hush problem with the exec command

[Denys Vlasenko]

On Thursday 20 March 2008 20:43, Martinb_ARM_NOMMU_KISSDVD wrote:
> #!/bin/hush
> # stage2 update script
> URL1=http://stage2d.googlepages.com
> STAGE2BASE=/hdd/stage2
> DOWNOUT=st508_rc2b
> wget http://stage2d.googlepages.com/st508_rc2b -O /hdd/stage2/st508_rc2b
> chmod 777 /hdd/stage2/st508_rc2b
> ls /hdd/stage2/st508_rc2b
> exec /hdd/stage2/st508_rc2b
> 
> if I use this on a new build firmware it "just don't work"
> 
> the output I get if I execute this from telnet prompt I get:
> 
> /hdd/newscript # ./setup.tst
> Connecting to stage2d.googlepages.com[74.125.47.118]:80
> st508_rc2b           100% |*****************************|   868       --:-- ETA
> /hdd/stage2/st508_rc2b
> hush: cannot exec '/hdd/stage2/st508_rc2b': No such file or directory

Ok, this is how that message is reached:

/* built-in 'exec' handler */
static int builtin_exec(char **argv)
{
        if (argv[1] == NULL)
                return EXIT_SUCCESS;   /* Really? */
        pseudo_exec_argv(argv + 1);
        /* never returns */
}

static void pseudo_exec_argv(char **argv)
{
....
        debug_printf_exec("execing '%s'\n", argv[0]);
        execvp(argv[0], argv);
        bb_perror_msg("cannot exec '%s'", argv[0]);  <====== MESSAGE
        _exit(1);
}

> so somehow the exec cant find the file but the file does exist for 100% sure
> 
> if I remove the exec I have the same behaviour (and the exact same output)
> its NOT related to wget because if I remove the wget and chmod (and the file
> does exist) I have the same problem
> 
> so to make the script as small as possible I have paste the following output
> to make it clear:
> 
> (this is a paste from a telnet session on my environment)
> 
> /hdd/newscript # cat setup.tst
> #!/bin/hush
> # stage2 initscript first setup
> ls -l /hdd/stage2/st508_rc2b
> /hdd/stage2/st508_rc2b
> /hdd/newscript # ./setup.tst
> -rwxrwxrwx    1 root     root          868 Mar 20 19:28 /hdd/stage2/st508_rc2b
> hush: cannot exec '/hdd/stage2/st508_rc2b': No such file or directory
> /hdd/newscript #

Trying to reproduce:

/.local/tmp # cat z
#!/bin/hush
# stage2 initscript first setup
ls -l /tmp/pwd
/tmp/pwd

/.local/tmp # ./z
-rwxr-xr-x    1 root     root       771336 Mar 20 21:31 /tmp/pwd
/.local/tmp
/.local/tmp #

For me, it works on x86: /tmp/pwd is just a renamed busybox binary
and it does what "pwd" is supposed to do.

> so I'm sure there is something wrong because this output is not normal
> behaviour

Yes
 
> Please tell me what to do to debug this problem
> its (for now) the last (fatal) error I have on my NOMMU system

Some ideas which come to mind:

1. ENOENT on exec may be cause by file not having all required
   libraries present. What "ldd /hdd/stage2/st508_rc2b" says?
   Is /hdd/stage2/st508_rc2b a shared binary?
   (For answer, try "file /hdd/stage2/st508_rc2b")
2. Replace /hdd/stage2/st508_rc2b with /hdd/stage2/pwd,
   to match my test. Does it still fail?
3. Send me your .config
4. Build busybox with the same .config on x86 desktop and test -
   does it still fails? (This is a good step in debugging in general,
   because way more people will be able to build busybox
   with your .config, try it on their systems, etc...).
--
vda