[lld] Define __arm64x_native_entrypoint symbol.

Author: cjacek

lld/COFF/Driver.cpp

@@ -2447,6 +2447,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   if (isArm64EC(config->machine)) {
     ctx.symtab.addAbsolute("__arm64x_extra_rfe_table", 0);
     ctx.symtab.addAbsolute("__arm64x_extra_rfe_table_size", 0);
+    ctx.symtab.addAbsolute("__arm64x_native_entrypoint", 0);
     ctx.symtab.addAbsolute("__arm64x_redirection_metadata", 0);
     ctx.symtab.addAbsolute("__arm64x_redirection_metadata_count", 0);
     ctx.symtab.addAbsolute("__hybrid_auxiliary_iat", 0);

lld/COFF/Writer.cpp

@@ -2306,6 +2306,9 @@ void Writer::setECSymbols() {
   replaceSymbol<DefinedSynthetic>(
       iatCopySym, "__hybrid_auxiliary_iat_copy",
       idata.auxIatCopy.empty() ? nullptr : idata.auxIatCopy.front());
+
+  Symbol *sym = ctx.symtab.findUnderscore("__arm64x_native_entrypoint");
+  cast<DefinedAbsolute>(sym)->setVA(ctx.config.imageBase);
 }
 
 // Write section contents to a mmap'ed file.

lld/test/COFF/Inputs/loadconfig-arm64ec.s

@@ -75,7 +75,7 @@ __chpe_metadata:
         .rva __os_arm64x_check_call
         .rva __os_arm64x_check_icall
         .rva __os_arm64x_check_icall_cfg
-        .word 0 // __arm64x_native_entrypoint
+        .rva __arm64x_native_entrypoint
         .rva __hybrid_auxiliary_iat
         .word __x64_code_ranges_to_entry_points_count
         .word __arm64x_redirection_metadata_count