[Bug regression/94436] New: incompatible-pointer-types warning with container_of

[Bug regression/94436] New: incompatible-pointer-types warning with container_of

[npfhrotynz-ptnqh.myvf at noclue dot notk.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94436

            Bug ID: 94436
           Summary: incompatible-pointer-types warning with container_of
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: regression
          Assignee: unassigned at gcc dot gnu.org
          Reporter: npfhrotynz-ptnqh.myvf at noclue dot notk.org
  Target Milestone: ---

Created attachment 48157
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48157&action=edit
test program.c

This looks like a regression in warnings: passing an argument straight from a
container_of construct fails with incompatible type warning.

In the attached code, the if 0'd implementation taken from the linux kernel
works, but the other one also seen in the linux kernel (why do they have
multiple implementations?!) produces the following warning:
------------
t.c: In function ‘main’:
t.c:14:41: warning: passing argument 1 of ‘func’ from incompatible pointer type
[-Wincompatible-pointer-types]
   14 | #define container_of(ptr, type, member) (type *)((char *)(ptr) - (char
*) &((type *)0)->member)
      |                                        
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                                         |
      |                                         char *
t.c:24:14: note: in expansion of macro ‘container_of’
   24 |  return func(container_of(&bar, struct foo, bar));
      |              ^~~~~~~~~~~~
t.c:17:22: note: expected ‘struct foo *’ but argument is of type ‘char *’
   17 | int func(struct foo* foo) {
      |          ~~~~~~~~~~~~^~~
-------------

Here is -E preprocessed interesting line:
return func((struct foo *)((char *)(&bar) - (char *) &((struct foo *)0)->bar));

For me the whole thing is cast with (struct foo*) so it should silence that
warning as it used to do (tested with gcc 7.4.0 and gcc 9.2.0)



In the case I'm looking at I could work around by using the other
implementation, but I see that macro defined all the time so would be
interested in seeing the old behaviour back.


Thanks!

[Bug regression/94436] incompatible-pointer-types warning with container_of

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94436

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this was fixed already. What git commit are you at?

[Bug regression/94436] incompatible-pointer-types warning with container_of

[npfhrotynz-ptnqh.myvf at noclue dot notk.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94436

Dominique Martinet <npfhrotynz-ptnqh.myvf at noclue dot notk.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Dominique Martinet <npfhrotynz-ptnqh.myvf at noclue dot notk.org> ---
Sorry I didn't check the latest git, I'm using whatever is shipped in fedora
32's gcc-10.0.1-0.9.fc32

. . . which I now see isn't even the latest ; and upgrading does fix this.

Sorry for the noise! And thanks for fast reply.

[Bug regression/94436] incompatible-pointer-types warning with container_of

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94436

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Indeed, this has been introduced with
r10-7127-gcb99630f254aaec6591e0a200b79905b31d24eb3
and fixed with r10-7237-g4e3d3e40726e1b68bf52fa205c68495124ea60b8

[Bug middle-end/94436] incompatible-pointer-types warning with container_of

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94436

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:e899d4b71255b9ae096a7ecd31a61fc76f200019

commit r10-7496-ge899d4b71255b9ae096a7ecd31a61fc76f200019
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Apr 1 14:33:32 2020 +0200

    Add testcase for already fixed PR [PR94436]

    2020-04-01  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/94436
            * gcc.dg/pr94436.c: New test.