Re: [SSSD] [PATCH] Suppress warning maybe-uninitialized

[Sumit Bose]

On Thu, Oct 02, 2014 at 10:20:56PM +0200, Lukas Slebodnik wrote:
> On (02/10/14 15:12), Simo Sorce wrote:
> > On Thu, 2 Oct 2014 19:33:02 +0200
> > Lukas Slebodnik  wrote:
> > > ehlo,
> > >
> > > There is a warning with some version of gcc (4.9.1, 4.4.7).
> > > Warning is not visible with gcc 4.8
> > > In my opinion, variable "a" should be initialized every time if
> > > "maps" is not NULL.
> >
> > I agree that "a" should be intialized every time, in fact I do not
> > agree with your patch where you set it to be a volatile, it is not.
> >
> > The main issue here is that the name and way this variable is used is
> > confusing.
> >
> > A better way would be to define a locally in the first loop, and in the
> > function define a better name initialized to a negative value.
> >
> > the name should probably be called something like base_attr_idx and
> > intialized as:
> >
> > int base_attr_idx = 0;
> >
> > and if the first part of the code finds the base_attr it is looking for
> > it would simply assing a to it (note we do away with "a" completely).
> >
> > if (map) {
> >    for (i = 1; i < attrs_num; i++) {
> >       ...
> >    }
> >    if (i < attrs_num) {
> >        store = true;
> >        base_attr_idx = i;
> >        ...
> >    }
> > }
> >
> > then the second for loop where you get the error would be change to:
> > for (ai = base_attr_idx; ai > 0 && ai < attrs_num; ai++) {
>
> I suppose you meant similar patch
> diff --git a/src/providers/ldap/sdap.c b/src/providers/ldap/sdap.c
> index 7034b11..6e8b16e 100644
> --- a/src/providers/ldap/sdap.c
> +++ b/src/providers/ldap/sdap.c
> @@ -305,6 +305,7 @@ int sdap_parse_entry(TALLOC_CTX *memctx,
>      char *str;
>      int lerrno;
>      int a, i, ret, ai;
> int base_attr_idx;
> const char *name;
> bool store;
> bool base64;
>
> @@ -412,6 +413,7 @@ int sdap_parse_entry(TALLOC_CTX *memctx,
>              /* interesting attr */
>              if (a < attrs_num) {
>                  store = true;
>            base_attr_idx = a;
>            name = map[a].sys_name;
>            if (strcmp(name, SYSDB_SSH_PUBKEY) == 0) {
>                base64 = true;
>
> @@ -478,7 +480,7 @@ int sdap_parse_entry(TALLOC_CTX *memctx,
>                           * attrs in case there is a map. Find all that match
>                           * and copy the value
>                           */
>                    for (ai = a; ai < attrs_num; ai++) {
>                    for (ai = base_attr_idx; ai < attrs_num; ai++) {
>                        /* check if this attr is valid with the chosen
>                         * schema */
>                        if (!map[ai].name) continue;
>
>
> It didn't help.
> src/providers/ldap/sdap.c: In function 'sdap_parse_entry':
> src/providers/ldap/sdap.c:308:9: error: 'base_attr_idx' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>      int base_attr_idx;
>          ^
> cc1: all warnings being treated as errors
> (BTW: There is no difference between using a and base_attr_idx)
>
> Any other better solution is welcomed.

Just a wild guess. Maybe the compiler is doing some wild optimizations
assuming that attrs_num might be 1, 0 or even smaller. Does it help to
check for (map && num_attrs > 1) ? (I would try myself, but I do not
have the right gcc version at hand)

bye,
Sumit
> LS
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