On 2023-08-25 11:24, Qing Zhao 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);
You're using this in a bunch of tests already; does it make sense to
consolidate it into builtin-object-size-common.h?
+
+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));
+}
Maybe another test where the allocation, size assignment and __bdos call
happen in the same function, where the allocator is not recognized by gcc:
void *
__attribute__ ((noinline))
alloc (size_t sz)
{
return __builtin_malloc (sz);
}
void test (size_t sz)
{
array_annotated = alloc (sz);
array_annotated->b = sz;
return __builtin_dynamic_object_size (array_annotated->c, 1);
}
The interesting thing to test (and ensure in the codegen) is that the
assignment to array_annotated->b does not get reordered to below the
__builtin_dynamic_object_size call since technically there is no data
dependency between the two.
+
+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? */
If the behaviour is undefined, does it make sense to add tests for this?
Maybe once you have a -Wmismatched-counted-by or similar, we could
have tests for that. I guess the counter-argument is that we keep track
of this behaviour but not necessarily guarantee it.
+/* { 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);
Same, maybe consolidate this into builtin-object-size-common.h.
+
+#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)
{
Hmm, only for subobject size? I thought we had consensus on using
sizeof (struct) + counted_by_size as the conservative maximum size for
whole object size too, didn't we?
@@ -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))
{
Unnecessary newline.
@@ -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;
+ }
I feel like this could make a good separate function (get_subobject_size
or something like that) to make it easier to read.
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)
Unrelated whitespace change?
{
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
Capitalize first word. Also s/represent/represents/
+ ref. This is a (possible nested) COMPONENT_REF to the counted_by_field
possibly nested
+ 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 *);
