[DO NOT COMMIT] Handle -hash-style

lld/ELF/Config.h

struct Configuration {
   bool DisableVerify;
   bool EhFrameHdr;
   bool EmitRelocs;
   bool EnableNewDtags;
   bool ExportDynamic;
   bool FatalWarnings;
   bool GcSections;
   bool GdbIndex;
-  bool GnuHash;
+  bool GnuHash = false;
   bool HasDynamicList = false;
   bool HasDynSymTab;
   bool ICF;
   bool MipsN32Abi = false;
   bool NoGnuUnique;
   bool NoUndefinedVersion;
   bool NoinhibitExec;
   bool Nostdlib;
   bool OFormatBinary;
   bool Omagic;
   bool OptRemarksWithHotness;
   bool Pie;
   bool PrintGcSections;
   bool Relocatable;
   bool SaveTemps;
   bool SingleRoRx;
   bool Shared;
   bool Static = false;
-  bool SysvHash;
+  bool SysvHash = false;
   bool Target1Rel;
   bool Threads;
   bool Trace;
   bool Verbose;
   bool WarnCommon;
   bool WarnMissingEntry;
   bool ZCombreloc;
   bool ZExecstack;

lld/ELF/Driver.cpp

if (S == "alignment")
     return SortSectionPolicy::Alignment;
   if (S == "name")
     return SortSectionPolicy::Name;
   if (!S.empty())
     error("unknown --sort-section rule: " + S);
   return SortSectionPolicy::Default;
 }
 
-static std::pair<bool, bool> getHashStyle(opt::InputArgList &Args) {
-  StringRef S = Args.getLastArgValue(OPT_hash_style, "sysv");
-  if (S == "sysv")
-    return {true, false};
-  if (S == "gnu")
-    return {false, true};
-  if (S != "both")
-    error("unknown -hash-style: " + S);
-  return {true, true};
-}
-
 // Parse --build-id or --build-id=<style>. We handle "tree" as a
 // synonym for "sha1" because all our hash functions including
 // -build-id=sha1 are actually tree hashes for performance reasons.
 static std::pair<BuildIdKind, std::vector<uint8_t>>
 getBuildId(opt::InputArgList &Args) {
   auto *Arg = Args.getLastArg(OPT_build_id, OPT_build_id_eq);
   if (!Arg)
     return {BuildIdKind::None, {}};
void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   if (auto *Arg = Args.getLastArg(OPT_m)) {
     StringRef S = Arg->getValue();
     std::tie(Config->EKind, Config->EMachine, Config->OSABI) =
         parseEmulation(S);
     Config->MipsN32Abi = (S == "elf32btsmipn32" || S == "elf32ltsmipn32");
     Config->Emulation = S;
   }
 
+  // Parse -hash-style={sysv,gnu,both}.
+  if (auto *Arg = Args.getLastArg(OPT_hash_style)) {
+    StringRef S = Arg->getValue();
+    if (S == "sysv")
+      Config->SysvHash = true;
+    else if (S == "gnu")
+      Config->GnuHash = true;
+    else if (S == "both")
+      Config->SysvHash = Config->GnuHash = true;
+    else
+      error("unknown -hash-style: " + S);
+  }
+
   if (Args.hasArg(OPT_print_map))
     Config->MapFile = "-";
 
   // --omagic is an option to create old-fashioned executables in which
   // .text segments are writable. Today, the option is still in use to
   // create special-purpose programs such as boot loaders. It doesn't
   // make sense to create PT_GNU_RELRO for such executables.
   if (Config->Omagic)
     Config->ZRelro = false;
 
-  std::tie(Config->SysvHash, Config->GnuHash) = getHashStyle(Args);
   std::tie(Config->BuildId, Config->BuildIdVector) = getBuildId(Args);
 
   if (auto *Arg = Args.getLastArg(OPT_symbol_ordering_file))
     if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
       Config->SymbolOrderingFile = getLines(*Buffer);
 
   // If --retain-symbol-file is used, we'll keep only the symbols listed in
   // the file and discard all others.

 // Do actual linking. Note that when this function is called,
 // all linker scripts have already been parsed.
 template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   Target = getTarget();
 
   Config->MaxPageSize = getMaxPageSize(Args);
   Config->ImageBase = getImageBase(Args);
 
+  // If a -hash-style option was not given, set to a default value,
+  // which varies depending on the target.
+  if (!Args.hasArg(OPT_hash_style)) {
+    if (Config->EMachine == EM_MIPS)
+      Config->SysvHash = true;
+    else
+      Config->SysvHash = Config->GnuHash = true;
+  }
+
   // Default output filename is "a.out" by the Unix tradition.
   if (Config->OutputFile.empty())
     Config->OutputFile = "a.out";
 
   // Fail early if the output file or map file is not writable. If a user has a
   // long link, e.g. due to a large LTO link, they do not wish to run it and
   // find that it failed because there was a mistake in their command-line.
   if (auto E = tryCreateFile(Config->OutputFile))