Re: [PATCH v8 3/5] Use the .ACCESS_WITH_SIZE in builtin object size.

[Qing Zhao <qing.zhao@oracle.com>]

Sid,

Thanks a lot for your review!


> On Apr 10, 2024, at 17:45, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
> 
> On 2024-03-29 12:07, Qing Zhao wrote:
>> gcc/ChangeLog:
>> 	* tree-object-size.cc (access_with_size_object_size): New function.
>> 	(call_object_size): Call the new function.
>> gcc/testsuite/ChangeLog:
>> 	* gcc.dg/builtin-object-size-common.h: Add a new macro EXPECT.
>> 	* gcc.dg/flex-array-counted-by-3.c: New test.
>> 	* gcc.dg/flex-array-counted-by-4.c: New test.
>> 	* gcc.dg/flex-array-counted-by-5.c: New test.
> 
> This version looks fine to me for stage 1, but I'm not a maintainer so you'll need an ack from one to commit.

Richard, 

Could you please comment on this patch? Is this one okay for stage 1?

Thanks

Qing


> 
> Thanks,
> Sid
> 
>> ---
>>  .../gcc.dg/builtin-object-size-common.h       |  11 ++
>>  .../gcc.dg/flex-array-counted-by-3.c          |  63 +++++++
>>  .../gcc.dg/flex-array-counted-by-4.c          | 178 ++++++++++++++++++
>>  .../gcc.dg/flex-array-counted-by-5.c          |  48 +++++
>>  gcc/tree-object-size.cc                       |  60 ++++++
>>  5 files changed, 360 insertions(+)
>>  create mode 100644 gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
>>  create mode 100644 gcc/testsuite/gcc.dg/flex-array-counted-by-4.c
>>  create mode 100644 gcc/testsuite/gcc.dg/flex-array-counted-by-5.c
>> diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-common.h b/gcc/testsuite/gcc.dg/builtin-object-size-common.h
>> index 66ff7cdd953a..b677067c6e6b 100644
>> --- a/gcc/testsuite/gcc.dg/builtin-object-size-common.h
>> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-common.h
>> @@ -30,3 +30,14 @@ unsigned nfails = 0;
>>        __builtin_abort ();						      \
>>      return 0;								      \
>>    } while (0)
>> +
>> +#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);
>> 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..78f50230e891
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
>> @@ -0,0 +1,63 @@
>> +/* 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"
>> +
>> +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-4.c b/gcc/testsuite/gcc.dg/flex-array-counted-by-4.c
>> new file mode 100644
>> index 000000000000..20103d58ef51
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-4.c
>> @@ -0,0 +1,178 @@
>> +/* 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?
>> +We should always use the latest value that is hold by the counted_by
>> +field.  */
>> +/* { 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 noinline __attribute__((__noinline__))
>> +#define SIZE_BUMP 10
>> +#define MAX(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;
>> +   (We treat counted_by attribute the same as the "alloc_size" attribute)
>> +
>> +   For B, we use the SIZE info of the TYPE attached to the corresponding access.
>> +
>> +   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.1 from observed allocation:
>> +    	allocated_size - offsetof (struct annotated, array[0])
>> +
>> +    A.2 from the counted-by attribute:
>> +    	p->foo * sizeof (char)
>> +
>> +    We always use the latest value that is hold by the counted-by field.
>> +   */
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 0),
>> +	 (p->foo) * sizeof(char));
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 1),
>> +	 (p->foo) * sizeof(char));
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 2),
>> +	 (p->foo) * sizeof(char));
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 3),
>> +	 (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.1 from observed allocation:
>> +    	allocated_size - offsetof (struct annotated, array[0])
>> +    A.2 from the counted-by attribute:
>> +    	p->foo * sizeof (char)
>> +
>> +    We always use the latest value that is hold by the counted-by field.
>> +   */
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 0),
>> +	 (p->foo) * sizeof(char));
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 1),
>> +	 (p->foo) * sizeof(char));
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 2),
>> +	 (p->foo) * sizeof(char));
>> +
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 3),
>> +	 (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 access p->array, we only have info on the counted-by
>> +    value.  */
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 0), p->foo * sizeof(char));
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 1), p->foo * sizeof(char));
>> +  EXPECT(__builtin_dynamic_object_size(p->array, 2), p->foo * sizeof(char));
>> +  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 access p->array, we only have info on the counted-by
>> +    value.  */
>> +  EXPECT(__builtin_dynamic_object_size(q->array, 0), q->foo * sizeof(char));
>> +  EXPECT(__builtin_dynamic_object_size(q->array, 1), q->foo * sizeof(char));
>> +  EXPECT(__builtin_dynamic_object_size(q->array, 2), q->foo * sizeof(char));
>> +  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/testsuite/gcc.dg/flex-array-counted-by-5.c b/gcc/testsuite/gcc.dg/flex-array-counted-by-5.c
>> new file mode 100644
>> index 000000000000..68f9b0f7c8d2
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-5.c
>> @@ -0,0 +1,48 @@
>> +/* Test the attribute counted_by and its usage in
>> + * __builtin_dynamic_object_size: when the counted_by field is negative.  */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2" } */
>> +
>> +#include "builtin-object-size-common.h"
>> +
>> +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 attr_count)
>> +{
>> +  array_annotated
>> +    = (struct annotated *)malloc (sizeof (struct annotated));
>> +  array_annotated->b = attr_count;
>> +
>> +  array_nested_annotated
>> +    = (struct nested_annotated *)malloc (sizeof (struct nested_annotated));
>> +  array_nested_annotated->b = attr_count -1;
>> +
>> +  return;
>> +}
>> +
>> +void __attribute__((__noinline__)) test ()
>> +{
>> +    EXPECT(__builtin_dynamic_object_size(array_annotated->c, 1), 0);
>> +    EXPECT(__builtin_dynamic_object_size(array_nested_annotated->c, 1), 0);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> +  setup (-10);
>> +  test ();
>> +  DONE ();
>> +}
>> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
>> index 018fbc30cbb6..8de264d1dee2 100644
>> --- a/gcc/tree-object-size.cc
>> +++ b/gcc/tree-object-size.cc
>> @@ -37,6 +37,7 @@ along with GCC; see the file COPYING3.  If not see
>>  #include "attribs.h"
>>  #include "builtins.h"
>>  #include "gimplify-me.h"
>> +#include "gimplify.h"
>>    struct object_size_info
>>  {
>> @@ -60,6 +61,7 @@ static tree compute_object_offset (tree, const_tree);
>>  static bool addr_object_size (struct object_size_info *,
>>  			      const_tree, int, tree *, tree *t = NULL);
>>  static tree alloc_object_size (const gcall *, int);
>> +static tree access_with_size_object_size (const gcall *, int);
>>  static tree pass_through_call (const gcall *);
>>  static void collect_object_sizes_for (struct object_size_info *, tree);
>>  static void expr_object_size (struct object_size_info *, tree, tree);
>> @@ -749,6 +751,60 @@ addr_object_size (struct object_size_info *osi, const_tree ptr,
>>    return false;
>>  }
>>  +/* Compute __builtin_object_size for a CALL to .ACCESS_WITH_SIZE,
>> +   OBJECT_SIZE_TYPE is the second argument from __builtin_object_size.
>> +   The 2nd, 3rd, and the 4th parameters of the call determine the size of
>> +   the CALL:
>> +
>> +   2nd argument REF_TO_SIZE: The reference to the size of the object,
>> +   3rd argument CLASS_OF_SIZE: The size referenced by the REF_TO_SIZE represents
>> +     0: the number of bytes;
>> +     1: the number of the elements of the object type;
>> +   4th argument TYPE_OF_SIZE: A constant 0 with its TYPE being the same as the TYPE
>> +    of the object referenced by REF_TO_SIZE
>> +
>> +   The size of the element can be retrived from the result type of the call,
>> +   which is the pointer to the array type.  */
>> +static tree
>> +access_with_size_object_size (const gcall *call, int object_size_type)
>> +{
>> +  /* If not for dynamic object size, return.  */
>> +  if ((object_size_type & OST_DYNAMIC) == 0)
>> +    return size_unknown (object_size_type);
>> +
>> +  gcc_assert (gimple_call_internal_p (call, IFN_ACCESS_WITH_SIZE));
>> +  /* Result type is a pointer type to the original flexible array type.  */
>> +  tree result_type = gimple_call_return_type (call);
>> +  gcc_assert (POINTER_TYPE_P (result_type));
>> +  tree element_size = TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (result_type)));
>> +  tree ref_to_size = gimple_call_arg (call, 1);
>> +  unsigned int class_of_size = TREE_INT_CST_LOW (gimple_call_arg (call, 2));
>> +  tree type = TREE_TYPE (gimple_call_arg (call, 3));
>> +
>> +  tree size = fold_build2 (MEM_REF, type, ref_to_size,
>> +			   build_int_cst (ptr_type_node, 0));
>> +
>> +  /* If size is negative value, treat it as zero.  */
>> +  if (!TYPE_UNSIGNED (type))
>> +  {
>> +    tree cond_expr = fold_build2 (LT_EXPR, boolean_type_node,
>> +				  unshare_expr (size), build_zero_cst (type));
>> +    size = fold_build3 (COND_EXPR, integer_type_node, cond_expr,
>> +			build_zero_cst (type), size);
>> +  }
>> +
>> +  if (class_of_size == 1)
>> +    size = size_binop (MULT_EXPR,
>> +		       fold_convert (sizetype, size),
>> +		       fold_convert (sizetype, element_size));
>> +  else
>> +    size = fold_convert (sizetype, size);
>> +
>> +  if (!todo)
>> +    todo = TODO_update_ssa_only_virtuals;
>> +
>> +  return size;
>> +}
>>    /* Compute __builtin_object_size for CALL, which is a GIMPLE_CALL.
>>     Handles calls to functions declared with attribute alloc_size.
>> @@ -1350,8 +1406,12 @@ call_object_size (struct object_size_info *osi, tree ptr, gcall *call)
>>      bool is_strdup = gimple_call_builtin_p (call, BUILT_IN_STRDUP);
>>    bool is_strndup = gimple_call_builtin_p (call, BUILT_IN_STRNDUP);
>> +  bool is_access_with_size
>> +	 = gimple_call_internal_p (call, IFN_ACCESS_WITH_SIZE);
>>    if (is_strdup || is_strndup)
>>      bytes = strdup_object_size (call, object_size_type, is_strndup);
>> +  else if (is_access_with_size)
>> +    bytes = access_with_size_object_size (call, object_size_type);
>>    else
>>      bytes = alloc_object_size (call, object_size_type);
>>