype", "Debug Info Options">;

lld/test/COFF/arm64x-export.test

@@ -162,6 +162,29 @@ EXPORTS-BOTH-NEXT:     RVA: 0x3000
 EXPORTS-BOTH-NEXT:   }
 EXPORTS-BOTH-NEXT: }
 
+# Export using both the -def and -defarm64native arguments.
+
+RUN: lld-link -machine:arm64x -dll -out:out-def-both.dll arm64ec-func.obj arm64-func.obj \
+RUN:          loadconfig-arm64.obj loadconfig-arm64ec.obj -def:func.def -defarm64native:func.def -noentry
+RUN: llvm-objdump -d out-def-both.dll | FileCheck --check-prefix=DISASM-BOTH %s
+RUN: llvm-readobj --headers --coff-exports out-def-both.dll | FileCheck --check-prefix=EXPORTS-BOTH %s
+
+# -defarm64native is ignored if -def is not specified.
+
+RUN: lld-link -machine:arm64x -dll -out:out-def-native.dll arm64ec-func.obj arm64-func.obj \
+RUN:          loadconfig-arm64.obj loadconfig-arm64ec.obj -defarm64native:func.def -noentry
+RUN: llvm-readobj --headers --coff-exports out-def-native.dll | FileCheck --check-prefix=NO-EXPORT %s
+NO-EXPORT:  ExportTableRVA: 0x0
+NO-EXPORT:  ExportTableSize: 0x0
+NO-EXPORT:  HybridObject {
+NO-EXPORT:    ExportTableRVA: 0x0
+NO-EXPORT:    ExportTableSize: 0x0
+NO-EXPORT:  }
+
+# -defarm64native is ignored on ARM64 target.
+
+RUN: lld-link -machine:arm64 -dll -out:out-arm64-def.dll arm64-func.obj -defarm64native:invalid.def -def:func.def -noentry 2>&1 | count 0
+
 # Export using both the native and EC .edata sections.
 
 RUN: lld-link -machine:arm64x -dll -out:out-edata-both.dll arm64ec-func.obj arm64-func.obj \