* [Bug middle-end/77432] warn about null check after pointer dereference
[not found] <bug-77432-4@http.gcc.gnu.org/bugzilla/>
@ 2020-06-08 19:42 ` msebor at gcc dot gnu.org
2022-11-09 14:02 ` dmalcolm at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 5+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-06-08 19:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77432
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |msebor at gcc dot gnu.org
Last reconfirmed|2016-08-31 00:00:00 |2020-6-8
Known to fail| |10.1.0, 11.0, 7.3.0, 8.2.0,
| |9.1.0
--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
Reconfirming with GCC 11. The if statement is simplified to if (1 != 0) by
EVRP:
Visiting stmt b_4 = *a_3(D);
Intersecting
int * [1B, +INF] EQUIVALENCES: { a_3(D) } (1 elements)
and
int * VARYING
to
int * [1B, +INF] EQUIVALENCES: { a_3(D) } (1 elements)
pushing new range for a_3(D): int * [1B, +INF] EQUIVALENCES: { a_3(D) } (1
elements)
Visiting stmt if (a_3(D) != 0B)
Visiting conditional with predicate: if (a_3(D) != 0B)
With known ranges
a_3(D): int * [1B, +INF] EQUIVALENCES: { a_3(D) } (1 elements)
Predicate evaluates to: 1
gimple_simplified to if (1 != 0)
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug middle-end/77432] warn about null check after pointer dereference
[not found] <bug-77432-4@http.gcc.gnu.org/bugzilla/>
2020-06-08 19:42 ` [Bug middle-end/77432] warn about null check after pointer dereference msebor at gcc dot gnu.org
@ 2022-11-09 14:02 ` dmalcolm at gcc dot gnu.org
2022-11-10 18:31 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 5+ messages in thread
From: dmalcolm at gcc dot gnu.org @ 2022-11-09 14:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77432
David Malcolm <dmalcolm at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |dmalcolm at gcc dot gnu.org
--- Comment #5 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
I hadn't seen this, and I filed PR analyzer/99671 last year to track adding a
-fanalyzer warning for this. I now have a mostly-working implementation of the
latter which I'm hoping to post for stage 1.
Not sure if these are dupes or not (would we want a non-analyzer implementation
of this warning?)
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug middle-end/77432] warn about null check after pointer dereference
[not found] <bug-77432-4@http.gcc.gnu.org/bugzilla/>
2020-06-08 19:42 ` [Bug middle-end/77432] warn about null check after pointer dereference msebor at gcc dot gnu.org
2022-11-09 14:02 ` dmalcolm at gcc dot gnu.org
@ 2022-11-10 18:31 ` cvs-commit at gcc dot gnu.org
2022-11-10 18:56 ` dmalcolm at gcc dot gnu.org
2023-08-08 22:28 ` egallager at gcc dot gnu.org
4 siblings, 0 replies; 5+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-11-10 18:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77432
--- Comment #6 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:5c6546ca7d8cab1f1c129f5b55f709e2ceee0f94
commit r13-3884-g5c6546ca7d8cab1f1c129f5b55f709e2ceee0f94
Author: David Malcolm <dmalcolm@redhat.com>
Date: Thu Nov 10 13:23:56 2022 -0500
analyzer: new warning: -Wanalyzer-deref-before-check [PR99671]
This patch implements a new -Wanalyzer-deref-before-check within
-fanalyzer. It complains about code paths in which a pointer is checked
for NULL after it has already been dereferenced.
For example, for the testcase in PR 77432 the diagnostic emits:
deref-before-check-1.c: In function 'test_from_pr77432':
deref-before-check-1.c:6:8: warning: check of 'a' for NULL after already
dereferencing it [-Wanalyzer-deref-before-check]
6 | if (a)
| ^
'test_from_pr77432': events 1-2
|
| 5 | int b = *a;
| | ^
| | |
| | (1) pointer 'a' is dereferenced here
| 6 | if (a)
| | ~
| | |
| | (2) pointer 'a' is checked for NULL here but it was
already dereferenced at (1)
|
and in PR 77425 we had an instance of this hidden behind a
macro, which the diagnostic complains about as follows:
deref-before-check-pr77425.c: In function 'get_odr_type':
deref-before-check-pr77425.c:35:10: warning: check of 'odr_types_ptr' for
NULL after already dereferencing it [-Wanalyzer-deref-before-check]
35 | if (odr_types_ptr)
| ^
'get_odr_type': events 1-3
|
| 27 | if (cond)
| | ^
| | |
| | (1) following 'false' branch...
|......
| 31 | else if (other_cond)
| | ~~~~~~~~~~~
| | ||
| | |(2) ...to here
| | (3) following 'true' branch...
|
'get_odr_type': event 4
|
| 11 | #define odr_types (*odr_types_ptr)
| | ~^~~~~~~~~~~~~~~
| | |
| | (4) ...to here
deref-before-check-pr77425.c:33:7: note: in expansion of macro 'odr_types'
| 33 | odr_types[val->id] = 0;
| | ^~~~~~~~~
|
'get_odr_type': event 5
|
| 11 | #define odr_types (*odr_types_ptr)
| | ~^~~~~~~~~~~~~~~
| | |
| | (5) pointer 'odr_types_ptr' is dereferenced
here
deref-before-check-pr77425.c:33:7: note: in expansion of macro 'odr_types'
| 33 | odr_types[val->id] = 0;
| | ^~~~~~~~~
|
'get_odr_type': event 6
|
| 35 | if (odr_types_ptr)
| | ^
| | |
| | (6) pointer 'odr_types_ptr' is checked for NULL here
but it was already dereferenced at (5)
|
gcc/analyzer/ChangeLog:
PR analyzer/99671
* analyzer.opt (Wanalyzer-deref-before-check): New warning.
* diagnostic-manager.cc
(null_assignment_sm_context::set_next_state): Only add state
change events for transition to "null" state.
(null_assignment_sm_context::is_transition_to_null): New.
* engine.cc (impl_region_model_context::on_pop_frame): New.
* exploded-graph.h (impl_region_model_context::on_pop_frame): New
decl.
* program-state.cc (sm_state_map::clear_any_state): New.
(sm_state_map::can_merge_with_p): New.
(program_state::can_merge_with_p): Replace requirement that
sm-states be equal in favor of an attempt to merge them.
* program-state.h (sm_state_map::clear_any_state): New decl.
(sm_state_map::can_merge_with_p): New decl.
* region-model.cc (region_model::eval_condition): Make const.
(region_model::pop_frame): Call ctxt->on_pop_frame.
* region-model.h (region_model::eval_condition): Make const.
(region_model_context::on_pop_frame): New vfunc.
(noop_region_model_context::on_pop_frame): New.
(region_model_context_decorator::on_pop_frame): New.
* sm-malloc.cc (enum resource_state): Add RS_ASSUMED_NON_NULL.
(allocation_state::dump_to_pp): Drop "final".
(struct assumed_non_null_state): New subclass.
(malloc_state_machine::m_assumed_non_null): New.
(assumed_non_null_p): New.
(class deref_before_check): New.
(assumed_non_null_state::dump_to_pp): New.
(malloc_state_machine::get_or_create_assumed_non_null_state_for_frame):
New.
(malloc_state_machine::maybe_assume_non_null): New.
(malloc_state_machine::on_stmt): Transition from start state to
"assumed-non-null" state for pointers passed to
__attribute__((nonnull)) arguments, and for pointers explicitly
dereferenced. Call maybe_complain_about_deref_before_check for
pointers explicitly compared against NULL.
(malloc_state_machine::maybe_complain_about_deref_before_check):
New.
(malloc_state_machine::on_deallocator_call): Also transition
"assumed-non-null" states to "freed".
(malloc_state_machine::on_pop_frame): New.
(malloc_state_machine::maybe_get_merged_states_nonequal): New.
* sm-malloc.dot: Update for changes to sm-malloc.cc.
* sm.h (state_machine::on_pop_frame): New.
(state_machine::maybe_get_merged_state): New.
(state_machine::maybe_get_merged_states_nonequal): New.
gcc/ChangeLog:
*
doc/gcc/gcc-command-options/options-that-control-static-analysis.rst:
Add -Wanalyzer-deref-before-check.
gcc/testsuite/ChangeLog:
* gcc.dg/analyzer/deref-before-check-1.c: New test.
* gcc.dg/analyzer/deref-before-check-2.c: New test.
* gcc.dg/analyzer/deref-before-check-pr77425.c: New test.
* gcc.dg/analyzer/malloc-1.c (test_51): New test.
gcc/ChangeLog:
PR analyzer/99671
* tristate.h (tristate::is_unknown): New.
Signed-off-by: David Malcolm <dmalcolm@redhat.com>
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug middle-end/77432] warn about null check after pointer dereference
[not found] <bug-77432-4@http.gcc.gnu.org/bugzilla/>
` (2 preceding siblings ...)
2022-11-10 18:31 ` cvs-commit at gcc dot gnu.org
@ 2022-11-10 18:56 ` dmalcolm at gcc dot gnu.org
2023-08-08 22:28 ` egallager at gcc dot gnu.org
4 siblings, 0 replies; 5+ messages in thread
From: dmalcolm at gcc dot gnu.org @ 2022-11-10 18:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77432
--- Comment #7 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
(In reply to David Malcolm from comment #5)
> I hadn't seen this, and I filed PR analyzer/99671 last year to track adding
> a -fanalyzer warning for this. I now have a mostly-working implementation
> of the latter which I'm hoping to post for stage 1.
I've now committed the above patch implementing -Wanalyzer-deref-before-check
for GCC 13 as part of -fanalyzer.
> Not sure if these are dupes or not (would we want a non-analyzer
> implementation of this warning?)
Do we want a non-analyzer implementation of this warning, or should we close
this out?
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug middle-end/77432] warn about null check after pointer dereference
[not found] <bug-77432-4@http.gcc.gnu.org/bugzilla/>
` (3 preceding siblings ...)
2022-11-10 18:56 ` dmalcolm at gcc dot gnu.org
@ 2023-08-08 22:28 ` egallager at gcc dot gnu.org
4 siblings, 0 replies; 5+ messages in thread
From: egallager at gcc dot gnu.org @ 2023-08-08 22:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77432
--- Comment #8 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to David Malcolm from comment #7)
> > Not sure if these are dupes or not (would we want a non-analyzer
> > implementation of this warning?)
>
> Do we want a non-analyzer implementation of this warning, or should we close
> this out?
Well how difficult would a non-analyzer implementation be?
^ permalink raw reply [flat|nested] 5+ messages in thread