9 files changed, 52 insertions, 11 deletions

diff --git a/contrib/llvm/tools/lld/ELF/Config.h b/contrib/llvm/tools/lld/ELF/Config.h
index fb29396926bf..e8bb6bf70ee0 100644
--- a/contrib/llvm/tools/lld/ELF/Config.h
+++ b/contrib/llvm/tools/lld/ELF/Config.h
@@ -122,6 +122,7 @@ struct Configuration {
                   uint64_t>
       CallGraphProfile;
   bool AllowMultipleDefinition;
+  bool AllowShlibUndefined;
   bool AndroidPackDynRelocs;
   bool ARMHasBlx = false;
   bool ARMHasMovtMovw = false;
diff --git a/contrib/llvm/tools/lld/ELF/Driver.cpp b/contrib/llvm/tools/lld/ELF/Driver.cpp
index 407f1734f143..3e565bcb8732 100644
--- a/contrib/llvm/tools/lld/ELF/Driver.cpp
+++ b/contrib/llvm/tools/lld/ELF/Driver.cpp
@@ -758,6 +758,9 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
       Args.hasFlag(OPT_allow_multiple_definition,
                    OPT_no_allow_multiple_definition, false) ||
       hasZOption(Args, "muldefs");
+  Config->AllowShlibUndefined =
+      Args.hasFlag(OPT_allow_shlib_undefined, OPT_no_allow_shlib_undefined,
+                   Args.hasArg(OPT_shared));
   Config->AuxiliaryList = args::getStrings(Args, OPT_auxiliary);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
   Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
diff --git a/contrib/llvm/tools/lld/ELF/InputFiles.cpp b/contrib/llvm/tools/lld/ELF/InputFiles.cpp
index bc7e61072e64..c5922d3155d9 100644
--- a/contrib/llvm/tools/lld/ELF/InputFiles.cpp
+++ b/contrib/llvm/tools/lld/ELF/InputFiles.cpp
@@ -865,7 +865,7 @@ SharedFile<ELFT>::SharedFile(MemoryBufferRef M, StringRef DefaultSoName)
 
 // Partially parse the shared object file so that we can call
 // getSoName on this object.
-template <class ELFT> void SharedFile<ELFT>::parseSoName() {
+template <class ELFT> void SharedFile<ELFT>::parseDynamic() {
   const Elf_Shdr *DynamicSec = nullptr;
   const ELFFile<ELFT> Obj = this->getObj();
   ArrayRef<Elf_Shdr> Sections = CHECK(Obj.sections(), this);
@@ -902,12 +902,16 @@ template <class ELFT> void SharedFile<ELFT>::parseSoName() {
   ArrayRef<Elf_Dyn> Arr =
       CHECK(Obj.template getSectionContentsAsArray<Elf_Dyn>(DynamicSec), this);
   for (const Elf_Dyn &Dyn : Arr) {
-    if (Dyn.d_tag == DT_SONAME) {
+    if (Dyn.d_tag == DT_NEEDED) {
+      uint64_t Val = Dyn.getVal();
+      if (Val >= this->StringTable.size())
+        fatal(toString(this) + ": invalid DT_NEEDED entry");
+      DtNeeded.push_back(this->StringTable.data() + Val);
+    } else if (Dyn.d_tag == DT_SONAME) {
       uint64_t Val = Dyn.getVal();
       if (Val >= this->StringTable.size())
         fatal(toString(this) + ": invalid DT_SONAME entry");
       SoName = this->StringTable.data() + Val;
-      return;
     }
   }
 }
@@ -975,7 +979,7 @@ uint32_t SharedFile<ELFT>::getAlignment(ArrayRef<Elf_Shdr> Sections,
   return (Ret > UINT32_MAX) ? 0 : Ret;
 }
 
-// Fully parse the shared object file. This must be called after parseSoName().
+// Fully parse the shared object file. This must be called after parseDynamic().
 //
 // This function parses symbol versions. If a DSO has version information,
 // the file has a ".gnu.version_d" section which contains symbol version
diff --git a/contrib/llvm/tools/lld/ELF/InputFiles.h b/contrib/llvm/tools/lld/ELF/InputFiles.h
index d7cbbc67a365..db9097fb868e 100644
--- a/contrib/llvm/tools/lld/ELF/InputFiles.h
+++ b/contrib/llvm/tools/lld/ELF/InputFiles.h
@@ -323,6 +323,7 @@ template <class ELFT> class SharedFile : public ELFFileBase<ELFT> {
 
 public:
   std::vector<const Elf_Verdef *> Verdefs;
+  std::vector<StringRef> DtNeeded;
   std::string SoName;
 
   static bool classof(const InputFile *F) {
@@ -331,7 +332,7 @@ public:
 
   SharedFile(MemoryBufferRef M, StringRef DefaultSoName);
 
-  void parseSoName();
+  void parseDynamic();
   void parseRest();
   uint32_t getAlignment(ArrayRef<Elf_Shdr> Sections, const Elf_Sym &Sym);
   std::vector<const Elf_Verdef *> parseVerdefs();
@@ -349,6 +350,9 @@ public:
   // data structures in the output file.
   std::map<const Elf_Verdef *, NeededVer> VerdefMap;
 
+  // Used for --no-allow-shlib-undefined.
+  bool AllNeededIsKnown;
+
   // Used for --as-needed
   bool IsNeeded;
 };
diff --git a/contrib/llvm/tools/lld/ELF/Options.td b/contrib/llvm/tools/lld/ELF/Options.td
index 439fe341644c..3a19b230780a 100644
--- a/contrib/llvm/tools/lld/ELF/Options.td
+++ b/contrib/llvm/tools/lld/ELF/Options.td
@@ -63,6 +63,10 @@ defm allow_multiple_definition: B<"allow-multiple-definition",
     "Allow multiple definitions",
     "Do not allow multiple definitions (default)">;
 
+defm allow_shlib_undefined: B<"allow-shlib-undefined",
+    "Allow unresolved references in shared libraries (default when linking a shared library)",
+    "Do not allow unresolved references in shared libraries (default when linking an executable)">;
+
 defm apply_dynamic_relocs: B<"apply-dynamic-relocs",
     "Apply link-time values for dynamic relocations",
     "Do not apply link-time values for dynamic relocations (default)">;
@@ -492,12 +496,10 @@ def plugin_opt_thinlto: J<"plugin-opt=thinlto">;
 def plugin_opt_slash: J<"plugin-opt=/">;
 
 // Options listed below are silently ignored for now for compatibility.
-def: F<"allow-shlib-undefined">;
 def: F<"detect-odr-violations">;
 def: Flag<["-"], "g">;
 def: F<"long-plt">;
 def: F<"no-add-needed">;
-def: F<"no-allow-shlib-undefined">;
 def: F<"no-copy-dt-needed-entries">;
 def: F<"no-ctors-in-init-array">;
 def: F<"no-keep-memory">;
diff --git a/contrib/llvm/tools/lld/ELF/SymbolTable.cpp b/contrib/llvm/tools/lld/ELF/SymbolTable.cpp
index 7615e12199fa..bf1bf4511e96 100644
--- a/contrib/llvm/tools/lld/ELF/SymbolTable.cpp
+++ b/contrib/llvm/tools/lld/ELF/SymbolTable.cpp
@@ -93,7 +93,7 @@ template <class ELFT> void SymbolTable::addFile(InputFile *File) {
   // .so file
   if (auto *F = dyn_cast<SharedFile<ELFT>>(File)) {
     // DSOs are uniquified not by filename but by soname.
-    F->parseSoName();
+    F->parseDynamic();
     if (errorCount())
       return;
 
diff --git a/contrib/llvm/tools/lld/ELF/SymbolTable.h b/contrib/llvm/tools/lld/ELF/SymbolTable.h
index 898185fc9612..675a4915598f 100644
--- a/contrib/llvm/tools/lld/ELF/SymbolTable.h
+++ b/contrib/llvm/tools/lld/ELF/SymbolTable.h
@@ -80,6 +80,9 @@ public:
 
   void handleDynamicList();
 
+  // Set of .so files to not link the same shared object file more than once.
+  llvm::DenseMap<StringRef, InputFile *> SoNames;
+
 private:
   std::pair<Symbol *, bool> insertName(StringRef Name);
 
@@ -107,9 +110,6 @@ private:
   // is used to uniquify them.
   llvm::DenseSet<llvm::CachedHashStringRef> ComdatGroups;
 
-  // Set of .so files to not link the same shared object file more than once.
-  llvm::DenseMap<StringRef, InputFile *> SoNames;
-
   // A map from demangled symbol names to their symbol objects.
   // This mapping is 1:N because two symbols with different versions
   // can have the same name. We use this map to handle "extern C++ {}"
diff --git a/contrib/llvm/tools/lld/ELF/Writer.cpp b/contrib/llvm/tools/lld/ELF/Writer.cpp
index 5c987ca5a813..dcabf52e64f3 100644
--- a/contrib/llvm/tools/lld/ELF/Writer.cpp
+++ b/contrib/llvm/tools/lld/ELF/Writer.cpp
@@ -1668,6 +1668,27 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
   if (In.Iplt && !In.Iplt->empty())
     In.Iplt->addSymbols();
 
+  if (!Config->AllowShlibUndefined) {
+    // Error on undefined symbols in a shared object, if all of its DT_NEEDED
+    // entires are seen. These cases would otherwise lead to runtime errors
+    // reported by the dynamic linker.
+    //
+    // ld.bfd traces all DT_NEEDED to emulate the logic of the dynamic linker to
+    // catch more cases. That is too much for us. Our approach resembles the one
+    // used in ld.gold, achieves a good balance to be useful but not too smart.
+    for (InputFile *File : SharedFiles) {
+      SharedFile<ELFT> *F = cast<SharedFile<ELFT>>(File);
+      F->AllNeededIsKnown = llvm::all_of(F->DtNeeded, [&](StringRef Needed) {
+        return Symtab->SoNames.count(Needed);
+      });
+    }
+    for (Symbol *Sym : Symtab->getSymbols())
+      if (Sym->isUndefined() && !Sym->isWeak())
+        if (auto *F = dyn_cast_or_null<SharedFile<ELFT>>(Sym->File))
+          if (F->AllNeededIsKnown)
+            error(toString(F) + ": undefined reference to " + toString(*Sym));
+  }
+
   // Now that we have defined all possible global symbols including linker-
   // synthesized ones. Visit all symbols to give the finishing touches.
   for (Symbol *Sym : Symtab->getSymbols()) {
diff --git a/contrib/llvm/tools/lld/docs/ld.lld.1 b/contrib/llvm/tools/lld/docs/ld.lld.1
index 04bf19d6b23c..6fd746f030dd 100644
--- a/contrib/llvm/tools/lld/docs/ld.lld.1
+++ b/contrib/llvm/tools/lld/docs/ld.lld.1
@@ -56,6 +56,9 @@ option.
 .It Fl -allow-multiple-definition
 Do not error if a symbol is defined multiple times.
 The first definition will be used.
+.It Fl -allow-shlib-undefined
+Allow unresolved references in shared libraries.
+This option is enabled by default when linking a shared library.
 .It Fl -apply-dynamic-relocs
 Apply link-time values for dynamic relocations.
 .It Fl -as-needed
@@ -252,6 +255,9 @@ Set target emulation.
 .It Fl -Map Ns = Ns Ar file , Fl M Ar file
 Print a link map to
 .Ar file .
+.It Fl -no-allow-shlib-undefined
+Do not allow unresolved references in shared libraries.
+This option is enabled by default when linking an executable.
 .It Fl -no-as-needed
 Always set
 .Dv DT_NEEDED