Re: [PATCH v2][BZ #832][BZ #3266] Make ldd try_trace more robust and portable

["Patrick 'P. J.' McDermott" <pj+sourceware-ml at pehjota dot net>]

On 2013-09-10 17:02, Mike Frysinger wrote:
> On Saturday 07 September 2013 11:45:45 Patrick "P. J." McDermott wrote:
>> +# The following command substitution is needed to make ldd work in
>> +# SELinux environments where the executed program might not have
>> +# permissions to write to the console/tty.  The extra "x" character
>> +# prevents the shell from trimming trailing newlines from command
>> +# substitution results.
>> +try_trace() {
>> +  output=$(eval $add_env '"$@"'; rc=$?; printf 'x'; exit $rc)
>> +  rc=$?
>> +  printf '%s' "${output%x}"
>> +  return $rc
>> +}
> 
> not really a new issue, but doesn't this also need to handle stderr ?
> 
> simply adding 2>&1 for the eval statement seems sufficient

Ah yes, stderr is of course also affected by the permissions issue.
I'll fix that.

> i dislike the missing `local` decls for output and rc.  but those aren't 
> exactly specified in POSIX (even if every reasonable shell supports it).  maybe 
> do a double sub-shell instead ?
> 
> try_trace() {
> 	(
> 	output=$(.....)
> 	rc=$?
> 	printf ....
> 	exit $rc
> 	)
> }

I discussed this in the original thread [1].  There are shells that
don't support local, so I'd rather avoid using it.  I proposed using a
subshell as you've suggested (though the outside curly braces aren't
necessary on any shell, as far as I know â either way the function is
defined as a compound list of commands).  At the time, though, no one
indicated any preferences.  So I think I'll adjust this to use a
subshell.

[1]: https://sourceware.org/ml/libc-alpha/2013-06/msg01155.html

Thanks,
-- 
Patrick "P. J." McDermott
  http://www.pehjota.net/
Lead Developer, ProteanOS
  http://www.proteanos.com/