[34/49] analyzer: new file: sm-malloc.cc
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Message ID 1573867416-55618-35-git-send-email-dmalcolm@redhat.com
State New
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Series
  • RFC: Add a static analysis framework to GCC
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Commit Message

David Malcolm Nov. 16, 2019, 1:23 a.m. UTC
This patch adds a state machine checker for malloc/free.

gcc/ChangeLog:
	* analyzer/sm-malloc.cc: New file.
---
 gcc/analyzer/sm-malloc.cc | 799 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 799 insertions(+)
 create mode 100644 gcc/analyzer/sm-malloc.cc

Patch
diff mbox series

diff --git a/gcc/analyzer/sm-malloc.cc b/gcc/analyzer/sm-malloc.cc
new file mode 100644
index 0000000..4e02f37
--- /dev/null
+++ b/gcc/analyzer/sm-malloc.cc
@@ -0,0 +1,799 @@ 
+/* A state machine for detecting misuses of the malloc/free API.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   Contributed by David Malcolm <dmalcolm@redhat.com>.
+
+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
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+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
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "gcc-plugin.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tree.h"
+#include "gimple.h"
+#include "diagnostic-path.h"
+#include "diagnostic-metadata.h"
+#include "analyzer/analyzer.h"
+#include "analyzer/pending-diagnostic.h"
+#include "analyzer/sm.h"
+
+namespace {
+
+////////////////////////////////////////////////////////////////////////////
+
+/* A state machine for detecting misuses of the malloc/free API.  */
+
+class malloc_state_machine : public state_machine
+{
+public:
+  malloc_state_machine (logger *logger);
+
+  bool inherited_state_p () const FINAL OVERRIDE { return false; }
+
+  bool on_stmt (sm_context *sm_ctxt,
+		const supernode *node,
+		const gimple *stmt) const FINAL OVERRIDE;
+
+  void on_condition (sm_context *sm_ctxt,
+		     const supernode *node,
+		     const gimple *stmt,
+		     tree lhs,
+		     enum tree_code op,
+		     tree rhs) const FINAL OVERRIDE;
+
+  void on_leak (sm_context *sm_ctxt,
+		const supernode *node,
+		const gimple *stmt,
+		tree var,
+		state_machine::state_t state) const FINAL OVERRIDE;
+  bool can_purge_p (state_t s) const FINAL OVERRIDE;
+
+  /* Start state.  */
+  state_t m_start;
+
+  /* State for a pointer returned from malloc that hasn't been checked for
+     NULL.
+     It could be a pointer to heap-allocated memory, or could be NULL.  */
+  state_t m_unchecked;
+
+  /* State for a pointer that's known to be NULL.  */
+  state_t m_null;
+
+  /* State for a pointer to heap-allocated memory, known to be non-NULL.  */
+  state_t m_nonnull;
+
+  /* State for a pointer to freed memory.  */
+  state_t m_freed;
+
+  /* State for a pointer that's known to not be on the heap (e.g. to a local
+     or global).  */
+  state_t m_non_heap; // TODO: or should this be a different state machine?
+  // or do we need child values etc?
+
+  /* Stop state, for pointers we don't want to track any more.  */
+  state_t m_stop;
+};
+
+////////////////////////////////////////////////////////////////////////////
+
+/* Class for diagnostics relating to malloc_state_machine.  */
+
+class malloc_diagnostic : public pending_diagnostic
+{
+public:
+  malloc_diagnostic (const malloc_state_machine &sm, tree arg)
+  : m_sm (sm), m_arg (arg)
+  {}
+
+  bool subclass_equal_p (const pending_diagnostic &base_other) const OVERRIDE
+  {
+    return m_arg == ((const malloc_diagnostic &)base_other).m_arg;
+  }
+
+  label_text describe_state_change (const evdesc::state_change &change)
+    OVERRIDE
+  {
+    if (change.m_old_state == m_sm.m_start
+	&& change.m_new_state == m_sm.m_unchecked)
+      // TODO: verify that it's the allocation stmt, not a copy
+      return label_text::borrow ("allocated here");
+    if (change.m_old_state == m_sm.m_unchecked
+	&& change.m_new_state == m_sm.m_nonnull)
+      return change.formatted_print ("assuming %qE is non-NULL",
+				     change.m_expr);
+    if (change.m_new_state == m_sm.m_null)
+      return change.formatted_print ("assuming %qE is NULL",
+				     change.m_expr);
+    return label_text ();
+  }
+
+protected:
+  const malloc_state_machine &m_sm;
+  tree m_arg;
+};
+
+/* Concrete subclass for reporting double-free diagnostics.  */
+
+class double_free : public malloc_diagnostic
+{
+public:
+  double_free (const malloc_state_machine &sm, tree arg)
+  : malloc_diagnostic (sm, arg)
+  {}
+
+  const char *get_kind () const FINAL OVERRIDE { return "double_free"; }
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    auto_diagnostic_group d;
+    diagnostic_metadata m;
+    m.add_cwe (415); /* CWE-415: Double Free.  */
+    return warning_at (rich_loc, m, OPT_Wanalyzer_double_free,
+		       "double-%<free%> of %qE", m_arg);
+  }
+
+  label_text describe_state_change (const evdesc::state_change &change)
+    FINAL OVERRIDE
+  {
+    if (change.m_new_state == m_sm.m_freed)
+      {
+	m_first_free_event = change.m_event_id;
+	return change.formatted_print ("first %qs here", "free");
+      }
+    return malloc_diagnostic::describe_state_change (change);
+  }
+
+  label_text describe_call_with_state (const evdesc::call_with_state &info)
+    FINAL OVERRIDE
+  {
+    if (info.m_state == m_sm.m_freed)
+      return info.formatted_print
+	("passing freed pointer %qE in call to %qE from %qE",
+	 info.m_expr, info.m_callee_fndecl, info.m_caller_fndecl);
+    return label_text ();
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    if (m_first_free_event.known_p ())
+      return ev.formatted_print ("second %qs here; first %qs was at %@",
+				 "free", "free",
+				 &m_first_free_event);
+    return ev.formatted_print ("second %qs here", "free");
+  }
+
+private:
+  diagnostic_event_id_t m_first_free_event;
+};
+
+/* Abstract subclass for describing possible bad uses of NULL.
+   Responsible for describing the call that could return NULL.  */
+
+class possible_null : public malloc_diagnostic
+{
+public:
+  possible_null (const malloc_state_machine &sm, tree arg)
+  : malloc_diagnostic (sm, arg)
+  {}
+
+  label_text describe_state_change (const evdesc::state_change &change)
+    FINAL OVERRIDE
+  {
+    if (change.m_old_state == m_sm.m_start
+	&& change.m_new_state == m_sm.m_unchecked)
+      {
+	m_origin_of_unchecked_event = change.m_event_id;
+	return label_text::borrow ("this call could return NULL");
+      }
+    return malloc_diagnostic::describe_state_change (change);
+  }
+
+  label_text describe_return_of_state (const evdesc::return_of_state &info)
+    FINAL OVERRIDE
+  {
+    if (info.m_state == m_sm.m_unchecked)
+      return info.formatted_print ("possible return of NULL to %qE from %qE",
+				   info.m_caller_fndecl, info.m_callee_fndecl);
+    return label_text ();
+  }
+
+protected:
+  diagnostic_event_id_t m_origin_of_unchecked_event;
+};
+
+/* Concrete subclass for describing dereference of a possible NULL
+   value.  */
+
+class possible_null_deref : public possible_null
+{
+public:
+  possible_null_deref (const malloc_state_machine &sm, tree arg)
+  : possible_null (sm, arg)
+  {}
+
+  const char *get_kind () const FINAL OVERRIDE { return "possible_null_deref"; }
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    /* CWE-690: Unchecked Return Value to NULL Pointer Dereference.  */
+    diagnostic_metadata m;
+    m.add_cwe (690);
+    return warning_at (rich_loc, m, OPT_Wanalyzer_possible_null_dereference,
+		       "dereference of possibly-NULL %qE", m_arg);
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    if (m_origin_of_unchecked_event.known_p ())
+      return ev.formatted_print ("%qE could be NULL: unchecked value from %@",
+				 ev.m_expr,
+				 &m_origin_of_unchecked_event);
+    else
+      return ev.formatted_print ("%qE could be NULL", ev.m_expr);
+  }
+
+};
+
+/* Subroutine for use by possible_null_arg::emit and null_arg::emit.
+   Issue a note informing that the pertinent argument must be non-NULL.  */
+
+static void
+inform_nonnull_attribute (tree fndecl, int arg_idx)
+{
+  inform (DECL_SOURCE_LOCATION (fndecl),
+	  "argument %u of %qD must be non-null",
+	  arg_idx + 1, fndecl);
+  /* Ideally we would use the location of the parm and underline the
+     attribute also - but we don't have the location_t values at this point
+     in the middle-end.
+     For reference, the C and C++ FEs have get_fndecl_argument_location.  */
+}
+
+/* Concrete subclass for describing passing a possibly-NULL value to a
+   function marked with __attribute__((nonnull)).  */
+
+class possible_null_arg : public possible_null
+{
+public:
+  possible_null_arg (const malloc_state_machine &sm, tree arg,
+		     tree fndecl, int arg_idx)
+  : possible_null (sm, arg),
+    m_fndecl (fndecl), m_arg_idx (arg_idx)
+  {}
+
+  const char *get_kind () const FINAL OVERRIDE { return "possible_null_arg"; }
+
+  bool subclass_equal_p (const pending_diagnostic &base_other) const
+  {
+    const possible_null_arg &sub_other
+      = (const possible_null_arg &)base_other;
+    return (m_arg == sub_other.m_arg
+	    && m_fndecl == sub_other.m_fndecl
+	    && m_arg_idx == sub_other.m_arg_idx);
+  }
+
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    /* CWE-690: Unchecked Return Value to NULL Pointer Dereference.  */
+    auto_diagnostic_group d;
+    diagnostic_metadata m;
+    m.add_cwe (690);
+    bool warned
+      = warning_at (rich_loc, m, OPT_Wanalyzer_possible_null_argument,
+		    "use of possibly-NULL %qE where non-null expected",
+		    m_arg);
+    if (warned)
+      inform_nonnull_attribute (m_fndecl, m_arg_idx);
+    return warned;
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    if (m_origin_of_unchecked_event.known_p ())
+      return ev.formatted_print ("argument %u (%qE) from %@ could be NULL"
+				 " where non-null expected",
+				 m_arg_idx + 1, ev.m_expr,
+				 &m_origin_of_unchecked_event);
+    else
+      return ev.formatted_print ("argument %u (%qE) could be NULL"
+				 " where non-null expected",
+				 m_arg_idx + 1, ev.m_expr);
+  }
+
+private:
+  tree m_fndecl;
+  int m_arg_idx;
+};
+
+/* Concrete subclass for describing a dereference of a NULL value.  */
+
+class null_deref : public malloc_diagnostic
+{
+public:
+  null_deref (const malloc_state_machine &sm, tree arg)
+  : malloc_diagnostic (sm, arg) {}
+
+  const char *get_kind () const FINAL OVERRIDE { return "null_deref"; }
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    /* CWE-690: Unchecked Return Value to NULL Pointer Dereference.  */
+    diagnostic_metadata m;
+    m.add_cwe (690);
+    return warning_at (rich_loc, m, OPT_Wanalyzer_null_dereference,
+		       "dereference of NULL %qE", m_arg);
+  }
+
+  label_text describe_return_of_state (const evdesc::return_of_state &info)
+    FINAL OVERRIDE
+  {
+    if (info.m_state == m_sm.m_null)
+      return info.formatted_print ("return of NULL to %qE from %qE",
+				   info.m_caller_fndecl, info.m_callee_fndecl);
+    return label_text ();
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    return ev.formatted_print ("dereference of NULL %qE", ev.m_expr);
+  }
+};
+
+/* Concrete subclass for describing passing a NULL value to a
+   function marked with __attribute__((nonnull)).  */
+
+class null_arg : public malloc_diagnostic
+{
+public:
+  null_arg (const malloc_state_machine &sm, tree arg,
+	    tree fndecl, int arg_idx)
+  : malloc_diagnostic (sm, arg),
+    m_fndecl (fndecl), m_arg_idx (arg_idx)
+  {}
+
+  const char *get_kind () const FINAL OVERRIDE { return "null_arg"; }
+
+  bool subclass_equal_p (const pending_diagnostic &base_other) const
+  {
+    const null_arg &sub_other
+      = (const null_arg &)base_other;
+    return (m_arg == sub_other.m_arg
+	    && m_fndecl == sub_other.m_fndecl
+	    && m_arg_idx == sub_other.m_arg_idx);
+  }
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    /* CWE-690: Unchecked Return Value to NULL Pointer Dereference.  */
+    auto_diagnostic_group d;
+    diagnostic_metadata m;
+    m.add_cwe (690);
+    bool warned = warning_at (rich_loc, m, OPT_Wanalyzer_null_argument,
+			      "use of NULL %qE where non-null expected", m_arg);
+    if (warned)
+      inform_nonnull_attribute (m_fndecl, m_arg_idx);
+    return warned;
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    return ev.formatted_print ("argument %u (%qE) NULL"
+			       " where non-null expected",
+			       m_arg_idx + 1, ev.m_expr);
+  }
+
+private:
+  tree m_fndecl;
+  int m_arg_idx;
+};
+
+class use_after_free : public malloc_diagnostic
+{
+public:
+  use_after_free (const malloc_state_machine &sm, tree arg)
+  : malloc_diagnostic (sm, arg)
+  {}
+
+  const char *get_kind () const FINAL OVERRIDE { return "use_after_free"; }
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    /* CWE-416: Use After Free.  */
+    diagnostic_metadata m;
+    m.add_cwe (416);
+    return warning_at (rich_loc, m, OPT_Wanalyzer_use_after_free,
+		       "use after %<free%> of %qE", m_arg);
+  }
+
+  label_text describe_state_change (const evdesc::state_change &change)
+    FINAL OVERRIDE
+  {
+    if (change.m_new_state == m_sm.m_freed)
+      {
+	m_free_event = change.m_event_id;
+	return label_text::borrow ("freed here");
+      }
+    return malloc_diagnostic::describe_state_change (change);
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    if (m_free_event.known_p ())
+      return ev.formatted_print ("use after %<free%> of %qE; freed at %@",
+				 ev.m_expr, &m_free_event);
+    else
+      return ev.formatted_print ("use after %<free%> of %qE", ev.m_expr);
+  }
+
+private:
+  diagnostic_event_id_t m_free_event;
+};
+
+class malloc_leak : public malloc_diagnostic
+{
+public:
+  malloc_leak (const malloc_state_machine &sm, tree arg)
+  : malloc_diagnostic (sm, arg) {}
+
+  const char *get_kind () const FINAL OVERRIDE { return "malloc_leak"; }
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    diagnostic_metadata m;
+    m.add_cwe (401);
+    return warning_at (rich_loc, m, OPT_Wanalyzer_malloc_leak,
+		       "leak of %qE", m_arg);
+  }
+
+  label_text describe_state_change (const evdesc::state_change &change)
+    FINAL OVERRIDE
+  {
+    if (change.m_new_state == m_sm.m_unchecked)
+      {
+	m_malloc_event = change.m_event_id;
+	return label_text::borrow ("allocated here");
+      }
+    return malloc_diagnostic::describe_state_change (change);
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    if (m_malloc_event.known_p ())
+      return ev.formatted_print ("%qE leaks here; was allocated at %@",
+				 ev.m_expr, &m_malloc_event);
+    else
+      return ev.formatted_print ("%qE leaks here", ev.m_expr);
+  }
+
+private:
+  diagnostic_event_id_t m_malloc_event;
+};
+
+class free_of_non_heap : public malloc_diagnostic
+{
+public:
+  free_of_non_heap (const malloc_state_machine &sm, tree arg)
+  : malloc_diagnostic (sm, arg), m_kind (KIND_UNKNOWN)
+  {
+  }
+
+  const char *get_kind () const FINAL OVERRIDE { return "free_of_non_heap"; }
+
+  bool subclass_equal_p (const pending_diagnostic &base_other) const
+    FINAL OVERRIDE
+  {
+    const free_of_non_heap &other = (const free_of_non_heap &)base_other;
+    return (m_arg == other.m_arg && m_kind == other.m_kind);
+  }
+
+  bool emit (rich_location *rich_loc) FINAL OVERRIDE
+  {
+    auto_diagnostic_group d;
+    diagnostic_metadata m;
+    m.add_cwe (590); /* CWE-590: Free of Memory not on the Heap.  */
+    switch (m_kind)
+      {
+      default:
+	gcc_unreachable ();
+      case KIND_UNKNOWN:
+	return warning_at (rich_loc, m, OPT_Wanalyzer_free_of_non_heap,
+			   "%<free%> of %qE which points to memory"
+			   " not on the heap",
+			   m_arg);
+	break;
+      case KIND_ALLOCA:
+	return warning_at (rich_loc, m, OPT_Wanalyzer_free_of_non_heap,
+			   "%<free%> of memory allocated on the stack by"
+			   " %qs (%qE) will corrupt the heap",
+			   "alloca", m_arg);
+	break;
+      }
+  }
+
+  label_text describe_state_change (const evdesc::state_change &change)
+    FINAL OVERRIDE
+  {
+    /* Attempt to reconstruct what kind of pointer it is.
+       (It seems neater for this to be a part of the state, though).  */
+    if (TREE_CODE (change.m_expr) == SSA_NAME)
+      {
+	gimple *def_stmt = SSA_NAME_DEF_STMT (change.m_expr);
+	if (gcall *call = dyn_cast <gcall *> (def_stmt))
+	  {
+	    if (is_named_call_p (call, "alloca", 1)
+		|| is_named_call_p (call, "__builtin_alloca", 1))
+	      {
+		m_kind = KIND_ALLOCA;
+		return label_text::borrow
+		  ("memory is allocated on the stack here");
+	      }
+	  }
+      }
+    return label_text::borrow ("pointer is from here");
+  }
+
+  label_text describe_final_event (const evdesc::final_event &ev) FINAL OVERRIDE
+  {
+    return ev.formatted_print ("call to %qs here", "free");
+  }
+
+private:
+  enum kind
+  {
+    KIND_UNKNOWN,
+    KIND_ALLOCA
+  };
+  enum kind m_kind;
+};
+
+////////////////////////////////////////////////////////////////////////////
+
+/* malloc_state_machine's ctor.  */
+
+malloc_state_machine::malloc_state_machine (logger *logger)
+: state_machine ("malloc", logger)
+{
+  m_start = add_state ("start");
+  m_unchecked = add_state ("unchecked");
+  m_null = add_state ("null");
+  m_nonnull = add_state ("nonnull");
+  m_freed = add_state ("freed");
+  m_non_heap = add_state ("non-heap");
+  m_stop = add_state ("stop");
+}
+
+/* Implementation of state_machine::on_stmt vfunc for malloc_state_machine.  */
+
+bool
+malloc_state_machine::on_stmt (sm_context *sm_ctxt,
+			       const supernode *node,
+			       const gimple *stmt) const
+{
+  if (const gcall *call = dyn_cast <const gcall *> (stmt))
+    {
+      if (is_named_call_p (call, "malloc", 1)
+	  || is_named_call_p (call, "calloc", 2))
+	{
+	  tree lhs = gimple_call_lhs (call);
+	  if (lhs)
+	    {
+	      lhs = sm_ctxt->get_readable_tree (lhs);
+	      sm_ctxt->on_transition (node, stmt, lhs, m_start, m_unchecked);
+	    }
+	  else
+	    {
+	      /* TODO: report leak.  */
+	    }
+	  return true;
+	}
+
+      if (is_named_call_p (call, "alloca", 1)
+	  || is_named_call_p (call, "__builtin_alloca", 1))
+	{
+	  tree lhs = gimple_call_lhs (call);
+	  if (lhs)
+	    {
+	      lhs = sm_ctxt->get_readable_tree (lhs);
+	      sm_ctxt->on_transition (node, stmt, lhs, m_start, m_non_heap);
+	    }
+	  return true;
+	}
+
+      if (is_named_call_p (call, "free", 1))
+	{
+	  tree arg = gimple_call_arg (call, 0);
+
+	  arg = sm_ctxt->get_readable_tree (arg);
+
+	  /* start/unchecked/nonnull -> free.  */
+	  sm_ctxt->on_transition (node, stmt, arg, m_start, m_freed);
+	  sm_ctxt->on_transition (node, stmt, arg, m_unchecked, m_freed);
+	  sm_ctxt->on_transition (node, stmt, arg, m_nonnull, m_freed);
+
+	  /* Keep state "null" as-is, rather than transitioning to "free";
+	     we don't want want to complain about double-free of NULL.  */
+
+	  /* free -> stop, with warning.  */
+	  sm_ctxt->warn_for_state (node, stmt, arg, m_freed,
+				   new double_free (*this, arg));
+	  sm_ctxt->on_transition (node, stmt, arg, m_freed, m_stop);
+
+	  /* non-heap -> stop, with warning.  */
+	  sm_ctxt->warn_for_state (node, stmt, arg, m_non_heap,
+				   new free_of_non_heap (*this, arg));
+	  sm_ctxt->on_transition (node, stmt, arg, m_non_heap, m_stop);
+	  return true;
+	}
+
+      /* Handle "__attribute__((nonnull))".   */
+      if (tree callee_fndecl = gimple_call_fndecl (stmt))
+	{
+	  tree fntype = TREE_TYPE (callee_fndecl);
+	  bitmap nonnull_args = get_nonnull_args (fntype);
+	  if (nonnull_args)
+	    {
+	      for (unsigned i = 0; i < gimple_call_num_args (stmt); i++)
+		{
+		  tree arg = gimple_call_arg (stmt, i);
+		  if (TREE_CODE (TREE_TYPE (arg)) != POINTER_TYPE)
+		    continue;
+		  /* If we have a nonnull-args, and either all pointers, or just
+		     the specified pointers.  */
+		  if (bitmap_empty_p (nonnull_args)
+		      || bitmap_bit_p (nonnull_args, i))
+		    {
+		      sm_ctxt->warn_for_state
+			(node, stmt, arg, m_unchecked,
+			 new possible_null_arg (*this, arg, callee_fndecl, i));
+		      sm_ctxt->on_transition (node, stmt, arg, m_unchecked,
+					      m_nonnull);
+
+		      sm_ctxt->warn_for_state
+			(node, stmt, arg, m_null,
+			 new null_arg (*this, arg, callee_fndecl, i));
+		      sm_ctxt->on_transition (node, stmt, arg, m_null, m_stop);
+		    }
+		}
+	      BITMAP_FREE (nonnull_args);
+	    }
+	}
+    }
+
+  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 (const gassign *assign_stmt = dyn_cast <const gassign *> (stmt))
+    {
+      enum tree_code op = gimple_assign_rhs_code (assign_stmt);
+      if (op == ADDR_EXPR)
+	{
+	  tree lhs = gimple_assign_lhs (assign_stmt);
+	  if (lhs)
+	    {
+	      lhs = sm_ctxt->get_readable_tree (lhs);
+	      sm_ctxt->on_transition (node, stmt, lhs, m_start, m_non_heap);
+	    }
+	}
+    }
+
+  /* Handle dereferences.  */
+  for (unsigned i = 0; i < gimple_num_ops (stmt); i++)
+    {
+      tree op = gimple_op (stmt, i);
+      if (!op)
+	continue;
+      if (TREE_CODE (op) == COMPONENT_REF)
+	op = TREE_OPERAND (op, 0);
+
+      if (TREE_CODE (op) == MEM_REF)
+	{
+	  tree arg = TREE_OPERAND (op, 0);
+	  arg = sm_ctxt->get_readable_tree (arg);
+
+	  sm_ctxt->warn_for_state (node, stmt, arg, m_unchecked,
+				   new possible_null_deref (*this, arg));
+	  sm_ctxt->on_transition (node, stmt, arg, m_unchecked, m_nonnull);
+
+	  sm_ctxt->warn_for_state (node, stmt, arg, m_null,
+				   new null_deref (*this, arg));
+	  sm_ctxt->on_transition (node, stmt, arg, m_null, m_stop);
+
+	  sm_ctxt->warn_for_state (node, stmt, arg, m_freed,
+				   new use_after_free (*this, arg));
+	  sm_ctxt->on_transition (node, stmt, arg, m_freed, m_stop);
+	}
+    }
+  return false;
+}
+
+/* Implementation of state_machine::on_condition vfunc for malloc_state_machine.
+   Potentially transition state 'unchecked' to 'nonnull' or to 'null'.  */
+
+void
+malloc_state_machine::on_condition (sm_context *sm_ctxt,
+				    const supernode *node,
+				    const gimple *stmt,
+				    tree lhs,
+				    enum tree_code op,
+				    tree rhs) const
+{
+  if (!zerop (rhs))
+    return;
+
+  if (!any_pointer_p (lhs))
+    return;
+  if (!any_pointer_p (rhs))
+    return;
+
+  if (op == NE_EXPR)
+    {
+      log ("got 'ARG != 0' match");
+      sm_ctxt->on_transition (node, stmt,
+			      lhs, m_unchecked, m_nonnull);
+    }
+  else if (op == EQ_EXPR)
+    {
+      log ("got 'ARG == 0' match");
+      sm_ctxt->on_transition (node, stmt,
+			      lhs, m_unchecked, m_null);
+    }
+}
+
+/* Implementation of state_machine::on_leak vfunc for malloc_state_machine.
+   Complain about leaks of pointers in state 'unchecked' and 'nonnull'.  */
+
+void
+malloc_state_machine::on_leak (sm_context *sm_ctxt,
+			       const supernode *node,
+			       const gimple *stmt,
+			       tree var,
+			       state_machine::state_t state ATTRIBUTE_UNUSED)
+  const
+{
+  sm_ctxt->warn_for_state (node, stmt, var, m_unchecked,
+			   new malloc_leak (*this, var));
+  sm_ctxt->warn_for_state (node, stmt, var, m_nonnull,
+			   new malloc_leak (*this, var));
+}
+
+/* Implementation of state_machine::can_purge_p vfunc for malloc_state_machine.
+   Don't allow purging of pointers in state 'unchecked' or 'nonnull'
+   (to avoid false leak reports).  */
+
+bool
+malloc_state_machine::can_purge_p (state_t s) const
+{
+  return s != m_unchecked && s != m_nonnull;
+}
+
+} // anonymous namespace
+
+/* Internal interface to this file. */
+
+state_machine *
+make_malloc_state_machine (logger *logger)
+{
+  return new malloc_state_machine (logger);
+}