[lld] [LLD][COFF] Redirect __imp_ Symbols to __imp_aux_ on ARM64EC for x64 sections (PR #108608)

[Martin Storsjö via llvm-commits]

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@@ -587,6 +591,19 @@ void SymbolTable::initializeECThunks() {
       sym = exitThunks.lookup(file->impECSym);
     file->impchkThunk->exitThunk = dyn_cast_or_null<Defined>(sym);
   }
+
+  // On ARM64EC, the __imp_ symbol references the auxiliary IAT, while the
+  // __imp_aux_ symbol references the regular IAT. However, x86_64 code expects
+  // both to reference the regular IAT, so adjust the symbol if necessary.
+  parallelForEach(ctx.objFileInstances, [&](ObjFile *file) {
+    if (file->getMachineType() != AMD64)
+      return;
+    for (auto &sym : file->getMutableSymbols()) {
+      auto impSym = dyn_cast_or_null<DefinedImportData>(sym);
+      if (impSym && impSym->file->impchkThunk && sym == impSym->file->impECSym)
+        sym = impSym->file->impSym;
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mstorsjo wrote:

So, this doesn't change the `Symbol` itself, which would affect every reference to the symbol in the link, but just makes this particular `InputObject` point to another symbol instead? That sounds reasonable.

https://github.com/llvm/llvm-project/pull/108608