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Re: [PATCH, MPX, 2/X] Pointers Checker [3/25] Attributes


On 24 Oct 23:34, Jeff Law wrote:
> On 10/21/13 05:59, Ilya Enkovich wrote:
> >Hi,
> >
> >This patch adds attributes 'bnd_variable_size' and 'bnd_legacy' used by Pointers Checker.
> >
> >Bootstrapped and tested on linux-x86_64.
> >
> >Thanks,
> >Ilya
> >--
> >
> >gcc/
> >
> >2013-10-21  Ilya Enkovich  <ilya.enkovich@intel.com>
> >
> >	* c-family/c-common.c (handle_bnd_variable_size_attribute): New.
> >	(handle_bnd_legacy): New.
> >	(c_common_attribute_table): Add bnd_variable_size and bnd_legacy.
> >	* doc/extend.texi: Document bnd_variable_size and bnd_legacy
> >	attributes.
> OK with the same terminology changes from the 2/25 Builtins patch.
> 
> jeff
> 
Thanks! Below is the installed version.

Ilya
--

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index b20fdd6..f519489 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -375,6 +375,8 @@ static tree handle_omp_declare_simd_attribute (tree *, tree, tree, int,
 					       bool *);
 static tree handle_omp_declare_target_attribute (tree *, tree, tree, int,
 						 bool *);
+static tree handle_bnd_variable_size_attribute (tree *, tree, tree, int, bool *);
+static tree handle_bnd_legacy (tree *, tree, tree, int, bool *);
 
 static void check_function_nonnull (tree, int, tree *);
 static void check_nonnull_arg (void *, tree, unsigned HOST_WIDE_INT);
@@ -757,6 +759,10 @@ const struct attribute_spec c_common_attribute_table[] =
 			      handle_omp_declare_simd_attribute, false },
   { "omp declare target",     0, 0, true, false, false,
 			      handle_omp_declare_target_attribute, false },
+  { "bnd_variable_size",      0, 0, true,  false, false,
+			      handle_bnd_variable_size_attribute, false },
+  { "bnd_legacy",             0, 0, true, false, false,
+			      handle_bnd_legacy, false },
   { NULL,                     0, 0, false, false, false, NULL, false }
 };
 
@@ -8013,6 +8019,38 @@ handle_fnspec_attribute (tree *node ATTRIBUTE_UNUSED, tree ARG_UNUSED (name),
   return NULL_TREE;
 }
 
+/* Handle a "bnd_variable_size" attribute; arguments as in
+   struct attribute_spec.handler.  */
+
+static tree
+handle_bnd_variable_size_attribute (tree *node, tree name, tree ARG_UNUSED (args),
+				    int ARG_UNUSED (flags), bool *no_add_attrs)
+{
+  if (TREE_CODE (*node) != FIELD_DECL)
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored", name);
+      *no_add_attrs = true;
+    }
+
+  return NULL_TREE;
+}
+
+/* Handle a "bnd_legacy" attribute; arguments as in
+   struct attribute_spec.handler.  */
+
+static tree
+handle_bnd_legacy (tree *node, tree name, tree ARG_UNUSED (args),
+		   int ARG_UNUSED (flags), bool *no_add_attrs)
+{
+  if (TREE_CODE (*node) != FUNCTION_DECL)
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored", name);
+      *no_add_attrs = true;
+    }
+
+  return NULL_TREE;
+}
+
 /* Handle a "warn_unused" attribute; arguments as in
    struct attribute_spec.handler.  */
 
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 8ca3137..1d52e42 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2138,7 +2138,7 @@ attributes are currently defined for functions on all targets:
 @code{returns_nonnull}, @code{gnu_inline},
 @code{externally_visible}, @code{hot}, @code{cold}, @code{artificial},
 @code{no_sanitize_address}, @code{no_address_safety_analysis},
-@code{no_sanitize_undefined},
+@code{no_sanitize_undefined}, @code{bnd_legacy},
 @code{error} and @code{warning}.
 Several other attributes are defined for functions on particular
 target systems.  Other attributes, including @code{section} are
@@ -3549,6 +3549,12 @@ The @code{no_sanitize_undefined} attribute on functions is used
 to inform the compiler that it should not check for undefined behavior
 in the function when compiling with the @option{-fsanitize=undefined} option.
 
+@item bnd_legacy
+@cindex @code{bnd_legacy} function attribute
+The @code{bnd_legacy} attribute on functions is used to inform
+compiler that function should not be instrumented when compiled
+with @option{-fcheck-pointers} option.
+
 @item regparm (@var{number})
 @cindex @code{regparm} attribute
 @cindex functions that are passed arguments in registers on the 386
@@ -5321,12 +5327,12 @@ placed in either the @code{.bss_below100} section or the
 The keyword @code{__attribute__} allows you to specify special
 attributes of @code{struct} and @code{union} types when you define
 such types.  This keyword is followed by an attribute specification
-inside double parentheses.  Seven attributes are currently defined for
+inside double parentheses.  Eight attributes are currently defined for
 types: @code{aligned}, @code{packed}, @code{transparent_union},
-@code{unused}, @code{deprecated}, @code{visibility}, and
-@code{may_alias}.  Other attributes are defined for functions
-(@pxref{Function Attributes}) and for variables (@pxref{Variable
-Attributes}).
+@code{unused}, @code{deprecated}, @code{visibility}, @code{may_alias}
+and @code{bnd_variable_size}.  Other attributes are defined for
+functions (@pxref{Function Attributes}) and for variables
+(@pxref{Variable Attributes}).
 
 You may also specify any one of these attributes with @samp{__}
 preceding and following its keyword.  This allows you to use these
@@ -5618,6 +5624,35 @@ and caught in another, the class must have default visibility.
 Otherwise the two shared objects are unable to use the same
 typeinfo node and exception handling will break.
 
+@item bnd_variable_size
+When applied to a structure field, this attribute tells Pointer
+Bounds Checker that the size of this field should not be computed
+using static type information.  It may be used to mark variable
+sized static array fields placed at the end of a structure.
+
+@smallexample
+struct S
+@{
+  int size;
+  char data[1];
+@}
+S *p = (S *)malloc (sizeof(S) + 100);
+p->data[10] = 0; //Bounds violation
+@end smallexample
+
+By using an attribute for a field we may avoid bound violation
+we most probably do not want to see:
+
+@smallexample
+struct S
+@{
+  int size;
+  char data[1] __attribute__((bnd_variable_size));
+@}
+S *p = (S *)malloc (sizeof(S) + 100);
+p->data[10] = 0; //OK
+@end smallexample
+
 @end table
 
 To specify multiple attributes, separate them by commas within the


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