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/* Detection of infinite recursion.
Copyright (C) 2022 Free Software Foundation, Inc.
Contributed by David Malcolm <>.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
General Public License for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tree.h"
#include "fold-const.h"
#include "gcc-rich-location.h"
#include "alloc-pool.h"
#include "fibonacci_heap.h"
#include "shortest-paths.h"
#include "diagnostic-core.h"
#include "diagnostic-event-id.h"
#include "diagnostic-path.h"
#include "diagnostic-metadata.h"
#include "function.h"
#include "pretty-print.h"
#include "sbitmap.h"
#include "bitmap.h"
#include "tristate.h"
#include "ordered-hash-map.h"
#include "selftest.h"
#include "json.h"
#include "analyzer/analyzer.h"
#include "analyzer/analyzer-logging.h"
#include "analyzer/call-string.h"
#include "analyzer/program-point.h"
#include "analyzer/store.h"
#include "analyzer/region-model.h"
#include "analyzer/constraint-manager.h"
#include "analyzer/sm.h"
#include "analyzer/pending-diagnostic.h"
#include "analyzer/diagnostic-manager.h"
#include "cfg.h"
#include "basic-block.h"
#include "gimple.h"
#include "gimple-iterator.h"
#include "gimple-pretty-print.h"
#include "cgraph.h"
#include "digraph.h"
#include "analyzer/supergraph.h"
#include "analyzer/program-state.h"
#include "analyzer/exploded-graph.h"
#include "make-unique.h"
#include "analyzer/checker-path.h"
/* A subclass of pending_diagnostic for complaining about suspected
infinite recursion. */
class infinite_recursion_diagnostic
: public pending_diagnostic_subclass<infinite_recursion_diagnostic>
infinite_recursion_diagnostic (const exploded_node *prev_entry_enode,
const exploded_node *new_entry_enode,
tree callee_fndecl)
: m_prev_entry_enode (prev_entry_enode),
m_new_entry_enode (new_entry_enode),
m_callee_fndecl (callee_fndecl),
m_prev_entry_event (NULL)
const char *get_kind () const final override
return "infinite_recursion_diagnostic";
bool operator== (const infinite_recursion_diagnostic &other) const
return m_callee_fndecl == other.m_callee_fndecl;
int get_controlling_option () const final override
return OPT_Wanalyzer_infinite_recursion;
bool emit (rich_location *rich_loc) final override
/* "CWE-674: Uncontrolled Recursion". */
diagnostic_metadata m;
m.add_cwe (674);
return warning_meta (rich_loc, m, get_controlling_option (),
"infinite recursion");
label_text describe_final_event (const evdesc::final_event &ev) final override
const int frames_consumed = (m_new_entry_enode->get_stack_depth ()
- m_prev_entry_enode->get_stack_depth ());
if (frames_consumed > 1)
return ev.formatted_print
("apparently infinite chain of mutually-recursive function calls,"
" consuming %i stack frames per recursion",
return ev.formatted_print ("apparently infinite recursion");
add_function_entry_event (const exploded_edge &eedge,
checker_path *emission_path) final override
/* Subclass of function_entry_event for use when reporting both
the initial and subsequent entries to the function of interest,
allowing for cross-referencing the first event in the description
of the second. */
class recursive_function_entry_event : public function_entry_event
recursive_function_entry_event (const program_point &dst_point,
const infinite_recursion_diagnostic &pd,
bool topmost)
: function_entry_event (dst_point),
m_pd (pd),
m_topmost (topmost)
get_desc (bool can_colorize) const final override
if (m_topmost)
if (m_pd.m_prev_entry_event
&& m_pd.m_prev_entry_event->get_id_ptr ()->known_p ())
return make_label_text
"recursive entry to %qE; previously entered at %@",
m_pd.m_prev_entry_event->get_id_ptr ());
return make_label_text (can_colorize, "recursive entry to %qE",
return make_label_text (can_colorize, "initial entry to %qE",
const infinite_recursion_diagnostic &m_pd;
bool m_topmost;
const exploded_node *dst_node = eedge.m_dest;
const program_point &dst_point = dst_node->get_point ();
if (eedge.m_dest == m_prev_entry_enode)
gcc_assert (m_prev_entry_event == NULL);
std::unique_ptr<checker_event> prev_entry_event
= make_unique <recursive_function_entry_event> (dst_point,
*this, false);
m_prev_entry_event = prev_entry_event.get ();
emission_path->add_event (std::move (prev_entry_event));
else if (eedge.m_dest == m_new_entry_enode)
(make_unique<recursive_function_entry_event> (dst_point, *this, true));
pending_diagnostic::add_function_entry_event (eedge, emission_path);
/* Customize the location where the warning_event appears, putting
it at the topmost entrypoint to the function. */
void add_final_event (const state_machine *,
const exploded_node *,
const gimple *,
checker_path *emission_path) final override
gcc_assert (m_new_entry_enode);
(m_new_entry_enode->get_supernode ()->get_start_location (),
m_new_entry_enode->get_stack_depth (),
const exploded_node *m_prev_entry_enode;
const exploded_node *m_new_entry_enode;
tree m_callee_fndecl;
const checker_event *m_prev_entry_event;
/* Return true iff ENODE is the PK_BEFORE_SUPERNODE at a function
entrypoint. */
static bool
is_entrypoint_p (exploded_node *enode)
/* Look for an entrypoint to a function... */
const supernode *snode = enode->get_supernode ();
if (!snode)
return false;
if (!snode->entry_p ())
return false;;
const program_point &point = enode->get_point ();
if (point.get_kind () != PK_BEFORE_SUPERNODE)
return false;
return true;
/* Walk backwards through the eg, looking for the first
enode we find that's also the entrypoint of the same function. */
exploded_node *
exploded_graph::find_previous_entry_to (function *top_of_stack_fun,
exploded_node *enode) const
auto_vec<exploded_node *> worklist;
hash_set<exploded_node *> visited;
visited.add (enode);
for (auto in_edge : enode->m_preds)
worklist.safe_push (in_edge->m_src);
while (worklist.length () > 0)
exploded_node *iter = worklist.pop ();
if (is_entrypoint_p (iter)
&& iter->get_function () == top_of_stack_fun)
return iter;
if (visited.contains (iter))
visited.add (iter);
for (auto in_edge : iter->m_preds)
worklist.safe_push (in_edge->m_src);
/* Not found. */
return NULL;
/* Given BASE_REG within ENCLOSING_FRAME (such as a function parameter),
remap it to the equivalent region within EQUIV_PREV_FRAME.
For example, given param "n" within frame "foo@3", and equiv prev frame
"foo@1", remap it to param "n" within frame "foo@1". */
static const region *
remap_enclosing_frame (const region *base_reg,
const frame_region *enclosing_frame,
const frame_region *equiv_prev_frame,
region_model_manager *mgr)
gcc_assert (base_reg->get_parent_region () == enclosing_frame);
switch (base_reg->get_kind ())
/* We should only encounter params and varargs at the topmost
entrypoint. */
gcc_unreachable ();
case RK_VAR_ARG:
const var_arg_region *var_arg_reg = (const var_arg_region *)base_reg;
return mgr->get_var_arg_region (equiv_prev_frame,
var_arg_reg->get_index ());
case RK_DECL:
const decl_region *decl_reg = (const decl_region *)base_reg;
return equiv_prev_frame->get_region_for_local (mgr,
decl_reg->get_decl (),
/* Compare the state of memory at NEW_ENTRY_ENODE and PREV_ENTRY_ENODE,
both of which are entrypoints to the same function, where recursion has
Return true if the state of NEW_ENTRY_ENODE is sufficiently different
from PREV_ENTRY_ENODE to suggests that some variant is being modified,
and thus the recursion isn't infinite.
Return false if the states are effectively the same, suggesting that
the recursion is infinite.
For example, consider mutually recursive functions "foo" and "bar".
At the entrypoint to a "foo" frame where we've detected recursion,
we might have three frames on the stack: the new 'foo'@3, an inner
'bar'@2, and the innermost 'foo'@1.
(gdb) call enode->dump(m_ext_state)
EN: 16
callstring: [(SN: 9 -> SN: 3 in foo), (SN: 5 -> SN: 8 in bar)]
before SN: 0 (NULL from-edge)
stack depth: 3
frame (index 2): frame: ‘foo’@3
frame (index 1): frame: ‘bar’@2
frame (index 0): frame: ‘foo’@1
clusters within root region
cluster for: (*INIT_VAL(f_4(D)))
clusters within frame: ‘bar’@2
cluster for: b_2(D): INIT_VAL(f_4(D))
clusters within frame: ‘foo’@3
cluster for: f_4(D): INIT_VAL(f_4(D))
m_called_unknown_fn: FALSE
whereas for the previous entry node we'd have just the innermost
(gdb) call prev_entry_enode->dump(m_ext_state)
EN: 1
callstring: []
before SN: 0 (NULL from-edge)
stack depth: 1
frame (index 0): frame: ‘foo’@1
clusters within root region
cluster for: (*INIT_VAL(f_4(D)))
m_called_unknown_fn: FALSE
We want to abstract away frames 1 and 2 in the new entry enode,
and compare its frame 3 with the frame 1 in the previous entry
enode, and determine if enough state changes between them to
rule out infinite recursion. */
static bool
sufficiently_different_p (exploded_node *new_entry_enode,
exploded_node *prev_entry_enode,
logger *logger)
LOG_SCOPE (logger);
gcc_assert (new_entry_enode);
gcc_assert (prev_entry_enode);
gcc_assert (is_entrypoint_p (new_entry_enode));
gcc_assert (is_entrypoint_p (prev_entry_enode));
const int new_stack_depth = new_entry_enode->get_stack_depth ();
/* Compare the stores of the two enodes. */
const region_model &new_model
= *new_entry_enode->get_state ().m_region_model;
const region_model &prev_model
= *prev_entry_enode->get_state ().m_region_model;
const store &new_store = *new_model.get_store ();
for (auto kv : new_store)
const region *base_reg = kv.first;
/* Get the value within the new frame. */
const svalue *new_sval
= new_model.get_store_value (base_reg, NULL);
/* If the value is UNKNOWN (e.g. due to hitting complexity limits)
assume that it differs from the previous value. */
if (new_sval->get_kind () == SK_UNKNOWN)
return true;
/* Get the equivalent value within the old enode. */
const svalue *prev_sval;
if (const frame_region *enclosing_frame
= base_reg->maybe_get_frame_region ())
/* We have a binding within a frame in the new entry enode. */
/* Ignore bindings within frames below the new entry node. */
if (enclosing_frame->get_stack_depth () < new_stack_depth)
/* We have a binding within the frame of the new entry node,
presumably a parameter. */
/* Get the value within the equivalent frame of
the old entrypoint; typically will be the initial_svalue
of the parameter. */
const frame_region *equiv_prev_frame
= prev_model.get_current_frame ();
const region *equiv_prev_base_reg
= remap_enclosing_frame (base_reg,
new_model.get_manager ());
prev_sval = prev_model.get_store_value (equiv_prev_base_reg, NULL);
prev_sval = prev_model.get_store_value (base_reg, NULL);
/* If the prev_sval is UNKNOWN (e.g. due to hitting complexity limits)
assume that it will differ from any new value. */
if (prev_sval->get_kind () == SK_UNKNOWN)
return true;
if (new_sval != prev_sval)
return true;
/* No significant differences found. */
return false;
/* Implementation of -Wanalyzer-infinite-recursion.
Called when adding ENODE to the graph, after adding its first in-edge.
For function entrypoints, see if recursion has occurred, and, if so,
check if the state of memory changed between the recursion levels,
which would suggest some kind of decreasing variant that leads to
For recursive calls where the state of memory is effectively unchanged
between recursion levels, warn with -Wanalyzer-infinite-recursion. */
exploded_graph::detect_infinite_recursion (exploded_node *enode)
if (!is_entrypoint_p (enode))
function *top_of_stack_fun = enode->get_function ();
gcc_assert (top_of_stack_fun);
/* ....where a call to that function is already in the call string. */
const call_string &call_string = enode->get_point ().get_call_string ();
if (call_string.count_occurrences_of_function (top_of_stack_fun) < 2)
tree fndecl = top_of_stack_fun->decl;
log_scope s (get_logger (),
"checking for infinite recursion",
"considering recursion at EN: %i entering %qE",
enode->m_index, fndecl);
/* Find enode that's the entrypoint for the previous frame for fndecl
in the recursion. */
exploded_node *prev_entry_enode
= find_previous_entry_to (top_of_stack_fun, enode);
gcc_assert (prev_entry_enode);
if (get_logger ())
get_logger ()->log ("previous entrypoint to %qE is EN: %i",
fndecl, prev_entry_enode->m_index);
/* Look for changes to the state of memory between the recursion levels. */
if (sufficiently_different_p (enode, prev_entry_enode, get_logger ()))
/* Otherwise, the state of memory is effectively the same between the two
recursion levels; warn. */
const supernode *caller_snode = call_string.get_top_of_stack ().m_caller;
const supernode *snode = enode->get_supernode ();
gcc_assert (caller_snode->m_returning_call);
get_diagnostic_manager ().add_diagnostic
(enode, snode, caller_snode->m_returning_call, NULL,
make_unique<infinite_recursion_diagnostic> (prev_entry_enode,