[lld/mac] Move handling of special undefineds later

[thakis]

Summary

treatUndefinedSymbol() was previously called before gatherInputSections()
and markLive() for these special symbols, but after them for normal
undefineds.

For PR50760, treatUndefinedSymbol() will have to potentially create
sections, so it's good to move treatUndefinedSymbol() for special
undefineds later, so that it can assume that gatherInputSections()
and markLive() has already been called always.

No intended behavior change, but part of PR50760 (and covered in
tests in the patch for the full feature).

[int3]

lgtm

lld/MachO/Driver.cpp

if (config->timeTraceEnabled)
 
     compileBitcodeFiles();
     replaceCommonSymbols();
 
     StringRef orderFile = args.getLastArgValue(OPT_order_file);
     if (!orderFile.empty())
       parseOrderFile(orderFile);
 
-    if (config->entry)
-      if (auto *undefined = dyn_cast<Undefined>(config->entry))
-        treatUndefinedSymbol(*undefined, "the entry point");
-
-    // FIXME: This prints symbols that are undefined both in input files and
-    // via -u flag twice.
-    for (const Symbol *sym : config->explicitUndefineds) {
-      if (const auto *undefined = dyn_cast<Undefined>(sym))
-        treatUndefinedSymbol(*undefined, "-u");
-    }
-    // Literal exported-symbol names must be defined, but glob
-    // patterns need not match.
-    for (const CachedHashStringRef &cachedName :
-         config->exportedSymbols.literals) {
-      if (const Symbol *sym = symtab->find(cachedName))
-        if (const auto *undefined = dyn_cast<Undefined>(sym))
-          treatUndefinedSymbol(*undefined, "-exported_symbol(s_list)");
-    }
-
     referenceStubBinder();
 
     // FIXME: should terminate the link early based on errors encountered so
     // far?
 
     createSyntheticSections();
     createSyntheticSymbols();
 

lld/MachO/Writer.cpp

 
 namespace {
 class LCUuid;
 
 class Writer {
 public:
   Writer() : buffer(errorHandler().outputBuffer) {}
 
+  void treatSpecialUndefineds();
   void scanRelocations();
   void scanSymbols();
   template <class LP> void createOutputSections();
   template <class LP> void createLoadCommands();
   void finalizeAddresses();
   void finalizeLinkEditSegment();
   void assignAddresses(OutputSegment *);
 
void writeTo(uint8_t *buf) const override {
     c->datasize = section->getSize();
   }
 
   CodeSignatureSection *section;
 };
 
 } // namespace
 
+void Writer::treatSpecialUndefineds() {
+  if (config->entry)
+    if (auto *undefined = dyn_cast<Undefined>(config->entry))
+      treatUndefinedSymbol(*undefined, "the entry point");
+
+  // FIXME: This prints symbols that are undefined both in input files and
+  // via -u flag twice.
+  for (const Symbol *sym : config->explicitUndefineds) {
+    if (const auto *undefined = dyn_cast<Undefined>(sym))
+      treatUndefinedSymbol(*undefined, "-u");
+  }
+  // Literal exported-symbol names must be defined, but glob
+  // patterns need not match.
+  for (const CachedHashStringRef &cachedName :
+       config->exportedSymbols.literals) {
+    if (const Symbol *sym = symtab->find(cachedName))
+      if (const auto *undefined = dyn_cast<Undefined>(sym))
+        treatUndefinedSymbol(*undefined, "-exported_symbol(s_list)");
+  }
+}
+
 // Add stubs and bindings where necessary (e.g. if the symbol is a
 // DylibSymbol.)
 static void prepareBranchTarget(Symbol *sym) {
   if (auto *dysym = dyn_cast<DylibSymbol>(sym)) {
     if (in.stubs->addEntry(dysym)) {
       if (sym->isWeakDef()) {
         in.binding->addEntry(dysym, in.lazyPointers->isec,
                              sym->stubsIndex * target->wordSize);
void Writer::writeOutputFile() {
   writeUuid();
   writeCodeSignature();
 
   if (auto e = buffer->commit())
     error("failed to write to the output file: " + toString(std::move(e)));
 }
 
 template <class LP> void Writer::run() {
+  treatSpecialUndefineds();
   if (config->entry && !isa<Undefined>(config->entry))
     prepareBranchTarget(config->entry);
   scanRelocations();
   if (in.stubHelper->isNeeded())
     in.stubHelper->setup();
   scanSymbols();
   createOutputSections<LP>();
   // After this point, we create no new segments; HOWEVER, we might