[Bug c/106416] New: -Wint-conversion should be an error, not a pedwarn

[Bug c/106416] New: -Wint-conversion should be an error, not a pedwarn

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

            Bug ID: 106416
           Summary: -Wint-conversion should be an error, not a pedwarn
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

Aaron Ballman and I discussed this recently, and now he just made this an error
in Clang, with the following justification:

  Clang has traditionally allowed C programs to implicitly convert
  integers to pointers and pointers to integers, despite it not being
  valid to do so except under special circumstances (like converting the
  integer 0, which is the null pointer constant, to a pointer). In C89,
  this would result in undefined behavior per 3.3.4, and in C99 this rule
  was strengthened to be a constraint violation instead. Constraint
  violations are most often handled as an error.

  This patch changes the warning to default to an error in all C modes
  (it is already an error in C++). This gives us better security posture
  by calling out potential programmer mistakes in code but still allows
  users who need this behavior to use -Wno-error=int-conversion to retain
  the warning behavior, or -Wno-int-conversion to silence the diagnostic
  entirely.

GCC should do the same, for the same reasons. It's an error, and should not be
accepted by default in 2022.

I tried to look at how to change gcc/c/c-typeck.cc so that the pedwarns in
convert_for_assignment are errors by default, unless you use
-Wno-error=int-conversion, but I'm not sure how to make that happen.

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |mpolacek at gcc dot gnu.org
   Last reconfirmed|                            |2022-07-25

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

Florian Weimer <fw at gcc dot gnu.org> changed:

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

--- Comment #1 from Florian Weimer <fw at gcc dot gnu.org> ---
This will likely need the same preparatory treatment as rejecting implicit
function declarations (bug 91092), for the same reason: Without some care
upfront, introducing the new compiler error will change configure test results
in fully consistent ways, resulting in silently dropped features.

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=91092

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, definitely in the same category.

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

David Binderman <dcb314 at hotmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dcb314 at hotmail dot com

--- Comment #3 from David Binderman <dcb314 at hotmail dot com> ---
Interestingly, for this C code:

extern void g( int);

void f( int *p)
{
        int a = p;
        int b = (int *) p;

        g( a);
        g( b);
}

gcc does this:

$ /home/dcb/gcc/results/bin/gcc -c -std=c2x jul31a.c
jul31a.c: In function ‘f’:
jul31a.c:6:17: warning: initialization of ‘int’ from ‘int *’ makes integer from
pointer without a cast [-Wint-conversion]
    6 |         int a = p;
      |                 ^
jul31a.c:7:17: warning: initialization of ‘int’ from ‘int *’ makes integer from
pointer without a cast [-Wint-conversion]
    7 |         int b = (int *) p;
      |                 ^
$

The second warning looks wrong to me.

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
> The second warning looks wrong to me.

It is right. Try doing the cast to int instead of a pointer (to int).

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

--- Comment #5 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Andrew Pinski from comment #4)
> > The second warning looks wrong to me.
> 
> It is right. Try doing the cast to int instead of a pointer (to int).

Thanks for the correction. gcc does the right thing.

New warning output is:

$ /home/dcb/gcc/results/bin/gcc -c -std=c2x bug834.c
bug834.c: In function ‘f’:
bug834.c:6:17: warning: initialization of ‘int’ from ‘int *’ makes integer from
pointer without a cast [-Wint-conversion]
    6 |         int a = p;
      |                 ^
bug834.c:7:17: warning: cast from pointer to integer of different size
[-Wpointer-to-int-cast]
    7 |         int b = (int) p;
      |                 ^
$

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Florian Weimer <fw@gcc.gnu.org>:

https://gcc.gnu.org/g:2c3db94d9fd07681f8806dae93d555779ff4dfb1

commit r14-6032-g2c3db94d9fd07681f8806dae93d555779ff4dfb1
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Dec 1 08:10:12 2023 +0100

    c: Turn int-conversion warnings into permerrors

    gcc/

            * doc/invoke.texi (Warning Options): Document changes.

    gcc/c/

            PR c/96284
            PR c/106416
            * c-typeck.cc (build_conditional_expr): Use permerror_opt for
            pointer/integer type mismatches, based on -Wint-conversion.
            (pedwarn_permerror_init, permerror_init): New function.
            (pedwarn_init): Call pedwarn_permerror_init.
            (convert_for_assignment): Use permerror_opt and
            permerror_init for -Wint-conversion warnings.

    gcc/testsuite/

            * gcc.dg/permerror-default.c (int_conversion_1)
            (int_conversion_2): Expect the new permerrors.
            * gcc.dg/permerror-gnu89-nopermissive.c (int_conversion_1)
            (int_conversion_2): Likewise.
            * gcc.dg/permerror-system.c: Likewise.
            * c-c++-common/pr77624-1.c (foo, bar): Expect
            error instead of warning.
            * gcc.dg/Wint-conversion-2.c: Compile with -fpermissive due
            to expected int-conversion warning.
            * gcc.dg/Wint-conversion-3.c: Likewise.
            * gcc.dg/Wint-conversion-4.c: New test.  Based on
            gcc.dg/Wint-conversion-3.c.  Expect int-conversion errors.
            * gcc.dg/assign-warn-1.c: Compile with -fpermissive.
            * gcc.dg/assign-warn-4.c: New file.  Extracted from
            assign-warn1.c.  Expect int-conversion errors.
            * gcc.dg/diagnostic-types-1.c: Compile with -fpermissive.
            * gcc.dg/diagnostic-types-2.c: New file.  Extracted from
            gcc.dg/diagnostic-types-1.c.  Expect some errors instead of
            warnings.
            * gcc.dg/gomp/pr35738.c: Compile with -fpermissive due to
            expected int-conversion error.
            * gcc.dg/gomp/pr35738-2.c: New test.  Based on
            gcc.dg/gomp/pr35738.c.  Expect int-converison errors.
            * gcc.dg/init-excess-3.c: Expect int-converison errors.
            * gcc.dg/overflow-warn-1.c: Likewise.
            * gcc.dg/overflow-warn-3.c: Likewise.
            * gcc.dg/param-type-mismatch.c: Compile with -fpermissive.
            * gcc.dg/param-type-mismatch-2.c: New test.  Copied from
            gcc.dg/param-type-mismatch.c.  Expect errors.
            * gcc.dg/pr61162-2.c: Compile with -fpermissive.
            * gcc.dg/pr61162-3.c: New test. Extracted from
            gcc.dg/pr61162-2.c.  Expect int-conversion errors.
            * gcc.dg/spec-barrier-3.c: Use -fpermissive due to expected
            int-conversion error.
            * gcc.dg/spec-barrier-3a.c: New test.  Based on
            gcc.dg/spec-barrier-3.c.  Expect int-conversion errors.
            * gcc.target/aarch64/acle/memtag_2.c: Use -fpermissive due to
expected
            int-conversion error.
            * gcc.target/aarch64/acle/memtag_2a.c: New test.  Copied from
            gcc.target/aarch64/acle/memtag_2.c.  Expect error.
            * gcc.target/aarch64/sve/acle/general-c/load_3.c (f1): Expect
            error.
            * gcc.target/aarch64/sve/acle/general-c/store_2.c (f1): Likewise.
            * gcc.target/aarch64/sve/acle/general-c/store_scatter_index_1.c
            (f1): Likewise.
            *
gcc.target/aarch64/sve/acle/general-c/store_scatter_index_restricted_1.c
            (f1): Likewise.
            * gcc.target/aarch64/sve/acle/general-c/store_scatter_offset_2.c
            (f1): Likewise.
            *
gcc.target/aarch64/sve/acle/general-c/store_scatter_offset_restricted_1.c
            (f1): Likewise.

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

Florian Weimer <fw at gcc dot gnu.org> changed:

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

--- Comment #7 from Florian Weimer <fw at gcc dot gnu.org> ---
Fixed for GCC 14.

[Bug c/106416] -Wint-conversion should be an error, not a pedwarn

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106416

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0