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execvp.c

/* Copyright (C) 2006 by Paolo Giarrusso - modified from glibc' execvp.c.
   Original copyright notice follows:

   Copyright (C) 1991,92,1995-99,2002,2004 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */
#include <unistd.h>

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <limits.h>

#ifndef TEST
#include "um_malloc.h"
#else
#include <stdio.h>
#define um_kmalloc malloc
#endif
#include "os.h"

/* Execute FILE, searching in the `PATH' environment variable if it contains
   no slashes, with arguments ARGV and environment from `environ'.  */
int execvp_noalloc(char *buf, const char *file, char *const argv[])
{
      if (*file == '\0') {
            return -ENOENT;
      }

      if (strchr (file, '/') != NULL) {
            /* Don't search when it contains a slash.  */
            execv(file, argv);
      } else {
            int got_eacces;
            size_t len, pathlen;
            char *name, *p;
            char *path = getenv("PATH");
            if (path == NULL)
                  path = ":/bin:/usr/bin";

            len = strlen(file) + 1;
            pathlen = strlen(path);
            /* Copy the file name at the top.  */
            name = memcpy(buf + pathlen + 1, file, len);
            /* And add the slash.  */
            *--name = '/';

            got_eacces = 0;
            p = path;
            do {
                  char *startp;

                  path = p;
                  //Let's avoid this GNU extension.
                  //p = strchrnul (path, ':');
                  p = strchr(path, ':');
                  if (!p)
                        p = strchr(path, '\0');

                  if (p == path)
                        /* Two adjacent colons, or a colon at the beginning or the end
                           of `PATH' means to search the current directory.  */
                        startp = name + 1;
                  else
                        startp = memcpy(name - (p - path), path, p - path);

                  /* Try to execute this name.  If it works, execv will not return.  */
                  execv(startp, argv);

                  /*
                  if (errno == ENOEXEC) {
                  }
                  */

                  switch (errno) {
                        case EACCES:
                              /* Record the we got a `Permission denied' error.  If we end
                                 up finding no executable we can use, we want to diagnose
                                 that we did find one but were denied access.  */
                              got_eacces = 1;
                        case ENOENT:
                        case ESTALE:
                        case ENOTDIR:
                              /* Those errors indicate the file is missing or not executable
                                 by us, in which case we want to just try the next path
                                 directory.  */
                        case ENODEV:
                        case ETIMEDOUT:
                              /* Some strange filesystems like AFS return even
                                 stranger error numbers.  They cannot reasonably mean
                                 anything else so ignore those, too.  */
                        case ENOEXEC:
                              /* We won't go searching for the shell
                               * if it is not executable - the Linux
                               * kernel already handles this enough,
                               * for us. */
                              break;

                        default:
                              /* Some other error means we found an executable file, but
                                 something went wrong executing it; return the error to our
                                 caller.  */
                              return -errno;
                  }
            } while (*p++ != '\0');

            /* We tried every element and none of them worked.  */
            if (got_eacces)
                  /* At least one failure was due to permissions, so report that
                     error.  */
                  return -EACCES;
      }

      /* Return the error from the last attempt (probably ENOENT).  */
      return -errno;
}
#ifdef TEST
int main(int argc, char**argv)
{
      char buf[PATH_MAX];
      int ret;
      argc--;
      if (!argc) {
            fprintf(stderr, "Not enough arguments\n");
            return 1;
      }
      argv++;
      if (ret = execvp_noalloc(buf, argv[0], argv)) {
            errno = -ret;
            perror("execvp_noalloc");
      }
      return 0;
}
#endif

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