[Bug c/63272] New: GCC should warn when using pointer to dead scoped variable within the same function

[Bug c/63272] New: GCC should warn when using pointer to dead scoped variable within the same function

[jacob.benoit.1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

            Bug ID: 63272
           Summary: GCC should warn when using pointer to dead scoped
                    variable within the same function
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jacob.benoit.1 at gmail dot com

Created attachment 33497
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33497&action=edit
testcase

Consider this testcase:

int foo(int i)
{
  int *p = 0;

  if (i)
  {
    int k = i;
    p = &k;
  } /* end of nested scope, k dies, p becomes a dangling pointer */

  return p ? *p : 0; /* the compiler should warn that p points to dead k */
}

Neither Clang 3.4 nor GCC 4.8 currently generate a warning. Yet, since all is
local to this function, it seems like something that a compiler could easily
warn against, and that would have saved me some time today!

Also see LLVM bug: http://llvm.org/bugs/show_bug.cgi?id=20952

[Bug c/63272] GCC should warn when using pointer to dead scoped variable within the same function

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-09-16
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
It would be nice to have. Perhaps related to PR49974.
>From gcc-bugs-return-461855-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Sep 16 06:38:12 2014
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #1)
> It would be nice to have. Perhaps related to PR49974.

Definitely related to PR 53855.
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Subject: [Bug c/63272] GCC should warn when using pointer to dead scoped variable within the same function
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc272

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
But really this is already talked about the warning in bug 60517 and really in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id`770#c1 .

[Bug c/63272] GCC should warn when using pointer to dead scoped variable within the same function

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

David Binderman <dcb314 at hotmail dot com> changed:

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

--- Comment #4 from David Binderman <dcb314 at hotmail dot com> ---
I can confirm that gcc version 11, some six years later, doesn't implement
this warning.

Fortunately, the cppcheck static analyser does.

Example code:

// Dangling pointer

void g( int *);

void f()
{
        int a;
        int * p = 0;

        {
                int b;

                p = &b;
        }
        g( p);
}

$ /home/dcb/cppcheck/trunk/cppcheck oct30a.cc
oct30a.cc:16:5: error: Using pointer to local variable 'b' that is out of
scope. [invalidLifetime]
 g( p);
    ^
oct30a.cc:14:7: note: Address of variable taken here.
  p = &b;
      ^
oct30a.cc:12:7: note: Variable created here.
  int b;
      ^
oct30a.cc:16:5: note: Using pointer to local variable 'b' that is out of scope.
 g( p);
    ^

[Bug c/63272] GCC should warn when using pointer to dead scoped variable within the same function

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |msebor at gcc dot gnu.org
           Keywords|                            |patch

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2021-November/583045.html

[Bug c/63272] GCC should warn when using pointer to dead scoped variable within the same function

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |oleg.pekar.2017 at gmail dot com

--- Comment #6 from Martin Sebor <msebor at gcc dot gnu.org> ---
*** Bug 98901 has been marked as a duplicate of this bug. ***

[Bug middle-end/63272] GCC should warn when using pointer to dead scoped variable within the same function

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

--- Comment #7 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Martin Sebor from comment #5)
> Patch: https://gcc.gnu.org/pipermail/gcc-patches/2021-November/583045.html

Weeks have rolled by and this patch doesn't seem to have made it into trunk.
Disappointing.

Time to nag someone with trunk write permission ?

[Bug middle-end/63272] GCC should warn when using pointer to dead scoped variable within the same function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>:

https://gcc.gnu.org/g:9d6a0f388eb048f8d87f47af78f07b5ce513bfe6

commit r12-6606-g9d6a0f388eb048f8d87f47af78f07b5ce513bfe6
Author: Martin Sebor <msebor@redhat.com>
Date:   Sat Jan 15 16:41:40 2022 -0700

    Add -Wdangling-pointer [PR63272].

    Resolves:
    PR c/63272 - GCC should warn when using pointer to dead scoped variable
with
    in the same function

    gcc/c-family/ChangeLog:

            PR c/63272
            * c.opt (-Wdangling-pointer): New option.

    gcc/ChangeLog:

            PR c/63272
            * diagnostic-spec.c (nowarn_spec_t::nowarn_spec_t): Handle
            -Wdangling-pointer.
            * doc/invoke.texi (-Wdangling-pointer): Document new option.
            * gimple-ssa-warn-access.cc (pass_waccess::clone): Set new member.
            (pass_waccess::check_pointer_uses): New function.
            (pass_waccess::gimple_call_return_arg): New function.
            (pass_waccess::gimple_call_return_arg_ref): New function.
            (pass_waccess::check_call_dangling): New function.
            (pass_waccess::check_dangling_uses): New function overloads.
            (pass_waccess::check_dangling_stores): New function.
            (pass_waccess::check_dangling_stores): New function.
            (pass_waccess::m_clobbers): New data member.
            (pass_waccess::m_func): New data member.
            (pass_waccess::m_run_number): New data member.
            (pass_waccess::m_check_dangling_p): New data member.
            (pass_waccess::check_alloca): Check m_early_checks_p.
            (pass_waccess::check_alloc_size_call): Same.
            (pass_waccess::check_strcat): Same.
            (pass_waccess::check_strncat): Same.
            (pass_waccess::check_stxcpy): Same.
            (pass_waccess::check_stxncpy): Same.
            (pass_waccess::check_strncmp): Same.
            (pass_waccess::check_memop_access): Same.
            (pass_waccess::check_read_access): Same.
            (pass_waccess::check_builtin): Call check_pointer_uses.
            (pass_waccess::warn_invalid_pointer): Add arguments.
            (is_auto_decl): New function.
            (pass_waccess::check_stmt): New function.
            (pass_waccess::check_block): Call check_stmt.
            (pass_waccess::execute): Call check_dangling_uses,
            check_dangling_stores.  Empty m_clobbers.
            * passes.def (pass_warn_access): Invoke pass two more times.

    gcc/testsuite/ChangeLog:

            PR c/63272
            * g++.dg/warn/Wfree-nonheap-object-6.C: Disable valid warnings.
            * g++.dg/warn/ref-temp1.C: Prune expected warning.
            * gcc.dg/uninit-pr50476.c: Expect a new warning.
            * c-c++-common/Wdangling-pointer-2.c: New test.
            * c-c++-common/Wdangling-pointer-3.c: New test.
            * c-c++-common/Wdangling-pointer-4.c: New test.
            * c-c++-common/Wdangling-pointer-5.c: New test.
            * c-c++-common/Wdangling-pointer-6.c: New test.
            * c-c++-common/Wdangling-pointer.c: New test.
            * g++.dg/warn/Wdangling-pointer-2.C: New test.
            * g++.dg/warn/Wdangling-pointer.C: New test.
            * gcc.dg/Wdangling-pointer-2.c: New test.
            * gcc.dg/Wdangling-pointer.c: New test.

[Bug middle-end/63272] GCC should warn when using pointer to dead scoped variable within the same function

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #9 from Martin Sebor <msebor at gcc dot gnu.org> ---
Implemented in GCC 12 as -Wdangling-pointer.

[Bug middle-end/63272] GCC should warn when using pointer to dead scoped variable within the same function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 88058 has been marked as a duplicate of this bug. ***

[Bug middle-end/63272] GCC should warn when using pointer to dead scoped variable within the same function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63272

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dgilbert at redhat dot com

--- Comment #11 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 89990 has been marked as a duplicate of this bug. ***