https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99774
--- Comment #1 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:3a66c289a3f395e50de79424e1e6f401a4dc1ab7 commit r11-8046-g3a66c289a3f395e50de79424e1e6f401a4dc1ab7 Author: David Malcolm <dmalc...@redhat.com> Date: Thu Apr 8 09:46:03 2021 -0400 analyzer: fix leak false +ves due to maybe-clobbered regions [PR99042,PR99774] Prior to this patch, program_state::detect_leaks worked by finding all live svalues in the old state and in the new state, and calling on_svalue_leak for each svalue that has changed from being live to not being live. PR analyzer/99042 and PR analyzer/99774 both describe false leak diagnostics from -fanalyzer (a false FILE * leak in git, and a false malloc leak in qemu, respectively). In both cases the root cause of the false leak diagnostic relates to svalues no longer being explicitly bound in the store due to regions being conservatively clobbered, due to an unknown function being called, or due to a write through a pointer that could alias the region, respectively. We have a transition from an svalue being explicitly live to not being explicitly live - but only because the store is being conservative, clobbering the binding. The leak detection is looking for transitions from "definitely live" to "not definitely live", when it should be looking for transitions from "definitely live" to "definitely not live". This patch introduces a new class to temporarily capture information about svalues that were explicitly live, but for which a region bound to them got clobbered for conservative reasons. This new "uncertainty_t" class is passed around to capture the data long enough for use in program_state::detect_leaks, where it is used to only complain about svalues that were definitely live and are now both not definitely live *or* possibly-live i.e. definitely not-live. The class also captures for which svalues we can't meaningfully track sm-state anymore, and resets the svalues back to the "start" state. Together, these changes fix the false leak reports. gcc/analyzer/ChangeLog: PR analyzer/99042 PR analyzer/99774 * engine.cc (impl_region_model_context::impl_region_model_context): Add uncertainty param and use it to initialize m_uncertainty. (impl_region_model_context::get_uncertainty): New. (impl_sm_context::get_fndecl_for_call): Add NULL for new uncertainty param when constructing impl_region_model_context. (impl_sm_context::get_state): Likewise. (impl_sm_context::set_next_state): Likewise. (impl_sm_context::warn): Likewise. (exploded_node::on_stmt): Add uncertainty param and use it when constructing impl_region_model_context. (exploded_node::on_edge): Add uncertainty param and pass to on_edge call. (exploded_node::detect_leaks): Create uncertainty_t and pass to impl_region_model_context. (exploded_graph::get_or_create_node): Create uncertainty_t and pass to prune_for_point. (maybe_process_run_of_before_supernode_enodes): Create uncertainty_t and pass to impl_region_model_context. (exploded_graph::process_node): Create uncertainty_t instances and pass around as needed. * exploded-graph.h (impl_region_model_context::impl_region_model_context): Add uncertainty param. (impl_region_model_context::get_uncertainty): New decl. (impl_region_model_context::m_uncertainty): New field. (exploded_node::on_stmt): Add uncertainty param. (exploded_node::on_edge): Likewise. * program-state.cc (sm_state_map::on_liveness_change): Get uncertainty from context and use it to unset sm-state from svalues as appropriate. (program_state::on_edge): Add uncertainty param and use it when constructing impl_region_model_context. Fix indentation. (program_state::prune_for_point): Add uncertainty param and use it when constructing impl_region_model_context. (program_state::detect_leaks): Get any uncertainty from ctxt and use it to get maybe-live svalues for dest_state, rather than definitely-live ones; use this when determining which svalues have leaked. (selftest::test_program_state_merging): Create uncertainty_t and pass to impl_region_model_context. * program-state.h (program_state::on_edge): Add uncertainty param. (program_state::prune_for_point): Likewise. * region-model-impl-calls.cc (call_details::get_uncertainty): New. (region_model::impl_call_memcpy): Pass uncertainty to mark_region_as_unknown call. (region_model::impl_call_memset): Likewise. (region_model::impl_call_strcpy): Likewise. * region-model-reachability.cc (reachable_regions::handle_sval): Also add sval to m_mutable_svals. * region-model.cc (region_model::on_assignment): Pass any uncertainty from ctxt to the store::set_value call. (region_model::handle_unrecognized_call): Get any uncertainty from ctxt and use it to record mutable svalues at the unknown call. (region_model::get_reachable_svalues): Add uncertainty param and use it to mark any maybe-bound svalues as being reachable. (region_model::set_value): Pass any uncertainty from ctxt to the store::set_value call. (region_model::mark_region_as_unknown): Add uncertainty param and pass it on to the store::mark_region_as_unknown call. (region_model::update_for_call_summary): Add uncertainty param and pass it on to the region_model::mark_region_as_unknown call. * region-model.h (call_details::get_uncertainty): New decl. (region_model::get_reachable_svalues): Add uncertainty param. (region_model::mark_region_as_unknown): Add uncertainty param. (region_model_context::get_uncertainty): New vfunc. (noop_region_model_context::get_uncertainty): New vfunc implementation. * store.cc (dump_svalue_set): New. (uncertainty_t::dump_to_pp): New. (uncertainty_t::dump): New. (binding_cluster::clobber_region): Pass NULL for uncertainty to remove_overlapping_bindings. (binding_cluster::mark_region_as_unknown): Add uncertainty param and pass it to remove_overlapping_bindings. (binding_cluster::remove_overlapping_bindings): Add uncertainty param. Use it to record any svalues that were in clobbered bindings. (store::set_value): Add uncertainty param. Pass it to binding_cluster::mark_region_as_unknown when handling symbolic regions. (store::mark_region_as_unknown): Add uncertainty param and pass it to binding_cluster::mark_region_as_unknown. (store::remove_overlapping_bindings): Add uncertainty param and pass it to binding_cluster::remove_overlapping_bindings. * store.h (binding_cluster::mark_region_as_unknown): Add uncertainty param. (binding_cluster::remove_overlapping_bindings): Likewise. (store::set_value): Likewise. (store::mark_region_as_unknown): Likewise. gcc/testsuite/ChangeLog: PR analyzer/99042 PR analyzer/99774 * gcc.dg/analyzer/pr99042.c: New test. * gcc.dg/analyzer/pr99774-1.c: New test. * gcc.dg/analyzer/pr99774-2.c: New test.
