From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2C0C5363C43 for ; Mon, 1 Jun 2026 18:35:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780338927; cv=none; b=l+1pCWtpAcFI6HpE4z/1OMejweAjownf/73X1aAKtTmKkYyYwGa4JldkpJFcPf9wUJB6yRmDWOEXRdl7nBu6niTibusp4GFqj1iwLSZx4LD7rVkOI1uNdAvc6sRpH2gATRB1tuCxKdK8QvlQrejemmiByQOMXwX43lJD8R7Dk5w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780338927; c=relaxed/simple; bh=56tdB5Cjnw4+uaX/wfGJ7DcCWJXHV7HiJlE9rfiYOH0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=poyVFuRCHkQGfXhy23zWL1F7MIh+41dyjrfTIncAD0DHvKd9A+dLKizwPC31A1xaosIsCsf1E9Bpd34vPpZlgXJ4wmrR6lKAil27Bux9jD/FdwkaiIE/XD5UibITtYfqyt6hYydY4ieV6NkdaHnYlkWh8GvFb2cpRQn2adW6G6w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=WJ1O/hFq; arc=none smtp.client-ip=91.218.175.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="WJ1O/hFq" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780338922; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Vm6kHYJ8on4TsZj23bzeIxKbN8OjKbeAVyOofUJj8Kc=; b=WJ1O/hFqakQ3UW6NIP8HxKJZUsVlMN9EdgrxoqGcJMp6AI69TVQLa+FeD2gXKFjxSERL5Y 8K5tLTSMK7ko9D6qhjJTXPA1Dls0tHxDGG1ZW3i8naYHVoUXsBDU1d1OrR6TZty3yRr85r yoH3wzSj2iUt4gxhiG7RjijTME1dxb8= From: Vineet Gupta To: dwarves@vger.kernel.org Cc: bpf@vger.kernel.org, Andrii Nakryiko , acme@kernel.org, Alan Maguire , jose.marchesi@oracle.com, David Faust , Vineet Gupta Subject: [PAHOLE v3 2/3] dwarf_loader: Add support for DW_TAG_GNU_annotation Date: Mon, 1 Jun 2026 11:35:10 -0700 Message-ID: <20260601183511.594100-2-vineet.gupta@linux.dev> In-Reply-To: <20260601183511.594100-1-vineet.gupta@linux.dev> References: <20260601183511.594100-1-vineet.gupta@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT gcc 16 was first release to support DW_TAG_GNU_annotation and this patch enables the same in pahole. Bulk of changes are in dwarf_loader but btf_encoder also gains support with minimal changes. GCC encodes btf_type_tag and btf_decl_tag annotations differently from LLVM. While LLVM uses DW_TAG_LLVM_annotation (0x6000) as child DIEs, GCC uses DW_TAG_GNU_annotation (0x6001) as standalone sibling DIEs referenced via DW_AT_GNU_annotation (0x2139) attributes, with chaining through the same attribute on annotation DIEs themselves. Handle both encoding styles: For btf_type_tag (pointer annotations): - Recognize DW_TAG_GNU_annotation alongside DW_TAG_LLVM_annotation in child annotation scanning. - Follow DW_AT_GNU_annotation attribute chains on pointer types for GCC-style btf_type_tag resolution, with cycle detection. - Normalize DW_TAG_GNU_annotation to DW_TAG_LLVM_annotation in the internal representation so downstream code works unchanged. For btf_decl_tag (function/struct/member annotations): - Add add_gnu_annotation_chain() to follow DW_AT_GNU_annotation attribute chains on function, struct, and member DIEs. - GCC puts DW_AT_GNU_annotation on the function/struct DIE itself (not as child DIEs), referencing sibling annotation DIEs that chain via the same attribute. Also: - Silently skip standalone DW_TAG_GNU_annotation DIEs at CU level. - Update pfunct-btf-decl-tags.sh test to use GCC 16+ when available and now passes. Signed-off-by: Vineet Gupta --- Changes since v2 [2] - Removed loop detection logic - Move test changes to different patch Changes since v1 [1] - NFC Reduce indentation with early exits (Alexei offlist) [2] https://lore.kernel.org/bpf/20260528223616.2035618-2-vineet.gupta@linux.dev/ [1] https://lore.kernel.org/bpf/20260526181818.4159927-2-vineet.gupta@linux.dev/ --- btf_encoder.c | 1 + dutil.h | 8 ++++ dwarf_loader.c | 102 ++++++++++++++++++++++++++++++++++++++++++---- dwarves.h | 3 +- dwarves_fprintf.c | 8 +++- 5 files changed, 110 insertions(+), 12 deletions(-) diff --git a/btf_encoder.c b/btf_encoder.c index 633bc6162ce0..d5af706d7638 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -1831,6 +1831,7 @@ static int btf_encoder__encode_tag(struct btf_encoder *encoder, struct tag *tag, name = namespace__name(tag__namespace(tag)); return btf_encoder__add_ref_type(encoder, BTF_KIND_TYPEDEF, ref_type_id, name, false); case DW_TAG_LLVM_annotation: + case DW_TAG_GNU_annotation: name = tag__btf_type_tag(tag)->value; return btf_encoder__add_ref_type(encoder, BTF_KIND_TYPE_TAG, ref_type_id, name, false); case DW_TAG_structure_type: diff --git a/dutil.h b/dutil.h index ff78aa6dfd10..abe0e62b412f 100644 --- a/dutil.h +++ b/dutil.h @@ -35,6 +35,14 @@ #define DW_TAG_LLVM_annotation 0x6000 #endif +#ifndef DW_TAG_GNU_annotation +#define DW_TAG_GNU_annotation 0x6001 +#endif + +#ifndef DW_AT_GNU_annotation +#define DW_AT_GNU_annotation 0x2139 +#endif + static inline __attribute__((const)) bool is_power_of_2(unsigned long n) { return (n != 0 && ((n & (n - 1)) == 0)); diff --git a/dwarf_loader.c b/dwarf_loader.c index 8b5b526299b5..878565884f85 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -908,6 +908,12 @@ static int tag__recode_dwarf_bitfield(struct tag *tag, struct cu *cu, uint16_t b return -ENOMEM; } +static bool die__tag_is_annotation(Dwarf_Die *die) +{ + unsigned int tag = dwarf_tag(die); + return tag == DW_TAG_LLVM_annotation || tag == DW_TAG_GNU_annotation; +} + static int add_llvm_annotation(Dwarf_Die *die, int component_idx, struct conf_load *conf, struct list_head *head) { @@ -943,7 +949,7 @@ static int add_child_llvm_annotations(Dwarf_Die *die, int component_idx, die = &child; do { - if (dwarf_tag(die) == DW_TAG_LLVM_annotation) { + if (die__tag_is_annotation(die)) { ret = add_llvm_annotation(die, component_idx, conf, head); if (ret) return ret; @@ -953,6 +959,35 @@ static int add_child_llvm_annotations(Dwarf_Die *die, int component_idx, return 0; } +/* Handle gcc sytle btf_decl_tag annotations for functions/struct/member tags + * Pointers are handled seperately, inline in die__create_new_pointer_tag () + */ +static int add_gnu_annotation_chain(Dwarf_Die *die, int component_idx, + struct conf_load *conf, struct list_head *head) +{ + Dwarf_Attribute attr; + Dwarf_Die annot_die; + + if (dwarf_attr(die, DW_AT_GNU_annotation, &attr) == NULL || + dwarf_formref_die(&attr, &annot_die) == NULL) + return 0; + + for (;;) { + if (dwarf_tag(&annot_die) != DW_TAG_GNU_annotation) + break; + + int ret = add_llvm_annotation(&annot_die, component_idx, conf, head); + if (ret) + return ret; + + if (dwarf_attr(&annot_die, DW_AT_GNU_annotation, &attr) == NULL || + dwarf_formref_die(&attr, &annot_die) == NULL) + break; + } + + return 0; +} + int class_member__dwarf_recode_bitfield(struct class_member *member, struct cu *cu) { @@ -1596,6 +1631,8 @@ static struct btf_type_tag_type *die__create_new_btf_type_tag_type(Dwarf_Die *di return NULL; tag__init(&tag->tag, cu, die); + /* Normalize DW_TAG_GNU_annotation to DW_TAG_LLVM_annotation internally */ + tag->tag.tag = DW_TAG_LLVM_annotation; tag->value = attr_string(die, DW_AT_const_value, conf); return tag; } @@ -1636,19 +1673,21 @@ static struct tag *die__create_new_pointer_tag(Dwarf_Die *die, struct cu *cu, { struct btf_type_tag_ptr_type *tag = NULL; Dwarf_Die *cdie, child; + Dwarf_Attribute attr; + Dwarf_Die annot_die; const char *name; - /* If no child tags or skipping btf_type_tag encoding, just create a new tag - * and return - */ - if (!dwarf_haschildren(die) || dwarf_child(die, &child) != 0 || - conf->skip_encoding_btf_type_tag) + /* If skipping btf_type_tag encoding, just create a new tag, return */ + if (conf->skip_encoding_btf_type_tag) return tag__new(die, cu); - /* Otherwise, check DW_TAG_LLVM_annotation child tags */ + /* Handle LLVM style annotation tags if present */ + if (!dwarf_haschildren(die) || dwarf_child(die, &child) != 0) + goto check_gnu_attr; + cdie = &child; do { - if (dwarf_tag(cdie) != DW_TAG_LLVM_annotation) + if (!die__tag_is_annotation(cdie)) continue; /* Only check btf_type_tag annotations */ @@ -1661,6 +1700,31 @@ static struct tag *die__create_new_pointer_tag(Dwarf_Die *die, struct cu *cu, return NULL; } while (dwarf_siblingof(cdie, cdie) == 0); +check_gnu_attr: + /* Check for GCC-style DW_AT_GNU_annotation attribute */ + if (tag != NULL || + dwarf_attr(die, DW_AT_GNU_annotation, &attr) == NULL || + dwarf_formref_die(&attr, &annot_die) == NULL) + goto out; + + for (;;) { + if (dwarf_tag(&annot_die) != DW_TAG_GNU_annotation) + break; + + name = attr_string(&annot_die, DW_AT_name, conf); + if (strcmp(name, "btf_type_tag") != 0) + break; + + tag = die__add_btf_type_tag(tag, die, &annot_die, cu, conf); + if (tag == NULL) + return NULL; + + if (dwarf_attr(&annot_die, DW_AT_GNU_annotation, &attr) == NULL || + dwarf_formref_die(&attr, &annot_die) == NULL) + break; + } + +out: return tag ? &tag->tag : tag__new(die, cu); } @@ -1689,6 +1753,12 @@ static struct tag *die__create_new_class(Dwarf_Die *die, struct cu *cu, struct c } } + if (class != NULL && + add_gnu_annotation_chain(die, -1, conf, &class->type.namespace.annots) != 0) { + class__delete(class, cu); + class = NULL; + } + return class ? &class->type.namespace.tag : NULL; } @@ -2050,10 +2120,13 @@ static int die__process_class(Dwarf_Die *die, struct type *class, cu__hash(cu, &member->tag); if (add_child_llvm_annotations(die, member_idx, conf, &class->namespace.annots)) return -ENOMEM; + if (add_gnu_annotation_chain(die, member_idx, conf, &class->namespace.annots)) + return -ENOMEM; member_idx++; } continue; case DW_TAG_LLVM_annotation: + case DW_TAG_GNU_annotation: if (add_llvm_annotation(die, -1, conf, &class->namespace.annots)) return -ENOMEM; continue; @@ -2359,6 +2432,7 @@ static int die__process_function(Dwarf_Die *die, struct ftype *ftype, goto out_enomem; continue; case DW_TAG_LLVM_annotation: + case DW_TAG_GNU_annotation: if (add_llvm_annotation(die, -1, conf, &(tag__function(&ftype->tag)->annots))) goto out_enomem; continue; @@ -2407,6 +2481,12 @@ static struct tag *die__create_new_function(Dwarf_Die *die, struct cu *cu, struc function = NULL; } + if (function != NULL && + add_gnu_annotation_chain(die, -1, conf, &function->annots) != 0) { + function__delete(function, cu); + function = NULL; + } + return function ? &function->proto.tag : NULL; } @@ -2468,6 +2548,9 @@ static struct tag *__die__process_tag(Dwarf_Die *die, struct cu *cu, */ tag = &unsupported_tag; break; + case DW_TAG_GNU_annotation: + tag = &unsupported_tag; + break; case DW_TAG_label: if (conf->ignore_labels) tag = &unsupported_tag; // callers will assume conf->ignore_labels is true @@ -2493,7 +2576,8 @@ static int die__process_unit(Dwarf_Die *die, struct cu *cu, struct conf_load *co // XXX special case DW_TAG_dwarf_procedure, appears when looking at a recent ~/bin/perf // Investigate later how to properly support this... if (dwarf_tag(die) != DW_TAG_dwarf_procedure && - dwarf_tag(die) != DW_TAG_label) // conf->ignore_labels == true, see die__process_tag() + dwarf_tag(die) != DW_TAG_label && // conf->ignore_labels == true, see die__process_tag() + dwarf_tag(die) != DW_TAG_GNU_annotation) tag__print_not_supported(die); continue; } diff --git a/dwarves.h b/dwarves.h index 5ec16e750e83..42b8e39aa2dd 100644 --- a/dwarves.h +++ b/dwarves.h @@ -670,7 +670,8 @@ static inline int tag__is_tag_type(const struct tag *tag) tag->tag == DW_TAG_volatile_type || tag->tag == DW_TAG_atomic_type || tag->tag == DW_TAG_unspecified_type || - tag->tag == DW_TAG_LLVM_annotation; + tag->tag == DW_TAG_LLVM_annotation || + tag->tag == DW_TAG_GNU_annotation; } static inline const char *tag__decl_file(const struct tag *tag, diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c index 1ec478c2a027..a514d7e98923 100644 --- a/dwarves_fprintf.c +++ b/dwarves_fprintf.c @@ -140,6 +140,8 @@ const char *dwarf_tag_name(const uint32_t tag) return dwarf_gnu_tag_names[tag - DW_TAG_MIPS_loop]; else if (tag == DW_TAG_LLVM_annotation) return "LLVM_annotation"; + else if (tag == DW_TAG_GNU_annotation) + return "GNU_annotation"; return "INVALID"; } @@ -658,6 +660,7 @@ static const char *__tag__name(const struct tag *tag, const struct cu *cu, snprintf(bf, len, "%s", variable__name(tag__variable(tag))); break; case DW_TAG_LLVM_annotation: + case DW_TAG_GNU_annotation: type = cu__type(cu, tag->type); if (type == NULL && tag->type != 0) tag__id_not_found_snprintf(bf, len, tag->type); @@ -731,7 +734,7 @@ static type_id_t skip_llvm_annotations(const struct cu *cu, type_id_t id) if (id == 0) break; type = cu__type(cu, id); - if (type == NULL || type->tag != DW_TAG_LLVM_annotation || type->type == id) + if (type == NULL || (type->tag != DW_TAG_LLVM_annotation && type->tag != DW_TAG_GNU_annotation) || type->type == id) break; id = type->type; } @@ -936,7 +939,8 @@ print_modifier: { else printed += enumeration__fprintf(type, &tconf, fp); break; - case DW_TAG_LLVM_annotation: { + case DW_TAG_LLVM_annotation: + case DW_TAG_GNU_annotation: { struct tag *ttype = cu__type(cu, type->type); if (ttype) { type = ttype; -- 2.54.0