[lld][WebAssembly] Handle stub symbol dependencies when an explicit import name is used (#80169)

Author: sbc100

lld/test/wasm/Inputs/libstub.so

@@ -1,6 +1,6 @@
 #STUB
 # This is a comment
-foo: foodep1,foodep2
+foo_import: foodep1,foodep2
 # This symbols as no dependencies
 bar
 baz: bazdep

lld/test/wasm/stub-library-archive.s

@@ -14,6 +14,7 @@
 # depeds on baz which is also defined in libstub.so.
 
 .functype foo () -> ()
+.import_name foo, foo_import
 
 .globl _start
 _start:

lld/test/wasm/stub-library.s

@@ -6,15 +6,12 @@
 # RUN: not wasm-ld %t.o %p/Inputs/libstub-missing-dep.so -o %t.wasm 2>&1 | FileCheck --check-prefix=MISSING-DEP %s
 
 # When the dependencies are missing the link fails
-# RUN: not wasm-ld %t.o %p/Inputs/libstub-missing-sym.so -o %t.wasm 2>&1 | FileCheck --check-prefix=MISSING-SYM %s
-
 # MISSING-DEP: libstub-missing-dep.so: undefined symbol: missing_dep. Required by foo
 # MISSING-DEP: libstub-missing-dep.so: undefined symbol: missing_dep2. Required by foo
 
-# MISSING-SYM: undefined symbol: foo
-
 # The function foo is defined in libstub.so but depend on foodep1 and foodep2
 .functype foo () -> ()
+.import_name foo, foo_import
 
 .globl foodep1
 foodep1:

lld/wasm/Driver.cpp

@@ -955,6 +955,47 @@ static void processStubLibrariesPreLTO() {
   }
 }
 
+static bool addStubSymbolDeps(const StubFile *stub_file, Symbol *sym,
+                              ArrayRef<StringRef> deps) {
+  // The first stub library to define a given symbol sets this and
+  // definitions in later stub libraries are ignored.
+  if (sym->forceImport)
+    return false; // Already handled
+  sym->forceImport = true;
+  if (sym->traced)
+    message(toString(stub_file) + ": importing " + sym->getName());
+  else
+    LLVM_DEBUG(llvm::dbgs() << toString(stub_file) << ": importing "
+                            << sym->getName() << "\n");
+  bool depsAdded = false;
+  for (const auto dep : deps) {
+    auto *needed = symtab->find(dep);
+    if (!needed) {
+      error(toString(stub_file) + ": undefined symbol: " + dep +
+            ". Required by " + toString(*sym));
+    } else if (needed->isUndefined()) {
+      error(toString(stub_file) + ": undefined symbol: " + toString(*needed) +
+            ". Required by " + toString(*sym));
+    } else {
+      if (needed->traced)
+        message(toString(stub_file) + ": exported " + toString(*needed) +
+                " due to import of " + sym->getName());
+      else
+        LLVM_DEBUG(llvm::dbgs()
+                   << "force export: " << toString(*needed) << "\n");
+      needed->forceExport = true;
+      if (auto *lazy = dyn_cast<LazySymbol>(needed)) {
+        depsAdded = true;
+        lazy->extract();
+        if (!config->whyExtract.empty())
+          ctx.whyExtractRecords.emplace_back(toString(stub_file),
+                                             sym->getFile(), *sym);
+      }
+    }
+  }
+  return depsAdded;
+}
+
 static void processStubLibraries() {
   log("-- processStubLibraries");
   bool depsAdded = false;
@@ -963,49 +1004,28 @@ static void processStubLibraries() {
     for (auto &stub_file : ctx.stubFiles) {
       LLVM_DEBUG(llvm::dbgs()
                  << "processing stub file: " << stub_file->getName() << "\n");
+
+      // First look for any imported symbols that directly match
+      // the names of the stub imports
       for (auto [name, deps]: stub_file->symbolDependencies) {
         auto* sym = symtab->find(name);
-        if (!sym || !sym->isUndefined()) {
+        if (sym && sym->isUndefined()) {
+          depsAdded |= addStubSymbolDeps(stub_file, sym, deps);
+        } else {
           if (sym && sym->traced)
             message(toString(stub_file) + ": stub symbol not needed: " + name);
           else
-            LLVM_DEBUG(llvm::dbgs() << "stub symbol not needed: `" << name << "`\n");
-          continue;
+            LLVM_DEBUG(llvm::dbgs()
+                       << "stub symbol not needed: `" << name << "`\n");
         }
-        // The first stub library to define a given symbol sets this and
-        // definitions in later stub libraries are ignored.
-        if (sym->forceImport)
-          continue;  // Already handled
-        sym->forceImport = true;
-        if (sym->traced)
-          message(toString(stub_file) + ": importing " + name);
-        else
-          LLVM_DEBUG(llvm::dbgs()
-                     << toString(stub_file) << ": importing " << name << "\n");
-        for (const auto dep : deps) {
-          auto* needed = symtab->find(dep);
-          if (!needed) {
-            error(toString(stub_file) + ": undefined symbol: " + dep +
-                  ". Required by " + toString(*sym));
-          } else if (needed->isUndefined()) {
-            error(toString(stub_file) +
-                  ": undefined symbol: " + toString(*needed) +
-                  ". Required by " + toString(*sym));
-          } else {
-            if (needed->traced)
-              message(toString(stub_file) + ": exported " + toString(*needed) +
-                      " due to import of " + name);
-            else
-              LLVM_DEBUG(llvm::dbgs()
-                         << "force export: " << toString(*needed) << "\n");
-            needed->forceExport = true;
-            if (auto *lazy = dyn_cast<LazySymbol>(needed)) {
-              depsAdded = true;
-              lazy->extract();
-              if (!config->whyExtract.empty())
-                ctx.whyExtractRecords.emplace_back(stub_file->getName(),
-                                                   sym->getFile(), *sym);
-            }
+      }
+
+      // Secondly looks for any symbols with an `importName` that matches
+      for (Symbol *sym : symtab->symbols()) {
+        if (sym->isUndefined() && sym->importName.has_value()) {
+          auto it = stub_file->symbolDependencies.find(sym->importName.value());
+          if (it != stub_file->symbolDependencies.end()) {
+            depsAdded |= addStubSymbolDeps(stub_file, sym, it->second);
           }
         }
       }