1 files changed, 91 insertions, 30 deletions

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index 0c33e47c29d..8b8a3b1d4f9 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -678,27 +678,24 @@ static std::string maybeReportDiscarded(Undefined &Sym) {
   return Msg;
 }
 
-// Report an undefined symbol if necessary.
-// Returns true if this function printed out an error message.
-template <class ELFT>
-static bool maybeReportUndefined(Symbol &Sym, InputSectionBase &Sec,
-                                 uint64_t Offset) {
-  if (!Sym.isUndefined() || Sym.isWeak())
-    return false;
+// Undefined diagnostics are collected in a vector and emitted once all of
+// them are known, so that some postprocessing on the list of undefined symbols
+// can happen before lld emits diagnostics.
+struct UndefinedDiag {
+  Symbol *Sym;
+  struct Loc {
+    InputSectionBase *Sec;
+    uint64_t Offset;
+  };
+  std::vector<Loc> Locs;
+  bool IsWarning;
+};
 
-  bool CanBeExternal = !Sym.isLocal() && Sym.computeBinding() != STB_LOCAL &&
-                       Sym.Visibility == STV_DEFAULT;
-  if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore && CanBeExternal)
-    return false;
+static std::vector<UndefinedDiag> Undefs;
 
-  // clang (as of 2019-06-12) / gcc (as of 8.2.1) PPC64 may emit a .rela.toc
-  // which references a switch table in a discarded .rodata/.text section. The
-  // .toc and the .rela.toc are incorrectly not placed in the comdat. The ELF
-  // spec says references from outside the group to a STB_LOCAL symbol are not
-  // allowed. Work around the bug.
-  if (Config->EMachine == EM_PPC64 &&
-      cast<Undefined>(Sym).DiscardedSecIdx != 0 && Sec.Name == ".toc")
-    return false;
+template <class ELFT>
+static void reportUndefinedSymbol(const UndefinedDiag &Undef) {
+  Symbol &Sym = *Undef.Sym;
 
   auto Visibility = [&]() -> std::string {
     switch (Sym.Visibility) {
@@ -717,24 +714,83 @@ static bool maybeReportUndefined(Symbol &Sym, InputSectionBase &Sec,
   if (Msg.empty())
     Msg = "undefined " + Visibility() + "symbol: " + toString(Sym);
 
-  Msg += "\n>>> referenced by ";
-  std::string Src = Sec.getSrcMsg(Sym, Offset);
-  if (!Src.empty())
-    Msg += Src + "\n>>>               ";
-  Msg += Sec.getObjMsg(Offset);
+  const size_t MaxUndefReferences = 10;
+  size_t I = 0;
+  for (UndefinedDiag::Loc L : Undef.Locs) {
+    if (I >= MaxUndefReferences)
+      break;
+    InputSectionBase &Sec = *L.Sec;
+    uint64_t Offset = L.Offset;
+
+    Msg += "\n>>> referenced by ";
+    std::string Src = Sec.getSrcMsg(Sym, Offset);
+    if (!Src.empty())
+      Msg += Src + "\n>>>               ";
+    Msg += Sec.getObjMsg(Offset);
+    I++;
+  }
+
+  if (I < Undef.Locs.size())
+    Msg += ("\n>>> referenced " + Twine(Undef.Locs.size() - I) + " more times")
+               .str();
 
   if (Sym.getName().startswith("_ZTV"))
     Msg += "\nthe vtable symbol may be undefined because the class is missing "
            "its key function (see https://lld.llvm.org/missingkeyfunction)";
 
-  if ((Config->UnresolvedSymbols == UnresolvedPolicy::Warn && CanBeExternal) ||
-      Config->NoinhibitExec) {
+  if (Undef.IsWarning)
     warn(Msg);
-    return false;
+  else
+    error(Msg);
+}
+
+template <class ELFT> void elf::reportUndefinedSymbols() {
+  // Find the first "undefined symbol" diagnostic for each diagnostic, and
+  // collect all "referenced from" lines at the first diagnostic.
+  DenseMap<Symbol *, UndefinedDiag *> FirstRef;
+  for (UndefinedDiag &Undef : Undefs) {
+    assert(Undef.Locs.size() == 1);
+    if (UndefinedDiag *Canon = FirstRef.lookup(Undef.Sym)) {
+      Canon->Locs.push_back(Undef.Locs[0]);
+      Undef.Locs.clear();
+    } else
+      FirstRef[Undef.Sym] = &Undef;
   }
 
-  error(Msg);
-  return true;
+  for (const UndefinedDiag &Undef : Undefs) {
+    if (!Undef.Locs.empty())
+      reportUndefinedSymbol<ELFT>(Undef);
+  }
+  Undefs.clear();
+}
+
+// Report an undefined symbol if necessary.
+// Returns true if the undefined symbol will produce an error message.
+template <class ELFT>
+static bool maybeReportUndefined(Symbol &Sym, InputSectionBase &Sec,
+                                 uint64_t Offset) {
+  if (!Sym.isUndefined() || Sym.isWeak())
+    return false;
+
+  bool CanBeExternal = !Sym.isLocal() && Sym.computeBinding() != STB_LOCAL &&
+                       Sym.Visibility == STV_DEFAULT;
+  if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore && CanBeExternal)
+    return false;
+
+  // clang (as of 2019-06-12) / gcc (as of 8.2.1) PPC64 may emit a .rela.toc
+  // which references a switch table in a discarded .rodata/.text section. The
+  // .toc and the .rela.toc are incorrectly not placed in the comdat. The ELF
+  // spec says references from outside the group to a STB_LOCAL symbol are not
+  // allowed. Work around the bug.
+  if (Config->EMachine == EM_PPC64 &&
+      cast<Undefined>(Sym).DiscardedSecIdx != 0 && Sec.Name == ".toc")
+    return false;
+
+  bool IsWarning =
+      (Config->UnresolvedSymbols == UnresolvedPolicy::Warn && CanBeExternal) ||
+      Config->NoinhibitExec;
+  Undefs.push_back({&Sym, {{&Sec, Offset}}, IsWarning});
+  return !IsWarning;
 }
 
 // MIPS N32 ABI treats series of successive relocations with the same offset
@@ -1734,7 +1790,8 @@ bool ThunkCreator::createThunks(ArrayRef<OutputSection *> OutputSections) {
             Rel.Sym = T->getThunkTargetSym();
             Rel.Expr = fromPlt(Rel.Expr);
 
-            // Addend of R_PPC_PLTREL24 should be ignored after changing to R_PC.
+            // The addend of R_PPC_PLTREL24 should be ignored after changing to
+            // R_PC.
             if (Config->EMachine == EM_PPC && Rel.Type == R_PPC_PLTREL24)
               Rel.Addend = 0;
           }
@@ -1756,3 +1813,7 @@ template void elf::scanRelocations<ELF32LE>(InputSectionBase &);
 template void elf::scanRelocations<ELF32BE>(InputSectionBase &);
 template void elf::scanRelocations<ELF64LE>(InputSectionBase &);
 template void elf::scanRelocations<ELF64BE>(InputSectionBase &);
+template void elf::reportUndefinedSymbols<ELF32LE>();
+template void elf::reportUndefinedSymbols<ELF32BE>();
+template void elf::reportUndefinedSymbols<ELF64LE>();
+template void elf::reportUndefinedSymbols<ELF64BE>();