On Wed, Apr 30, 2025 at 7:26 PM David Faust <david.fa...@oracle.com> wrote:
>
> The btf_decl_tag and btf_type_tag attributes provide a means to annotate
> declarations and types respectively with arbitrary user provided
> strings. These strings are recorded in debug information for
> post-compilation uses, and despite the name they are meant to be
> recorded in DWARF as well as BTF. New DWARF extensions
> DW_TAG_GNU_annotation and DW_AT_GNU_annotation are used to represent
> these user annotations in DWARF.
>
> This patch introduces the new DWARF extension DIE and attribute, and
> generates them as necessary to represent user annotations from
> btf_decl_tag and btf_type_tag.
>
> The format of the new DIE is as follows:
>
> DW_TAG_GNU_annotation
> DW_AT_name: "btf_decl_tag" or "btf_type_tag"
> DW_AT_const_value: <arbitrary user-supplied string>
> DW_AT_GNU_annotation: <reference to another TAG_GNU_annotation DIE>
>
> DW_AT_GNU_annotation is a new attribute extension used to refer to these
> new annotation DIEs. If non-null in any given declaration or type DIE,
> it is a reference to a DW_TAG_GNU_annotation DIE holding an annotation
> for that declaration or type. In addition, the DW_TAG_GNU_annotation
> DIEs may also have a non-null DW_AT_GNU_annotation, referring to another
> annotation DIE. This allows chains of annotation DIEs to be formed,
> such as in the case where a single declaration has multiple instances of
> btf_decl_tag with different string annotations.
>
> gcc/
> * dwarf2out.cc (struct annotation_node, struct annotation_node_hasher)
> (btf_tag_htab): New ancillary structures and hash table.
> (annotation_node_hasher::hash, annotation_node_hasher::equal): New.
> (hash_btf_tag, gen_btf_tag_dies, gen_btf_type_tag_dies)
> (maybe_gen_btf_type_tag_dies, gen_btf_decl_tag_dies): New functions.
> (modified_type_die): Handle btf_type_tag attribute.
> (gen_array_type_die): Call maybe_gen_btf_type_tags for the type.
> (gen_formal_parameter_die): Call gen_btf_decl_tags for the parameter.
> (gen_decl_die): Call gen_btf_decl_tags for the decl.
> (gen_tagged_type_die): Call maybe_gen_btf_type_tag_dies for the type.
> (dwarf2out_early_finish): Empty btf_tag_htab hash table.
> (dwarf2out_cc_finalize): Delete btf_tag_htab hash table.
>
> include/
> * dwarf2.def (DW_TAG_GNU_annotation): New DWARF extension.
> (DW_AT_GNU_annotation): Likewise.
>
> gcc/testsuite/
> * gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-1.c: New test.
> * gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-2.c: New test.
> * gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-3.c: New test.
> * gcc.dg/debug/dwarf2/dwarf-btf-type-tag-1.c: New test.
> * gcc.dg/debug/dwarf2/dwarf-btf-type-tag-2.c: New test.
> * gcc.dg/debug/dwarf2/dwarf-btf-type-tag-3.c: New test.
> * gcc.dg/debug/dwarf2/dwarf-btf-type-tag-4.c: New test.
> * gcc.dg/debug/dwarf2/dwarf-btf-type-tag-5.c: New test.
> ---
> gcc/dwarf2out.cc | 270 +++++++++++++++++-
> .../debug/dwarf2/dwarf-btf-decl-tag-1.c | 11 +
> .../debug/dwarf2/dwarf-btf-decl-tag-2.c | 25 ++
> .../debug/dwarf2/dwarf-btf-decl-tag-3.c | 21 ++
> .../debug/dwarf2/dwarf-btf-type-tag-1.c | 10 +
> .../debug/dwarf2/dwarf-btf-type-tag-2.c | 31 ++
> .../debug/dwarf2/dwarf-btf-type-tag-3.c | 15 +
> .../debug/dwarf2/dwarf-btf-type-tag-4.c | 33 +++
> .../debug/dwarf2/dwarf-btf-type-tag-5.c | 10 +
> include/dwarf2.def | 4 +
> 10 files changed, 426 insertions(+), 4 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-1.c
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-2.c
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-3.c
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-1.c
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-2.c
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-3.c
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-4.c
> create mode 100644 gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-5.c
>
> diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
> index 34ffeed86ff..1ec3b24e773 100644
> --- a/gcc/dwarf2out.cc
> +++ b/gcc/dwarf2out.cc
> @@ -3696,6 +3696,32 @@ static bool frame_pointer_fb_offset_valid;
>
> static vec<dw_die_ref> base_types;
>
> +/* A cached btf_type_tag or btf_decl_tag user annotation. */
> +struct GTY ((for_user)) annotation_node
> +{
> + const char *name;
> + const char *value;
> + hashval_t hash;
> + dw_die_ref die;
> + struct annotation_node *next;
> +};
> +
> +struct annotation_node_hasher : ggc_ptr_hash<annotation_node>
> +{
> + typedef const struct annotation_node *compare_type;
> +
> + static hashval_t hash (struct annotation_node *);
> + static bool equal (const struct annotation_node *,
> + const struct annotation_node *);
> +};
> +
> +/* A hash table of tag annotation nodes for btf_type_tag and btf_decl_tag C
> + attributes. DIEs for these user annotations may be reused if they are
> + structurally equivalent; this hash table is used to ensure the DIEs are
> + reused wherever possible. */
> +static GTY (()) hash_table<annotation_node_hasher> *btf_tag_htab;
> +
> +
> /* Flags to represent a set of attribute classes for attributes that
> represent
> a scalar value (bounds, pointers, ...). */
> enum dw_scalar_form
> @@ -13659,6 +13685,180 @@ long_double_as_float128 (tree type)
> return NULL_TREE;
> }
>
> +
> +hashval_t
> +annotation_node_hasher::hash (struct annotation_node *node)
> +{
> + return node->hash;
> +}
> +
> +bool
> +annotation_node_hasher::equal (const struct annotation_node *node1,
> + const struct annotation_node *node2)
> +{
> + return (node1->hash == node2->hash);
never any hash collision? I'd have expected name/value to be compared here,
and also 'next' (the "chain")?
Are we ever able to share partial chains this way? LTO streaming does
for example "share" list tails. I think attribute list generation
does not perform
any attempt to share.
> +}
> +
> +/* Return an appropriate entry in the btf tag hash table for a given btf tag.
> + If a structurally equivalent tag (one with the same name, value, and
> + subsequent chain of further tags) has already been processed, then the
> + existing entry for that tag is returned and should be reused.
> + Otherwise, a new entry is added to the hash table and returned. */
> +
> +static struct annotation_node *
> +hash_btf_tag (tree attr)
> +{
> + if (attr == NULL_TREE || TREE_CODE (attr) != TREE_LIST)
> + return NULL;
> +
> + if (!btf_tag_htab)
> + btf_tag_htab = hash_table<annotation_node_hasher>::create_ggc (10);
> +
> + const char * name = IDENTIFIER_POINTER (get_attribute_name (attr));
> + const char * value = TREE_STRING_POINTER (TREE_VALUE (TREE_VALUE (attr)));
> + tree chain = lookup_attribute (name, TREE_CHAIN (attr));
> +
> + /* Hash for one tag depends on hash of next tag in the chain, because
> + the chain is part of structural equivalence. */
> + struct annotation_node *chain_node = hash_btf_tag (chain);
> + gcc_checking_assert (chain == NULL_TREE || chain_node != NULL);
> +
> + /* Skip any non-btf-tag attributes that might be in the chain. */
> + if (strcmp (name, "btf_type_tag") != 0 && strcmp (name, "btf_decl_tag") !=
> 0)
> + return chain_node;
> +
> + /* Hash for a given tag is determined by the name, value, and chain of
> + further tags. */
> + inchash::hash h;
> + h.merge_hash (htab_hash_string (name));
> + h.merge_hash (htab_hash_string (value));
> + h.merge_hash (chain_node ? chain_node->hash : 0);
> +
> + struct annotation_node node;
> + node.name = name;
> + node.value = value;
> + node.hash = h.end ();
> + node.next = chain_node;
> +
> + struct annotation_node **slot = btf_tag_htab->find_slot (&node, INSERT);
> + if (*slot == NULL)
> + {
> + /* Create new htab entry for this annotation. */
> + struct annotation_node *new_slot
> + = ggc_cleared_alloc<struct annotation_node> ();
> + new_slot->name = name;
> + new_slot->value = value;
> + new_slot->hash = node.hash;
> + new_slot->next = chain_node;
> +
> + *slot = new_slot;
> + return new_slot;
> + }
> + else
> + {
> + /* This node is already in the hash table. */
> + return *slot;
> + }
> +}
> +
> +/* Generate (or reuse) DW_TAG_annotation DIEs representing the btf_type_tag
> or
> + btf_decl_tag user annotations in ATTR, and update DIE to refer to them
> + via DW_AT_annotation. If there are multiple type_tag or decl_tag
> + annotations in ATTR, they are all processed recursively by this function
> + to build a chain of annotation DIEs.
> + Return the first annotation DIE in the created (or reused) chain. */
> +
> +static dw_die_ref
> +gen_btf_tag_dies (tree attr, dw_die_ref die, dw_die_ref context_die)
> +{
> + if (attr == NULL_TREE)
> + return die;
> +
> + while (dw_get_die_tag (context_die) != DW_TAG_compile_unit)
> + context_die = context_die->die_parent;
> +
> + const char * name = IDENTIFIER_POINTER (get_attribute_name (attr));
> + const char * value = TREE_STRING_POINTER (TREE_VALUE (TREE_VALUE (attr)));
> +
> + dw_die_ref tag_die, prev = NULL;
> +
> + /* Multiple annotations on the same item form a singly-linked list of
> + annotation DIEs; generate recursively backward from the end so we can
> + chain each created DIE to the next, which has already been created. */
> + tree rest = lookup_attribute (name, TREE_CHAIN (attr));
> + if (rest)
> + prev = gen_btf_tag_dies (rest, NULL, context_die);
> +
> + /* Calculate a hash value for the tag based on its structure, find the
> + existing entry for it (if any) in the hash table, or create a new entry
> + which can be reused by structurally-equivalent tags. */
> + struct annotation_node *entry = hash_btf_tag (attr);
> + if (!entry)
> + return die;
> +
> + /* If the node already has an associated DIE, reuse it.
> + Otherwise, create the new annotation DIE, and associate it with
> + the hash table entry for future reuse. Any structurally-equivalent
> + tag we process later will find and share the same DIE. */
> + if (entry->die)
> + tag_die = entry->die;
> + else
> + {
> + tag_die = new_die (DW_TAG_GNU_annotation, context_die, NULL);
> + add_name_attribute (tag_die, name);
> + add_AT_string (tag_die, DW_AT_const_value, value);
> + if (prev)
> + add_AT_die_ref (tag_die, DW_AT_GNU_annotation, prev);
So I can see this saves DWARF space compared to adding multiple
DW_AT_GNU_annotation to the annotated object. It does feel a bit
un-DWARFish, I suppose using DIE children (with the same tag?)
would have been more DWARFish here. That would of course
remove the ability to share sub-lists (but as said, I'm unsure this
works now). So for a three-item list you'd have
DW_TAG_GNU_annotation
name
value
DW_TAG_GNU_annotation (first child)
name
value
DW_TAG_GNU_annotation (second child)
name
value
or alternatively, make the outer one "empty" (a container)
and add a third child with the above outers name/value.
It's a bit of bike-shedding of course.
> +
> + entry->die = tag_die;
> + }
> +
> + if (die)
> + add_AT_die_ref (die, DW_AT_GNU_annotation, tag_die);
> +
> + return tag_die;
> +}
> +
> +static void
> +gen_btf_type_tag_dies (tree t, tree attr, dw_die_ref target,
> + dw_die_ref context_die)
> +{
> + if (t == NULL_TREE || !TYPE_P (t) || !target)
> + return;
> +
> + gen_btf_tag_dies (attr, target, context_die);
> +}
> +
> +static void
> +maybe_gen_btf_type_tag_dies (tree t, dw_die_ref die, dw_die_ref context_die)
> +{
> + tree tags = lookup_attribute ("btf_type_tag", TYPE_ATTRIBUTES (t));
> + if (tags)
> + {
> + TYPE_ATTRIBUTES (t)
> + = remove_attribute ("btf_type_tag", TYPE_ATTRIBUTES (t));
> + gen_btf_type_tag_dies (t, tags, die, context_die);
> + }
> +}
> +
Most of the functions miss a function-level comment.
> +static void
> +gen_btf_decl_tag_dies (tree t, dw_die_ref target, dw_die_ref context_die)
> +{
> + if (t == NULL_TREE || !DECL_P (t) || !target)
> + return;
> +
> + tree attr = lookup_attribute ("btf_decl_tag", DECL_ATTRIBUTES (t));
> + if (attr == NULL_TREE)
> + return;
> +
> + gen_btf_tag_dies (attr, target, context_die);
> +
> + /* Strip the decl tag attribute once we have created the annotation DIEs
> + to avoid attempting process it multiple times. */
> + DECL_ATTRIBUTES (t)
> + = remove_attribute ("btf_decl_tag", DECL_ATTRIBUTES (t));
Hmm, you should get a type/decl DIE created only once, so why would you
run into this multiple times?
> +}
> +
> /* Given a pointer to an arbitrary ..._TYPE tree node, return a debugging
> entry that chains the modifiers specified by CV_QUALS in front of the
> given type. REVERSE is true if the type is to be interpreted in the
> @@ -13783,10 +13983,44 @@ modified_type_die (tree type, int cv_quals, bool
> reverse,
> dquals &= cv_qual_mask;
> if ((dquals & ~cv_quals) != TYPE_UNQUALIFIED
> || (cv_quals == dquals && DECL_ORIGINAL_TYPE (name) != type))
> - /* cv-unqualified version of named type. Just use
> - the unnamed type to which it refers. */
> - return modified_type_die (DECL_ORIGINAL_TYPE (name), cv_quals,
> - reverse, context_die);
> + {
> + if (lookup_attribute ("btf_type_tag", TYPE_ATTRIBUTES (type)))
> + {
> + /* Use of a typedef with additional btf_type_tags. Create
> + a distinct typedef DIE for this version of the named type
> + so that the btf_type_tag annotations may be attached to
> + it without affecting other users of the plain typedef.
> */
> + tree tags = lookup_attribute ("btf_type_tag",
> + TYPE_ATTRIBUTES (type));
you did this in the if () check already. Note I think this is only executed
when the type was qualified or typedef-ed?
> + tree dtags = lookup_attribute ("btf_type_tag",
> + TYPE_ATTRIBUTES (dtype));
> +
> + /* Remove type tags before the recursive call to avoid
> + processing the same attribute multiple times. */
> + TYPE_ATTRIBUTES (type)
> + = remove_attribute ("btf_type_tag", TYPE_ATTRIBUTES
> (type));
> +
> + dw_die_ref mod_die = modified_type_die (dtype, cv_quals,
> + reverse,
> context_die);
> +
> + /* Create a new typedef DIE since the btf_type_tag-ed use of
> + the typedef has really created a distinct type. */
> + if (!attribute_list_equal (tags, dtags))
> + {
> + mod_die = clone_die (mod_die);
> + add_child_die (comp_unit_die (), mod_die);
> + if (!lookup_type_die (type))
> + equate_type_number_to_die (type, mod_die);
> + }
> +
> + gen_btf_type_tag_dies (type, tags, mod_die, context_die);
> + return mod_die;
> + }
> + /* cv-unqualified version of named type. Just use
> + the unnamed type to which it refers. */
> + return modified_type_die (DECL_ORIGINAL_TYPE (name), cv_quals,
> + reverse, context_die);
> + }
> /* Else cv-qualified version of named type; fall through. */
> }
> }
> @@ -13887,6 +14121,18 @@ modified_type_die (tree type, int cv_quals, bool
> reverse,
> first_quals |= dwarf_qual_info[i].q;
> }
> }
> + else if (lookup_attribute ("btf_type_tag", TYPE_ATTRIBUTES (type)))
> + {
> + /* Remove type tags before the recursive call to avoid processing the
> + same attribute multiple times. */
> + tree attr = lookup_attribute ("btf_type_tag", TYPE_ATTRIBUTES (type));
twice again - if (tree attr = lookup_...) is a thing.
> + TYPE_ATTRIBUTES (type) = remove_attribute ("btf_type_tag",
> + TYPE_ATTRIBUTES (type));
> + dw_die_ref mod_die = modified_type_die (type, cv_quals, reverse,
> + context_die);
While recusing might look "convenient" here I think given modified_type_die's
complexity a more obvious handling should be prefered ;)
I think you want the tags to work like qualifiers, but I'm not sure
how this works
with your patch. Consider
struct S { int i ; };
struct S __attribute__((btf_type_tag("foo"))) a;
const struct S b;
struct S c;
const struct S __attribute__((btf_type_tag("foo"))) d;
how does the DWARF for 'a' look like? In particular the iffy thing is
dwarf_qual_info and the way we check we already have a qualified
type.
How do you represent having both the type S and the attributed type S?
And how do you go between having a const qualified variant of both?
> + gen_btf_type_tag_dies (type, attr, mod_die, context_die);
> + return mod_die;
> + }
> else if (code == POINTER_TYPE || code == REFERENCE_TYPE)
> {
> dwarf_tag tag = DW_TAG_pointer_type;
> @@ -22729,6 +22975,7 @@ gen_array_type_die (tree type, dw_die_ref context_die)
> add_pubtype (type, array_die);
>
> add_alignment_attribute (array_die, type);
> + maybe_gen_btf_type_tag_dies (type, array_die, context_die);
> }
>
> /* This routine generates DIE for array with hidden descriptor, details
> @@ -23099,6 +23346,8 @@ gen_formal_parameter_die (tree node, tree origin,
> bool emit_name_p,
> else
> {
> add_child_die (context_die, parm_die);
> +
> + gen_btf_decl_tag_dies (node_or_origin, parm_die, context_die);
> return parm_die;
> }
> }
> @@ -23167,6 +23416,8 @@ gen_formal_parameter_die (tree node, tree origin,
> bool emit_name_p,
> gcc_unreachable ();
> }
>
> + gen_btf_decl_tag_dies (node_or_origin, parm_die, context_die);
> +
> return parm_die;
> }
>
> @@ -26391,6 +26642,10 @@ gen_tagged_type_die (tree type,
> else
> gen_struct_or_union_type_die (type, context_die, usage);
>
> + dw_die_ref die = lookup_type_die (type);
> + if (die)
> + maybe_gen_btf_type_tag_dies (type, die, context_die);
> +
> /* Don't set TREE_ASM_WRITTEN on an incomplete struct; we want to fix
> it up if it is ever completed. gen_*_type_die will set it for us
> when appropriate. */
> @@ -27401,6 +27656,9 @@ gen_decl_die (tree decl, tree origin, struct
> vlr_context *ctx,
> break;
> }
>
> + gen_btf_decl_tag_dies (decl_or_origin, lookup_decl_die (decl_or_origin),
> + context_die);
> +
> return NULL;
> }
>
> @@ -33321,6 +33579,9 @@ dwarf2out_early_finish (const char *filename)
> print_die (comp_unit_die (), dump_file);
> }
>
> + if (btf_tag_htab)
> + btf_tag_htab->empty ();
> +
> /* Generate CTF/BTF debug info. */
> if ((ctf_debug_info_level > CTFINFO_LEVEL_NONE
> || btf_debuginfo_p ()) && lang_GNU_C ())
> @@ -33516,6 +33777,7 @@ dwarf2out_cc_finalize (void)
> switch_text_ranges = NULL;
> switch_cold_ranges = NULL;
> current_unit_personality = NULL;
> + btf_tag_htab = NULL;
>
> early_dwarf = false;
> early_dwarf_finished = false;
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-1.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-1.c
> new file mode 100644
> index 00000000000..a1c1676a7ba
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-1.c
> @@ -0,0 +1,11 @@
> +/* Test simple generation of DW_TAG_GNU_annotation DIE for
> + btf_decl_tag attribute. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +int *foo __attribute__((btf_decl_tag ("my_foo")));
> +
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_decl_tag\"" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_const_value: \"my_foo\"" 1 } }
> */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_annotation" 1 } } */
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-2.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-2.c
> new file mode 100644
> index 00000000000..76583840439
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-2.c
> @@ -0,0 +1,25 @@
> +/* Test dwarf generation for btf_decl_tag on struct and union members. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +#define __tag1 __attribute__((btf_decl_tag ("decl1")))
> +#define __tag2 __attribute__((btf_decl_tag ("decl2")))
> +
> +union U {
> + int i __tag1;
> + unsigned char ub[4];
> +};
> +
> +struct S {
> + union U u;
> + int b __tag2;
> + char *z __tag1;
> +};
> +
> +struct S my_s __tag1 __tag2;
> +
> +/* We must have two occurrances of one of the two annotation DIEs due to
> + the different attribute sets between declarations above. */
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 3 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_decl_tag\"" 3 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_annotation" 5 } } */
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-3.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-3.c
> new file mode 100644
> index 00000000000..f3fad8fe3d2
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-decl-tag-3.c
> @@ -0,0 +1,21 @@
> +/* Test dwarf generation for btf_decl_tag on functions and function args. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +#define __tag1 __attribute__((btf_decl_tag ("decl1")))
> +#define __tag2 __attribute__((btf_decl_tag ("decl2")))
> +
> +int __tag1 __tag2 func (int arg_a __tag1, int arg_b __tag2)
> +{
> + return arg_a * arg_b;
> +}
> +
> +int foo (int x) {
> + return func (x, x + 1);
> +}
> +
> +/* In this case one of the decl tag DIEs must be duplicated due to differing
> + DW_AT_GNU_annotation chain between the three uses. */
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 3 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_decl_tag\"" 3 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_annotation" 4 } } */
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-1.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-1.c
> new file mode 100644
> index 00000000000..772aab09cfb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-1.c
> @@ -0,0 +1,10 @@
> +/* Test simple generation for btf_type_tag attribute. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +int * __attribute__((btf_type_tag("__user"))) ptr;
> +
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_type_tag\"" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_const_value: \"__user\"" 1 } }
> */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_annotation" 1 } } */
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-2.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-2.c
> new file mode 100644
> index 00000000000..9c44e0ee0b9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-2.c
> @@ -0,0 +1,31 @@
> +/* Test that DW_TAG_GNU_annotation DIEs for attribute btf_type_tag are shared
> + where possible. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +#define __tag1 __attribute__((btf_type_tag("tag1")))
> +#define __tag2 __attribute__((btf_type_tag("tag2")))
> +
> +int __tag1 foo;
> +char * __tag1 __tag2 bar;
> +
> +struct S
> +{
> + unsigned char bytes[8];
> + unsigned long __tag1 t;
> + void *ptr;
> +};
> +
> +struct S * __tag1 __tag2 my_S;
> +
> +/* Only 2 DW_TAG_GNU_annotation DIEs should be generated, one each for "tag1"
> + and "tag2", and they should be reused. */
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 2 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_type_tag\"" 2 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_const_value: \"tag1\"" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_const_value: \"tag2\"" 1 } } */
> +
> +/* Each attribute-ed type shall refer via DW_AT_GNU_annotation to the
> + appropriate annotation DIE, including the annotation DIE for "tag2" which
> + is always chained to the DIE for "tag1" in this construction. */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_annotation" 5 } } */
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-3.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-3.c
> new file mode 100644
> index 00000000000..d02144c8004
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-3.c
> @@ -0,0 +1,15 @@
> +/* Test dwarf generation for btf_type_tag with cv-quals and typedefs. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +#define __tag1 __attribute__((btf_type_tag ("tag1")))
> +#define __tag2 __attribute__((btf_type_tag ("tag2")))
> +
> +typedef const int foo;
> +typedef int __tag1 bar;
> +
> +foo __tag2 x;
> +const bar y;
> +
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 2 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_type_tag\"" 2 } } */
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-4.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-4.c
> new file mode 100644
> index 00000000000..2e916e8b443
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-4.c
> @@ -0,0 +1,33 @@
> +/* Test generating annotation DIEs for struct/union/enum types. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +enum E
> +{
> + ONE,
> + TWO
> +} __attribute__((btf_type_tag("foo")));
> +
> +enum E some_e;
> +
> +struct S
> +{
> + int i;
> + char c;
> +} __attribute__((btf_type_tag("foo")));
> +
> +typedef struct S S1;
> +const S1 some_s1;
> +
> +union U
> +{
> + int x;
> + char y;
> +} __attribute__((btf_type_tag("foo")));
> +
> +volatile union U volatile_u;
> +
> +/* One annotation DIE may be shared by all three annotated types. */
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_type_tag\"" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_annotation" 3 } } */
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-5.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-5.c
> new file mode 100644
> index 00000000000..1a6b29f99a1
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/dwarf-btf-type-tag-5.c
> @@ -0,0 +1,10 @@
> +/* Test generation for btf_type_tag attribute on array type. */
> +/* { dg-do compile } */
> +/* { dg-options "-gdwarf -dA" } */
> +
> +int arr[8] __attribute__((btf_type_tag("tagged_arr")));
> +
> +/* { dg-final { scan-assembler-times "DIE \\(\[^\n\]*\\)
> DW_TAG_GNU_annotation" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_name: \"btf_type_tag\"" 1 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_const_value: \"tagged_arr\"" 1
> } } */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_annotation" 1 } } */
> diff --git a/include/dwarf2.def b/include/dwarf2.def
> index 989f078041d..37b8d6b99d0 100644
> --- a/include/dwarf2.def
> +++ b/include/dwarf2.def
> @@ -174,6 +174,9 @@ DW_TAG (DW_TAG_GNU_formal_parameter_pack, 0x4108)
> are properly part of DWARF 5. */
> DW_TAG (DW_TAG_GNU_call_site, 0x4109)
> DW_TAG (DW_TAG_GNU_call_site_parameter, 0x410a)
> +
> +DW_TAG (DW_TAG_GNU_annotation, 0x6001)
> +
> /* Extensions for UPC. See: http://dwarfstd.org/doc/DWARF4.pdf. */
> DW_TAG (DW_TAG_upc_shared_type, 0x8765)
> DW_TAG (DW_TAG_upc_strict_type, 0x8766)
> @@ -456,6 +459,7 @@ DW_AT (DW_AT_GNU_pubtypes, 0x2135)
> DW_AT (DW_AT_GNU_discriminator, 0x2136)
> DW_AT (DW_AT_GNU_locviews, 0x2137)
> DW_AT (DW_AT_GNU_entry_view, 0x2138)
> +DW_AT (DW_AT_GNU_annotation, 0x2139)
> /* VMS extensions. */
> DW_AT (DW_AT_VMS_rtnbeg_pd_address, 0x2201)
> /* GNAT extensions. */
> --
> 2.47.2
>
