On Wed, Sep 11, 2024 at 2:13 PM Qing Zhao <qing.z...@oracle.com> wrote:
>
> compared to the 4th version, the changes are (address Jacub's concerns):
>
> 1. change the global "in_builtin_counted_by_ref" from a boolean to an int;
> 2. delete the label for the error handling code, and decress the global
> "in_builtin_counted_by_ref" before each break;
>
> the 4th version compared to the 3rd version, the only change is the
> size calculation in the testing case.
>
> The 3rd version compared to the 2nd version, the major change is:
> the update in testing cases per Martin's suggestions.
>
> when the 2nd version is compared to the first version, the major changes are:
>
> 1. change the name of the builtin from __builtin_get_counted_by to
> __builtin_counted_by_ref in order to reflect the fact that the returned
> value of it is a reference to the object.
>
> 2. make typeof(__builtin_counted_by_ref) working.
>
> 3. update the testing case to use the new builtin inside _Generic.
>
> bootstrapped and regress tested on both X86 and aarch64. no issue.
>
> Okay for the trunk?
>
> thanks.
>
> Qing.
>
> ==============================================
>
> With the addition of the 'counted_by' attribute and its wide roll-out
> within the Linux kernel, a use case has been found that would be very
> nice to have for object allocators: being able to set the counted_by
> counter variable without knowing its name.
>
> For example, given:
>
> struct foo {
> ...
> int counter;
> ...
> struct bar array[] __attribute__((counted_by (counter)));
> } *p;
>
> The existing Linux object allocators are roughly:
>
> #define MAX(A, B) (A > B) ? (A) : (B)
> #define alloc(P, FAM, COUNT) ({ \
> __auto_type __p = &(P); \
> size_t __size = MAX (sizeof(*P),
> __builtin_offsetof (__typeof(*P), FAM)
> + sizeof (*(P->FAM)) * COUNT); \
> *__p = kmalloc(__size); \
> })
>
> Right now, any addition of a counted_by annotation must also
> include an open-coded assignment of the counter variable after
> the allocation:
>
> p = alloc(p, array, how_many);
> p->counter = how_many;
>
> In order to avoid the tedious and error-prone work of manually adding
> the open-coded counted-by intializations everywhere in the Linux
> kernel, a new GCC builtin __builtin_counted_by_ref will be very useful
> to be added to help the adoption of the counted-by attribute.
>
> -- Built-in Function: TYPE __builtin_counted_by_ref (PTR)
> The built-in function '__builtin_counted_by_ref' checks whether the
> array object pointed by the pointer PTR has another object
> associated with it that represents the number of elements in the
> array object through the 'counted_by' attribute (i.e. the
> counted-by object). If so, returns a pointer to the corresponding
> counted-by object. If such counted-by object does not exist,
> returns a NULL pointer.
>
> This built-in function is only available in C for now.
>
> The argument PTR must be a pointer to an array. The TYPE of the
> returned value must be a pointer type pointing to the corresponding
> type of the counted-by object or VOID pointer type in case of a
> NULL pointer being returned.
>
> With this new builtin, the central allocator could be updated to:
>
> #define MAX(A, B) (A > B) ? (A) : (B)
> #define alloc(P, FAM, COUNT) ({ \
> __auto_type __p = &(P); \
> __auto_type __c = (COUNT); \
> size_t __size = MAX (sizeof (*(*__p)),\
> __builtin_offsetof (__typeof(*(*__p)),FAM) \
> + sizeof (*((*__p)->FAM)) * __c); \
> if ((*__p = kmalloc(__size))) { \
> __auto_type ret = __builtin_counted_by_ref((*__p)->FAM); \
> *_Generic(ret, void *: &(size_t){0}, default: ret) = __c; \
> } \
> })
>
> And then structs can gain the counted_by attribute without needing
> additional open-coded counter assignments for each struct, and
> unannotated structs could still use the same allocator.
>
> PR c/116016
>
> gcc/c-family/ChangeLog:
>
> * c-common.cc: Add new __builtin_counted_by_ref.
> * c-common.h (enum rid): Add RID_BUILTIN_COUNTED_BY_REF.
>
> gcc/c/ChangeLog:
>
> * c-decl.cc (names_builtin_p): Add RID_BUILTIN_COUNTED_BY_REF.
> * c-parser.cc (has_counted_by_object): New routine.
> (get_counted_by_ref): New routine.
> (c_parser_postfix_expression): Handle New RID_BUILTIN_COUNTED_BY_REF.
> * c-tree.h: New global in_builtin_counted_by_ref.
> * c-typeck.cc (build_component_ref): Enable generating
> .ACCESS_WITH_SIZE inside typeof when inside builtin_counted_by_ref.
>
> gcc/ChangeLog:
>
> * doc/extend.texi: Add documentation for __builtin_counted_by_ref.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/builtin-counted-by-ref-1.c: New test.
> * gcc.dg/builtin-counted-by-ref.c: New test.
> ---
> gcc/c-family/c-common.cc | 1 +
> gcc/c-family/c-common.h | 1 +
> gcc/c/c-decl.cc | 1 +
> gcc/c/c-parser.cc | 78 +++++++++++++++
> gcc/c/c-tree.h | 1 +
> gcc/c/c-typeck.cc | 7 +-
> gcc/doc/extend.texi | 55 +++++++++++
> .../gcc.dg/builtin-counted-by-ref-1.c | 97 +++++++++++++++++++
> gcc/testsuite/gcc.dg/builtin-counted-by-ref.c | 61 ++++++++++++
> 9 files changed, 301 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.dg/builtin-counted-by-ref-1.c
> create mode 100644 gcc/testsuite/gcc.dg/builtin-counted-by-ref.c
>
> diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
> index e7e371fd26f..15b90bae8b5 100644
> --- a/gcc/c-family/c-common.cc
> +++ b/gcc/c-family/c-common.cc
> @@ -430,6 +430,7 @@ const struct c_common_resword c_common_reswords[] =
> { "__builtin_choose_expr", RID_CHOOSE_EXPR, D_CONLY },
> { "__builtin_complex", RID_BUILTIN_COMPLEX, D_CONLY },
> { "__builtin_convertvector", RID_BUILTIN_CONVERTVECTOR, 0 },
> + { "__builtin_counted_by_ref", RID_BUILTIN_COUNTED_BY_REF, D_CONLY },
> { "__builtin_has_attribute", RID_BUILTIN_HAS_ATTRIBUTE, 0 },
> { "__builtin_launder", RID_BUILTIN_LAUNDER, D_CXXONLY },
> { "__builtin_shuffle", RID_BUILTIN_SHUFFLE, 0 },
> diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
> index 027f077d51b..4400d2c5d43 100644
> --- a/gcc/c-family/c-common.h
> +++ b/gcc/c-family/c-common.h
> @@ -110,6 +110,7 @@ enum rid
> RID_TYPES_COMPATIBLE_P, RID_BUILTIN_COMPLEX,
> RID_BUILTIN_SHUFFLE,
> RID_BUILTIN_SHUFFLEVECTOR, RID_BUILTIN_CONVERTVECTOR,
> RID_BUILTIN_TGMATH,
> RID_BUILTIN_HAS_ATTRIBUTE, RID_BUILTIN_ASSOC_BARRIER, RID_BUILTIN_STDC,
> + RID_BUILTIN_COUNTED_BY_REF,
> RID_DFLOAT32, RID_DFLOAT64, RID_DFLOAT128,
>
> /* TS 18661-3 keywords, in the same sequence as the TI_* values. */
> diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
> index aa7f69d1b7b..1145dde9bb1 100644
> --- a/gcc/c/c-decl.cc
> +++ b/gcc/c/c-decl.cc
> @@ -11788,6 +11788,7 @@ names_builtin_p (const char *name)
> case RID_BUILTIN_SHUFFLE:
> case RID_BUILTIN_SHUFFLEVECTOR:
> case RID_BUILTIN_STDC:
> + case RID_BUILTIN_COUNTED_BY_REF:
> case RID_CHOOSE_EXPR:
> case RID_OFFSETOF:
> case RID_TYPES_COMPATIBLE_P:
> diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
> index aff5af17430..91bd91f4be1 100644
> --- a/gcc/c/c-parser.cc
> +++ b/gcc/c/c-parser.cc
> @@ -10647,6 +10647,35 @@ c_parser_predefined_identifier (c_parser *parser)
> return expr;
> }
>
> +/* Check whether the ARRAY_REF has an counted-by object associated with it
> + through the "counted_by" attribute. */
> +static bool
> +has_counted_by_object (tree array_ref)
> +{
> + /* Currently, only when the array_ref is an indirect_ref to a call to the
> + .ACCESS_WITH_SIZE, return true.
> + More cases can be included later when the counted_by attribute is
> + extended to other situations. */
> + if ((TREE_CODE (array_ref) == INDIRECT_REF)
> + && is_access_with_size_p (TREE_OPERAND (array_ref, 0)))
> + return true;
> + return false;
> +}
> +
> +/* Get the reference to the counted-by object associated with the ARRAY_REF.
> */
> +static tree
> +get_counted_by_ref (tree array_ref)
> +{
> + /* Currently, only when the array_ref is an indirect_ref to a call to the
> + .ACCESS_WITH_SIZE, get the corresponding counted_by ref.
> + More cases can be included later when the counted_by attribute is
> + extended to other situations. */
> + if ((TREE_CODE (array_ref) == INDIRECT_REF)
> + && is_access_with_size_p (TREE_OPERAND (array_ref, 0)))
> + return CALL_EXPR_ARG (TREE_OPERAND (array_ref, 0), 1);
> + return NULL_TREE;
> +}
> +
> /* Parse a postfix expression (C90 6.3.1-6.3.2, C99 6.5.1-6.5.2,
> C11 6.5.1-6.5.2). Compound literals aren't handled here; callers have to
> call c_parser_postfix_expression_after_paren_type on encountering them.
> @@ -11741,6 +11770,55 @@ c_parser_postfix_expression (c_parser *parser)
> set_c_expr_source_range (&expr, loc, close_paren_loc);
> break;
> }
> + case RID_BUILTIN_COUNTED_BY_REF:
> + {
> + vec<c_expr_t, va_gc> *cexpr_list;
> + c_expr_t *e_p;
> + location_t close_paren_loc;
> +
> + in_builtin_counted_by_ref++;
> +
> + c_parser_consume_token (parser);
> + if (!c_parser_get_builtin_args (parser,
> + "__builtin_counted_by_ref",
> + &cexpr_list, false,
> + &close_paren_loc))
> + {
> + expr.set_error ();
> + in_builtin_counted_by_ref--;
> + break;
> + }
> + if (vec_safe_length (cexpr_list) != 1)
> + {
> + error_at (loc, "wrong number of arguments to "
> + "%<__builtin_counted_by_ref%>");
> + expr.set_error ();
> + in_builtin_counted_by_ref--;
> + break;
> + }
> +
> + e_p = &(*cexpr_list)[0];
> +
> + if (TREE_CODE (TREE_TYPE (e_p->value)) != ARRAY_TYPE)
> + {
> + error_at (loc, "the argument must be an array"
> + "%<__builtin_counted_by_ref%>");
> + expr.set_error ();
> + in_builtin_counted_by_ref--;
> + break;
> + }
> +
> + if (has_counted_by_object ((*cexpr_list)[0].value))
> + expr.value
> + = get_counted_by_ref ((*cexpr_list)[0].value);
> + else
> + expr.value
> + = build_int_cst (build_pointer_type (void_type_node), 0);
> +
> + set_c_expr_source_range (&expr, loc, close_paren_loc);
> + in_builtin_counted_by_ref--;
> + break;
> + }
> case RID_BUILTIN_SHUFFLE:
> {
> vec<c_expr_t, va_gc> *cexpr_list;
> diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
> index 57befb94c08..6f46b2ff5a0 100644
> --- a/gcc/c/c-tree.h
> +++ b/gcc/c/c-tree.h
> @@ -737,6 +737,7 @@ extern int c_type_dwarf_attribute (const_tree, int);
> extern int in_alignof;
> extern int in_sizeof;
> extern int in_typeof;
> +extern int in_builtin_counted_by_ref;
> extern bool c_in_omp_for;
> extern bool c_omp_array_section_p;
>
> diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
> index 58b2724b39e..8cb2cb60f6a 100644
> --- a/gcc/c/c-typeck.cc
> +++ b/gcc/c/c-typeck.cc
> @@ -74,6 +74,9 @@ int in_sizeof;
> /* The level of nesting inside "typeof". */
> int in_typeof;
>
> +/* The level of nesting inside "builtin_counted_by_ref". */
> +int in_builtin_counted_by_ref;
> +
> /* True when parsing OpenMP loop expressions. */
> bool c_in_omp_for;
>
> @@ -2848,7 +2851,9 @@ build_component_ref (location_t loc, tree datum, tree
> component,
> bool use_datum_quals;
> tree counted_by_type = NULL_TREE;
> /* Do not handle counted_by when in typeof and alignof operator. */
> - handle_counted_by = handle_counted_by && !in_typeof && !in_alignof;
> + handle_counted_by = handle_counted_by
> + && !(in_typeof && !in_builtin_counted_by_ref)
> + && !in_alignof;
> tree counted_by_ref = handle_counted_by
> ? build_counted_by_ref (datum, subdatum,
> &counted_by_type)
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 2d795ba7e59..268e50677d7 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -15287,6 +15287,61 @@ initializers of variables usable in constant
> expressions. For more details
> refer to the latest revision of the C++ standard.
> @enddefbuiltin
>
> +@defbuiltin{@var{type} __builtin_counted_by_ref (@var{ptr})}
> +The built-in function @code{__builtin_counted_by_ref} checks whether the
> array
> +object pointed by the pointer @var{ptr} has another object associated with it
> +that represents the number of elements in the array object through the
> +@code{counted_by} attribute (i.e. the counted-by object). If so, returns a
> +pointer to the corresponding counted-by object.
> +If such counted-by object does not exist, returns a NULL pointer.
> +
> +This built-in function is only available in C for now.
> +
> +The argument @var{ptr} must be a pointer to an array.
> +The @var{type} of the returned value must be a pointer type pointing to the
> +corresponding type of the counted-by object or a VOID pointer type in case
> +of a NULL pointer being returned.
> +
Having the return type default to a VOID pointer restricts it from this use:
if (__builtin_counted_by_ref(p->FAM))
*__builtin_counted_by_ref(p->FAM) = 42;
The second line will emit a diagnostic. Is VOID pointer just to make
using _Generic a bit cleaner? Is that now the prefered way to use this
builtin?
-bw
> +For example:
> +
> +@smallexample
> +struct foo1 @{
> + int counter;
> + struct bar1 array[] __attribute__((counted_by (counter)));
> +@} *p;
> +
> +struct foo2 @{
> + int other;
> + struct bar2 array[];
> +@} *q;
> +@end smallexample
> +
> +@noindent
> +the following call to the built-in
> +
> +@smallexample
> +__builtin_counted_by_ref (p->array)
> +@end smallexample
> +
> +@noindent
> +returns:
> +
> +@smallexample
> +&p->counter with type @code{int *}.
> +@end smallexample
> +
> +@noindent
> +However, the following call to the built-in
> +
> +@smallexample
> +__builtin_counted_by_ref (q->array)
> +@end smallexample
> +
> +@noindent
> +returns a void NULL pointer.
> +
> +@enddefbuiltin
> +
> @defbuiltin{void __builtin_clear_padding (@var{ptr})}
> The built-in function @code{__builtin_clear_padding} function clears
> padding bits inside of the object representation of object pointed by
> diff --git a/gcc/testsuite/gcc.dg/builtin-counted-by-ref-1.c
> b/gcc/testsuite/gcc.dg/builtin-counted-by-ref-1.c
> new file mode 100644
> index 00000000000..d055cf1defc
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/builtin-counted-by-ref-1.c
> @@ -0,0 +1,97 @@
> +/* Test the code generation for the new __builtin_counted_by_ref. */
> +/* { dg-do run } */
> +/* { dg-options "-O2" } */
> +#include <stdio.h>
> +
> +struct annotated {
> + char b;
> + int c[] __attribute ((counted_by (b)));
> +} *array_annotated;
> +
> +struct flex {
> + short b;
> + int c[];
> +} *array_flex;
> +
> +struct nested_annotated {
> + struct {
> + union {
> + int b;
> + float f;
> + };
> + int n;
> + };
> + char c[] __attribute__ ((counted_by (b)));
> +} *array_nested_annotated;
> +
> +struct nested_flex {
> + struct {
> + union {
> + unsigned int b;
> + float f;
> + };
> + int n;
> + };
> + char c[];
> +} *array_nested_flex;
> +
> +#define MAX(A, B) (A > B) ? (A) : (B)
> +#define MY_ALLOC(P, FAM, COUNT) ({ \
> + __auto_type __p = &(P); \
> + __auto_type __c = (COUNT); \
> + size_t __size = MAX (sizeof (*(*__p)),\
> + __builtin_offsetof (__typeof(*(*__p)),FAM) \
> + + sizeof (*((*__p)->FAM)) * __c); \
> + if ((*__p = __builtin_malloc(__size))) { \
> + __builtin_memset(*__p, 0, __size); \
> + __auto_type ret = __builtin_counted_by_ref((*__p)->FAM); \
> + *_Generic(ret, void *: &(size_t){0}, default: ret) = __c; \
> + if (sizeof (__builtin_counted_by_ref ((*__p)->FAM)) != sizeof (char *)) \
> + __builtin_abort (); \
> + } \
> +})
> +
> +int count;
> +
> +int main(int argc, char *argv[])
> +{
> + MY_ALLOC(array_annotated, c, 10);
> + if (array_annotated->b != 10)
> + __builtin_abort ();
> +
> + MY_ALLOC(array_flex, c, 20);
> + if (array_flex->b == 20)
> + __builtin_abort ();
> +
> + MY_ALLOC(array_nested_annotated, c, 30);
> + if (array_nested_annotated->b != 30)
> + __builtin_abort ();
> +
> + MY_ALLOC(array_nested_flex, c, 40);
> + if (array_nested_flex->b == 40)
> + __builtin_abort ();
> +
> + count = array_annotated->b * 2 + array_nested_annotated->b * 3;
> + struct annotated * annotated_p;
> + struct flex * flex_p;
> + struct nested_annotated * nested_annotated_p;
> + struct nested_flex * nested_flex_p;
> +
> + MY_ALLOC(annotated_p, c, count);
> + if (annotated_p->b != count)
> + __builtin_abort ();
> +
> + MY_ALLOC(flex_p, c, count * 2);
> + if (flex_p->b == count * 2)
> + __builtin_abort ();
> +
> + MY_ALLOC(nested_annotated_p, c, count * 3);
> + if (nested_annotated_p->b != count * 3)
> + __builtin_abort ();
> +
> + MY_ALLOC(nested_flex_p, c, count * 4);
> + if (nested_flex_p->b == count * 4)
> + __builtin_abort ();
> +
> + return 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/builtin-counted-by-ref.c
> b/gcc/testsuite/gcc.dg/builtin-counted-by-ref.c
> new file mode 100644
> index 00000000000..4aa57ffb916
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/builtin-counted-by-ref.c
> @@ -0,0 +1,61 @@
> +/* Testing the correct usage of the new __builtin_counted_by_ref. */
> +/* { dg-do compile } */
> +/* { dg-options "-O" } */
> +
> +#include <stdio.h>
> +
> +struct annotated {
> + size_t b;
> + int other;
> + int c[] __attribute ((counted_by (b)));
> +} *array_annotated;
> +
> +struct flex {
> + size_t b;
> + int other;
> + int c[];
> +} *array_flex;
> +
> +#define MAX(A, B) (A > B) ? (A) : (B)
> +#define MY_ALLOC(P, FAM, COUNT) ({ \
> + __auto_type __p = &(P); \
> + __auto_type __c = (COUNT); \
> + size_t __size = MAX (sizeof (*(*__p)),\
> + __builtin_offsetof (__typeof(*(*__p)),FAM) \
> + + sizeof (*((*__p)->FAM)) * __c); \
> + if ((*__p = __builtin_malloc(__size))) { \
> + __builtin_memset(*__p, 0, __size); \
> + __auto_type ret = __builtin_counted_by_ref((*__p)->FAM); \
> + *_Generic(ret, void *: &(size_t){0}, default: ret) = __c; \
> + if (sizeof (__builtin_counted_by_ref ((*__p)->FAM)) != sizeof (char *)) \
> + __builtin_abort (); \
> + } \
> +})
> +
> +extern char c_count;
> +extern short s_count;
> +extern int i_count;
> +extern long l_count;
> +extern float f_count;
> +
> +extern int * foo ();
> +
> +int main(int argc, char *argv[])
> +{
> + /* The good usages. */
> + MY_ALLOC(array_annotated, c, 10);
> + MY_ALLOC(array_flex, c, 20);
> + MY_ALLOC(array_annotated, c, c_count);
> + MY_ALLOC(array_flex, c, i_count);
> + MY_ALLOC(array_annotated, c, l_count);
> + MY_ALLOC(array_flex, c, c_count * 3);
> + MY_ALLOC(array_annotated, c, l_count * i_count);
> +
> + /* The bad usages, issue errors. */
> + __builtin_counted_by_ref (); /* { dg-error "wrong number of arguments to"
> } */
> + __builtin_counted_by_ref (array_annotated->c, 10); /* { dg-error "wrong
> number of arguments to" } */
> + __builtin_counted_by_ref (array_annotated->other); /* { dg-error "the
> argument must be an array" } */
> + __builtin_counted_by_ref (foo()); /* { dg-error "the argument must be an
> array" } */
> +
> + return 0;
> +}
> --
> 2.31.1
>
