[Bug c/106537] New: GCC doesn't support -W[no-]compare-distinct-pointer-types

[Bug c/106537] New: GCC doesn't support -W[no-]compare-distinct-pointer-types

[jose.marchesi at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

            Bug ID: 106537
           Summary: GCC doesn't support
                    -W[no-]compare-distinct-pointer-types
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jose.marchesi at oracle dot com
  Target Milestone: ---

GCC emits pedwarns unconditionally when comparing pointers of different types,
for example:

  int xdp_context (struct xdp_md *xdp)
  {
    void *data = (void *)(long)xdp->data;
    __u32 *metadata = (void *)(long)xdp->data_meta;
    __u32 ret;

    if (metadata + 1 > data)
      return 0;
    return 1;
  }

  /home/jemarch/foo.c: In function ‘xdp_context’:
  /home/jemarch/foo.c:15:20: warning: comparison of distinct pointer types
lacks a cast
     15 |   if (metadata + 1 > data)
        |                    ^

LLVM supports an option -W[no-]compare-distinct-pointer-types that can be used
in order to enable or disable the emission of such warnings.  It is enabled by
default.

This option is used in the kernel source tree for some BPF programs.

I already got a patch for this.

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
           Keywords|                            |diagnostic

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
> This option is used in the kernel source tree for some BPF programs.

Why not fix the sources? Seems not hard to add a cast or two.

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[jose.marchesi at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

--- Comment #2 from Jose E. Marchesi <jose.marchesi at oracle dot com> ---
(In reply to Andrew Pinski from comment #1)
> > This option is used in the kernel source tree for some BPF programs.
> 
> Why not fix the sources? Seems not hard to add a cast or two.

That's what I would recommend.  But since LLVM supports that switch it becomes
difficult to convince people to not use it in case they are already using it.

Sent a proposal patch in:
https://gcc.gnu.org/pipermail/gcc-patches/2022-August/599393.html

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

Eric Gallager <egallager at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |egallager at gcc dot gnu.org
             Blocks|                            |44209

--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
This is an example of bug 44209


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44209
[Bug 44209] [meta-bug] Some warnings are not linked to diagnostics options

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jose E. Marchesi <jemarch@gcc.gnu.org>:

https://gcc.gnu.org/g:e1f45bea2741c271efbc4c2f9dfad93cbcd644c0

commit r14-3291-ge1f45bea2741c271efbc4c2f9dfad93cbcd644c0
Author: Jose E. Marchesi <jose.marchesi@oracle.com>
Date:   Thu Aug 17 15:36:26 2023 +0200

    Add warning options -W[no-]compare-distinct-pointer-types

    GCC emits pedwarns unconditionally when comparing pointers of
    different types, for example:

      int xdp_context (struct xdp_md *xdp)
        {
            void *data = (void *)(long)xdp->data;
            __u32 *metadata = (void *)(long)xdp->data_meta;
            __u32 ret;

            if (metadata + 1 > data)
              return 0;
            return 1;
       }

      /home/jemarch/foo.c: In function âxdp_contextâ:
      /home/jemarch/foo.c:15:20: warning: comparison of distinct pointer types
lacks a cast
             15 |   if (metadata + 1 > data)
                     |                    ^

    LLVM supports an option -W[no-]compare-distinct-pointer-types that can
    be used in order to enable or disable the emission of such warnings.
    It is enabled by default.

    This patch adds the same options to GCC.

    Documentation and testsuite updated included.
    Regtested in x86_64-linu-gnu.
    No regressions observed.

    gcc/ChangeLog:

            PR c/106537
            * doc/invoke.texi (Option Summary): Mention
            -Wcompare-distinct-pointer-types under `Warning Options'.
            (Warning Options): Document -Wcompare-distinct-pointer-types.

    gcc/c-family/ChangeLog:

            PR c/106537
            * c.opt (Wcompare-distinct-pointer-types): New option.

    gcc/c/ChangeLog:

            PR c/106537
            * c-typeck.cc (build_binary_op): Warning on comparing distinct
            pointer types only when -Wcompare-distinct-pointer-types.

    gcc/testsuite/ChangeLog:

            PR c/106537
            * gcc.c-torture/compile/pr106537-1.c: New test.
            * gcc.c-torture/compile/pr106537-2.c: Likewise.
            * gcc.c-torture/compile/pr106537-3.c: Likewise.

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[jemarch at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

Jose E. Marchesi <jemarch at gcc dot gnu.org> changed:

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

--- Comment #5 from Jose E. Marchesi <jemarch at gcc dot gnu.org> ---
Fixed in the commit above.

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

--- Comment #6 from Eric Gallager <egallager at gcc dot gnu.org> ---
Would it be possible to add a fix-it hint to this warning, too, while you're at
it?

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[dje at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

David Edelsohn <dje at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dje at gcc dot gnu.org

--- Comment #7 from David Edelsohn <dje at gcc dot gnu.org> ---
The new testcases in the testsuite for this PR are failing.  Is anyone working
on these new failures? Is this being tracked in this PR or a new PR for the
failures?

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[jemarch at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

Jose E. Marchesi <jemarch at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|RESOLVED                    |REOPENED
   Last reconfirmed|                            |2023-08-24
         Resolution|FIXED                       |---

--- Comment #8 from Jose E. Marchesi <jemarch at gcc dot gnu.org> ---
I am on it.

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jose E. Marchesi <jemarch@gcc.gnu.org>:

https://gcc.gnu.org/g:721f7e2c4e5eed645593258624dd91e6c39f3bd2

commit r14-3470-g721f7e2c4e5eed645593258624dd91e6c39f3bd2
Author: Jose E. Marchesi <jose.marchesi@oracle.com>
Date:   Thu Aug 24 17:10:52 2023 +0200

    Fix tests for PR 106537.

    This patch fixes the tests for PR 106537 (support for
    -W[no]-compare-distinct-pointer-types) which were expecting the
    warning when checking for equality/inequality of void pointers with
    non-function pointers.

    gcc/testsuite/ChangeLog:

            PR c/106537
            * gcc.c-torture/compile/pr106537-1.c: Comparing void pointers to
            non-function pointers is legit.
            * gcc.c-torture/compile/pr106537-2.c: Likewise.

[Bug c/106537] GCC doesn't support -W[no-]compare-distinct-pointer-types

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106537

Sam James <sjames at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
           Assignee|unassigned at gcc dot gnu.org      |jemarch at gcc dot gnu.org
   Target Milestone|---                         |14.0
         Resolution|---                         |FIXED

--- Comment #10 from Sam James <sjames at gcc dot gnu.org> ---
Done for 14, I think?