[Bug middle-end/90404] No warning on attempts to modify a const object

[Bug middle-end/90404] No warning on attempts to modify a const object

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
          Component|c                           |middle-end

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
No progress for GCC 10.  I plan to work on it for GCC 11.

Here's a test case where the fact that the modification is invalid is less
obvious and doesn't trigger a warning.  The dump shows how the code emitted by
GCC makes assumptions that make the undefined behavior manifest without ever
causing the program to crash at runtime.

$ cat x.C && gcc -O2 -S -Wall -Wextra -Wcast-qual -Wpedantic
-fdump-tree-optimized=/dev/stdout x.C
const char a[] = "012.45";

int f (void)
{
  char *p = __builtin_strchr (a, '.');
  *p = 0;

  if (__builtin_strlen (p) != 3)   // folded to false
    __builtin_abort ();

  return a[3] == 0;                // also folded to false
}

;; Function f (_Z1fv, funcdef_no=0, decl_uid=2328, cgraph_uid=1,
symbol_order=1)

f ()
{
  <bb 2> [local count: 1073741824]:
  return 0;

}

[Bug middle-end/90404] No warning on attempts to modify a const object

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=94169

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
See also pr94169 for a related class of problems that would be worth warning
on.

[Bug middle-end/90404] No warning on attempts to modify a const object

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=94313

--- Comment #6 from Martin Sebor <msebor at gcc dot gnu.org> ---
See also pr94313 which shows how reliably diagnosing some of these invalid
stores is made challenging by optimizations that remove them.

[Bug middle-end/90404] No warning on attempts to modify a const object

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:3175d40fc52fb8eb3c3b18cc343d773da24434fb

commit r11-3829-g3175d40fc52fb8eb3c3b18cc343d773da24434fb
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Wed Oct 7 18:34:09 2020 -0400

    analyzer: add warnings about writes to constant regions [PR95007]

    This patch adds two new warnings:
      -Wanalyzer-write-to-const
      -Wanalyzer-write-to-string-literal
    for code paths where the analyzer detects a write to a constant region.

    As noted in the documentation part of the patch, the analyzer doesn't
    prioritize detection of such writes, in that the state-merging logic
    will blithely lose the distinction between const and non-const regions.
    Hence false negatives are likely to arise due to state-merging.

    However, if the analyzer does happen to spot such a write, it seems worth
    reporting, hence this patch.

    gcc/analyzer/ChangeLog:
            * analyzer.opt (Wanalyzer-write-to-const): New.
            (Wanalyzer-write-to-string-literal): New.
            * region-model-impl-calls.cc (region_model::impl_call_memcpy):
            Call check_for_writable_region.
            (region_model::impl_call_memset): Likewise.
            (region_model::impl_call_strcpy): Likewise.
            * region-model.cc (class write_to_const_diagnostic): New.
            (class write_to_string_literal_diagnostic): New.
            (region_model::check_for_writable_region): New.
            (region_model::set_value): Call check_for_writable_region.
            * region-model.h (region_model::check_for_writable_region): New
            decl.

    gcc/ChangeLog:
            * doc/invoke.texi: Document -Wanalyzer-write-to-const and
            -Wanalyzer-write-to-string-literal.

    gcc/testsuite/ChangeLog:
            PR c/83347
            PR middle-end/90404
            PR analyzer/95007
            * gcc.dg/analyzer/write-to-const-1.c: New test.
            * gcc.dg/analyzer/write-to-string-literal-1.c: New test.

[Bug middle-end/90404] No warning on attempts to modify a const object

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.0                        |11.2

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 11.1 has been released, retargeting bugs to GCC 11.2.

[Bug middle-end/90404] No warning on attempts to modify a const object

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jamborm at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=100994

--- Comment #9 from Martin Jambor <jamborm at gcc dot gnu.org> ---
As discussed on the mailing list, such warning should also catch situations
like the testcase in pr100994 comment #4.

[Bug middle-end/90404] No warning on attempts to modify a const object

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.2                        |---

[Bug middle-end/90404] No warning on attempts to modify a const object

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
           Assignee|msebor at gcc dot gnu.org          |unassigned at gcc dot gnu.org

--- Comment #10 from Martin Sebor <msebor at gcc dot gnu.org> ---
I'm not working on this anymore.