[ELF] Add support for -z {now, origin}

[davide]

Summary

Note: Needs to wait until D9958 lands for a testcase/commit.

[ruiu]

LGTM

include/lld/ReaderWriter/ELFLinkingContext.h

enum class OutputMagic : uint8_t {
     // Disallow shared libraries and don't align sections
     // PageAlign Data, Mark Text Segment/Data segment RW
     NMAGIC,
     // Disallow shared libraries and don't align sections,
     // Mark Text Segment/Data segment RW
     OMAGIC,
   };
 
+  /// \brief ELF DT_FLAGS.
+  enum DTFlag : uint32_t {
+    DT_NOW = 1 << 1,
+    DT_ORIGIN = 1 << 2,
+  };
+
   llvm::Triple getTriple() const { return _triple; }
 
   uint64_t getPageSize() const { return _maxPageSize; }
   void setMaxPageSize(uint64_t v) { _maxPageSize = v; }
 
   OutputMagic getOutputMagic() const { return _outputMagic; }
   uint16_t getOutputELFType() const { return _outputELFType; }
   uint16_t getOutputMachine() const;
public:
 
   /// \brief Collect statistics.
   bool collectStats() const { return _collectStats; }
   void setCollectStats(bool s) { _collectStats = s; }
 
   // --wrap option.
   void addWrapForSymbol(StringRef sym) { _wrapCalls.insert(sym); }
 
+  // \brief Set DT_FLAGS flag.
+  void setDTFlag(DTFlag f) { _dtFlags |= f; };
+  bool getDTFlag(DTFlag f) { return (_dtFlags & f); };
+
   const llvm::StringSet<> &wrapCalls() const { return _wrapCalls; }
 
   void setUndefinesResolver(std::unique_ptr<File> resolver);
 
   script::Sema &linkerScriptSema() { return _linkerScriptSema; }
   const script::Sema &linkerScriptSema() const { return _linkerScriptSema; }
 
   // Set R_ARM_TARGET1 relocation behaviour
protected:
   bool _discardLocals = false;
   bool _stripSymbols = false;
   bool _alignSegments = true;
   bool _enableNewDtags = false;
   bool _collectStats = false;
   bool _armTarget1Rel = false;
   bool _mipsPcRelEhRel = false;
   uint64_t _maxPageSize = 0x1000;
+  uint32_t _dtFlags = 0;
 
   OutputMagic _outputMagic = OutputMagic::DEFAULT;
   StringRefVector _inputSearchPaths;
   std::unique_ptr<Writer> _writer;
   llvm::Optional<StringRef> _dynamicLinkerPath;
   StringRef _initFunction = "_init";
   StringRef _finiFunction = "_fini";
   StringRef _sysrootPath = "";

lib/Driver/GnuLdDriver.cpp

     } else {
       diag << "invalid --defsym: " << arg->getValue() << "\n";
       return false;
     }
   }
 
   for (auto *arg : parsedArgs->filtered(OPT_z)) {
     StringRef opt = arg->getValue();
-    if (opt == "muldefs") {
+    if (opt == "muldefs")
       ctx->setAllowDuplicates(true);
-    } else if (opt.startswith("max-page-size")) {
+    else if (opt == "now")
+      ctx->setDTFlag(ELFLinkingContext::DTFlag::DT_NOW);
+    else if (opt == "origin")
+      ctx->setDTFlag(ELFLinkingContext::DTFlag::DT_ORIGIN);
+    else if (opt.startswith("max-page-size")) {
       // Parse -z max-page-size option.
       // The default page size is considered the minimum page size the user
       // can set, check the user input if its atleast the minimum page size
       // and does not exceed the maximum page size allowed for the target.
       uint64_t maxPageSize = 0;
 
       // Error if the page size user set is less than the maximum page size
       // and greather than the default page size and the user page size is a

lib/ReaderWriter/ELF/OutputELFWriter.cpp

auto rpath =
         new (_alloc) std::string(join(rpathList.begin(), rpathList.end(), ":"));
     _dynamicTable->addEntry(_ctx.getEnableNewDtags() ? DT_RUNPATH : DT_RPATH,
                             _dynamicStringTable->addString(*rpath));
   }
   StringRef soname = _ctx.sharedObjectName();
   if (!soname.empty() && _ctx.getOutputELFType() == llvm::ELF::ET_DYN)
     _dynamicTable->addEntry(DT_SONAME, _dynamicStringTable->addString(soname));
 
+  // Add DT_FLAGS/DT_FLAGS_1 entries if necessary.
+  uint32_t dtflags = 0, dt1flags = 0;
+  if (_ctx.getDTFlag(ELFLinkingContext::DTFlag::DT_NOW)) {
+    dtflags |= DF_BIND_NOW;
+    dt1flags |= DF_1_NOW;
+  }
+  if (_ctx.getDTFlag(ELFLinkingContext::DTFlag::DT_ORIGIN)) {
+    dtflags |= DF_ORIGIN;
+    dt1flags |= DF_1_ORIGIN;
+  }
+  if (dtflags != 0)
+    _dynamicTable->addEntry(DT_FLAGS, dtflags);
+  if (dt1flags != 0)
+    _dynamicTable->addEntry(DT_FLAGS_1, dt1flags);
+
   // The dynamic symbol table need to be sorted earlier because the hash
   // table needs to be built using the dynamic symbol table. It would be
   // late to sort the symbols due to that in finalize. In the dynamic symbol
   // table finalize, we call the symbol table finalize and we don't want to
   // sort again
   _dynamicSymbolTable->sortSymbols();
 
   // Add the dynamic symbols into the hash table