[Toybox] weird timeout flake

[Rob Landley]

On 8/2/23 11:04, enh via Toybox wrote:
> i've not seen this myself, but i have _one_ report from CI of this failure:
> 
> FAIL: timeout can't execute
> echo -ne '' | "/system/bin/timeout" .1 / 2>/dev/null ; echo $?
> --- expected 2023-06-21 04:02:52.424000000 +0000
> +++ actual 2023-06-21 04:02:52.476000000 +0000
> @@ -1 +1 @@
> -126
> +127

Hmmm...

  testcmd "can't execute" '.1 / 2>/dev/null ; echo $?' '126\n' '' ''

Trying that by hand on devuan (using coreutils' timeout):

  $ timeout .1 /
  timeout: failed to run command ‘/’: Permission denied
  $ echo $?
  126

>From the bash man page:

  If a command is not found, the child process created to execute it  re‐
  turns  a  status  of 127.  If a command is found but is not executable,
  the return status is 126.

I'm not sure how you can "file not found" the root directory? (Selinux?
Filehandle exhaustion? Even chmod 000 should return EPERM not ENOENT.)

The relevant code is xwrap.c line 233:

  execvp(argv[0], argv);

  toys.exitval = 126+(errno == ENOENT);

Rob

P.S. Ok, TECHNICALLY there's also an _exit(127); on line 312, but that codepath
only triggers when both A) argv is NULL (fork self), and B) you're on a nommu
system when /proc/self/exe can't exec. We're not CALLING xpopen_setup() with a
NULL argv (it's "/" here which is taken as an absolute path to the file to
open), so even if you did somehow enable nommu support (either the compile time
probe doesn't find fork() or you switch on TOYBOX_FORCE_NOMMU in menuconfig's
global settings menu) that still shouldn't trigger.