[lld][elf] Add --dynamic-linker option to the ELF linker.

Users can override the default value of the dynamic linker to be set to the
one that appears in the command line. The path can even be empty!. 

Added a test for the option.

llvm-svn: 182889

lld/include/lld/ReaderWriter/ELFTargetInfo.h

@@ -81,10 +81,18 @@ public:
     return false;
   }
 
-  virtual StringRef getInterpreter() const {
+  /// \brief The path to the dynamic interpreter
+  virtual StringRef getDefaultInterpreter() const {
     return "/lib64/ld-linux-x86-64.so.2";
   }
 
+  /// \brief The dynamic linker path set by the --dynamic-linker option
+  virtual StringRef getInterpreter() const {
+    if (_dynamicLinkerArg)
+      return _dynamicLinkerPath;
+    return getDefaultInterpreter();
+  }
+
   /// \brief Does the output have dynamic sections.
   virtual bool isDynamic() const;
 
@@ -106,6 +114,13 @@ public:
   void setIsStaticExecutable(bool v) { _isStaticExecutable = v; }
   void setMergeCommonStrings(bool v) { _mergeCommonStrings = v; }
   void setUseShlibUndefines(bool use) { _useShlibUndefines = use; }
+
+  /// \brief Set the dynamic linker path
+  void setInterpreter(StringRef dynamicLinker) {
+    _dynamicLinkerArg = true;
+    _dynamicLinkerPath = dynamicLinker;
+  }
+
   void appendSearchPath(StringRef dirPath) {
     _inputSearchPaths.push_back(dirPath);
   }
@@ -129,12 +144,14 @@ protected:
   bool                               _mergeCommonStrings;
   bool                               _runLayoutPass;
   bool                               _useShlibUndefines;
+  bool                               _dynamicLinkerArg;
   std::vector<StringRef>             _inputSearchPaths;
   llvm::BumpPtrAllocator             _extraStrings;
   std::unique_ptr<Reader>            _elfReader;
   std::unique_ptr<Reader>            _yamlReader;
   std::unique_ptr<Writer>            _writer;
   std::unique_ptr<Reader>            _linkerScriptReader;
+  StringRef                          _dynamicLinkerPath;
 };
 } // end namespace lld
 

lld/lib/Driver/GnuLdDriver.cpp

@@ -193,6 +193,11 @@ GnuLdDriver::parse(int argc, const char *argv[], raw_ostream &diagnostics) {
   if (parsedArgs->getLastArg(OPT_use_shlib_undefs))
     options->setUseShlibUndefines(true);
 
+  // Handle --dynamic-linker
+  if (llvm::opt::Arg *dynamicLinker =
+          parsedArgs->getLastArg(OPT_dynamic_linker))
+    options->setInterpreter(dynamicLinker->getValue());
+
   // Handle -Lxxx
   for (llvm::opt::arg_iterator it = parsedArgs->filtered_begin(OPT_L),
                                ie = parsedArgs->filtered_end();

lld/lib/Driver/LDOptions.td

@@ -18,8 +18,9 @@ def output : Separate<["-"], "o">,
 def relocatable : Flag<["--"], "relocatable">;
 def relocatable_r : Flag<["-"], "r">, Alias<relocatable>;
 
-def dynamic_linker : Separate<["-"], "dynamic-linker">;
-
+def dynamic_linker : Joined<["--"], "dynamic-linker=">,
+    HelpText<"Set the path to the dynamic linker">;
+def dynamic_linker_alias : Separate<["-"], "dynamic-linker">, Alias<dynamic_linker>;
 
 def m : Separate<["-"], "m">;
 def z : Separate<["-"], "z">;

lld/lib/ReaderWriter/ELF/ELFTargetInfo.cpp

@@ -22,7 +22,8 @@
 #include "llvm/Support/Path.h"
 
 namespace lld {
-ELFTargetInfo::ELFTargetInfo(llvm::Triple triple, std::unique_ptr<TargetHandlerBase> targetHandler)
+ELFTargetInfo::ELFTargetInfo(llvm::Triple triple,
+                             std::unique_ptr<TargetHandlerBase> targetHandler)
     : _outputFileType(elf::ET_EXEC),
       _triple(triple),
       _targetHandler(std::move(targetHandler)),
@@ -32,11 +33,10 @@ ELFTargetInfo::ELFTargetInfo(llvm::Triple triple, std::unique_ptr<TargetHandlerB
       _noInhibitExec(false),
       _mergeCommonStrings(false),
       _runLayoutPass(true),
-      _useShlibUndefines(false) {}
+      _useShlibUndefines(false),
+      _dynamicLinkerArg(false) {}
 
-bool ELFTargetInfo::is64Bits() const {
-  return getTriple().isArch64Bit();
-}
+bool ELFTargetInfo::is64Bits() const { return getTriple().isArch64Bit(); }
 
 bool ELFTargetInfo::isLittleEndian() const {
   // TODO: Do this properly. It is not defined purely by arch.

lld/test/elf/options/dynamic-linker.test

@@ -0,0 +1,14 @@
+# This tests the functionality of specifying dynamic-linker argument in the
+# command line 
+RUN: lld -flavor gnu --dynamic-linker="/xyz.so" %p/../Inputs/foo.o.x86-64 --noinhibit-exec -o %t
+RUN: llvm-objdump -s %t | FileCheck -check-prefix=DYNAMICINTERP1 %s
+RUN: lld -flavor gnu --dynamic-linker="" %p/../Inputs/foo.o.x86-64 --noinhibit-exec -o %t1
+RUN: llvm-objdump -s %t1 | FileCheck -check-prefix=DYNAMICINTERP2 %s
+RUN: lld -flavor gnu -dynamic-linker /xyz.so %p/../Inputs/foo.o.x86-64 --noinhibit-exec -o %t2
+RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=DYNAMICINTERP1 %s
+
+DYNAMICINTERP1:Contents of section .interp:
+DYNAMICINTERP1: 400158 2f78797a 2e736f00                    /xyz.so.
+DYNAMICINTERP2:Contents of section .interp:
+DYNAMICINTERP2: 400158 00
+