From 8525d1f5f57b11fe04a97674cc2fc2b7727621d0 Mon Sep 17 00:00:00 2001 From: David Malcolm Date: Mon, 3 Feb 2020 11:23:09 -0500 Subject: [PATCH] analyzer: detect zero-assignment in phis (PR 93544) MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit PR analyzer/93544 reports an ICE when attempting to report a double-free within diagnostic_manager::prune_for_sm_diagnostic, in which the variable of interest has become an INTEGER_CST. Additionally, it picks a nonsensical path through the function in which the pointer being double-freed is known to be NULL, which we shouldn't complain about. The dump shows that it picks the INTEGER_CST when updating var at a phi node: considering event 4, with var: ‘iftmp.0_2’, state: ‘start’ updating from ‘iftmp.0_2’ to ‘0B’ based on phi node phi: iftmp.0_2 = PHI considering event 3, with var: ‘0B’, state: ‘start’ and that it has picked the shortest path through the exploded graph, and on this path the pointer has been assigned NULL. The root cause is that the state machine's on_stmt isn't called for phi nodes (and wouldn't make much sense, as we wouldn't know which arg to choose). malloc state machine::on_stmt "sees" a GIMPLE_ASSIGN to NULL and handles it by transitioning the lhs to the "null" state, but never "sees" GIMPLE_PHI nodes. This patch fixes the ICE by wiring up phi-handling with state machines, so that state machines have an on_phi vfunc. It updates the only current user of "is_zero_assignment" (the malloc sm) to implement equivalent logic for phi nodes. Doing so ensures that the pointer is in a separate sm-state for the NULL vs non-NULL cases, and so gets separate exploded nodes, and hence the path-finding logic chooses the correct path, and the correct non-NULL phi argument. The patch also adds some bulletproofing to prune_for_sm_diagnostic to avoid crashing in the event of a bad path. gcc/analyzer/ChangeLog: PR analyzer/93544 * diagnostic-manager.cc (diagnostic_manager::prune_for_sm_diagnostic): Bulletproof against bad choices due to bad paths. * engine.cc (impl_region_model_context::on_phi): New. * exploded-graph.h (impl_region_model_context::on_phi): New decl. * region-model.cc (region_model::on_longjmp): Likewise. (region_model::handle_phi): Add phi param. Call the ctxt's on_phi vfunc. (region_model::update_for_phis): Pass phi to handle_phi. * region-model.h (region_model::handle_phi): Add phi param. (region_model_context::on_phi): New vfunc. (test_region_model_context::on_phi): New. * sm-malloc.cc (malloc_state_machine::on_phi): New. (malloc_state_machine::on_zero_assignment): New. * sm.h (state_machine::on_phi): New vfunc. gcc/testsuite/ChangeLog: PR analyzer/93544 * gcc.dg/analyzer/torture/pr93544.c: New test. --- gcc/analyzer/ChangeLog | 19 +++++++ gcc/analyzer/diagnostic-manager.cc | 9 ++++ gcc/analyzer/engine.cc | 21 ++++++++ gcc/analyzer/exploded-graph.h | 2 + gcc/analyzer/region-model.cc | 8 ++- gcc/analyzer/region-model.h | 12 ++++- gcc/analyzer/sm-malloc.cc | 52 +++++++++++++++---- gcc/analyzer/sm.h | 7 +++ gcc/testsuite/ChangeLog | 5 ++ .../gcc.dg/analyzer/torture/pr93544.c | 17 ++++++ 10 files changed, 140 insertions(+), 12 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/analyzer/torture/pr93544.c diff --git a/gcc/analyzer/ChangeLog b/gcc/analyzer/ChangeLog index 9b8820ede03..5e444895101 100644 --- a/gcc/analyzer/ChangeLog +++ b/gcc/analyzer/ChangeLog @@ -1,3 +1,22 @@ +2020-02-03 David Malcolm + + PR analyzer/93544 + * diagnostic-manager.cc + (diagnostic_manager::prune_for_sm_diagnostic): Bulletproof + against bad choices due to bad paths. + * engine.cc (impl_region_model_context::on_phi): New. + * exploded-graph.h (impl_region_model_context::on_phi): New decl. + * region-model.cc (region_model::on_longjmp): Likewise. + (region_model::handle_phi): Add phi param. Call the ctxt's on_phi + vfunc. + (region_model::update_for_phis): Pass phi to handle_phi. + * region-model.h (region_model::handle_phi): Add phi param. + (region_model_context::on_phi): New vfunc. + (test_region_model_context::on_phi): New. + * sm-malloc.cc (malloc_state_machine::on_phi): New. + (malloc_state_machine::on_zero_assignment): New. + * sm.h (state_machine::on_phi): New vfunc. + 2020-02-03 David Malcolm * engine.cc (supernode_cluster::dump_dot): Show BB index as diff --git a/gcc/analyzer/diagnostic-manager.cc b/gcc/analyzer/diagnostic-manager.cc index 023fda9fa7c..1a82d5f22ec 100644 --- a/gcc/analyzer/diagnostic-manager.cc +++ b/gcc/analyzer/diagnostic-manager.cc @@ -1087,6 +1087,15 @@ diagnostic_manager::prune_for_sm_diagnostic (checker_path *path, pp_gimple_stmt_1 (&pp, phi, 0, (dump_flags_t)0); log (" phi: %s", pp_formatted_text (&pp)); } + /* If we've chosen a bad exploded_path, then the + phi arg might be a constant. Fail gracefully for + this case. */ + if (CONSTANT_CLASS_P (var)) + { + log ("new var is a constant (bad path?);" + " setting var to NULL"); + var = NULL; + } } } diff --git a/gcc/analyzer/engine.cc b/gcc/analyzer/engine.cc index 66ca37ea33b..90f7067dec1 100644 --- a/gcc/analyzer/engine.cc +++ b/gcc/analyzer/engine.cc @@ -663,6 +663,27 @@ impl_region_model_context::on_condition (tree lhs, enum tree_code op, tree rhs) } } +/* Implementation of region_model_context::on_phi vfunc. + Notify all state machines about the phi, which could lead to + state transitions. */ + +void +impl_region_model_context::on_phi (const gphi *phi, tree rhs) +{ + int sm_idx; + sm_state_map *smap; + FOR_EACH_VEC_ELT (m_new_state->m_checker_states, sm_idx, smap) + { + const state_machine &sm = m_ext_state.get_sm (sm_idx); + impl_sm_context sm_ctxt (*m_eg, sm_idx, sm, m_enode_for_diag, + m_old_state, m_new_state, + m_change, + m_old_state->m_checker_states[sm_idx], + m_new_state->m_checker_states[sm_idx]); + sm.on_phi (&sm_ctxt, m_enode_for_diag->get_supernode (), phi, rhs); + } +} + /* struct point_and_state. */ /* Assert that this object is sane. */ diff --git a/gcc/analyzer/exploded-graph.h b/gcc/analyzer/exploded-graph.h index c72319cb5c1..6a1b9b20277 100644 --- a/gcc/analyzer/exploded-graph.h +++ b/gcc/analyzer/exploded-graph.h @@ -74,6 +74,8 @@ class impl_region_model_context : public region_model_context void on_unknown_change (svalue_id sid ATTRIBUTE_UNUSED) FINAL OVERRIDE; + void on_phi (const gphi *phi, tree rhs) FINAL OVERRIDE; + exploded_graph *m_eg; log_user m_logger; const exploded_node *m_enode_for_diag; diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc index 38cf3b93b28..2cfded836b6 100644 --- a/gcc/analyzer/region-model.cc +++ b/gcc/analyzer/region-model.cc @@ -4568,7 +4568,8 @@ region_model::on_longjmp (const gcall *longjmp_call, const gcall *setjmp_call, where RHS is for the appropriate edge. */ void -region_model::handle_phi (tree lhs, tree rhs, bool is_back_edge, +region_model::handle_phi (const gphi *phi, + tree lhs, tree rhs, bool is_back_edge, region_model_context *ctxt) { /* For now, don't bother tracking the .MEM SSA names. */ @@ -4593,6 +4594,9 @@ region_model::handle_phi (tree lhs, tree rhs, bool is_back_edge, } else set_value (get_lvalue (lhs, ctxt), rhs_sid, ctxt); + + if (ctxt) + ctxt->on_phi (phi, rhs); } /* Implementation of region_model::get_lvalue; the latter adds type-checking. @@ -5584,7 +5588,7 @@ region_model::update_for_phis (const supernode *snode, /* Update next_state based on phi. */ bool is_back_edge = last_cfg_superedge->back_edge_p (); - handle_phi (lhs, src, is_back_edge, ctxt); + handle_phi (phi, lhs, src, is_back_edge, ctxt); } } diff --git a/gcc/analyzer/region-model.h b/gcc/analyzer/region-model.h index 7768e45134f..9c9a936fae2 100644 --- a/gcc/analyzer/region-model.h +++ b/gcc/analyzer/region-model.h @@ -1691,7 +1691,8 @@ class region_model const cfg_superedge *last_cfg_superedge, region_model_context *ctxt); - void handle_phi (tree lhs, tree rhs, bool is_back_edge, + void handle_phi (const gphi *phi, + tree lhs, tree rhs, bool is_back_edge, region_model_context *ctxt); bool maybe_update_for_edge (const superedge &edge, @@ -1932,6 +1933,10 @@ class region_model_context /* Hooks for clients to be notified when an unknown change happens to SID (in response to a call to an unknown function). */ virtual void on_unknown_change (svalue_id sid) = 0; + + /* Hooks for clients to be notified when a phi node is handled, + where RHS is the pertinent argument. */ + virtual void on_phi (const gphi *phi, tree rhs) = 0; }; /* A bundle of data for use when attempting to merge two region_model @@ -2108,6 +2113,11 @@ public: { } + void on_phi (const gphi *phi ATTRIBUTE_UNUSED, + tree rhs ATTRIBUTE_UNUSED) FINAL OVERRIDE + { + } + private: /* Implicitly delete any diagnostics in the dtor. */ auto_delete_vec m_diagnostics; diff --git a/gcc/analyzer/sm-malloc.cc b/gcc/analyzer/sm-malloc.cc index 9415a074135..bdd0731b5d1 100644 --- a/gcc/analyzer/sm-malloc.cc +++ b/gcc/analyzer/sm-malloc.cc @@ -57,6 +57,11 @@ public: const supernode *node, const gimple *stmt) const FINAL OVERRIDE; + void on_phi (sm_context *sm_ctxt, + const supernode *node, + const gphi *phi, + tree rhs) const FINAL OVERRIDE; + void on_condition (sm_context *sm_ctxt, const supernode *node, const gimple *stmt, @@ -91,6 +96,12 @@ public: /* Stop state, for pointers we don't want to track any more. */ state_t m_stop; + +private: + void on_zero_assignment (sm_context *sm_ctxt, + const supernode *node, + const gimple *stmt, + tree lhs) const; }; /* Class for diagnostics relating to malloc_state_machine. */ @@ -682,15 +693,8 @@ malloc_state_machine::on_stmt (sm_context *sm_ctxt, } if (tree lhs = is_zero_assignment (stmt)) - { - if (any_pointer_p (lhs)) - { - sm_ctxt->on_transition (node, stmt, lhs, m_start, m_null); - sm_ctxt->on_transition (node, stmt, lhs, m_unchecked, m_null); - sm_ctxt->on_transition (node, stmt, lhs, m_nonnull, m_null); - sm_ctxt->on_transition (node, stmt, lhs, m_freed, m_null); - } - } + if (any_pointer_p (lhs)) + on_zero_assignment (sm_ctxt, node, stmt,lhs); if (const gassign *assign_stmt = dyn_cast (stmt)) { @@ -736,6 +740,21 @@ malloc_state_machine::on_stmt (sm_context *sm_ctxt, return false; } +/* Implementation of state_machine::on_phi vfunc for malloc_state_machine. */ + +void +malloc_state_machine::on_phi (sm_context *sm_ctxt, + const supernode *node, + const gphi *phi, + tree rhs) const +{ + if (zerop (rhs)) + { + tree lhs = gimple_phi_result (phi); + on_zero_assignment (sm_ctxt, node, phi, lhs); + } +} + /* Implementation of state_machine::on_condition vfunc for malloc_state_machine. Potentially transition state 'unchecked' to 'nonnull' or to 'null'. */ @@ -789,6 +808,21 @@ malloc_state_machine::on_leak (tree var) const return new malloc_leak (*this, var); } +/* Shared logic for handling GIMPLE_ASSIGNs and GIMPLE_PHIs that + assign zero to LHS. */ + +void +malloc_state_machine::on_zero_assignment (sm_context *sm_ctxt, + const supernode *node, + const gimple *stmt, + tree lhs) const +{ + sm_ctxt->on_transition (node, stmt, lhs, m_start, m_null); + sm_ctxt->on_transition (node, stmt, lhs, m_unchecked, m_null); + sm_ctxt->on_transition (node, stmt, lhs, m_nonnull, m_null); + sm_ctxt->on_transition (node, stmt, lhs, m_freed, m_null); +} + } // anonymous namespace /* Internal interface to this file. */ diff --git a/gcc/analyzer/sm.h b/gcc/analyzer/sm.h index 3e8f4b6891d..2f00aaec7cc 100644 --- a/gcc/analyzer/sm.h +++ b/gcc/analyzer/sm.h @@ -62,6 +62,13 @@ public: const supernode *node, const gimple *stmt) const = 0; + virtual void on_phi (sm_context *sm_ctxt ATTRIBUTE_UNUSED, + const supernode *node ATTRIBUTE_UNUSED, + const gphi *phi ATTRIBUTE_UNUSED, + tree rhs ATTRIBUTE_UNUSED) const + { + } + virtual void on_condition (sm_context *sm_ctxt, const supernode *node, const gimple *stmt, diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index ca5dda58e7b..9e2bbda7fdf 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2020-02-03 David Malcolm + + PR analyzer/93544 + * gcc.dg/analyzer/torture/pr93544.c: New test. + 2020-02-03 David Malcolm PR analyzer/93546 diff --git a/gcc/testsuite/gcc.dg/analyzer/torture/pr93544.c b/gcc/testsuite/gcc.dg/analyzer/torture/pr93544.c new file mode 100644 index 00000000000..43edc970d36 --- /dev/null +++ b/gcc/testsuite/gcc.dg/analyzer/torture/pr93544.c @@ -0,0 +1,17 @@ +/* { dg-skip-if "" { *-*-* } { "-fno-fat-lto-objects" } { "" } } */ + +int ja; + +int * +qd (void); + +void +lk (void) +{ + int *bs, *dx; + + bs = dx = !!ja ? qd () : 0; /* { dg-message "following 'true' branch" } */ + + __builtin_free (dx); + __builtin_free (bs); /* { dg-warning "double-'free'" } */ +} -- 2.30.2