On Fri, 24 Feb 2023, Qing Zhao wrote:
> GCC extension accepts the case when a struct with a C99 flexible array member
> is embedded into another struct or union (possibly recursively).
> __builtin_object_size should treat such struct as flexible size.
>
> gcc/c/ChangeLog:
>
> PR tree-optimization/101832
> * c-decl.cc (finish_struct): Set TYPE_INCLUDE_FLEXARRAY for
> struct/union type.
I can't really comment on the correctness of this part but since
only the C frontend will ever set this and you are using it from
addr_object_size which is also used for other C family languages
(at least), I wonder if you can really test
+ if (!TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (v)))
there.
Originally I was suggesting to set this flag in stor-layout.cc
which eventually all languages funnel their types through and
if there's language specific handling use a langhook (with the
default implementation preserving the status quo).
Some more comments below ...
> gcc/cp/ChangeLog:
>
> PR tree-optimization/101832
> * module.cc (trees_out::core_bools): Stream out new bit
> type_include_flexarray.
> (trees_in::core_bools): Stream in new bit type_include_flexarray.
>
> gcc/ChangeLog:
>
> PR tree-optimization/101832
> * print-tree.cc (print_node): Print new bit type_include_flexarray.
> * tree-core.h (struct tree_type_common): New bit
> type_include_flexarray.
> * tree-object-size.cc (addr_object_size): Handle structure/union type
> when it has flexible size.
> * tree-streamer-in.cc (unpack_ts_type_common_value_fields): Stream
> in new bit type_include_flexarray.
> * tree-streamer-out.cc (pack_ts_type_common_value_fields): Stream
> out new bit type_include_flexarray.
> * tree.h (TYPE_INCLUDE_FLEXARRAY): New macro
> TYPE_INCLUDE_FLEXARRAY.
>
> gcc/testsuite/ChangeLog:
>
> PR tree-optimization/101832
> * gcc.dg/builtin-object-size-pr101832.c: New test.
> ---
> gcc/c/c-decl.cc | 12 ++
> gcc/cp/module.cc | 2 +
> gcc/print-tree.cc | 5 +
> .../gcc.dg/builtin-object-size-pr101832.c | 134 ++++++++++++++++++
> gcc/tree-core.h | 4 +-
> gcc/tree-object-size.cc | 79 +++++++----
> gcc/tree-streamer-in.cc | 1 +
> gcc/tree-streamer-out.cc | 1 +
> gcc/tree.h | 6 +
> 9 files changed, 215 insertions(+), 29 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
>
> diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
> index 08078eadeb8..f589a2f5192 100644
> --- a/gcc/c/c-decl.cc
> +++ b/gcc/c/c-decl.cc
> @@ -9284,6 +9284,18 @@ finish_struct (location_t loc, tree t, tree fieldlist,
> tree attributes,
> /* Set DECL_NOT_FLEXARRAY flag for FIELD_DECL x. */
> DECL_NOT_FLEXARRAY (x) = !is_flexible_array_member_p (is_last_field,
> x);
>
> + /* Set TYPE_INCLUDE_FLEXARRAY for the context of x, t
> + * when x is an array. */
> + if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE)
> + TYPE_INCLUDE_FLEXARRAY (t) = flexible_array_member_type_p (TREE_TYPE
> (x)) ;
> + /* Recursively set TYPE_INCLUDE_FLEXARRAY for the context of x, t
> + when x is the last field. */
> + else if ((TREE_CODE (TREE_TYPE (x)) == RECORD_TYPE
> + || TREE_CODE (TREE_TYPE (x)) == UNION_TYPE)
> + && TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (x))
> + && is_last_field)
> + TYPE_INCLUDE_FLEXARRAY (t) = true;
> +
> if (DECL_NAME (x)
> || RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
> saw_named_field = true;
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index ac2fe66b080..c750361b704 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -5371,6 +5371,7 @@ trees_out::core_bools (tree t)
> WB (t->type_common.lang_flag_5);
> WB (t->type_common.lang_flag_6);
> WB (t->type_common.typeless_storage);
> + WB (t->type_common.type_include_flexarray);
> }
>
> if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
> @@ -5551,6 +5552,7 @@ trees_in::core_bools (tree t)
> RB (t->type_common.lang_flag_5);
> RB (t->type_common.lang_flag_6);
> RB (t->type_common.typeless_storage);
> + RB (t->type_common.type_include_flexarray);
> }
>
> if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
> diff --git a/gcc/print-tree.cc b/gcc/print-tree.cc
> index 1f3afcbbc86..efacdb7686f 100644
> --- a/gcc/print-tree.cc
> +++ b/gcc/print-tree.cc
> @@ -631,6 +631,11 @@ print_node (FILE *file, const char *prefix, tree node,
> int indent,
> && TYPE_CXX_ODR_P (node))
> fputs (" cxx-odr-p", file);
>
> + if ((code == RECORD_TYPE
> + || code == UNION_TYPE)
> + && TYPE_INCLUDE_FLEXARRAY (node))
> + fputs (" include-flexarray", file);
> +
> /* The transparent-union flag is used for different things in
> different nodes. */
> if ((code == UNION_TYPE || code == RECORD_TYPE)
> diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> new file mode 100644
> index 00000000000..60078e11634
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> @@ -0,0 +1,134 @@
> +/* PR 101832:
> + GCC extension accepts the case when a struct with a C99 flexible array
> + member is embedded into another struct (possibly recursively).
> + __builtin_object_size will treat such struct as flexible size.
> + However, when a structure with non-C99 flexible array member, i.e,
> trailing
> + [0], [1], or [4], is embedded into anther struct, the stucture will not
> + be treated as flexible 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 A {
> + int n;
> + char data[];
> +};
> +
> +struct B {
> + int m;
> + struct A a;
> +};
> +
> +struct C {
> + int q;
> + struct B b;
> +};
> +
> +struct A0 {
> + int n;
> + char data[0];
> +};
> +
> +struct B0 {
> + int m;
> + struct A0 a;
> +};
> +
> +struct C0 {
> + int q;
> + struct B0 b;
> +};
> +
> +struct A1 {
> + int n;
> + char data[1];
> +};
> +
> +struct B1 {
> + int m;
> + struct A1 a;
> +};
> +
> +struct C1 {
> + int q;
> + struct B1 b;
> +};
> +
> +struct An {
> + int n;
> + char data[8];
> +};
> +
> +struct Bn {
> + int m;
> + struct An a;
> +};
> +
> +struct Cn {
> + int q;
> + struct Bn b;
> +};
> +
> +volatile void *magic1, *magic2;
> +
> +int main (int argc, char *argv[])
> +{
> + struct B *outer;
> + struct C *outest;
> +
> + /* Make sure optimization can't find some other object size. */
> + outer = (void *)magic1;
> + outest = (void *)magic2;
> +
> + expect (__builtin_object_size (&outer->a, 1), -1);
> + expect (__builtin_object_size (&outest->b, 1), -1);
> + expect (__builtin_object_size (&outest->b.a, 1), -1);
> +
> + struct B0 *outer0;
> + struct C0 *outest0;
> +
> + /* Make sure optimization can't find some other object size. */
> + outer0 = (void *)magic1;
> + outest0 = (void *)magic2;
> +
> + expect (__builtin_object_size (&outer0->a, 1), sizeof (outer0->a));
> + expect (__builtin_object_size (&outest0->b, 1), sizeof (outest0->b));
> + expect (__builtin_object_size (&outest0->b.a, 1), sizeof (outest0->b.a));
> +
> + struct B1 *outer1;
> + struct C1 *outest1;
> +
> + /* Make sure optimization can't find some other object size. */
> + outer1 = (void *)magic1;
> + outest1 = (void *)magic2;
> +
> + expect (__builtin_object_size (&outer1->a, 1), sizeof (outer1->a));
> + expect (__builtin_object_size (&outest1->b, 1), sizeof (outest1->b));
> + expect (__builtin_object_size (&outest1->b.a, 1), sizeof (outest1->b.a));
> +
> + struct Bn *outern;
> + struct Cn *outestn;
> +
> + /* Make sure optimization can't find some other object size. */
> + outern = (void *)magic1;
> + outestn = (void *)magic2;
> +
> + expect (__builtin_object_size (&outern->a, 1), sizeof (outern->a));
> + expect (__builtin_object_size (&outestn->b, 1), sizeof (outestn->b));
> + expect (__builtin_object_size (&outestn->b.a, 1), sizeof (outestn->b.a));
> +
> + DONE ();
> + return 0;
> +}
> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> index acd8deea34e..705d5702b9c 100644
> --- a/gcc/tree-core.h
> +++ b/gcc/tree-core.h
> @@ -1718,7 +1718,9 @@ struct GTY(()) tree_type_common {
> unsigned empty_flag : 1;
> unsigned indivisible_p : 1;
> unsigned no_named_args_stdarg_p : 1;
> - unsigned spare : 15;
> + /* TYPE_INCLUDE_FLEXARRAY flag for RECORD_TYPE and UNION_TYPE. */
> + unsigned int type_include_flexarray : 1;
> + unsigned spare : 14;
it looks like the bit could be eventually shared with
no_named_args_stdarg_p (but its accessor doesn't use
FUNC_OR_METHOD_CHECK)
> alias_set_type alias_set;
> tree pointer_to;
> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
> index 9a936a91983..22b3c72ea6e 100644
> --- a/gcc/tree-object-size.cc
> +++ b/gcc/tree-object-size.cc
> @@ -633,45 +633,68 @@ addr_object_size (struct object_size_info *osi,
> const_tree ptr,
> v = NULL_TREE;
> break;
> case COMPONENT_REF:
> - if (TREE_CODE (TREE_TYPE (v)) != ARRAY_TYPE)
> + /* When the ref is not to an array, a record or a union, it
> + will not have flexible size, compute the object size
> + directly. */
> + if ((TREE_CODE (TREE_TYPE (v)) != ARRAY_TYPE)
> + && (TREE_CODE (TREE_TYPE (v)) != RECORD_TYPE)
> + && (TREE_CODE (TREE_TYPE (v)) != UNION_TYPE))
> {
> v = NULL_TREE;
> break;
> }
> - is_flexible_array_mem_ref = array_ref_flexible_size_p (v);
> - while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
> - if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> - != UNION_TYPE
> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> - != QUAL_UNION_TYPE)
> - break;
> - else
> - v = TREE_OPERAND (v, 0);
> - if (TREE_CODE (v) == COMPONENT_REF
> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> - == RECORD_TYPE)
> + if (TREE_CODE (TREE_TYPE (v)) == RECORD_TYPE
> + || TREE_CODE (TREE_TYPE (v)) == UNION_TYPE)
> + /* if the record or union does not include a flexible array
> + recursively, compute the object size directly. */
> {
> - /* compute object size only if v is not a
> - flexible array member. */
> - if (!is_flexible_array_mem_ref)
> + if (!TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (v)))
> {
> v = NULL_TREE;
> break;
> }
> - v = TREE_OPERAND (v, 0);
> + else
> + v = TREE_OPERAND (v, 0);
> }
> - while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
> - if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> - != UNION_TYPE
> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> - != QUAL_UNION_TYPE)
> - break;
> - else
> - v = TREE_OPERAND (v, 0);
> - if (v != pt_var)
> - v = NULL_TREE;
> else
> - v = pt_var;
> + {
> + /* Now the ref is to an array type. */
> + is_flexible_array_mem_ref
> + = array_ref_flexible_size_p (v);
> + while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
> + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> + != UNION_TYPE
> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> + != QUAL_UNION_TYPE)
> + break;
> + else
> + v = TREE_OPERAND (v, 0);
> + if (TREE_CODE (v) == COMPONENT_REF
> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> + == RECORD_TYPE)
> + {
> + /* compute object size only if v is not a
> + flexible array member. */
> + if (!is_flexible_array_mem_ref)
> + {
> + v = NULL_TREE;
> + break;
> + }
> + v = TREE_OPERAND (v, 0);
> + }
> + while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
> + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> + != UNION_TYPE
> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> + != QUAL_UNION_TYPE)
> + break;
> + else
> + v = TREE_OPERAND (v, 0);
> + if (v != pt_var)
> + v = NULL_TREE;
> + else
> + v = pt_var;
> + }
> break;
> default:
> v = pt_var;
> diff --git a/gcc/tree-streamer-in.cc b/gcc/tree-streamer-in.cc
> index d4dc30f048f..c19ede0631d 100644
> --- a/gcc/tree-streamer-in.cc
> +++ b/gcc/tree-streamer-in.cc
> @@ -390,6 +390,7 @@ unpack_ts_type_common_value_fields (struct bitpack_d *bp,
> tree expr)
> TYPE_TRANSPARENT_AGGR (expr) = (unsigned) bp_unpack_value (bp, 1);
> TYPE_FINAL_P (expr) = (unsigned) bp_unpack_value (bp, 1);
> TYPE_CXX_ODR_P (expr) = (unsigned) bp_unpack_value (bp, 1);
> + TYPE_INCLUDE_FLEXARRAY (expr) = (unsigned) bp_unpack_value (bp, 1);
> }
> else if (TREE_CODE (expr) == ARRAY_TYPE)
> TYPE_NONALIASED_COMPONENT (expr) = (unsigned) bp_unpack_value (bp, 1);
> diff --git a/gcc/tree-streamer-out.cc b/gcc/tree-streamer-out.cc
> index d107229da5c..73e4b4e547c 100644
> --- a/gcc/tree-streamer-out.cc
> +++ b/gcc/tree-streamer-out.cc
> @@ -357,6 +357,7 @@ pack_ts_type_common_value_fields (struct bitpack_d *bp,
> tree expr)
> bp_pack_value (bp, flag_wpa && TYPE_CANONICAL (expr)
> ? TYPE_CXX_ODR_P (TYPE_CANONICAL (expr))
> : TYPE_CXX_ODR_P (expr), 1);
> + bp_pack_value (bp, TYPE_INCLUDE_FLEXARRAY (expr), 1);
> }
> else if (TREE_CODE (expr) == ARRAY_TYPE)
> bp_pack_value (bp, TYPE_NONALIASED_COMPONENT (expr), 1);
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 92ac0e6a214..ab1cdc3dc85 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -778,6 +778,12 @@ extern void omp_clause_range_check_failed (const_tree,
> const char *, int,
> #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
> (TYPE_CHECK (NODE)->type_common.no_named_args_stdarg_p)
>
> +/* True if this RECORD_TYPE or UNION_TYPE includes a flexible array member
> + at the last field recursively. */
> +#define TYPE_INCLUDE_FLEXARRAY(NODE) \
> + (TYPE_CHECK (NODE)->type_common.type_include_flexarray)
Please use RECORD_OR_UNION_CHECK. The comment "at the last field"
doesn't seem to match implementation? (at least not obviously)
Given this is a generic header expanding on what a "flexible array member"
is to the middle-end here would be good. Especially the guarantees
made when the bit is _not_ set (we've evaded that with DECL_NOT_FLEXARRAY
vs. DECL_FLEXARRAY).
Thanks,
Richard.
