Warn on nonexistent comdat sections in an /order file.

[ruiu]

Summary

I didn't implement the feature in the original patch because I didn't
come up with an idea to do that easily and efficiently. Turned out that
that is actually easy to implement.

In this patch, we collect comdat sections before gc is run and warn on
nonexistent symbols in an order file.

[pcc]

LGTM

COFF/Driver.cpp

 static void parseOrderFile(StringRef Arg) {
   // For some reason, the MSVC linker requires a filename to be
   // preceded by "@".
   if (!Arg.startswith("@")) {
     error("malformed /order option: '@' missing");
     return;
   }
 
+  // Get a list of all comdat sections for error checking.
+  DenseSet<StringRef> Set;
+  for (Chunk *C : Symtab->getChunks())
+    if (auto *Sec = dyn_cast<SectionChunk>(C))
+      if (Sec->Sym)
+        Set.insert(Sec->Sym->getName());
+
   // Open a file.
   StringRef Path = Arg.substr(1);
   std::unique_ptr<MemoryBuffer> MB = CHECK(
       MemoryBuffer::getFile(Path, -1, false, true), "could not open " + Path);
 
   // Parse a file. An order file contains one symbol per line.
   // All symbols that were not present in a given order file are
   // considered to have the lowest priority 0 and are placed at
   // end of an output section.
   for (std::string S : args::getLines(MB->getMemBufferRef())) {
     if (Config->Machine == I386 && !isDecorated(S))
       S = "_" + S;
+
+    if (Set.count(S) == 0)
+      warn("/order:" + Arg + ": missing symbol: " + S);
+    else
       Config->Order[S] = INT_MIN + Config->Order.size();
   }
 }
 
 void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   // If the first command line argument is "/lib", link.exe acts like lib.exe.
   // We call our own implementation of lib.exe that understands bitcode files.
   if (ArgsArr.size() > 1 && StringRef(ArgsArr[1]).equals_lower("/lib")) {
     if (llvm::libDriverMain(ArgsArr.slice(1)) != 0)
if (Args.hasArg(OPT_dll)) {
       StringRef S = findDefaultEntry();
       if (S.empty())
         fatal("entry point must be defined");
       Config->Entry = addUndefined(S);
       log("Entry name inferred: " + S);
     }
   }
 
-  // Handle /order
-  if (auto *Arg = Args.getLastArg(OPT_order))
-    parseOrderFile(Arg->getValue());
-
   // Handle /export
   for (auto *Arg : Args.filtered(OPT_export)) {
     Export E = parseExport(Arg->getValue());
     if (Config->Machine == I386) {
       if (!isDecorated(E.Name))
         E.Name = Saver.save("_" + E.Name);
       if (!E.ExtName.empty() && !isDecorated(E.ExtName))
         E.ExtName = Saver.save("_" + E.ExtName);
for (auto Pair : Config->AlignComm) {
     CommonChunk *C = DC->getChunk();
     C->Alignment = std::max(C->Alignment, Alignment);
   }
 
   // Windows specific -- Create a side-by-side manifest file.
   if (Config->Manifest == Configuration::SideBySide)
     createSideBySideManifest();
 
+  // Handle /order. We want to do this at this moment because we
+  // need a complete list of comdat sections to warn on nonexistent
+  // functions.
+  if (auto *Arg = Args.getLastArg(OPT_order))
+    parseOrderFile(Arg->getValue());
+
   // Identify unreferenced COMDAT sections.
   if (Config->DoGC)
     markLive(Symtab->getChunks());
 
   // Identify identical COMDAT sections to merge them.
   if (Config->DoICF)
     doICF(Symtab->getChunks());
 

test/COFF/order.test

 # RUN:   -lldmap:- -out:%t.exe | FileCheck -check-prefix=DEFAULT %s
 # DEFAULT: fn2
 # DEFAULT: fn3
 # DEFAULT: unrelated1
 # DEFAULT: unrelated2
 # DEFAULT: fn4
 # DEFAULT: fn1
 
+# RUN: echo fn1 > %t2.order
+# RUN: echo fn2 >> %t2.order
+# RUN: echo fn3 >> %t2.order
+# RUN: echo fn4 >> %t2.order
+# RUN: echo foo >> %t2.order
+# RUN: lld-link -entry:fn1 -subsystem:console -debug %t1.obj %t2.obj \
+# RUN:   -out:%t.exe -order:@%t2.order 2>&1 | FileCheck -check-prefix=WARN %s
+# WARN: warning: /order:{{.*}} missing symbol: foo
+# WARN-NOT: f2
+# WARN-NOT: f3
+# WARN-NOT: f4
+
 --- !COFF
 header:
   Machine:         IMAGE_FILE_MACHINE_AMD64
   Characteristics: [  ]
 sections:
   - Name:            .text
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       16