[lld] [LLD][COFF] Implement support for hybrid IAT on ARM64X (PR #124189)

[Jacek Caban via llvm-commits]

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@@ -717,52 +717,155 @@ class ExportOrdinalChunk : public NonSectionChunk {
 void IdataContents::create(COFFLinkerContext &ctx) {
   std::vector<std::vector<DefinedImportData *>> v = binImports(ctx, imports);
 
+  // Merge compatible EC and native import files in hybrid images.
+  if (ctx.hybridSymtab) {
+    for (std::vector<DefinedImportData *> &syms : v) {
+      // At this point, symbols are sorted by base name, ensuring that
+      // compatible import files, if present, are adjacent.
+      std::vector<DefinedImportData *> hybridSyms;
+      ImportFile *prev = nullptr;
+      for (DefinedImportData *sym : syms) {
+        ImportFile *file = sym->file;
+        if (!prev || file->isEC() == prev->isEC() ||
+            !file->isSameImport(prev)) {
+          hybridSyms.push_back(sym);
+          prev = file;
+          continue;
+        }
+
+        // The native variant exposes a subset of EC symbols and chunks. Use the
+        // EC variant to represent both.
+        if (file->isEC()) {
+          hybridSyms.pop_back();
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cjacek wrote:

> Since the export name is the same, isSameImport() will return true, and they might appear next to each other. I'll add a test for this scenario.

I've pushed a new version that adds a test for this. While experimenting, I noticed that MSVC is buggy when using EXPORTAS in this way. It handles the test I attached here correctly, but I was able to make it import incorrect symbols due to improper merging. It seems that MSVC compares only symbol names rather than import names, which might also explain the previously mentioned issues with NONAME handling. I didn't follow MSVC's approach here and instead kept what I believe to be the correct behavior.

I also added more comments.

https://github.com/llvm/llvm-project/pull/124189