builtins.c (unterminated_array): Add new arguments.

	* builtins.c (unterminated_array): Add new arguments.
	If argument is not terminated, bubble up size and exact
	state to callers.
	(expand_builtin_strnlen): Detect, avoid expanding
	and diagnose unterminated arrays.
	(c_strlen): Fill in offset of start of unterminated strings.
	* builtins.h (unterminated_array): Update prototype.

	* gcc.dg/warn-strnlen-no-nul.c: New.

Co-Authored-By: Jeff Law <law@redhat.com>

From-SVN: r264787

gcc/ChangeLog

+2018-10-02  Martin Sebor  <msebor@redhat.com>
+	    Jeff Law  <law@redhat.com>
+
+	* builtins.c (unterminated_array): Add new arguments.
+	If argument is not terminated, bubble up size and exact
+	state to callers.
+	(expand_builtin_strnlen): Detect, avoid expanding
+	and diagnose unterminated arrays.
+	(c_strlen): Fill in offset of start of unterminated strings.
+	* builtins.h (unterminated_array): Update prototype.
+
 2018-10-02  Richard Biener  <rguenther@suse.de>
 
 	* config/i386/sse.md (reduc_plus_scal_v4df): Avoid the use

gcc/builtins.c

@@ -565,15 +565,50 @@ warn_string_no_nul (location_t loc, const char *fn, tree arg, tree decl)
 
 /* If EXP refers to an unterminated constant character array return
    the declaration of the object of which the array is a member or
-   element.  Otherwise return null.  */
+   element and if SIZE is not null, set *SIZE to the size of
+   the unterminated array and set *EXACT if the size is exact or
+   clear it otherwise.  Otherwise return null.  */
 
 tree
-unterminated_array (tree exp)
+unterminated_array (tree exp, tree *size /* = NULL */, bool *exact /* = NULL */)
 {
+  /* C_STRLEN will return NULL and set DECL in the info
+     structure if EXP references a unterminated array.  */
   c_strlen_data data;
   memset (&data, 0, sizeof (c_strlen_data));
-  c_strlen (exp, 1, &data);
-  return data.decl;
+  tree len = c_strlen (exp, 1, &data);
+  if (len == NULL_TREE && data.len && data.decl)
+     {
+       if (size)
+	{
+	  len = data.len;
+	  if (data.off)
+	    {
+	      /* Constant offsets are already accounted for in data.len, but
+		 not in a SSA_NAME + CST expression.  */
+	      if (TREE_CODE (data.off) == INTEGER_CST)
+		*exact = true;
+	      else if (TREE_CODE (data.off) == PLUS_EXPR
+		       && TREE_CODE (TREE_OPERAND (data.off, 1)) == INTEGER_CST)
+		{
+		  /* Subtract the offset from the size of the array.  */
+		  *exact = false;
+		  tree temp = TREE_OPERAND (data.off, 1);
+		  temp = fold_convert (ssizetype, temp);
+		  len = fold_build2 (MINUS_EXPR, ssizetype, len, temp);
+		}
+	      else
+		*exact = false;
+	    }
+	  else
+	    *exact = true;
+
+	  *size = len;
+	}
+       return data.decl;
+     }
+
+  return NULL_TREE;
 }
 
 /* Compute the length of a null-terminated character string or wide
@@ -685,6 +720,7 @@ c_strlen (tree src, int only_value, c_strlen_data *data, unsigned eltsize)
       else if (len >= maxelts)
 	{
 	  data->decl = decl;
+	  data->off = byteoff;
 	  data->len = ssize_int (len);
 	  return NULL_TREE;
 	}
@@ -755,6 +791,7 @@ c_strlen (tree src, int only_value, c_strlen_data *data, unsigned eltsize)
   if (len >= maxelts - eltoff)
     {
       data->decl = decl;
+      data->off = byteoff;
       data->len = ssize_int (len);
       return NULL_TREE;
     }
@@ -3037,9 +3074,11 @@ expand_builtin_strnlen (tree exp, rtx target, machine_mode target_mode)
   tree maxobjsize = max_object_size ();
   tree func = get_callee_fndecl (exp);
 
-  tree len = c_strlen (src, 0);
   /* FIXME: Change c_strlen() to return sizetype instead of ssizetype
      so these conversions aren't necessary.  */
+  c_strlen_data data;
+  memset (&data, 0, sizeof (c_strlen_data));
+  tree len = c_strlen (src, 0, &data, 1);
   if (len)
     len = fold_convert_loc (loc, TREE_TYPE (bound), len);
 
@@ -3053,7 +3092,43 @@ expand_builtin_strnlen (tree exp, rtx target, machine_mode target_mode)
 			 exp, func, bound, maxobjsize))
 	  TREE_NO_WARNING (exp) = true;
 
+      bool exact = true;
       if (!len || TREE_CODE (len) != INTEGER_CST)
+	{
+	  /* Clear EXACT if LEN may be less than SRC suggests,
+	     such as in
+	       strnlen (&a[i], sizeof a)
+	     where the value of i is unknown.  Unless i's value is
+	     zero, the call is unsafe because the bound is greater. */
+	  data.decl = unterminated_array (src, &len, &exact);
+	  if (!data.decl)
+	    return NULL_RTX;
+	}
+
+      if (data.decl
+	  && !TREE_NO_WARNING (exp)
+	  && ((tree_int_cst_lt (len, bound))
+	      || !exact))
+	{
+	  location_t warnloc
+	    = expansion_point_location_if_in_system_header (loc);
+
+	  if (warning_at (warnloc, OPT_Wstringop_overflow_,
+			  exact
+			  ? G_("%K%qD specified bound %E exceeds the size %E "
+			       "of unterminated array")
+			  : G_("%K%qD specified bound %E may exceed the size "
+			       "of at most %E of unterminated array"),
+			  exp, func, bound, len))
+	    {
+	      inform (DECL_SOURCE_LOCATION (data.decl),
+		      "referenced argument declared here");
+	      TREE_NO_WARNING (exp) = true;
+	      return NULL_RTX;
+	    }
+	}
+
+      if (!len)
 	return NULL_RTX;
 
       len = fold_build2_loc (loc, MIN_EXPR, size_type_node, len, bound);
@@ -3079,6 +3154,18 @@ expand_builtin_strnlen (tree exp, rtx target, machine_mode target_mode)
   if (!len || TREE_CODE (len) != INTEGER_CST)
     return NULL_RTX;
 
+  if (!TREE_NO_WARNING (exp)
+      && wi::ltu_p (wi::to_wide (len), min)
+      && warning_at (loc, OPT_Wstringop_overflow_,
+		     "%K%qD specified bound [%wu, %wu] "
+		     "exceeds the size %E of unterminated array",
+		     exp, func, min.to_uhwi (), max.to_uhwi (), len))
+    {
+      inform (DECL_SOURCE_LOCATION (data.decl),
+	      "referenced argument declared here");
+      TREE_NO_WARNING (exp) = true;
+    }
+
   if (wi::gtu_p (min, wi::to_wide (len)))
     return expand_expr (len, target, target_mode, EXPAND_NORMAL);
 

gcc/builtins.h

@@ -111,7 +111,7 @@ extern internal_fn associated_internal_fn (tree);
 extern internal_fn replacement_internal_fn (gcall *);
 
 extern void warn_string_no_nul (location_t, const char *, tree, tree);
-extern tree unterminated_array (tree);
+extern tree unterminated_array (tree, tree * = NULL, bool * = NULL);
 extern tree max_object_size ();
 
 #endif /* GCC_BUILTINS_H */

gcc/testsuite/ChangeLog

+2018-10-01  Martin Sebor  <msebor@redhat.com>
+
+	* gcc.dg/warn-strnlen-no-nul.c: New.
+
 2018-10-01  Carl Love  <cel@us.ibm.com>
 
 	PR 69431