[LLD][COFF] Add support for delay-load imports on ARM64X

For each imported module, emit null-terminated native import entries, followed by
null-terminated EC entries. If a view lacks imports for a given module,
only terminators are emitted. Use ARM64X relocations to skip native entries in
the EC view.

Move delayLoadHelper and tailMergeUnwindInfoChunk to SymbolTable since they are
different for each symbol table.

Author: cjacek

lld/COFF/DLL.cpp

@@ -921,54 +921,89 @@ void DelayLoadContents::create() {
     auto *dir = make<DelayDirectoryChunk>(dllNames.back());
 
     size_t base = addresses.size();
-    Chunk *tm = newTailMergeChunk(ctx.symtab, dir);
-    Chunk *pdataChunk = newTailMergePDataChunk(ctx.symtab, tm);
-    for (DefinedImportData *s : syms) {
-      Chunk *t = newThunkChunk(s, tm);
-      auto *a = make<DelayAddressChunk>(ctx, t);
-      addresses.push_back(a);
-      thunks.push_back(t);
-      StringRef extName = s->getExternalName();
-      if (extName.empty()) {
-        names.push_back(make<OrdinalOnlyChunk>(ctx, s->getOrdinal()));
-      } else {
-        auto *c = make<HintNameChunk>(extName, 0);
-        names.push_back(make<LookupChunk>(ctx, c));
-        hintNames.push_back(c);
-        // Add a synthetic symbol for this load thunk, using the "__imp___load"
-        // prefix, in case this thunk needs to be added to the list of valid
-        // call targets for Control Flow Guard.
-        StringRef symName = saver().save("__imp___load_" + extName);
-        s->loadThunkSym =
-            cast<DefinedSynthetic>(ctx.symtab.addSynthetic(symName, t));
+    ctx.forEachSymtab([&](SymbolTable &symtab) {
+      if (ctx.hybridSymtab && symtab.isEC()) {
+        // For hybrid images, emit null-terminated native import entries
+        // followed by null-terminated EC entries. If a view is missing imports
+        // for a given module, only terminators are emitted. Emit ARM64X
+        // relocations to skip native entries in the EC view.
+        ctx.dynamicRelocs->add(
+            IMAGE_DVRT_ARM64X_FIXUP_TYPE_DELTA, 0,
+            Arm64XRelocVal(dir, offsetof(delay_import_directory_table_entry,
+                                         DelayImportAddressTable)),
+            (addresses.size() - base) * sizeof(uint64_t));
+        ctx.dynamicRelocs->add(
+            IMAGE_DVRT_ARM64X_FIXUP_TYPE_DELTA, 0,
+            Arm64XRelocVal(dir, offsetof(delay_import_directory_table_entry,
+                                         DelayImportNameTable)),
+            (addresses.size() - base) * sizeof(uint64_t));
       }
 
-      if (s->file->impECSym) {
-        auto chunk = make<AuxImportChunk>(s->file);
-        auxIat.push_back(chunk);
-        s->file->impECSym->setLocation(chunk);
+      Chunk *tm = nullptr;
 
-        chunk = make<AuxImportChunk>(s->file);
-        auxIatCopy.push_back(chunk);
-        s->file->auxImpCopySym->setLocation(chunk);
+      for (DefinedImportData *s : syms) {
+        // Process only the symbols belonging to the current symtab.
+        if (symtab.isEC() != s->file->isEC())
+          continue;
+
+        if (!tm) {
+          tm = newTailMergeChunk(symtab, dir);
+          Chunk *pdataChunk = newTailMergePDataChunk(symtab, tm);
+          if (pdataChunk)
+            pdata.push_back(pdataChunk);
+        }
+
+        Chunk *t = newThunkChunk(s, tm);
+        auto *a = make<DelayAddressChunk>(ctx, t);
+        addresses.push_back(a);
+        s->setLocation(a);
+        thunks.push_back(t);
+        StringRef extName = s->getExternalName();
+        if (extName.empty()) {
+          names.push_back(make<OrdinalOnlyChunk>(ctx, s->getOrdinal()));
+        } else {
+          auto *c = make<HintNameChunk>(extName, 0);
+          names.push_back(make<LookupChunk>(ctx, c));
+          hintNames.push_back(c);
+          // Add a synthetic symbol for this load thunk, using the
+          // "__imp___load" prefix, in case this thunk needs to be added to the
+          // list of valid call targets for Control Flow Guard.
+          StringRef symName = saver().save("__imp___load_" + extName);
+          s->loadThunkSym =
+              cast<DefinedSynthetic>(symtab.addSynthetic(symName, t));
+        }
+
+        if (symtab.isEC()) {
+          auto chunk = make<AuxImportChunk>(s->file);
+          auxIat.push_back(chunk);
+          s->file->impECSym->setLocation(chunk);
+
+          chunk = make<AuxImportChunk>(s->file);
+          auxIatCopy.push_back(chunk);
+          s->file->auxImpCopySym->setLocation(chunk);
+        } else if (ctx.hybridSymtab) {
+          // Fill the auxiliary IAT with null chunks for native imports.
+          auxIat.push_back(make<NullChunk>(ctx));
+          auxIatCopy.push_back(make<NullChunk>(ctx));
+        }
       }
-    }
-    thunks.push_back(tm);
-    if (pdataChunk)
-      pdata.push_back(pdataChunk);
-    StringRef tmName =
-        saver().save("__tailMerge_" + syms[0]->getDLLName().lower());
-    ctx.symtab.addSynthetic(tmName, tm);
-    // Terminate with null values.
-    addresses.push_back(make<NullChunk>(ctx, 8));
-    names.push_back(make<NullChunk>(ctx, 8));
-    if (ctx.config.machine == ARM64EC) {
-      auxIat.push_back(make<NullChunk>(ctx, 8));
-      auxIatCopy.push_back(make<NullChunk>(ctx, 8));
-    }
 
-    for (int i = 0, e = syms.size(); i < e; ++i)
-      syms[i]->setLocation(addresses[base + i]);
+      if (tm) {
+        thunks.push_back(tm);
+        StringRef tmName =
+            saver().save("__tailMerge_" + syms[0]->getDLLName().lower());
+        symtab.addSynthetic(tmName, tm);
+      }
+
+      // Terminate with null values.
+      addresses.push_back(make<NullChunk>(ctx, 8));
+      names.push_back(make<NullChunk>(ctx, 8));
+      if (ctx.symtabEC) {
+        auxIat.push_back(make<NullChunk>(ctx, 8));
+        auxIatCopy.push_back(make<NullChunk>(ctx, 8));
+      }
+    });
+
     auto *mh = make<NullChunk>(8, 8);
     moduleHandles.push_back(mh);