execvp.c

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/* 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