[Bug analyzer/104560] New: False positive from -Wanalyzer-free-of-non-heap seen with rdma-core

[Bug analyzer/104560] New: False positive from -Wanalyzer-free-of-non-heap seen with rdma-core

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104560

            Bug ID: 104560
           Summary: False positive from -Wanalyzer-free-of-non-heap seen
                    with rdma-core
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

Created attachment 52450
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52450&action=edit
Reduced reproducer

I'm seeing various -Wanalyzer-free-of-non-heap when compiling rdma-core with
-fanalyzer, e.g.:

rdma-core-33.0/providers/mlx5/mlx5.c: scope_hint: In function
'mlx5_uninit_device'
rdma-core-33.0/providers/mlx5/mlx5.c:2101:9:
warning[-Wanalyzer-free-of-non-heap]: 'free' of '&*verbs_device.device' which
points to memory not on the heap
# 2099|         struct mlx5_device *dev = to_mdev(&verbs_device->device);
# 2100|   
# 2101|->       free(dev);
# 2102|   }
# 2103|   

Am attaching a reproducer, which triggers the current false positive with trunk
when compiled without optimization:

<source>: In function 'mlx5_uninit_device':
<source>:42:9: warning: 'free' of 'dev' which points to memory not on the heap
[CWE-590] [-Wanalyzer-free-of-non-heap]
   42 |         __builtin_free(dev);
      |         ^~~~~~~~~~~~~~~~~~~
  'mlx5_uninit_device': events 1-3
    |
    |   40 |         struct mlx5_device *dev = to_mdev(&verbs_device->device);
    |      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    |      |                                   |
    |      |                                   (1) pointer is from here
    |      |                                   (2) pointer is from here
    |   41 | 
    |   42 |         __builtin_free(dev);
    |      |         ~~~~~~~~~~~~~~~~~~~        
    |      |         |
    |      |         (3) call to 'free' here
    |

Uploaded to Compiler Explorer as:
  https://godbolt.org/z/nazc15z1h

[Bug analyzer/104560] False positive from -Wanalyzer-free-of-non-heap seen with rdma-core

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104560

--- Comment #1 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:a61aaee63848d422e8443e17bbec3257ee59d5d8

commit r12-7268-ga61aaee63848d422e8443e17bbec3257ee59d5d8
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Wed Feb 16 09:06:46 2022 -0500

    analyzer: fixes to free of non-heap detection [PR104560]

    PR analyzer/104560 reports various false positives from
    -Wanalyzer-free-of-non-heap seen with rdma-core, on what's
    effectively:

      free (&ptr->field)

    where in this case "field" is the first element of its struct, and thus
    &ptr->field == ptr, and could be on the heap.

    The root cause is due to malloc_state_machine::on_stmt making
      "LHS = &EXPR;"
    transition LHS from start to non_heap when EXPR is not a MEM_REF;
    this assumption doesn't hold for the above case.

    This patch eliminates that state transition, instead relying on
    malloc_state_machine::get_default_state to detect regions known to
    not be on the heap.
    Doing so fixes the false positive, but eliminates some events relating
    to free-of-alloca identifying the alloca, so the patch also reworks
    free_of_non_heap to capture which region has been freed, adding
    region creation events to diagnostic paths, so that the alloca calls
    can be identified, and using the memory space of the region for more
    precise wording of the diagnostic.
    The improvement to malloc_state_machine::get_default_state also
    means we now detect attempts to free VLAs, functions and code labels.

    In doing so I spotted that I wasn't adding region creation events for
    regions for global variables, and for cases where an allocation is the
    last stmt within its basic block, so the patch also fixes these issues.

    gcc/analyzer/ChangeLog:
            PR analyzer/104560
            * diagnostic-manager.cc (diagnostic_manager::build_emission_path):
            Add region creation events for globals of interest.
            (null_assignment_sm_context::get_old_program_state): New.
            (diagnostic_manager::add_events_for_eedge): Move check for
            changing dynamic extents from PK_BEFORE_STMT case to after the
            switch on the dst_point's kind so that we can emit them for the
            final stmt in a basic block.
            * engine.cc (impl_sm_context::get_old_program_state): New.
            * sm-malloc.cc (malloc_state_machine::get_default_state): Rewrite
            detection of m_non_heap to use get_memory_space.
            (free_of_non_heap::free_of_non_heap): Add freed_reg param.
            (free_of_non_heap::subclass_equal_p): Update for changes to
            fields.
            (free_of_non_heap::emit): Drop m_kind in favor of
            get_memory_space.
            (free_of_non_heap::describe_state_change): Remove logic for
            detecting alloca.
            (free_of_non_heap::mark_interesting_stuff): Add region-creation of
            m_freed_reg.
            (free_of_non_heap::get_memory_space): New.
            (free_of_non_heap::kind): Drop enum.
            (free_of_non_heap::m_freed_reg): New field.
            (free_of_non_heap::m_kind): Drop field.
            (malloc_state_machine::on_stmt): Drop transition to m_non_heap.
            (malloc_state_machine::handle_free_of_non_heap): New function,
            split out from on_deallocator_call and on_realloc_call, adding
            detection of the freed region.
            (malloc_state_machine::on_deallocator_call): Use it.
            (malloc_state_machine::on_realloc_call): Likewise.
            * sm.h (sm_context::get_old_program_state): New vfunc.

    gcc/testsuite/ChangeLog:
            PR analyzer/104560
            * g++.dg/analyzer/placement-new.C: Update expected wording.
            * g++.dg/analyzer/pr100244.C: Likewise.
            * gcc.dg/analyzer/attr-malloc-1.c (test_7): Likewise.
            * gcc.dg/analyzer/malloc-1.c (test_24): Likewise.
            (test_25): Likewise.
            (test_26): Likewise.
            (test_50a, test_50b, test_50c): New.
            * gcc.dg/analyzer/malloc-callbacks.c (test_5): Update expected
            wording.
            * gcc.dg/analyzer/malloc-paths-8.c: Likewise.
            * gcc.dg/analyzer/pr104560-1.c: New test.
            * gcc.dg/analyzer/pr104560-2.c: New test.
            * gcc.dg/analyzer/realloc-1.c (test_7): Updated expected wording.
            * gcc.dg/analyzer/vla-1.c (test_2): New.  Prune output from
            -Wfree-nonheap-object.

    Signed-off-by: David Malcolm <dmalcolm@redhat.com>

[Bug analyzer/104560] False positive from -Wanalyzer-free-of-non-heap seen with rdma-core

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104560

David Malcolm <dmalcolm at gcc dot gnu.org> changed:

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

--- Comment #2 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Should be fixed by the above commit