Function RecoverGuestProgramFilename

Source/Common/Config.cpp:337–401

}

fextl::string RecoverGuestProgramFilename(fextl::string Program, bool ExecFDInterp, int ProgramFDFromEnv) {
  // If executed with a FEX FD then the Program argument might be empty.
  // In this case we need to scan the FD node to recover the application binary that exists on disk.
  // Only do this if the Program argument is empty, since we would prefer the application's expectation
  // of application name.
  if (ProgramFDFromEnv != -1 && Program.empty()) {
    // Get the `dev` node of the execveat fd string.
    Program = fextl::fmt::format("/dev/fd/{}", ProgramFDFromEnv);
  }

  // If we were provided a relative path then we need to canonicalize it to become absolute.
  // If the program name isn't resolved to an absolute path then glibc breaks inside it's `_dl_get_origin` function.
  // This is because we rewrite `/proc/self/exe` to the absolute program path calculated in here.
  if (!Program.starts_with('/')) {
    char ExistsTempPath[PATH_MAX];
    char* RealPath = FHU::Filesystem::Absolute(Program.c_str(), ExistsTempPath);
    if (RealPath) {
      Program = RealPath;
    }
  }

  // If FEX was invoked through an FD path (either binfmt_misc or execveat) then we need to check the
  // Program to see if it is a symlink to find the real path.
  //
  // binfmt_misc: Arg[0] is actually the execve `pathname` argument or `/dev/fd/<FD>` path
  //   - `pathname` with execve (See Side Note)
  //   - FD path with execveat and FD doesn't have an existing file on the disk
  //
  // ProgramFDFromEnv: Arg[0] is Application provided data or `/dev/fd/<FD>` from above fix-up.
  //   - execveat was either passed no arguments (argv=NULL) or the first argument is an empty string (argv[0]="").
  //   - FD path with execveat and FD doesn't have an existing file on the disk
  //
  // Side Note:
  //  The `execve` syscall doesn't take an FD but binfmt_misc will give FEX an FD to execute still.
  //  Arg[0] will always contain the `pathname` argument provided to execve.
  //  It does not resolve symlinks, and it does not convert the path to absolute.
  //
  // Examples:
  //  - Regular execve. Application must exist on disk.
  //    execve binfmt_misc args layout:   `FEXInterpreter <Path provided to execve pathname> <user provided argv[0]> <user provided argv[n]>...`
  //  - Regular execveat with FD. FD is backed by application on disk.
  //    execveat binfmt_misc args layout: `FEXInterpreter <Path provided to execve pathname> <user provided argv[0]> <user provided argv[n]>...`
  //  - Regular execveat with FD. FD points to file on disk that has been deleted.
  //    execveat binfmt_misc args layout: `FEXInterpreter /dev/fd/<FD> <user provided argv[0]> <user provided argv[n]>...`
#ifndef _WIN32
  if (ExecFDInterp || ProgramFDFromEnv != -1) {
    // Only in the case that FEX is executing an FD will the program argument potentially be a symlink.
    // This symlink will be in the style of `/dev/fd/<FD>`.
    //
    // If the argument /is/ a symlink then resolve its path to get the original application name.
    if (FHU::Symlinks::IsSymlink(Program)) {
      char Filename[PATH_MAX];
      auto SymlinkPath = FHU::Symlinks::ResolveSymlink(Program, Filename);
      if (SymlinkPath.starts_with('/')) {
        // This file was executed through an FD.
        // Remove the ` (deleted)` text if the file was deleted after the fact.
        // Otherwise just get the symlink without the deleted text.
        return fextl::string {SymlinkPath.substr(0, SymlinkPath.rfind(" (deleted)"))};