//===- 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/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 const char* progname = 0;

/// 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 std::string &llc,
                            char ** const envp) {
  // Run LLC to convert the bytecode file into assembly code.
  const char *cmd[6];
  cmd[0] = llc.c_str();
  cmd[1] = "-f";
  cmd[2] = "-o";
  cmd[3] = OutputFilename.c_str();
  cmd[4] = InputFilename.c_str();
  cmd[5] = 0;

  return ExecWait(cmd, envp);
}

/// 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 std::string &llc, char ** const envp) {
  // Run LLC to convert the bytecode file into C.
  const char *cmd[7];

  cmd[0] = llc.c_str();
  cmd[1] = "-march=c";
  cmd[2] = "-f";
  cmd[3] = "-o";
  cmd[4] = OutputFile.c_str();
  cmd[5] = InputFile.c_str();
  cmd[6] = 0;
  return ExecWait(cmd, envp);
}

/// 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 std::vector<std::string> &LibPaths,
                          const std::string &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);

  std::vector<const char *> cmd;

  // 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.
  cmd.push_back(gcc.c_str());
  cmd.push_back("-fno-strict-aliasing");
  cmd.push_back("-O3");
  cmd.push_back("-o");
  cmd.push_back(OutputFilename.c_str());
  cmd.push_back(InputFilename.c_str());

  // Adding the library paths creates a problem for native generation.  If we
  // include the search paths from llvmgcc, then we'll be telling normal gcc
  // to look inside of llvmgcc's library directories for libraries.  This is
  // bad because those libraries hold only bytecode files (not native object
  // files).  In the end, we attempt to link the bytecode libgcc into a native
  // program.
#if 0
  // Add in the library path options.
  for (unsigned index=0; index < LibPaths.size(); index++) {
    cmd.push_back("-L");
    cmd.push_back(LibPaths[index].c_str());
  }
#endif

  // Add in the libraries to link.
  std::vector<std::string> Libs(Libraries);
  for (unsigned index = 0; index < Libs.size(); index++) {
    if (Libs[index] != "crtend") {
      Libs[index] = "-l" + Libs[index];
      cmd.push_back(Libs[index].c_str());
    }
  }
  cmd.push_back(NULL);

  // Run the compiler to assembly and link together the program.
  return ExecWait(&(cmd[0]), 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) {
    std::string FullLibraryPath = FindLib(*i, LibPaths, true);
    if (!FullLibraryPath.empty() && IsSharedObject(FullLibraryPath))
      Out2 << "    -load=" << FullLibraryPath << " \\\n";
  }
  Out2 << "    $0.bc ${1+\"$@\"}\n";
  Out2.close();
}

// 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 = argv[0];

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

  std::string ModuleID("llvm-ld-output");
  std::auto_ptr<Module> Composite(new Module(ModuleID));

  // We always look first in the current directory when searching for libraries.
  LibPaths.insert(LibPaths.begin(), ".");

  // If the user specified an extra search path in their environment, respect
  // it.
  if (char *SearchPath = getenv("LLVM_LIB_SEARCH_PATH"))
    LibPaths.push_back(SearchPath);

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

  // Link in all of the files
  if (LinkFiles(argv[0], Composite.get(), InputFilenames, Verbose))
    return 1; // Error already printed

  // Link in all of the libraries next...
  if (!LinkAsLibrary)
    LinkLibraries(argv[0], Composite.get(), Libraries, LibPaths,
                  Verbose, Native);

  // 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
      std::string AssemblyFile = OutputFilename + ".s";

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

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

      if (gcc.empty())
        return PrintAndReturn("Failed to find gcc");

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

      // Remove the assembly language file.
      removeFile (AssemblyFile);
    } else if (NativeCBE) {
      std::string CFile = OutputFilename + ".cbe.c";

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

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

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

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

    } else {
      EmitShellScript(argv);
    }
  
    // Make the script executable...
    MakeFileExecutable(OutputFilename);

    // Make the bytecode file readable and directly executable in LLEE as well
    MakeFileExecutable(RealBytecodeOutput);
    MakeFileReadable(RealBytecodeOutput);
  }

  return 0;
}