[LLD][COFF] Do as many passes of resolveRemainingUndefines as necessary for undefined lazy symbols

Author: glandium

lld/COFF/Driver.cpp

@@ -2601,7 +2601,9 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
     createECExportThunks();
 
   // Resolve remaining undefined symbols and warn about imported locals.
-  ctx.symtab.resolveRemainingUndefines();
+  while (ctx.symtab.resolveRemainingUndefines())
+    run();
+
   if (errorCount())
     return;
 

lld/COFF/SymbolTable.cpp

@@ -479,10 +479,11 @@ void SymbolTable::reportUnresolvable() {
                        /* localImports */ nullptr, true);
 }
 
-void SymbolTable::resolveRemainingUndefines() {
+bool SymbolTable::resolveRemainingUndefines() {
   llvm::TimeTraceScope timeScope("Resolve remaining undefined symbols");
   SmallPtrSet<Symbol *, 8> undefs;
   DenseMap<Symbol *, Symbol *> localImports;
+  bool foundLazy = false;
 
   for (auto &i : symMap) {
     Symbol *sym = i.second;
@@ -510,6 +511,11 @@ void SymbolTable::resolveRemainingUndefines() {
           undef->resolveWeakAlias();
         }
       }
+      if (imp && imp->isLazy()) {
+        forceLazy(imp);
+        foundLazy = true;
+        continue;
+      }
       if (imp && isa<Defined>(imp)) {
         auto *d = cast<Defined>(imp);
         replaceSymbol<DefinedLocalImport>(sym, ctx, name, d);
@@ -537,6 +543,7 @@ void SymbolTable::resolveRemainingUndefines() {
   reportProblemSymbols(
       ctx, undefs,
       ctx.config.warnLocallyDefinedImported ? &localImports : nullptr, false);
+  return foundLazy;
 }
 
 std::pair<Symbol *, bool> SymbolTable::insert(StringRef name) {

lld/COFF/SymbolTable.h

@@ -57,7 +57,10 @@ class SymbolTable {
   // Try to resolve any undefined symbols and update the symbol table
   // accordingly, then print an error message for any remaining undefined
   // symbols and warn about imported local symbols.
-  void resolveRemainingUndefines();
+  // Returns whether more files might need to be linked in to resolve lazy
+  // symbols, in which case the caller is expected to call the function again
+  // after linking those files.
+  bool resolveRemainingUndefines();
 
   // Load lazy objects that are needed for MinGW automatic import and for
   // doing stdcall fixups.

lld/test/COFF/undefined_lazy.test

@@ -0,0 +1,26 @@
+# REQUIRES: x86
+
+# RUN: split-file %s %t.dir
+# RUN: llvm-mc --filetype=obj -triple=x86_64-windows-msvc %t.dir/foo.s -o %t.foo.obj
+# RUN: llvm-mc --filetype=obj -triple=x86_64-windows-msvc %t.dir/bar.s -o %t.bar.obj
+# RUN: llvm-mc --filetype=obj -triple=x86_64-windows-msvc %t.dir/qux.s -o %t.qux.obj
+# RUN: llvm-lib %t.foo.obj -out:%t.foo.lib
+# RUN: llvm-lib %t.bar.obj -out:%t.bar.lib
+# RUN: lld-link %t.foo.lib %t.bar.lib %t.qux.obj -out:%t.dll -dll
+#
+#--- foo.s
+.text
+.globl foo
+foo:
+  call bar
+#--- bar.s
+.text
+.globl bar
+bar:
+  ret
+#--- qux.s
+.text
+.global _DllMainCRTStartup
+_DllMainCRTStartup:
+  call *__imp_foo(%rip)
+  ret