[ELF] - Fix for: bug 30237 - lld does not implement -f option

[grimar]

Summary

From PR30237 description:

FreeBSD's libstdc++ build (used on tier-2 architectures) uses GNU ld's
-f <name> option, which sets the DT_AUXILIARY field to the specified name.
Multiple -f options may be specified and the DT_AUXILIARY entries
will be added in the order in which they appear.

Patch implements that option.

[ruiu]

LGTM

ELF/OutputSections.cpp

653

nit: Since the scope is just two lines, I'd give even shorter name, say S.

ELF/Config.h

struct Configuration {
   llvm::StringRef Init;
   llvm::StringRef LtoAAPipeline;
   llvm::StringRef LtoNewPmPasses;
   llvm::StringRef OutputFile;
   llvm::StringRef SoName;
   llvm::StringRef Sysroot;
   std::string RPath;
   std::vector<VersionDefinition> VersionDefinitions;
+  std::vector<llvm::StringRef> AuxiliaryList;
   std::vector<llvm::StringRef> DynamicList;
   std::vector<llvm::StringRef> SearchPaths;
   std::vector<llvm::StringRef> Undefined;
   std::vector<SymbolVersion> VersionScriptGlobals;
   std::vector<uint8_t> BuildIdVector;
   bool AllowMultipleDefinition;
   bool AsNeeded = false;
   bool Bsymbolic;

ELF/Driver.cpp

if (S == "md5") {
       Config->BuildIdVector = parseHex(S.substr(2));
     } else {
       error("unknown --build-id style: " + S);
     }
   }
 
   Config->OFormatBinary = isOutputFormatBinary(Args);
 
+  for (auto *Arg : Args.filtered(OPT_auxiliary))
+    Config->AuxiliaryList.push_back(Arg->getValue());
+  if (!Config->Shared && !Config->AuxiliaryList.empty())
+    error("-f may not be used without -shared");
+
   for (auto *Arg : Args.filtered(OPT_undefined))
     Config->Undefined.push_back(Arg->getValue());
 
   Config->UnresolvedSymbols = getUnresolvedSymbolOption(Args);
 
   if (auto *Arg = Args.getLastArg(OPT_dynamic_list))
     if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
       parseDynamicList(*Buffer);

ELF/Options.td

 include "llvm/Option/OptParser.td"
 
 // For options whose names are multiple letters, either one dash or
 // two can precede the option name except those that start with 'o'.
 class F<string name>: Flag<["--", "-"], name>;
 class J<string name>: Joined<["--", "-"], name>;
 class S<string name>: Separate<["--", "-"], name>;
 class JS<string name>: JoinedOrSeparate<["--", "-"], name>;
 
+def auxiliary: S<"auxiliary">, HelpText<"Set DT_AUXILIARY field to the specified name">;
+
 def Bsymbolic: F<"Bsymbolic">, HelpText<"Bind defined symbols locally">;
 
 def Bsymbolic_functions: F<"Bsymbolic-functions">,
   HelpText<"Bind defined function symbols locally">;
 
 def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 
 def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;

 
 def wrap: S<"wrap">, MetaVarName<"<symbol>">,
   HelpText<"Use wrapper functions for symbol">;
 
 def z: JoinedOrSeparate<["-"], "z">, MetaVarName<"<option>">,
   HelpText<"Linker option extensions">;
 
 // Aliases
+def alias_auxiliary: Separate<["-"], "f">, Alias<auxiliary>;
 def alias_Bdynamic_call_shared: F<"call_shared">, Alias<Bdynamic>;
 def alias_Bdynamic_dy: F<"dy">, Alias<Bdynamic>;
 def alias_Bstatic_dn: F<"dn">, Alias<Bstatic>;
 def alias_Bstatic_non_shared: F<"non_shared">, Alias<Bstatic>;
 def alias_Bstatic_static: F<"static">, Alias<Bstatic>;
 def alias_L__library_path: J<"library-path=">, Alias<L>;
 def alias_discard_all_x: Flag<["-"], "x">, Alias<discard_all>;
 def alias_discard_locals_X: Flag<["-"], "X">, Alias<discard_locals>;

ELF/OutputSections.cpp

template <class ELFT> void DynamicSection<ELFT>::finalize() {
 
   Elf_Shdr &Header = this->Header;
   Header.sh_link = Out<ELFT>::DynStrTab->SectionIndex;
 
   auto Add = [=](Entry E) { Entries.push_back(E); };
 
   // Add strings. We know that these are the last strings to be added to
   // DynStrTab and doing this here allows this function to set DT_STRSZ.
+  for (StringRef Aux : Config->AuxiliaryList)
+    Add({DT_AUXILIARY, Out<ELFT>::DynStrTab->addString(Aux)});
   if (!Config->RPath.empty())
     Add({Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
          Out<ELFT>::DynStrTab->addString(Config->RPath)});
   for (const std::unique_ptr<SharedFile<ELFT>> &F :
        Symtab<ELFT>::X->getSharedFiles())
     if (F->isNeeded())
       Add({DT_NEEDED, Out<ELFT>::DynStrTab->addString(F->getSoName())});
   if (!Config->SoName.empty())

test/ELF/auxiliary.s

+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: ld.lld %t.o -shared -f aaa --auxiliary bbb -o %t
+# RUN: llvm-readobj --dynamic-table %t | FileCheck %s
+
+# CHECK:      DynamicSection [
+# CHECK-NEXT: Tag                Type          Name/Value
+# CHECK-NEXT: 0x000000007FFFFFFD AUXILIARY     Auxiliary library: [aaa]
+# CHECK-NEXT: 0x000000007FFFFFFD AUXILIARY     Auxiliary library: [bbb]
+
+# RUN: not ld.lld %t.o -f aaa --auxiliary bbb -o %t 2>&1 \
+# RUN:    | FileCheck -check-prefix=ERR %s
+# ERR: -f may not be used without -shared