https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106473
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by David Malcolm <dmalc...@gcc.gnu.org>: https://gcc.gnu.org/g:ce917b0422c145779b83e005afd8433c0c86fb06 commit r13-4276-gce917b0422c145779b83e005afd8433c0c86fb06 Author: David Malcolm <dmalc...@redhat.com> Date: Wed Nov 23 20:43:33 2022 -0500 analyzer: revamp of heap-allocated regions [PR106473] PR analyzer/106473 reports a false positive from -Wanalyzer-malloc-leak on: void foo(char **args[], int *argc) { *argc = 1; (*args)[0] = __builtin_malloc(42); } The issue is that at the write to *argc we don't know if argc could point within *args, and so we conservatiely set *args to be unknown. At the write "(*args)[0] = __builtin_malloc(42)" we have the result of the allocation written through an unknown pointer, so we mark the heap_allocated_region as having escaped. Unfortunately, within store::canonicalize we overzealously purge the heap allocated region, losing the information that it has escaped, and thus errnoeously report a leak. The first part of the fix is to update store::canonicalize so that it doesn't purge heap_allocated_regions that are marked as escaping. Doing so fixes the leak false positive, but leads to various state explosions relating to anywhere we have a malloc/free pair in a loop, where the analysis of the iteration appears to only have been reaching a fixed state due to a bug in the state merger code that was erroneously merging state about the region allocated in one iteration with that of another. On touching that, the analyzer fails to reach a fixed state on any loops containing a malloc/free pair, since each analysis of a malloc was creating a new heap_allocated_region instance. Hence the second part of the fix is to revamp how heap_allocated_regions are managed within the analyzer. Rather than create a new one at each analysis of a malloc call, instead we reuse them across the analysis, only creating a new one if the current path's state is referencing all of the existing ones. Hence the heap_allocated_region instances get used in a fixed order along every analysis path, so e.g. at: if (flag) p = malloc (4096); else p = malloc (1024); both paths now use the same heap_allocated_region for their malloc calls - but we still end up with two enodes after the CFG merger, by rejecting merger of states with non-equal dynamic extents. gcc/analyzer/ChangeLog: PR analyzer/106473 * call-summary.cc (call_summary_replay::convert_region_from_summary_1): Update for change to creation of heap-allocated regions. * program-state.cc (test_program_state_1): Likewise. (test_program_state_merging): Likewise. * region-model-impl-calls.cc (kf_calloc::impl_call_pre): Likewise. (kf_malloc::impl_call_pre): Likewise. (kf_operator_new::impl_call_pre): Likewise. (kf_realloc::impl_call_postsuccess_with_move::update_model): Likewise. * region-model-manager.cc (region_model_manager::create_region_for_heap_alloc): Convert to... (region_model_manager::get_or_create_region_for_heap_alloc): ...this, reusing an existing region if it's unreferenced in the client state. * region-model-manager.h (region_model_manager::get_num_regions): New. (region_model_manager::create_region_for_heap_alloc): Convert to... (region_model_manager::get_or_create_region_for_heap_alloc): ...this. * region-model.cc (region_to_value_map::can_merge_with_p): Reject merger when the values are different. (region_model::create_region_for_heap_alloc): Convert to... (region_model::get_or_create_region_for_heap_alloc): ...this. (region_model::get_referenced_base_regions): New. (selftest::test_state_merging): Update for change to creation of heap-allocated regions. (selftest::test_malloc_constraints): Likewise. (selftest::test_malloc): Likewise. * region-model.h: Include "sbitmap.h". (region_model::create_region_for_heap_alloc): Convert to... (region_model::get_or_create_region_for_heap_alloc): ...this. (region_model::get_referenced_base_regions): New decl. * store.cc (store::canonicalize): Don't purge a heap-allocated region that's been marked as escaping. gcc/testsuite/ChangeLog: PR analyzer/106473 * gcc.dg/analyzer/aliasing-pr106473.c: New test. * gcc.dg/analyzer/allocation-size-2.c: Add -fanalyzer-fine-grained". * gcc.dg/analyzer/allocation-size-3.c: Likewise. * gcc.dg/analyzer/explode-1.c: Mark leak with XFAIL. * gcc.dg/analyzer/explode-3.c: New test. * gcc.dg/analyzer/malloc-reuse.c: New test. Signed-off-by: David Malcolm <dmalc...@redhat.com>
