Fix -Wincompatible-pointer-types warning from gcc (issue #15)

Fix warning that gcc 14 will make into an error

Thanks, this lgtm and it also fixes the reported issue.

approved this merge request

merged

Looks like still some cleanups are necessary and this commit is not enough

make[2]: Entering directory '/home/tkloczko/rpmbuild/BUILD/xdm-1.1.14/greeter'
/bin/sh ../libtool  --tag=CC   --mode=compile /usr/bin/gcc -DHAVE_CONFIG_H -I. -I..  -I../include  -fno-strict-aliasing -I/usr/include/freetype2   -DGREET_LIB -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -O2 -g -grecord-gcc-switches -pipe -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -fdata-sections -ffunction-sections -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -flto=auto -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -Wall -Werror=format-security -Os -c -o greet.lo greet.c
libtool: compile:  /usr/bin/gcc -DHAVE_CONFIG_H -I. -I.. -I../include -fno-strict-aliasing -I/usr/include/freetype2 -DGREET_LIB -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -O2 -g -grecord-gcc-switches -pipe -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -fdata-sections -ffunction-sections -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -flto=auto -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -Wall -Werror=format-security -Os -c greet.c  -fPIC -DPIC -o .libs/greet.o
greet.c: In function 'log_to_audit_system':
greet.c:435:40: error: passing argument 3 of 'pam_get_item' from incompatible pointer type [-Wincompatible-pointer-types]
  435 |         pam_get_item(pamhp, PAM_RHOST, &hostname);
      |                                        ^~~~~~~~~
      |                                        |
      |                                        char **
In file included from /usr/include/security/pam_appl.h:18,
                 from ../include/dm.h:105,
                 from greet.c:73:
/usr/include/security/_pam_types.h:175:68: note: expected 'const void **' but argument is of type 'char **'
  175 | pam_get_item(const pam_handle_t *pamh, int item_type, const void **item);
      |                                                       ~~~~~~~~~~~~~^~~~
greet.c:436:38: error: passing argument 3 of 'pam_get_item' from incompatible pointer type [-Wincompatible-pointer-types]
  436 |         pam_get_item(pamhp, PAM_TTY, &tty);
      |                                      ^~~~
      |                                      |
      |                                      char **
/usr/include/security/_pam_types.h:175:68: note: expected 'const void **' but argument is of type 'char **'
  175 | pam_get_item(const pam_handle_t *pamh, int item_type, const void **item);
      |                                                       ~~~~~~~~~~~~~^~~~
greet.c:437:39: error: passing argument 3 of 'pam_get_item' from incompatible pointer type [-Wincompatible-pointer-types]
  437 |         pam_get_item(pamhp, PAM_USER, &login);
      |                                       ^~~~~~
      |                                       |
      |                                       char **
/usr/include/security/_pam_types.h:175:68: note: expected 'const void **' but argument is of type 'char **'
  175 | pam_get_item(const pam_handle_t *pamh, int item_type, const void **item);
      |                                                       ~~~~~~~~~~~~~^~~~
greet.c:440:9: warning: ignoring return value of 'audit_log_acct_message' declared with attribute 'warn_unused_result' [-Wunused-result]
  440 |         audit_log_acct_message(audit_fd, AUDIT_USER_LOGIN,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  441 |                 NULL, "login", login ? login : "(unknown)",
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  442 |                 pw ? pw->pw_uid : -1, hostname, NULL, tty, success);
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
make[2]: *** [Makefile:539: greet.lo] Error 1

Ah, I didn't see those in my Solaris builds because the Solaris pam_appl.h has:

extern int
pam_get_item(
        const pam_handle_t *__pamh,     /* PAM handle */
        int __item_type,                /* Type of object - see below */
        void ** __item                  /* Address of place to put pointer */
                                        /*   to object */
);

Strangely, I also don't see any warnings for pam_get_item() in our CI logs when building on Debian stable.

!19 (merged) is my attempt to fix.

Strangely, I also don't see any warnings for pam_get_item() in our CI logs when building on Debian stable.

Please try to build with -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3. This define is used by devel glibc so testing this on top of Debian stable does not make to much sense.

Building on a Linux system with those flags gives me a few more warnings, but no new errors. If you're having problems with your particular setup after pulling the changes I merged for the PAM functions already, you can submit a merge request to fix them.

mentioned in issue #16 (closed)