Hi,
I’d like to ping this patch set one more time.
Thanks
Qing
> On Aug 25, 2023, at 11:24 AM, Qing Zhao <qing.z...@oracle.com> wrote:
>
> Use the counted_by atribute info in builtin object size to compute the
> subobject size for flexible array members.
>
> gcc/ChangeLog:
>
> PR C/108896
> * tree-object-size.cc (addr_object_size): Use the counted_by
> attribute info.
> * tree.cc (component_ref_has_counted_by_p): New function.
> (component_ref_get_counted_by): New function.
> * tree.h (component_ref_has_counted_by_p): New prototype.
> (component_ref_get_counted_by): New prototype.
>
> gcc/testsuite/ChangeLog:
>
> PR C/108896
> * gcc.dg/flex-array-counted-by-2.c: New test.
> * gcc.dg/flex-array-counted-by-3.c: New test.
> ---
> .../gcc.dg/flex-array-counted-by-2.c | 74 ++++++
> .../gcc.dg/flex-array-counted-by-3.c | 210 ++++++++++++++++++
> gcc/tree-object-size.cc | 37 ++-
> gcc/tree.cc | 95 +++++++-
> gcc/tree.h | 10 +
> 5 files changed, 418 insertions(+), 8 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/flex-array-counted-by-2.c
> create mode 100644 gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
>
> diff --git a/gcc/testsuite/gcc.dg/flex-array-counted-by-2.c
> b/gcc/testsuite/gcc.dg/flex-array-counted-by-2.c
> new file mode 100644
> index 000000000000..ec580c1f1f01
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-2.c
> @@ -0,0 +1,74 @@
> +/* test the attribute counted_by and its usage in
> + * __builtin_dynamic_object_size. */
> +/* { dg-do run } */
> +/* { dg-options "-O2" } */
> +
> +#include "builtin-object-size-common.h"
> +
> +#define expect(p, _v) do { \
> + size_t v = _v; \
> + if (p == v) \
> + __builtin_printf ("ok: %s == %zd\n", #p, p); \
> + else \
> + { \
> + __builtin_printf ("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
> + FAIL (); \
> + } \
> +} while (0);
> +
> +struct flex {
> + int b;
> + int c[];
> +} *array_flex;
> +
> +struct annotated {
> + int b;
> + int c[] __attribute__ ((counted_by (b)));
> +} *array_annotated;
> +
> +struct nested_annotated {
> + struct {
> + union {
> + int b;
> + float f;
> + };
> + int n;
> + };
> + int c[] __attribute__ ((counted_by (b)));
> +} *array_nested_annotated;
> +
> +void __attribute__((__noinline__)) setup (int normal_count, int attr_count)
> +{
> + array_flex
> + = (struct flex *)malloc (sizeof (struct flex)
> + + normal_count * sizeof (int));
> + array_flex->b = normal_count;
> +
> + array_annotated
> + = (struct annotated *)malloc (sizeof (struct annotated)
> + + attr_count * sizeof (int));
> + array_annotated->b = attr_count;
> +
> + array_nested_annotated
> + = (struct nested_annotated *)malloc (sizeof (struct nested_annotated)
> + + attr_count * sizeof (int));
> + array_nested_annotated->b = attr_count;
> +
> + return;
> +}
> +
> +void __attribute__((__noinline__)) test ()
> +{
> + expect(__builtin_dynamic_object_size(array_flex->c, 1), -1);
> + expect(__builtin_dynamic_object_size(array_annotated->c, 1),
> + array_annotated->b * sizeof (int));
> + expect(__builtin_dynamic_object_size(array_nested_annotated->c, 1),
> + array_nested_annotated->b * sizeof (int));
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + setup (10,10);
> + test ();
> + DONE ();
> +}
> diff --git a/gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
> b/gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
> new file mode 100644
> index 000000000000..a0c3cb88ec71
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
> @@ -0,0 +1,210 @@
> +/* test the attribute counted_by and its usage in
> +__builtin_dynamic_object_size: what's the correct behavior when the
> +allocation size mismatched with the value of counted_by attribute? */
> +/* { dg-do run } */
> +/* { dg-options "-O -fstrict-flex-arrays=3" } */
> +
> +#include "builtin-object-size-common.h"
> +
> +struct annotated {
> + size_t foo;
> + char others;
> + char array[] __attribute__((counted_by (foo)));
> +};
> +
> +#define expect(p, _v) do { \
> + size_t v = _v; \
> + if (p == v) \
> + __builtin_printf ("ok: %s == %zd\n", #p, p); \
> + else \
> + { \
> + __builtin_printf ("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
> + FAIL (); \
> + } \
> +} while (0);
> +
> +#define noinline __attribute__((__noinline__))
> +#define SIZE_BUMP 10
> +#define MAX(a, b) ((a) > (b) ? (a) : (b))
> +#define MIN(a, b) ((a) < (b) ? (a) : (b))
> +
> +/* In general, Due to type casting, the type for the pointee of a pointer
> + does not say anything about the object it points to,
> + So, __builtin_object_size can not directly use the type of the pointee
> + to decide the size of the object the pointer points to.
> +
> + there are only two reliable ways:
> + A. observed allocations (call to the allocation functions in the routine)
> + B. observed accesses (read or write access to the location of the
> + pointer points to)
> +
> + that provide information about the type/existence of an object at
> + the corresponding address.
> +
> + for A, we use the "alloc_size" attribute for the corresponding allocation
> + functions to determine the object size;
> +
> + For B, we use the SIZE info of the TYPE attached to the corresponding
> access.
> + (We treat counted_by attribute as a complement to the SIZE info of the
> TYPE
> + for FMA)
> +
> + The only other way in C which ensures that a pointer actually points
> + to an object of the correct type is 'static':
> +
> + void foo(struct P *p[static 1]);
> +
> + See https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624814.html
> + for more details. */
> +
> +/* in the following function, malloc allocated more space than the value
> + of counted_by attribute. Then what's the correct behavior we expect
> + the __builtin_dynamic_object_size should have for each of the cases? */
> +
> +static struct annotated * noinline alloc_buf_more (size_t index)
> +{
> + struct annotated *p;
> + size_t allocated_size
> + = MAX (sizeof (struct annotated),
> + (__builtin_offsetof (struct annotated, array[0])
> + + (index + SIZE_BUMP) * sizeof (char)));
> + p = (struct annotated *) malloc (allocated_size);
> +
> + p->foo = index;
> +
> + /*when checking the observed access p->array, we have info on both
> + observered allocation and observed access,
> + A. from observed allocation:
> + allocated_size - offsetof (struct annotated, array[0])
> + B. from observed access: p->foo * sizeof (char)
> + */
> +
> + /* for size in the whole object: always uses A. */
> + /* for size in the sub-object: chose the smaller of A and B.
> + * Please see
> https://gcc.gnu.org/pipermail/gcc-patches/2023-July/625891.html
> + * for details on why. */
> +
> + /* for MAXIMUM size in the whole object: use the allocation size
> + for the whole object. */
> + expect(__builtin_dynamic_object_size(p->array, 0),
> + allocated_size - __builtin_offsetof (struct annotated, array[0]));
> +
> + /* for MAXIMUM size in the sub-object. use the smaller of A and B. */
> + expect(__builtin_dynamic_object_size(p->array, 1),
> + MIN (allocated_size - __builtin_offsetof (struct annotated, array[0]),
> + (p->foo) * sizeof(char)));
> +
> + /* for MINIMUM size in the whole object: use the allocation size
> + for the whole object. */
> + expect(__builtin_dynamic_object_size(p->array, 2),
> + allocated_size - __builtin_offsetof (struct annotated, array[0]));
> +
> + /* for MINIMUM size in the sub-object: use the smaller of A and B. */
> + expect(__builtin_dynamic_object_size(p->array, 3),
> + MIN (allocated_size - __builtin_offsetof (struct annotated, array[0]),
> + (p->foo) * sizeof(char)));
> +
> + /*when checking the pointer p, we only have info on the observed
> allocation.
> + So, the object size info can only been obtained from the call to malloc.
> + for both MAXIMUM and MINIMUM: A = (index + SIZE_BUMP) * sizeof (char) */
> + expect(__builtin_dynamic_object_size(p, 0), allocated_size);
> + expect(__builtin_dynamic_object_size(p, 1), allocated_size);
> + expect(__builtin_dynamic_object_size(p, 2), allocated_size);
> + expect(__builtin_dynamic_object_size(p, 3), allocated_size);
> + return p;
> +}
> +
> +/* in the following function, malloc allocated less space than the value
> + of counted_by attribute. Then what's the correct behavior we expect
> + the __builtin_dynamic_object_size should have for each of the cases?
> + NOTE: this is an user error, GCC should issue warnings for such case.
> + this is a seperate issue we should address later. */
> +
> +static struct annotated * noinline alloc_buf_less (size_t index)
> +{
> + struct annotated *p;
> + size_t allocated_size
> + = MAX (sizeof (struct annotated),
> + (__builtin_offsetof (struct annotated, array[0])
> + + (index) * sizeof (char)));
> + p = (struct annotated *) malloc (allocated_size);
> +
> + p->foo = index + SIZE_BUMP;
> +
> + /*when checking the observed access p->array, we have info on both
> + observered allocation and observed access,
> + A. from observed allocation:
> + allocated_size - offsetof (struct annotated, array[0])
> + B. from observed access: p->foo * sizeof (char)
> + */
> +
> + /* for size in the whole object: always uses A. */
> + /* for size in the sub-object: chose the smaller of A and B.
> + * Please see
> https://gcc.gnu.org/pipermail/gcc-patches/2023-July/625891.html
> + * for details on why. */
> +
> + /* for MAXIMUM size in the whole object: use the allocation size
> + for the whole object. */
> + expect(__builtin_dynamic_object_size(p->array, 0),
> + allocated_size - __builtin_offsetof (struct annotated, array[0]));
> +
> + /* for MAXIMUM size in the sub-object. use the smaller of A and B. */
> + expect(__builtin_dynamic_object_size(p->array, 1),
> + MIN (allocated_size - __builtin_offsetof (struct annotated, array[0]),
> + (p->foo) * sizeof(char)));
> +
> + /* for MINIMUM size in the whole object: use the allocation size
> + for the whole object. */
> + expect(__builtin_dynamic_object_size(p->array, 2),
> + allocated_size - __builtin_offsetof (struct annotated, array[0]));
> +
> + /* for MINIMUM size in the sub-object: use the smaller of A and B. */
> + expect(__builtin_dynamic_object_size(p->array, 3),
> + MIN (allocated_size - __builtin_offsetof (struct annotated, array[0]),
> + (p->foo) * sizeof(char)));
> +
> + /*when checking the pointer p, we only have info on the observed
> + allocation. So, the object size info can only been obtained from
> + the call to malloc. */
> + expect(__builtin_dynamic_object_size(p, 0), allocated_size);
> + expect(__builtin_dynamic_object_size(p, 1), allocated_size);
> + expect(__builtin_dynamic_object_size(p, 2), allocated_size);
> + expect(__builtin_dynamic_object_size(p, 3), allocated_size);
> + return p;
> +}
> +
> +int main ()
> +{
> + struct annotated *p, *q;
> + p = alloc_buf_more (10);
> + q = alloc_buf_less (10);
> +
> + /*when checking the observed access p->array, we only have info on the
> + observed access, i.e, the TYPE_SIZE info from the access. We don't have
> + info on the whole object. */
> + expect(__builtin_dynamic_object_size(p->array, 0), -1);
> + expect(__builtin_dynamic_object_size(p->array, 1), p->foo * sizeof(char));
> + expect(__builtin_dynamic_object_size(p->array, 2), 0);
> + expect(__builtin_dynamic_object_size(p->array, 3), p->foo * sizeof(char));
> + /*when checking the pointer p, we have no observed allocation nor observed
> + access, therefore, we cannot determine the size info here. */
> + expect(__builtin_dynamic_object_size(p, 0), -1);
> + expect(__builtin_dynamic_object_size(p, 1), -1);
> + expect(__builtin_dynamic_object_size(p, 2), 0);
> + expect(__builtin_dynamic_object_size(p, 3), 0);
> +
> + /*when checking the observed access p->array, we only have info on the
> + observed access, i.e, the TYPE_SIZE info from the access. We don't have
> + info on the whole object. */
> + expect(__builtin_dynamic_object_size(q->array, 0), -1);
> + expect(__builtin_dynamic_object_size(q->array, 1), q->foo * sizeof(char));
> + expect(__builtin_dynamic_object_size(q->array, 2), 0);
> + expect(__builtin_dynamic_object_size(q->array, 3), q->foo * sizeof(char));
> + /*when checking the pointer p, we have no observed allocation nor observed
> + access, therefore, we cannot determine the size info here. */
> + expect(__builtin_dynamic_object_size(q, 0), -1);
> + expect(__builtin_dynamic_object_size(q, 1), -1);
> + expect(__builtin_dynamic_object_size(q, 2), 0);
> + expect(__builtin_dynamic_object_size(q, 3), 0);
> +
> + DONE ();
> +}
> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
> index a62af0500563..cf7843c5684b 100644
> --- a/gcc/tree-object-size.cc
> +++ b/gcc/tree-object-size.cc
> @@ -585,6 +585,7 @@ addr_object_size (struct object_size_info *osi,
> const_tree ptr,
> if (pt_var != TREE_OPERAND (ptr, 0))
> {
> tree var;
> + tree counted_by_ref = NULL_TREE;
>
> if (object_size_type & OST_SUBOBJECT)
> {
> @@ -600,11 +601,12 @@ addr_object_size (struct object_size_info *osi,
> const_tree ptr,
> var = TREE_OPERAND (var, 0);
> if (var != pt_var && TREE_CODE (var) == ARRAY_REF)
> var = TREE_OPERAND (var, 0);
> - if (! TYPE_SIZE_UNIT (TREE_TYPE (var))
> + if (! component_ref_has_counted_by_p (var)
> + && ((! TYPE_SIZE_UNIT (TREE_TYPE (var))
> || ! tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (var)))
> || (pt_var_size && TREE_CODE (pt_var_size) == INTEGER_CST
> && tree_int_cst_lt (pt_var_size,
> - TYPE_SIZE_UNIT (TREE_TYPE (var)))))
> + TYPE_SIZE_UNIT (TREE_TYPE (var)))))))
> var = pt_var;
> else if (var != pt_var && TREE_CODE (pt_var) == MEM_REF)
> {
> @@ -612,6 +614,7 @@ addr_object_size (struct object_size_info *osi,
> const_tree ptr,
> /* For &X->fld, compute object size if fld isn't a flexible array
> member. */
> bool is_flexible_array_mem_ref = false;
> +
> while (v && v != pt_var)
> switch (TREE_CODE (v))
> {
> @@ -660,6 +663,8 @@ addr_object_size (struct object_size_info *osi,
> const_tree ptr,
> /* Now the ref is to an array type. */
> gcc_assert (TREE_CODE (TREE_TYPE (v)) == ARRAY_TYPE);
> is_flexible_array_mem_ref = array_ref_flexible_size_p (v);
> + counted_by_ref = component_ref_get_counted_by (v);
> +
> while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
> if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> != UNION_TYPE
> @@ -673,8 +678,11 @@ addr_object_size (struct object_size_info *osi,
> const_tree ptr,
> == RECORD_TYPE)
> {
> /* compute object size only if v is not a
> - flexible array member. */
> - if (!is_flexible_array_mem_ref)
> + flexible array member or the flexible array member
> + has a known element count indicated by the user
> + through attribute counted_by. */
> + if (!is_flexible_array_mem_ref
> + || counted_by_ref)
> {
> v = NULL_TREE;
> break;
> @@ -707,9 +715,24 @@ addr_object_size (struct object_size_info *osi,
> const_tree ptr,
>
> if (var != pt_var)
> {
> - var_size = TYPE_SIZE_UNIT (TREE_TYPE (var));
> - if (!TREE_CONSTANT (var_size))
> - var_size = get_or_create_ssa_default_def (cfun, var_size);
> + if (!counted_by_ref)
> + {
> + var_size = TYPE_SIZE_UNIT (TREE_TYPE (var));
> + if (!TREE_CONSTANT (var_size))
> + var_size = get_or_create_ssa_default_def (cfun, var_size);
> + }
> + else
> + {
> + gcc_assert (TREE_CODE (var) == COMPONENT_REF
> + && TREE_CODE (TREE_TYPE (var)) == ARRAY_TYPE);
> + tree element_size = TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (var)));
> + var_size
> + = size_binop (MULT_EXPR,
> + fold_convert (sizetype, counted_by_ref),
> + fold_convert (sizetype, element_size));
> + if (!todo)
> + todo = TODO_update_ssa_only_virtuals;
> + }
> if (!var_size)
> return false;
> }
> diff --git a/gcc/tree.cc b/gcc/tree.cc
> index fcd36ae0cd74..3b6ddcbdcbf8 100644
> --- a/gcc/tree.cc
> +++ b/gcc/tree.cc
> @@ -12745,6 +12745,32 @@ array_ref_element_size (tree exp)
> return SUBSTITUTE_PLACEHOLDER_IN_EXPR (TYPE_SIZE_UNIT (elmt_type), exp);
> }
>
> +/* For a component_ref that has an array type ARRAY_REF, return TRUE when
> + an counted_by attribute attached to the corresponding FIELD_DECL.
> + return FALSE otherwise. */
> +bool
> +component_ref_has_counted_by_p (tree array_ref)
> +{
> + if (TREE_CODE (array_ref) != COMPONENT_REF)
> + return false;
> +
> + if (TREE_CODE (TREE_TYPE (array_ref)) != ARRAY_TYPE)
> + return false;
> +
> + tree struct_object = TREE_OPERAND (array_ref, 0);
> + tree struct_type = TREE_TYPE (struct_object);
> +
> + if (!RECORD_OR_UNION_TYPE_P (struct_type))
> + return false;
> + tree field_decl = TREE_OPERAND (array_ref, 1);
> + tree attr_counted_by = lookup_attribute ("counted_by",
> + DECL_ATTRIBUTES (field_decl));
> +
> + if (!attr_counted_by)
> + return false;
> + return true;
> +}
> +
> /* Given a field list, FIELDLIST, of a structure/union, return a TREE_LIST,
> with each TREE_VALUE a FIELD_DECL stepping down the chain to the FIELD
> whose name is FIELDNAME, which is the last TREE_VALUE of the list.
> @@ -12771,7 +12797,7 @@ get_named_field (tree fieldlist, const char
> *fieldname)
> fields inside it recursively. */
> else if (RECORD_OR_UNION_TYPE_P (TREE_TYPE (field)))
> if ((named_field = get_named_field (TYPE_FIELDS (TREE_TYPE (field)),
> - fieldname)) != NULL_TREE)
> + fieldname)) != NULL_TREE)
> {
> named_field = tree_cons (NULL_TREE, field, named_field);
> break;
> @@ -12784,6 +12810,73 @@ get_named_field (tree fieldlist, const char
> *fieldname)
> return named_field;
> }
>
> +/* For a component_ref that has an array type ARRAY_REF, get the object that
> + represents its counted_by per the attribute counted_by attached to
> + the corresponding FIELD_DECL. return NULL_TREE when cannot find such
> + object.
> + For example, if:
> +
> + struct P {
> + int k;
> + int x[] __attribute__ ((counted_by (k)));
> + } *p;
> +
> + for the following reference:
> +
> + p->x[b]
> +
> + the object that represents its element count will be:
> +
> + p->k
> +
> + So, when component_ref_get_counted_by (p->x[b]) is called, p->k should be
> + returned.
> +*/
> +
> +tree
> +component_ref_get_counted_by (tree array_ref)
> +{
> + if (! component_ref_has_counted_by_p (array_ref))
> + return NULL_TREE;
> +
> + tree struct_object = TREE_OPERAND (array_ref, 0);
> + tree struct_type = TREE_TYPE (struct_object);
> + tree field_decl = TREE_OPERAND (array_ref, 1);
> + tree attr_counted_by = lookup_attribute ("counted_by",
> + DECL_ATTRIBUTES (field_decl));
> + gcc_assert (attr_counted_by);
> +
> + /* If there is an counted_by attribute attached to the field,
> + get the field that maps to the counted_by. */
> +
> + const char *fieldname
> + = IDENTIFIER_POINTER (TREE_VALUE (TREE_VALUE (attr_counted_by)));
> +
> + tree counted_by_field = get_named_field (TYPE_FIELDS (struct_type),
> + fieldname);
> +
> + gcc_assert (counted_by_field);
> +
> + /* generate the tree node that represent the counted_by of this array
> + ref. This is a (possible nested) COMPONENT_REF to the counted_by_field
> + of the containing structure. */
> +
> + tree counted_by_ref = NULL_TREE;
> + tree object = struct_object;
> + do
> + {
> + tree field = TREE_VALUE (counted_by_field);
> +
> + counted_by_ref = build3 (COMPONENT_REF,
> + TREE_TYPE (field),
> + unshare_expr (object), field,
> + NULL_TREE);
> + object = counted_by_ref;
> + counted_by_field = TREE_CHAIN (counted_by_field);
> + }
> + while (counted_by_field);
> + return counted_by_ref;
> +}
>
> /* Return a tree representing the lower bound of the array mentioned in
> EXP, an ARRAY_REF or an ARRAY_RANGE_REF. */
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 4859becaa1e7..07eed7219835 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -5619,11 +5619,21 @@ extern tree get_base_address (tree t);
> of EXP, an ARRAY_REF or an ARRAY_RANGE_REF. */
> extern tree array_ref_element_size (tree);
>
> +/* Give a component_ref that has an array type, return true when an
> + attribute counted_by attached to the corresponding FIELD_DECL. */
> +extern bool component_ref_has_counted_by_p (tree);
> +
> /* Given a field list, FIELDLIST, of a structure/union, return the FIELD whose
> name is FIELDNAME, return NULL_TREE if such field is not found.
> searching nested anonymous structure/union recursively. */
> extern tree get_named_field (tree, const char *);
>
> +/* Give a component_ref that has an array type, return the object that
> + represents its counted_by per the attribute counted_by attached to
> + the corresponding FIELD_DECL. return NULL_TREE when cannot find such
> + object. */
> +extern tree component_ref_get_counted_by (tree);
> +
> /* Return a typenode for the "standard" C type with a given name. */
> extern tree get_typenode_from_name (const char *);
>
> --
> 2.31.1
>
