path: root/gcc/analyzer/region-model-impl-calls.cc

/* Handling for the known behavior of various specific functions.
   Copyright (C) 2020-2021 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 "system.h"
#include "coretypes.h"
#include "tree.h"
#include "function.h"
#include "basic-block.h"
#include "gimple.h"
#include "gimple-iterator.h"
#include "diagnostic-core.h"
#include "graphviz.h"
#include "options.h"
#include "cgraph.h"
#include "tree-dfa.h"
#include "stringpool.h"
#include "convert.h"
#include "target.h"
#include "fold-const.h"
#include "tree-pretty-print.h"
#include "diagnostic-color.h"
#include "diagnostic-metadata.h"
#include "tristate.h"
#include "bitmap.h"
#include "selftest.h"
#include "function.h"
#include "json.h"
#include "analyzer/analyzer.h"
#include "analyzer/analyzer-logging.h"
#include "ordered-hash-map.h"
#include "options.h"
#include "cgraph.h"
#include "cfg.h"
#include "digraph.h"
#include "analyzer/supergraph.h"
#include "sbitmap.h"
#include "analyzer/call-string.h"
#include "analyzer/program-point.h"
#include "analyzer/store.h"
#include "analyzer/region-model.h"
#include "gimple-pretty-print.h"

#if ENABLE_ANALYZER

namespace ana {

/* class call_details.  */

/* call_details's ctor.  */

call_details::call_details (const gcall *call, region_model *model,
			    region_model_context *ctxt)
: m_call (call), m_model (model), m_ctxt (ctxt),
  m_lhs_type (NULL_TREE), m_lhs_region (NULL)
{
  m_lhs_type = NULL_TREE;
  if (tree lhs = gimple_call_lhs (call))
    {
      m_lhs_region = model->get_lvalue (lhs, ctxt);
      m_lhs_type = TREE_TYPE (lhs);
    }
}

/* Get any uncertainty_t associated with the region_model_context.  */

uncertainty_t *
call_details::get_uncertainty () const
{
  return m_ctxt->get_uncertainty ();
}

/* If the callsite has a left-hand-side region, set it to RESULT
   and return true.
   Otherwise do nothing and return false.  */

bool
call_details::maybe_set_lhs (const svalue *result) const
{
  gcc_assert (result);
  if (m_lhs_region)
    {
      m_model->set_value (m_lhs_region, result, m_ctxt);
      return true;
    }
  else
    return false;
}

/* Return the number of arguments used by the call statement.  */

unsigned
call_details::num_args () const
{
  return gimple_call_num_args (m_call);
}

/* Get argument IDX at the callsite as a tree.  */

tree
call_details::get_arg_tree (unsigned idx) const
{
  return gimple_call_arg (m_call, idx);
}

/* Get the type of argument IDX.  */

tree
call_details::get_arg_type (unsigned idx) const
{
  return TREE_TYPE (gimple_call_arg (m_call, idx));
}

/* Get argument IDX at the callsite as an svalue.  */

const svalue *
call_details::get_arg_svalue (unsigned idx) const
{
  tree arg = get_arg_tree (idx);
  return m_model->get_rvalue (arg, m_ctxt);
}

/* Dump a multiline representation of this call to PP.  */

void
call_details::dump_to_pp (pretty_printer *pp, bool simple) const
{
  pp_string (pp, "gcall: ");
  pp_gimple_stmt_1 (pp, m_call, 0 /* spc */, TDF_NONE /* flags */);
  pp_newline (pp);
  pp_string (pp, "return region: ");
  if (m_lhs_region)
    m_lhs_region->dump_to_pp (pp, simple);
  else
    pp_string (pp, "NULL");
  pp_newline (pp);
  for (unsigned i = 0; i < gimple_call_num_args (m_call); i++)
    {
      const svalue *arg_sval = get_arg_svalue (i);
      pp_printf (pp, "arg %i: ", i);
      arg_sval->dump_to_pp (pp, simple);
      pp_newline (pp);
    }
}

/* Dump a multiline representation of this call to stderr.  */

DEBUG_FUNCTION void
call_details::dump (bool simple) const
{
  pretty_printer pp;
  pp_format_decoder (&pp) = default_tree_printer;
  pp_show_color (&pp) = pp_show_color (global_dc->printer);
  pp.buffer->stream = stderr;
  dump_to_pp (&pp, simple);
  pp_flush (&pp);
}

/* Implementations of specific functions.  */

/* Handle the on_call_pre part of "alloca".  */

bool
region_model::impl_call_alloca (const call_details &cd)
{
  const svalue *size_sval = cd.get_arg_svalue (0);
  const region *new_reg = create_region_for_alloca (size_sval);
  const svalue *ptr_sval
    = m_mgr->get_ptr_svalue (cd.get_lhs_type (), new_reg);
  cd.maybe_set_lhs (ptr_sval);
  return true;
}

/* Handle a call to "__analyzer_describe".

   Emit a warning describing the 2nd argument (which can be of any
   type), at the given verbosity level.  This is for use when
   debugging, and may be of use in DejaGnu tests.  */

void
region_model::impl_call_analyzer_describe (const gcall *call,
					   region_model_context *ctxt)
{
  tree t_verbosity = gimple_call_arg (call, 0);
  tree t_val = gimple_call_arg (call, 1);
  const svalue *sval = get_rvalue (t_val, ctxt);
  bool simple = zerop (t_verbosity);
  label_text desc = sval->get_desc (simple);
  warning_at (call->location, 0, "svalue: %qs", desc.m_buffer);
}

/* Handle a call to "__analyzer_dump_capacity".

   Emit a warning describing the capacity of the base region of
   the region pointed to by the 1st argument.
   This is for use when debugging, and may be of use in DejaGnu tests.  */

void
region_model::impl_call_analyzer_dump_capacity (const gcall *call,
						region_model_context *ctxt)
{
  tree t_ptr = gimple_call_arg (call, 0);
  const svalue *sval_ptr = get_rvalue (t_ptr, ctxt);
  const region *reg = deref_rvalue (sval_ptr, t_ptr, ctxt);
  const region *base_reg = reg->get_base_region ();
  const svalue *capacity = get_capacity (base_reg);
  label_text desc = capacity->get_desc (true);
  warning_at (call->location, 0, "capacity: %qs", desc.m_buffer);
}

/* Handle a call to "__analyzer_eval" by evaluating the input
   and dumping as a dummy warning, so that test cases can use
   dg-warning to validate the result (and so unexpected warnings will
   lead to DejaGnu failures).
   Broken out as a subroutine to make it easier to put a breakpoint on it
   - though typically this doesn't help, as we have an SSA name as the arg,
   and what's more interesting is usually the def stmt for that name.  */

void
region_model::impl_call_analyzer_eval (const gcall *call,
				       region_model_context *ctxt)
{
  tree t_arg = gimple_call_arg (call, 0);
  tristate t = eval_condition (t_arg, NE_EXPR, integer_zero_node, ctxt);
  warning_at (call->location, 0, "%s", t.as_string ());
}

/* Handle the on_call_pre part of "__builtin_expect" etc.  */

bool
region_model::impl_call_builtin_expect (const call_details &cd)
{
  /* __builtin_expect's return value is its initial argument.  */
  const svalue *sval = cd.get_arg_svalue (0);
  cd.maybe_set_lhs (sval);
  return false;
}

/* Handle the on_call_pre part of "calloc".  */

bool
region_model::impl_call_calloc (const call_details &cd)
{
  const svalue *nmemb_sval = cd.get_arg_svalue (0);
  const svalue *size_sval = cd.get_arg_svalue (1);
  /* TODO: check for overflow here?  */
  const svalue *prod_sval
    = m_mgr->get_or_create_binop (size_type_node, MULT_EXPR,
				  nmemb_sval, size_sval);
  const region *new_reg = create_region_for_heap_alloc (prod_sval);
  zero_fill_region (new_reg);
  if (cd.get_lhs_type ())
    {
      const svalue *ptr_sval
	= m_mgr->get_ptr_svalue (cd.get_lhs_type (), new_reg);
      cd.maybe_set_lhs (ptr_sval);
    }
  return true;
}

/* Handle the on_call_pre part of "error" and "error_at_line" from
   GNU's non-standard <error.h>.
   MIN_ARGS identifies the minimum number of expected arguments
   to be consistent with such a call (3 and 5 respectively).
   Return true if handling it as one of these functions.
   Write true to *OUT_TERMINATE_PATH if this execution path should be
   terminated (e.g. the function call terminates the process).  */

bool
region_model::impl_call_error (const call_details &cd, unsigned min_args,
			       bool *out_terminate_path)
{
  /* Bail if not enough args.  */
  if (cd.num_args () < min_args)
    return false;

  /* Initial argument ought to be of type "int".  */
  if (cd.get_arg_type (0) != integer_type_node)
    return false;

  /* The process exits if status != 0, so it only continues
     for the case where status == 0.
     Add that constraint, or terminate this analysis path.  */
  tree status = cd.get_arg_tree (0);
  if (!add_constraint (status, EQ_EXPR, integer_zero_node, cd.get_ctxt ()))
    *out_terminate_path = true;

  return true;
}

/* Handle the on_call_post part of "free", after sm-handling.

   If the ptr points to an underlying heap region, delete the region,
   poisoning pointers to it and regions within it.

   We delay this until after sm-state has been updated so that the
   sm-handling can transition all of the various casts of the pointer
   to a "freed" state *before* we delete the related region here.

   This has to be done here so that the sm-handling can use the fact
   that they point to the same region to establish that they are equal
   (in region_model::eval_condition_without_cm), and thus transition
   all pointers to the region to the "freed" state together, regardless
   of casts.  */

void
region_model::impl_call_free (const call_details &cd)
{
  const svalue *ptr_sval = cd.get_arg_svalue (0);
  if (const region_svalue *ptr_to_region_sval
      = ptr_sval->dyn_cast_region_svalue ())
    {
      /* If the ptr points to an underlying heap region, delete it,
	 poisoning pointers.  */
      const region *freed_reg = ptr_to_region_sval->get_pointee ();
      unbind_region_and_descendents (freed_reg, POISON_KIND_FREED);
      m_dynamic_extents.remove (freed_reg);
    }
}

/* Handle the on_call_pre part of "malloc".  */

bool
region_model::impl_call_malloc (const call_details &cd)
{
  const svalue *size_sval = cd.get_arg_svalue (0);
  const region *new_reg = create_region_for_heap_alloc (size_sval);
  if (cd.get_lhs_type ())
    {
      const svalue *ptr_sval
	= m_mgr->get_ptr_svalue (cd.get_lhs_type (), new_reg);
      cd.maybe_set_lhs (ptr_sval);
    }
  return true;
}

/* Handle the on_call_pre part of "memcpy" and "__builtin_memcpy".  */

void
region_model::impl_call_memcpy (const call_details &cd)
{
  const svalue *dest_sval = cd.get_arg_svalue (0);
  const svalue *num_bytes_sval = cd.get_arg_svalue (2);

  const region *dest_reg = deref_rvalue (dest_sval, cd.get_arg_tree (0),
					 cd.get_ctxt ());

  cd.maybe_set_lhs (dest_sval);

  if (tree num_bytes = num_bytes_sval->maybe_get_constant ())
    {
      /* "memcpy" of zero size is a no-op.  */
      if (zerop (num_bytes))
	return;
    }

  check_for_writable_region (dest_reg, cd.get_ctxt ());

  /* Otherwise, mark region's contents as unknown.  */
  mark_region_as_unknown (dest_reg, cd.get_uncertainty ());
}

/* Handle the on_call_pre part of "memset" and "__builtin_memset".  */

bool
region_model::impl_call_memset (const call_details &cd)
{
  const svalue *dest_sval = cd.get_arg_svalue (0);
  const svalue *fill_value_sval = cd.get_arg_svalue (1);
  const svalue *num_bytes_sval = cd.get_arg_svalue (2);

  const region *dest_reg = deref_rvalue (dest_sval, cd.get_arg_tree (0),
					  cd.get_ctxt ());

  if (tree num_bytes = num_bytes_sval->maybe_get_constant ())
    {
      /* "memset" of zero size is a no-op.  */
      if (zerop (num_bytes))
	return true;

      /* Set with known amount.  */
      byte_size_t reg_size;
      if (dest_reg->get_byte_size (&reg_size))
	{
	  /* Check for an exact size match.  */
	  if (reg_size == wi::to_offset (num_bytes))
	    {
	      if (tree cst = fill_value_sval->maybe_get_constant ())
		{
		  if (zerop (cst))
		    {
		      zero_fill_region (dest_reg);
		      return true;
		    }
		}
	    }
	}
    }

  check_for_writable_region (dest_reg, cd.get_ctxt ());

  /* Otherwise, mark region's contents as unknown.  */
  mark_region_as_unknown (dest_reg, cd.get_uncertainty ());
  return false;
}

/* Handle the on_call_pre part of "operator new".  */

bool
region_model::impl_call_operator_new (const call_details &cd)
{
  const svalue *size_sval = cd.get_arg_svalue (0);
  const region *new_reg = create_region_for_heap_alloc (size_sval);
  if (cd.get_lhs_type ())
    {
      const svalue *ptr_sval
	= m_mgr->get_ptr_svalue (cd.get_lhs_type (), new_reg);
      cd.maybe_set_lhs (ptr_sval);
    }
  return false;
}

/* Handle the on_call_pre part of "operator delete", which comes in
   both sized and unsized variants (2 arguments and 1 argument
   respectively).  */

bool
region_model::impl_call_operator_delete (const call_details &cd)
{
  const svalue *ptr_sval = cd.get_arg_svalue (0);
  if (const region_svalue *ptr_to_region_sval
      = ptr_sval->dyn_cast_region_svalue ())
    {
      /* If the ptr points to an underlying heap region, delete it,
	 poisoning pointers.  */
      const region *freed_reg = ptr_to_region_sval->get_pointee ();
      unbind_region_and_descendents (freed_reg, POISON_KIND_FREED);
    }
  return false;
}

/* Handle the on_call_pre part of "realloc".  */

void
region_model::impl_call_realloc (const call_details &)
{
  /* Currently we don't support bifurcating state, so there's no good
     way to implement realloc(3).
     For now, malloc_state_machine::on_realloc_call has a minimal
     implementation to suppress false positives.  */
}

/* Handle the on_call_pre part of "strcpy" and "__builtin_strcpy_chk".  */

void
region_model::impl_call_strcpy (const call_details &cd)
{
  const svalue *dest_sval = cd.get_arg_svalue (0);
  const region *dest_reg = deref_rvalue (dest_sval, cd.get_arg_tree (0),
					 cd.get_ctxt ());

  cd.maybe_set_lhs (dest_sval);

  check_for_writable_region (dest_reg, cd.get_ctxt ());

  /* For now, just mark region's contents as unknown.  */
  mark_region_as_unknown (dest_reg, cd.get_uncertainty ());
}

/* Handle the on_call_pre part of "strlen".
   Return true if the LHS is updated.  */

bool
region_model::impl_call_strlen (const call_details &cd)
{
  region_model_context *ctxt = cd.get_ctxt ();
  const svalue *arg_sval = cd.get_arg_svalue (0);
  const region *buf_reg = deref_rvalue (arg_sval, cd.get_arg_tree (0), ctxt);
  if (const string_region *str_reg
      = buf_reg->dyn_cast_string_region ())
    {
      tree str_cst = str_reg->get_string_cst ();
      /* TREE_STRING_LENGTH is sizeof, not strlen.  */
      int sizeof_cst = TREE_STRING_LENGTH (str_cst);
      int strlen_cst = sizeof_cst - 1;
      if (cd.get_lhs_type ())
	{
	  tree t_cst = build_int_cst (cd.get_lhs_type (), strlen_cst);
	  const svalue *result_sval
	    = m_mgr->get_or_create_constant_svalue (t_cst);
	  cd.maybe_set_lhs (result_sval);
	  return true;
	}
    }
  /* Otherwise an unknown value.  */
  return true;
}

/* Handle calls to functions referenced by
   __attribute__((malloc(FOO))).  */

void
region_model::impl_deallocation_call (const call_details &cd)
{
  impl_call_free (cd);
}

} // namespace ana

#endif /* #if ENABLE_ANALYZER */