Re: [PATCH 2/2] maint: pacify GCC 6 with -Wnull-dereference

[Pádraig Brady]

On 27/07/16 08:33, Bernhard Voelker wrote:
> src/id.c:249:29: error: potential null pointer dereference \
> [-Werror=null-dereference]
>        pw_name = xstrdup (pwd->pw_name);
>                           ~~~^~~~~~~~~
> src/whoami.c:89:11: error: potential null pointer dereference \
> [-Werror=null-dereference]
>    puts (pw->pw_name);
>          ~~^~~~~~~~~
> 
> * src/id.c (main): Explicitly exit with EXIT_FAILURE after an eror to
> help gcc-6 to detect that the dereferenced pointer is valid.
> * src/whoami.c (main): Likewise.
> ---
>  src/id.c     | 5 ++++-
>  src/whoami.c | 7 +++++--
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/src/id.c b/src/id.c
> index 218ee5a..35cbeb5 100644
> --- a/src/id.c
> +++ b/src/id.c
> @@ -245,7 +245,10 @@ main (int argc, char **argv)
>              }
>          }
>        if (pwd == NULL)
> -        error (EXIT_FAILURE, 0, _("%s: no such user"), quote (spec));
> +        {
> +          error (0, 0, _("%s: no such user"), quote (spec));
> +          exit (EXIT_FAILURE);
> +        }
>        pw_name = xstrdup (pwd->pw_name);
>        ruid = euid = pwd->pw_uid;
>        rgid = egid = pwd->pw_gid;
> diff --git a/src/whoami.c b/src/whoami.c
> index e58c575..972cd55 100644
> --- a/src/whoami.c
> +++ b/src/whoami.c
> @@ -84,8 +84,11 @@ main (int argc, char **argv)
>    uid = geteuid ();
>    pw = (uid == NO_UID && errno ? NULL : getpwuid (uid));
>    if (!pw)
> -    error (EXIT_FAILURE, errno, _("cannot find name for user ID %lu"),
> -           (unsigned long int) uid);
> +    {
> +      error (0, errno, _("cannot find name for user ID %lu"),
> +             (unsigned long int) uid);
> +      exit (EXIT_FAILURE);
> +    }
>    puts (pw->pw_name);
>    return EXIT_SUCCESS;
>  }
> 

Hrm, I wonder should we have an errorx to wrap error (EXIT_FAILURE, ...)
and that can be marked as noreturn? I.E. stick this somewhere?

#include <assert.h>
#include "verror.h"
static inline void
_GL_ATTRIBUTE_FORMAT ((__printf__, 3, 4))
ATTRIBUTE_NORETURN
errorx (int status, int errnum, const char *fmt, ...)
{
  assert (status);
  va_list ap;
  va_start (ap, fmt);
  verror (status, errnum, fmt, ap);
  va_end (ap);
}