Used-uninitalized error I hadn't seen before

Used-uninitalized error I hadn't seen before

[Bart Schaefer]

Just built zsh 5.6 on a new host.

computil.c: In function 'ca_inactive':
computil.c:1832: warning: 'grplen' may be used uninitialized in this function

It's not immediately clear to me to what grplen should be initialized.

Re: Used-uninitalized error I hadn't seen before

[Oliver Kiddle]

Bart wrote:
> Just built zsh 5.6 on a new host.

What compiler is this and what options? I don't get the warning with any
compiler I've got. It'd be useful to track down which uses of the
variable cause the warning.

> computil.c: In function 'ca_inactive':
> computil.c:1832: warning: 'grplen' may be used uninitialized in this function
>
> It's not immediately clear to me to what grplen should be initialized.

I'm fairly sure that it is wrong and grplen can't be used uninitialized.
The trouble with adding an initialisation to silence the warning is that
it wouldn't be a meaningful value. That can make the code harder to follow
later because someone reading the code might puzzle over that initial
value.

Oliver

Re: Used-uninitalized error I hadn't seen before

[Bart Schaefer]

On Fri, Sep 7, 2018 at 4:22 PM, Oliver Kiddle <okiddle@yahoo.co.uk> wrote:
>
> What compiler is this and what options? I don't get the warning with any
> compiler I've got. It'd be useful to track down which uses of the
> variable cause the warning.

This is on what I have to assume (I'm not the admin) is a stock CentOS 6.9 host:

gcc -c -I. -I../../Src -I../../Src -I../../Src/Zle -I.
-DHAVE_CONFIG_H -DMODULE -Wall -Wmissing-prototypes -O2 -fPIC -o
computil..o computil.c

gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18)

> I'm fairly sure that it is wrong and grplen can't be used uninitialized.

So we have this:

   1847             if (sep > x) { /* exclusion included a set or group name */
   1848                 grp = x;
   1849                 grplen = sep - grp;
   1850                 x = sep;
   1851             }

and then later uses of grplen are protected by expressions like

   1853             if (excludeall || (x[0] == ':' && !x[1])) {
   1854                 if (grp) {

e.g., at line 1858 grplen is passed to strncmp() and at line 1859 is
used in a subscript.  It's not obvious to me why the conditions on
1853-1854 are a superset of 1847.