//===- llvm-ld.cpp - LLVM 'ld' compatible linker --------------------------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This utility is intended to be compatible with GCC, and follows standard
// system 'ld' conventions.  As such, the default output file is ./a.out.
// Additionally, this program outputs a shell script that is used to invoke LLI
// to execute the program.  In this manner, the generated executable (a.out for
// example), is directly executable, whereas the bytecode file actually lives in
// the a.out.bc file generated by this program.  Also, Force is on by default.
//
// Note that if someone (or a script) deletes the executable program generated,
// the .bc file will be left around.  Considering that this is a temporary hack,
// I'm not too worried about this.
//
//===----------------------------------------------------------------------===//

#include "llvm/Linker.h"
#include "llvm/System/Program.h"
#include "llvm/Module.h"
#include "llvm/PassManager.h"
#include "llvm/Bytecode/Reader.h"
#include "llvm/Bytecode/Writer.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetMachineRegistry.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/FileUtilities.h"
#include "llvm/Support/SystemUtils.h"
#include "llvm/System/Signals.h"
#include <fstream>
#include <iostream>
#include <memory>

using namespace llvm;

// Input/Output Options
static cl::list<std::string> InputFilenames(cl::Positional, cl::OneOrMore,
  cl::desc("<input bytecode files>"));

static cl::opt<std::string> OutputFilename("o", cl::init("a.out"),
  cl::desc("Override output filename"), 
  cl::value_desc("filename"));

static cl::opt<bool> Verbose("v", 
  cl::desc("Print information about actions taken"));
  
static cl::list<std::string> LibPaths("L", cl::Prefix,
  cl::desc("Specify a library search path"), 
  cl::value_desc("directory"));

static cl::list<std::string> Libraries("l", cl::Prefix,
  cl::desc("Specify libraries to link to"), 
  cl::value_desc("library prefix"));

static cl::opt<bool> LinkAsLibrary("link-as-library", 
  cl::desc("Link the .bc files together as a library, not an executable"));

static cl::alias Relink("r", cl::aliasopt(LinkAsLibrary),
  cl::desc("Alias for -link-as-library"));

static cl::opt<const TargetMachineRegistry::Entry*, false, TargetNameParser>
  MachineArch("march", cl::desc("Architecture to generate assembly for:"));

static cl::opt<bool> Native("native",
  cl::desc("Generate a native binary instead of a shell script"));

static cl::opt<bool>NativeCBE("native-cbe",
  cl::desc("Generate a native binary with the C backend and GCC"));

static cl::opt<bool>DisableCompression("disable-compression",cl::init(false),
  cl::desc("Disable writing of compressed bytecode files"));
  
// Compatibility options that are ignored but supported by LD
static cl::opt<std::string> CO3("soname", cl::Hidden, 
  cl::desc("Compatibility option: ignored"));

static cl::opt<std::string> CO4("version-script", cl::Hidden, 
  cl::desc("Compatibility option: ignored"));

static cl::opt<bool> CO5("eh-frame-hdr", cl::Hidden, 
  cl::desc("Compatibility option: ignored"));

static  cl::opt<std::string> CO6("h", cl::Hidden, 
  cl::desc("Compatibility option: ignored"));

/// This is just for convenience so it doesn't have to be passed around
/// everywhere.
static std::string progname;

/// PrintAndReturn - Prints a message to standard error and returns true.
///
/// Inputs:
///  progname - The name of the program (i.e. argv[0]).
///  Message  - The message to print to standard error.
///
static int PrintAndReturn(const std::string &Message) {
  std::cerr << progname << ": " << Message << "\n";
  return 1;
}

/// CopyEnv - This function takes an array of environment variables and makes a
/// copy of it.  This copy can then be manipulated any way the caller likes
/// without affecting the process's real environment.
///
/// Inputs:
///  envp - An array of C strings containing an environment.
///
/// Return value:
///  NULL - An error occurred.
///
///  Otherwise, a pointer to a new array of C strings is returned.  Every string
///  in the array is a duplicate of the one in the original array (i.e. we do
///  not copy the char *'s from one array to another).
///
static char ** CopyEnv(char ** const envp) {
  // Count the number of entries in the old list;
  unsigned entries;   // The number of entries in the old environment list
  for (entries = 0; envp[entries] != NULL; entries++)
    /*empty*/;

  // Add one more entry for the NULL pointer that ends the list.
  ++entries;

  // If there are no entries at all, just return NULL.
  if (entries == 0)
    return NULL;

  // Allocate a new environment list.
  char **newenv = new char* [entries];
  if ((newenv = new char* [entries]) == NULL)
    return NULL;

  // Make a copy of the list.  Don't forget the NULL that ends the list.
  entries = 0;
  while (envp[entries] != NULL) {
    newenv[entries] = new char[strlen (envp[entries]) + 1];
    strcpy (newenv[entries], envp[entries]);
    ++entries;
  }
  newenv[entries] = NULL;

  return newenv;
}


/// RemoveEnv - Remove the specified environment variable from the environment
/// array.
///
/// Inputs:
///  name - The name of the variable to remove.  It cannot be NULL.
///  envp - The array of environment variables.  It cannot be NULL.
///
/// Notes:
///  This is mainly done because functions to remove items from the environment
///  are not available across all platforms.  In particular, Solaris does not
///  seem to have an unsetenv() function or a setenv() function (or they are
///  undocumented if they do exist).
///
static void RemoveEnv(const char * name, char ** const envp) {
  for (unsigned index=0; envp[index] != NULL; index++) {
    // Find the first equals sign in the array and make it an EOS character.
    char *p = strchr (envp[index], '=');
    if (p == NULL)
      continue;
    else
      *p = '\0';

    // Compare the two strings.  If they are equal, zap this string.
    // Otherwise, restore it.
    if (!strcmp(name, envp[index]))
      *envp[index] = '\0';
    else
      *p = '=';
  }

  return;
}

/// GenerateBytecode - generates a bytecode file from the module provided
void GenerateBytecode(Module* M, const std::string& FileName) {

  // Create the output file.
  std::ofstream Out(FileName.c_str());
  if (!Out.good()) {
    PrintAndReturn("error opening '" + FileName + "' for writing!");
    return;
  }

  // Ensure that the bytecode file gets removed from the disk if we get a
  // terminating signal.
  sys::RemoveFileOnSignal(sys::Path(FileName));

  // Write it out
  WriteBytecodeToFile(M, Out, !DisableCompression);

  // Close the bytecode file.
  Out.close();
}

/// GenerateAssembly - generates a native assembly language source file from the
/// specified bytecode file.
///
/// Inputs:
///  InputFilename  - The name of the output bytecode file.
///  OutputFilename - The name of the file to generate.
///  llc            - The pathname to use for LLC.
///  envp           - The environment to use when running LLC.
///
/// Return non-zero value on error.
///
static int GenerateAssembly(const std::string &OutputFilename,
                            const std::string &InputFilename,
                            const sys::Path &llc) {
  // Run LLC to convert the bytecode file into assembly code.
  std::vector<std::string> args;
  args.push_back( "-f");
  args.push_back( "-o");
  args.push_back( OutputFilename);
  args.push_back( InputFilename);

  return sys::Program::ExecuteAndWait(llc,args);
}

/// GenerateAssembly - generates a native assembly language source file from the
/// specified bytecode file.
static int GenerateCFile(const std::string &OutputFile,
                         const std::string &InputFile,
                         const sys::Path &llc) {
  // Run LLC to convert the bytecode file into C.
  std::vector<std::string> args;
  args.push_back( "-march=c");
  args.push_back( "-f");
  args.push_back( "-o");
  args.push_back( OutputFile);
  args.push_back( InputFile);
  return sys::Program::ExecuteAndWait(llc, args);
}

/// GenerateNative - generates a native assembly language source file from the
/// specified assembly source file.
///
/// Inputs:
///  InputFilename  - The name of the output bytecode file.
///  OutputFilename - The name of the file to generate.
///  Libraries      - The list of libraries with which to link.
///  LibPaths       - The list of directories in which to find libraries.
///  gcc            - The pathname to use for GGC.
///  envp           - A copy of the process's current environment.
///
/// Outputs:
///  None.
///
/// Returns non-zero value on error.
///
static int GenerateNative(const std::string &OutputFilename,
                          const std::string &InputFilename,
                          const std::vector<std::string> &Libraries,
                          const sys::Path &gcc, char ** const envp) {
  // Remove these environment variables from the environment of the
  // programs that we will execute.  It appears that GCC sets these
  // environment variables so that the programs it uses can configure
  // themselves identically.
  //
  // However, when we invoke GCC below, we want it to use its normal
  // configuration.  Hence, we must sanitize its environment.
  char ** clean_env = CopyEnv(envp);
  if (clean_env == NULL)
    return 1;
  RemoveEnv("LIBRARY_PATH", clean_env);
  RemoveEnv("COLLECT_GCC_OPTIONS", clean_env);
  RemoveEnv("GCC_EXEC_PREFIX", clean_env);
  RemoveEnv("COMPILER_PATH", clean_env);
  RemoveEnv("COLLECT_GCC", clean_env);


  // Run GCC to assemble and link the program into native code.
  //
  // Note:
  //  We can't just assemble and link the file with the system assembler
  //  and linker because we don't know where to put the _start symbol.
  //  GCC mysteriously knows how to do it.
  std::vector<std::string> args;
  args.push_back("-fno-strict-aliasing");
  args.push_back("-O3");
  args.push_back("-o");
  args.push_back(OutputFilename);
  args.push_back(InputFilename);

  // Add in the libraries to link.
  for (unsigned index = 0; index < Libraries.size(); index++)
    if (Libraries[index] != "crtend")
      args.push_back("-l" + Libraries[index]);

  // Run the compiler to assembly and link together the program.
  return sys::Program::ExecuteAndWait(gcc, args, (const char**)clean_env);
}

/// EmitShellScript - Output the wrapper file that invokes the JIT on the LLVM
/// bytecode file for the program.
static void EmitShellScript(char **argv) {
#if defined(_WIN32) || defined(__CYGWIN__)
  // Windows doesn't support #!/bin/sh style shell scripts in .exe files.  To
  // support windows systems, we copy the llvm-stub.exe executable from the
  // build tree to the destination file.
  std::string llvmstub = FindExecutable("llvm-stub.exe", argv[0]);
  if (llvmstub.empty()) {
    std::cerr << "Could not find llvm-stub.exe executable!\n";
    exit(1);
  }
  if (CopyFile(OutputFilename, llvmstub)) {
    std::cerr << "Could not copy the llvm-stub.exe executable!\n";
    exit(1);
  }
  return;
#endif

  // Output the script to start the program...
  std::ofstream Out2(OutputFilename.c_str());
  if (!Out2.good())
    exit(PrintAndReturn("error opening '" + OutputFilename + "' for writing!"));

  Out2 << "#!/bin/sh\n";
  // Allow user to setenv LLVMINTERP if lli is not in their PATH.
  Out2 << "lli=${LLVMINTERP-lli}\n";
  Out2 << "exec $lli \\\n";
  // gcc accepts -l<lib> and implicitly searches /lib and /usr/lib.
  LibPaths.push_back("/lib");
  LibPaths.push_back("/usr/lib");
  LibPaths.push_back("/usr/X11R6/lib");
  // We don't need to link in libc! In fact, /usr/lib/libc.so may not be a
  // shared object at all! See RH 8: plain text.
  std::vector<std::string>::iterator libc = 
    std::find(Libraries.begin(), Libraries.end(), "c");
  if (libc != Libraries.end()) Libraries.erase(libc);
  // List all the shared object (native) libraries this executable will need
  // on the command line, so that we don't have to do this manually!
  for (std::vector<std::string>::iterator i = Libraries.begin(), 
         e = Libraries.end(); i != e; ++i) {
    sys::Path FullLibraryPath = sys::Path::FindLibrary(*i);
    if (!FullLibraryPath.isEmpty() && FullLibraryPath.isDynamicLibrary())
      Out2 << "    -load=" << FullLibraryPath.toString() << " \\\n";
  }
  Out2 << "    $0.bc ${1+\"$@\"}\n";
  Out2.close();
}

// BuildLinkItems -- This function generates a LinkItemList for the LinkItems
// linker function by combining the Files and Libraries in the order they were
// declared on the command line.
static void BuildLinkItems(
  Linker::ItemList& Items,
  const cl::list<std::string>& Files,
  const cl::list<std::string>& Libraries) {

  // Build the list of linkage items for LinkItems. 

  cl::list<std::string>::const_iterator fileIt = Files.begin();
  cl::list<std::string>::const_iterator libIt  = Libraries.begin();

  int libPos = -1, filePos = -1;
  while ( libIt != Libraries.end() || fileIt != Files.end() ) {
    if (libIt != Libraries.end())
      libPos = Libraries.getPosition(libIt - Libraries.begin());
    else
      libPos = -1;
    if (fileIt != Files.end())
      filePos = Files.getPosition(fileIt - Files.begin());
    else
      filePos = -1;

    if (filePos != -1 && (libPos == -1 || filePos < libPos)) {
      // Add a source file
      Items.push_back(std::make_pair(*fileIt++, false));
    } else if (libPos != -1 && (filePos == -1 || libPos < filePos)) {
      // Add a library
      Items.push_back(std::make_pair(*libIt++, true));
    }
  }
}

// Rightly this should go in a header file but it just seems such a waste.
namespace llvm {
extern void Optimize(Module*);
}

int main(int argc, char **argv, char **envp) {
  // Initial global variable above for convenience printing of program name.
  progname = sys::Path(argv[0]).getBasename();
  Linker TheLinker(progname, Verbose);
  
  // Set up the library paths for the Linker
  TheLinker.addPaths(LibPaths);
  TheLinker.addSystemPaths();

  // Parse the command line options
  cl::ParseCommandLineOptions(argc, argv, " llvm linker\n");
  sys::PrintStackTraceOnErrorSignal();

  // Remove any consecutive duplicates of the same library...
  Libraries.erase(std::unique(Libraries.begin(), Libraries.end()),
                  Libraries.end());

  if (LinkAsLibrary) {
    std::vector<sys::Path> Files;
    for (unsigned i = 0; i < InputFilenames.size(); ++i )
      Files.push_back(sys::Path(InputFilenames[i]));
    if (TheLinker.LinkInFiles(Files))
      return 1; // Error already printed

    // The libraries aren't linked in but are noted as "dependent" in the
    // module.
    for (cl::list<std::string>::const_iterator I = Libraries.begin(), 
         E = Libraries.end(); I != E ; ++I) {
      TheLinker.getModule()->addLibrary(*I);
    }
  } else {
    // Build a list of the items from our command line
    Linker::ItemList Items;
    BuildLinkItems(Items, InputFilenames, Libraries);

    // Link all the items together
    if (TheLinker.LinkInItems(Items) )
      return 1;
  }

  std::auto_ptr<Module> Composite(TheLinker.releaseModule());

  // Optimize the module
  Optimize(Composite.get());

  // Generate the bytecode for the optimized module.
  std::string RealBytecodeOutput = OutputFilename;
  if (!LinkAsLibrary) RealBytecodeOutput += ".bc";
  GenerateBytecode(Composite.get(), RealBytecodeOutput);

  // If we are not linking a library, generate either a native executable
  // or a JIT shell script, depending upon what the user wants.
  if (!LinkAsLibrary) {
    // If the user wants to generate a native executable, compile it from the
    // bytecode file.
    //
    // Otherwise, create a script that will run the bytecode through the JIT.
    if (Native) {
      // Name of the Assembly Language output file
      sys::Path AssemblyFile ( OutputFilename);
      AssemblyFile.appendSuffix("s");

      // Mark the output files for removal if we get an interrupt.
      sys::RemoveFileOnSignal(AssemblyFile);
      sys::RemoveFileOnSignal(sys::Path(OutputFilename));

      // Determine the locations of the llc and gcc programs.
      sys::Path llc = FindExecutable("llc", argv[0]);
      if (llc.isEmpty())
        return PrintAndReturn("Failed to find llc");

      sys::Path gcc = FindExecutable("gcc", argv[0]);
      if (gcc.isEmpty())
        return PrintAndReturn("Failed to find gcc");

      // Generate an assembly language file for the bytecode.
      if (Verbose) std::cout << "Generating Assembly Code\n";
      GenerateAssembly(AssemblyFile.toString(), RealBytecodeOutput, llc);
      if (Verbose) std::cout << "Generating Native Code\n";
      GenerateNative(OutputFilename, AssemblyFile.toString(), Libraries, 
                     gcc, envp);

      // Remove the assembly language file.
      AssemblyFile.destroyFile();
    } else if (NativeCBE) {
      sys::Path CFile (OutputFilename);
      CFile.appendSuffix("cbe.c");

      // Mark the output files for removal if we get an interrupt.
      sys::RemoveFileOnSignal(CFile);
      sys::RemoveFileOnSignal(sys::Path(OutputFilename));

      // Determine the locations of the llc and gcc programs.
      sys::Path llc = FindExecutable("llc", argv[0]);
      if (llc.isEmpty())
        return PrintAndReturn("Failed to find llc");

      sys::Path gcc = FindExecutable("gcc", argv[0]);
      if (gcc.isEmpty())
        return PrintAndReturn("Failed to find gcc");

      // Generate an assembly language file for the bytecode.
      if (Verbose) std::cout << "Generating Assembly Code\n";
      GenerateCFile(CFile.toString(), RealBytecodeOutput, llc);
      if (Verbose) std::cout << "Generating Native Code\n";
      GenerateNative(OutputFilename, CFile.toString(), Libraries, gcc, envp);

      // Remove the assembly language file.
      CFile.destroyFile();

    } else {
      EmitShellScript(argv);
    }
  
    // Make the script executable...
    sys::Path(OutputFilename).makeExecutable();

    // Make the bytecode file readable and directly executable in LLEE as well
    sys::Path(RealBytecodeOutput).makeExecutable();
    sys::Path(RealBytecodeOutput).makeReadable();
  }

  return 0;
}