@@ -105,6 +105,8 @@ static tree handle_warn_if_not_aligned_attribute (tree *, tree, tree,
int, bool *);
static tree handle_strict_flex_array_attribute (tree *, tree, tree,
int, bool *);
+static tree handle_counted_by_attribute (tree *, tree, tree,
+ int, bool *);
static tree handle_weak_attribute (tree *, tree, tree, int, bool *) ;
static tree handle_noplt_attribute (tree *, tree, tree, int, bool *) ;
static tree handle_alias_ifunc_attribute (bool, tree *, tree, tree, bool *);
@@ -412,6 +414,8 @@ const struct attribute_spec c_common_gnu_attributes[] =
handle_warn_if_not_aligned_attribute, NULL },
{ "strict_flex_array", 1, 1, true, false, false, false,
handle_strict_flex_array_attribute, NULL },
+ { "counted_by", 1, 1, true, false, false, false,
+ handle_counted_by_attribute, NULL },
{ "weak", 0, 0, true, false, false, false,
handle_weak_attribute, NULL },
{ "noplt", 0, 0, true, false, false, false,
@@ -659,7 +663,8 @@ attribute_takes_identifier_p (const_tree attr_id)
else if (!strcmp ("mode", spec->name)
|| !strcmp ("format", spec->name)
|| !strcmp ("cleanup", spec->name)
- || !strcmp ("access", spec->name))
+ || !strcmp ("access", spec->name)
+ || !strcmp ("counted_by", spec->name))
return true;
else
return targetm.attribute_takes_identifier_p (attr_id);
@@ -2806,6 +2811,53 @@ handle_strict_flex_array_attribute (tree *node, tree name,
return NULL_TREE;
}
+/* Handle a "counted_by" attribute; arguments as in
+ struct attribute_spec.handler. */
+
+static tree
+handle_counted_by_attribute (tree *node, tree name,
+ tree args, int ARG_UNUSED (flags),
+ bool *no_add_attrs)
+{
+ tree decl = *node;
+ tree argval = TREE_VALUE (args);
+
+ /* This attribute only applies to field decls of a structure. */
+ if (TREE_CODE (decl) != FIELD_DECL)
+ {
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%qE attribute may not be specified for non-field"
+ " declaration %q+D", name, decl);
+ *no_add_attrs = true;
+ }
+ /* This attribute only applies to field with array type. */
+ else if (TREE_CODE (TREE_TYPE (decl)) != ARRAY_TYPE)
+ {
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%qE attribute may not be specified for a non-array field",
+ name);
+ *no_add_attrs = true;
+ }
+ /* This attribute only applies to a C99 flexible array member type. */
+ else if (! c_flexible_array_member_type_p (TREE_TYPE (decl)))
+ {
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%qE attribute may not be specified for a non"
+ " flexible array member field",
+ name);
+ *no_add_attrs = true;
+ }
+ /* The argument should be an identifier. */
+ else if (TREE_CODE (argval) != IDENTIFIER_NODE)
+ {
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%<counted_by%> argument not an identifier");
+ *no_add_attrs = true;
+ }
+
+ return NULL_TREE;
+}
+
/* Handle a "weak" attribute; arguments as in
struct attribute_spec.handler. */
@@ -9909,6 +9909,19 @@ c_common_finalize_early_debug (void)
(*debug_hooks->early_global_decl) (cnode->decl);
}
+/* Determine whether TYPE is a ISO C99 flexible array memeber type "[]". */
+bool
+c_flexible_array_member_type_p (const_tree type)
+{
+ if (TREE_CODE (type) == ARRAY_TYPE
+ && TYPE_SIZE (type) == NULL_TREE
+ && TYPE_DOMAIN (type) != NULL_TREE
+ && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
+ return true;
+
+ return false;
+}
+
/* Get the LEVEL of the strict_flex_array for the ARRAY_FIELD based on the
values of attribute strict_flex_array and the flag_strict_flex_arrays. */
unsigned int
@@ -904,6 +904,7 @@ extern tree fold_for_warn (tree);
extern tree c_common_get_narrower (tree, int *);
extern bool get_attribute_operand (tree, unsigned HOST_WIDE_INT *);
extern void c_common_finalize_early_debug (void);
+extern bool c_flexible_array_member_type_p (const_tree);
extern unsigned int c_strict_flex_array_level_of (tree);
extern bool c_option_is_from_cpp_diagnostics (int);
extern tree c_hardbool_type_attr_1 (tree, tree *, tree *);
@@ -5301,19 +5301,6 @@ set_array_declarator_inner (struct c_declarator *decl,
return decl;
}
-/* Determine whether TYPE is a ISO C99 flexible array memeber type "[]". */
-static bool
-flexible_array_member_type_p (const_tree type)
-{
- if (TREE_CODE (type) == ARRAY_TYPE
- && TYPE_SIZE (type) == NULL_TREE
- && TYPE_DOMAIN (type) != NULL_TREE
- && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
- return true;
-
- return false;
-}
-
/* Determine whether TYPE is a one-element array type "[1]". */
static bool
one_element_array_type_p (const_tree type)
@@ -5350,7 +5337,7 @@ add_flexible_array_elts_to_size (tree decl, tree init)
elt = CONSTRUCTOR_ELTS (init)->last ().value;
type = TREE_TYPE (elt);
- if (flexible_array_member_type_p (type))
+ if (c_flexible_array_member_type_p (type))
{
complete_array_type (&type, elt, false);
DECL_SIZE (decl)
@@ -9317,7 +9304,7 @@ is_flexible_array_member_p (bool is_last_field,
bool is_zero_length_array = zero_length_array_type_p (TREE_TYPE (x));
bool is_one_element_array = one_element_array_type_p (TREE_TYPE (x));
- bool is_flexible_array = flexible_array_member_type_p (TREE_TYPE (x));
+ bool is_flexible_array = c_flexible_array_member_type_p (TREE_TYPE (x));
unsigned int strict_flex_array_level = c_strict_flex_array_level_of (x);
@@ -9347,6 +9334,60 @@ is_flexible_array_member_p (bool is_last_field,
return false;
}
+/* Verify the argument of the counted_by attribute of the flexible array
+ member FIELD_DECL is a valid field of the containing structure,
+ STRUCT_TYPE, Report error and remove this attribute when it's not. */
+static void
+verify_counted_by_attribute (tree struct_type, tree field_decl)
+{
+ tree attr_counted_by = lookup_attribute ("counted_by",
+ DECL_ATTRIBUTES (field_decl));
+
+ if (!attr_counted_by)
+ return;
+
+ /* If there is an counted_by attribute attached to the field,
+ verify it. */
+
+ tree fieldname = TREE_VALUE (TREE_VALUE (attr_counted_by));
+
+ /* Verify the argument of the attrbute is a valid field of the
+ containing structure. */
+
+ tree counted_by_field = lookup_field (struct_type, fieldname);
+
+ /* Error when the field is not found in the containing structure. */
+ if (!counted_by_field)
+ {
+ error_at (DECL_SOURCE_LOCATION (field_decl),
+ "%qE attribute argument not a field declaration"
+ " in the same structure, ignore it",
+ (get_attribute_name (attr_counted_by)));
+
+ DECL_ATTRIBUTES (field_decl)
+ = remove_attribute ("counted_by", DECL_ATTRIBUTES (field_decl));
+ }
+ else
+ /* Error when the field is not with an integer type. */
+ {
+ while (TREE_CHAIN (counted_by_field))
+ counted_by_field = TREE_CHAIN (counted_by_field);
+ tree real_field = TREE_VALUE (counted_by_field);
+
+ if (TREE_CODE (TREE_TYPE (real_field)) != INTEGER_TYPE)
+ {
+ error_at (DECL_SOURCE_LOCATION (field_decl),
+ "%qE attribute argument not a field declaration"
+ " with integer type, ignore it",
+ (get_attribute_name (attr_counted_by)));
+
+ DECL_ATTRIBUTES (field_decl)
+ = remove_attribute ("counted_by", DECL_ATTRIBUTES (field_decl));
+ }
+ }
+
+ return;
+}
/* Fill in the fields of a RECORD_TYPE or UNION_TYPE node, T.
LOC is the location of the RECORD_TYPE or UNION_TYPE's definition.
@@ -9408,6 +9449,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
until now.) */
bool saw_named_field = false;
+ tree counted_by_fam_field = NULL_TREE;
for (x = fieldlist; x; x = DECL_CHAIN (x))
{
/* Whether this field is the last field of the structure or union.
@@ -9468,7 +9510,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
DECL_PACKED (x) = 1;
/* Detect flexible array member in an invalid context. */
- if (flexible_array_member_type_p (TREE_TYPE (x)))
+ if (c_flexible_array_member_type_p (TREE_TYPE (x)))
{
if (TREE_CODE (t) == UNION_TYPE)
{
@@ -9489,6 +9531,12 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
"members");
TREE_TYPE (x) = error_mark_node;
}
+
+ /* If there is a counted_by attribute attached to this field,
+ record it here and do more verification later after the
+ whole structure is complete. */
+ if (lookup_attribute ("counted_by", DECL_ATTRIBUTES (x)))
+ counted_by_fam_field = x;
}
if (pedantic && TREE_CODE (t) == RECORD_TYPE
@@ -9503,7 +9551,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
when x is an array and is the last field. */
if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE)
TYPE_INCLUDES_FLEXARRAY (t)
- = is_last_field && flexible_array_member_type_p (TREE_TYPE (x));
+ = is_last_field && c_flexible_array_member_type_p (TREE_TYPE (x));
/* Recursively set TYPE_INCLUDES_FLEXARRAY for the context of x, t
when x is an union or record and is the last field. */
else if (RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
@@ -9758,6 +9806,9 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
struct_parse_info->struct_types.safe_push (t);
}
+ if (counted_by_fam_field)
+ verify_counted_by_attribute (t, counted_by_fam_field);
+
return t;
}
@@ -776,6 +776,7 @@ extern struct c_expr convert_lvalue_to_rvalue (location_t, struct c_expr,
extern tree decl_constant_value_1 (tree, bool);
extern void mark_exp_read (tree);
extern tree composite_type (tree, tree);
+extern tree lookup_field (tree, tree);
extern tree build_component_ref (location_t, tree, tree, location_t,
location_t);
extern tree build_array_ref (location_t, tree, tree);
@@ -101,7 +101,6 @@ static bool function_types_compatible_p (const_tree, const_tree,
struct comptypes_data *);
static bool type_lists_compatible_p (const_tree, const_tree,
struct comptypes_data *);
-static tree lookup_field (tree, tree);
static int convert_arguments (location_t, vec<location_t>, tree,
vec<tree, va_gc> *, vec<tree, va_gc> *, tree,
tree);
@@ -2375,7 +2374,7 @@ default_conversion (tree exp)
the component is embedded within (nested) anonymous structures or
unions, the list steps down the chain to the component. */
-static tree
+tree
lookup_field (tree type, tree component)
{
tree field;
@@ -7753,6 +7753,70 @@ align them on any target.
The @code{aligned} attribute can also be used for functions
(@pxref{Common Function Attributes}.)
+@cindex @code{counted_by} variable attribute
+@item counted_by (@var{count})
+The @code{counted_by} attribute may be attached to the C99 flexible array
+member of a structure. It indicates that the number of the elements of the
+array is given by the field named "@var{count}" in the same structure as the
+flexible array member. GCC uses this information to improve the results of
+the array bound sanitizer and the @code{__builtin_dynamic_object_size}.
+
+For instance, the following code:
+
+@smallexample
+struct P @{
+ size_t count;
+ char other;
+ char array[] __attribute__ ((counted_by (count)));
+@} *p;
+@end smallexample
+
+@noindent
+specifies that the @code{array} is a flexible array member whose number of
+elements is given by the field @code{count} in the same structure.
+
+The field that represents the number of the elements should have an
+integer type. Otherwise, the compiler will report a warning and ignore
+the attribute.
+When the field that represents the number of the elements is assigned a
+negative integer value, the compiler will treat the value as zero.
+
+An explicit @code{counted_by} annotation defines a relationship between
+two objects, @code{p->array} and @code{p->count}, and there are the
+following requirementthat on the relationship between this pair:
+
+@itemize @bullet
+@item
+@code{p->count} should be initialized before the first reference to
+@code{p->array};
+
+@item
+@code{p->array} has @emph{at least} @code{p->count} number of elements
+available all the time. This relationship must hold even after any of
+these related objects are updated during the program.
+@end itemize
+
+It's the user's responsibility to make sure the above requirements to
+be kept all the time. Otherwise the compiler will report warnings,
+at the same time, the results of the array bound sanitizer and the
+@code{__builtin_dynamic_object_size} is undefined.
+
+One important feature of the attribute is, a reference to the flexible
+array member field will use the latest value assigned to the field that
+represents the number of the elements before that reference. For example,
+
+@smallexample
+ p->count = val1;
+ p->array[20] = 0; // ref1 to p->array
+ p->count = val2;
+ p->array[30] = 0; // ref2 to p->array
+@end smallexample
+
+@noindent
+in the above, @code{ref1} will use @code{val1} as the number of the elements in
+@code{p->array}, and @code{ref2} will use @code{val2} as the number of elements
+in @code{p->array}.
+
@cindex @code{alloc_size} variable attribute
@item alloc_size (@var{position})
@itemx alloc_size (@var{position-1}, @var{position-2})
new file mode 100644
@@ -0,0 +1,40 @@
+/* testing the correct usage of attribute counted_by. */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#include <wchar.h>
+
+int size;
+int x __attribute ((counted_by (size))); /* { dg-error "attribute may not be specified for non-field declaration" } */
+
+struct trailing {
+ int count;
+ int field __attribute ((counted_by (count))); /* { dg-error "attribute may not be specified for a non-array field" } */
+};
+
+struct trailing_1 {
+ int count;
+ int array_1[0] __attribute ((counted_by (count))); /* { dg-error "attribute may not be specified for a non flexible array member field" } */
+};
+
+int count;
+struct trailing_array_2 {
+ int count;
+ int array_2[] __attribute ((counted_by ("count"))); /* { dg-error "argument not an identifier" } */
+};
+
+struct trailing_array_3 {
+ int other;
+ int array_3[] __attribute ((counted_by (L"count"))); /* { dg-error "argument not an identifier" } */
+};
+
+struct trailing_array_4 {
+ int other;
+ int array_4[] __attribute ((counted_by (count))); /* { dg-error "attribute argument not a field declaration in the same structure, ignore it" } */
+};
+
+int count;
+struct trailing_array_5 {
+ float count;
+ int array_5[] __attribute ((counted_by (count))); /* { dg-error "attribute argument not a field declaration with integer type, ignore it" } */
+};
'counted_by (COUNT)' The 'counted_by' attribute may be attached to the C99 flexible array member of a structure. It indicates that the number of the elements of the array is given by the field named "COUNT" in the same structure as the flexible array member. GCC uses this information to improve the results of the array bound sanitizer and the '__builtin_dynamic_object_size'. For instance, the following code: struct P { size_t count; char other; char array[] __attribute__ ((counted_by (count))); } *p; specifies that the 'array' is a flexible array member whose number of elements is given by the field 'count' in the same structure. The field that represents the number of the elements should have an integer type. Otherwise, the compiler will report a warning and ignore the attribute. When the field that represents the number of the elements is assigned a negative integer value, the compiler will treat the value as zero. An explicit 'counted_by' annotation defines a relationship between two objects, 'p->array' and 'p->count', and there are the following requirementthat on the relationship between this pair: * 'p->count' should be initialized before the first reference to 'p->array'; * 'p->array' has _at least_ 'p->count' number of elements available all the time. This relationship must hold even after any of these related objects are updated during the program. It's the user's responsibility to make sure the above requirements to be kept all the time. Otherwise the compiler will report warnings, at the same time, the results of the array bound sanitizer and the '__builtin_dynamic_object_size' is undefined. One important feature of the attribute is, a reference to the flexible array member field will use the latest value assigned to the field that represents the number of the elements before that reference. For example, p->count = val1; p->array[20] = 0; // ref1 to p->array p->count = val2; p->array[30] = 0; // ref2 to p->array in the above, 'ref1' will use 'val1' as the number of the elements in 'p->array', and 'ref2' will use 'val2' as the number of elements in 'p->array'. gcc/c-family/ChangeLog: PR C/108896 * c-attribs.cc (handle_counted_by_attribute): New function. (attribute_takes_identifier_p): Add counted_by attribute to the list. * c-common.cc (c_flexible_array_member_type_p): ...To this. * c-common.h (c_flexible_array_member_type_p): New prototype. gcc/c/ChangeLog: PR C/108896 * c-decl.cc (flexible_array_member_type_p): Renamed and moved to... (add_flexible_array_elts_to_size): Use renamed function. (is_flexible_array_member_p): Use renamed function. (verify_counted_by_attribute): New function. (finish_struct): Use renamed function and verify counted_by attribute. * c-tree.h (lookup_field): New prototype. * c-typeck.cc (lookup_field): Expose as extern function. gcc/ChangeLog: PR C/108896 * doc/extend.texi: Document attribute counted_by. gcc/testsuite/ChangeLog: PR C/108896 * gcc.dg/flex-array-counted-by.c: New test. --- gcc/c-family/c-attribs.cc | 54 ++++++++++++- gcc/c-family/c-common.cc | 13 +++ gcc/c-family/c-common.h | 1 + gcc/c/c-decl.cc | 85 ++++++++++++++++---- gcc/c/c-tree.h | 1 + gcc/c/c-typeck.cc | 3 +- gcc/doc/extend.texi | 64 +++++++++++++++ gcc/testsuite/gcc.dg/flex-array-counted-by.c | 40 +++++++++ 8 files changed, 241 insertions(+), 20 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/flex-array-counted-by.c