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resolve_btfids: Emit arena attributes from kfunc parameter suffixes

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Kfunc declarations can identify arena arguments through parameter name
suffixes without repeating KF_ARENA_ARG flags in their BTF ID sets.
resolve_btfids currently misses those arguments when synthesizing the
address_space(1) attributes used by generated vmlinux.h files.

Teach the arena prototype rewrite to recognize __arena and
__arena__nullable directly on each parameter. Keep KF_ARENA_ARG1 and
KF_ARENA_ARG2 handling for explicitly flagged kfuncs, while allowing
suffixes on any argument without synthesizing kfunc flags.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://patch.msgid.link/20260812193842.2879226-2-memxor@gmail.com
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
This commit is contained in:
Kumar Kartikeya Dwivedi 2026-08-12 21:38:40 +02:00 committed by Eduard Zingerman
parent 108d44070e
commit 5e31d32843
2 changed files with 54 additions and 22 deletions
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4
Documentation/bpf/kfuncs.rst
View File

@ -513,8 +513,8 @@ At kernel build time the ``resolve_btfids`` tool finds all kfuncs declared with
``BTF_KFUNCS_START()`` and emits their BTF annotations into the kernel's BTF.
For each kfunc it emits a ``bpf_kfunc`` BTF decl tag, a ``bpf_fastcall`` decl
tag when the kfunc is flagged ``KF_FASTCALL``, and the ``address_space(1)`` type
attribute on the return value and/or arguments flagged ``KF_ARENA_RET``,
``KF_ARENA_ARG1`` or ``KF_ARENA_ARG2`` (see section 2.8).
attribute on the return value and/or arguments that use arena pointers (see
sections 2.3.8 and 2.8).
2.7 Specifying no-cast aliases with ___init
--------------------------------------------

72
tools/bpf/resolve_btfids/main.c
View File

@ -64,8 +64,8 @@
* each such kfunc it:
*
* - emits a "bpf_kfunc" decl tag, and "bpf_fastcall" when KF_FASTCALL is set;
* - wraps the return value and/or arguments flagged KF_ARENA_RET,
* KF_ARENA_ARG1 or KF_ARENA_ARG2 with the "address_space(1)" type attribute;
* - wraps the return value and/or arguments that use arena pointers
* with the "address_space(1)" type attribute;
* - rewrites the prototype of KF_IMPLICIT_ARGS kfuncs.
*
* These kfunc annotations were historically produced by pahole.
@ -182,6 +182,8 @@ struct object {
#define KF_IMPLICIT_ARGS (1 << 16)
#define KF_IMPL_SUFFIX "_impl"
#define TYPE_ATTR_ARENA "address_space(1)"
#define PARAM_SUFFIX_ARENA "__arena"
#define PARAM_SUFFIX_ARENA_NULLABLE "__arena__nullable"
struct kfunc {
struct rb_node rb_node;
@ -1067,6 +1069,22 @@ static int collect_decl_tags(struct btf2btf_context *ctx)
return 0;
}
static bool param_name_has_suffix(const char *name, const char *suffix)
{
size_t name_len = strlen(name);
size_t suffix_len = strlen(suffix);
return name_len >= suffix_len && !strcmp(name + name_len - suffix_len, suffix);
}
static bool is_arena_param(const struct btf *btf, const struct btf_param *param)
{
const char *name = btf__name_by_offset(btf, param->name_off);
return param_name_has_suffix(name, PARAM_SUFFIX_ARENA) ||
param_name_has_suffix(name, PARAM_SUFFIX_ARENA_NULLABLE);
}
static int collect_kfuncs(struct object *obj, struct btf2btf_context *ctx)
{
Elf_Data *idlist = obj->efile.idlist;
@ -1299,8 +1317,12 @@ static int process_kfunc_with_implicit_args(struct btf2btf_context *ctx, struct
return 0;
}
static bool is_arena_arg(struct kfunc *kfunc, u32 idx)
static bool is_arena_arg(const struct btf *btf, const struct kfunc *kfunc,
const struct btf_param *param, u32 idx)
{
if (is_arena_param(btf, param))
return true;
switch (idx) {
case 0:
return kfunc->flags & KF_ARENA_ARG1;
@ -1339,23 +1361,36 @@ static s32 arena_tag_ptr(struct btf *btf, u32 ptr_id, struct kfunc *kfunc)
}
/*
* Add a FUNC_PROTO for @kfunc with each relevant pointer tagged with
* an "address_space(1)" attribute. The original proto may be shared
* with other FUNCs, so it is never modified in place.
* Add a FUNC_PROTO for @kfunc with each arena pointer tagged with an
* "address_space(1)" attribute. The original proto may be shared with
* other FUNCs, so it is never modified in place. Returns the original
* proto id when @kfunc has no arena return value or arguments.
*/
static s32 add_arena_tagged_proto(struct btf *btf, struct kfunc *kfunc)
{
const struct btf_type *func = btf__type_by_id(btf, kfunc->btf_id);
u32 proto_id = func->type;
const struct btf_type *proto = btf__type_by_id(btf, proto_id);
const struct btf_param *params = btf_params(proto);
u32 nr_params = btf_vlen(proto);
s32 ret_type_id = proto->type;
const struct btf_type *t;
struct btf_param *params;
struct btf_param *tag_params;
s32 new_proto_id, id;
const char *name;
bool has_arena_arg = false;
int err, i;
for (i = 0; i < nr_params; i++) {
if (is_arena_arg(btf, kfunc, &params[i], i)) {
has_arena_arg = true;
break;
}
}
if (!(kfunc->flags & KF_ARENA_RET) && !has_arena_arg)
return proto_id;
if (kfunc->flags & KF_ARENA_RET) {
ret_type_id = arena_tag_ptr(btf, ret_type_id, kfunc);
if (ret_type_id < 0)
@ -1383,19 +1418,18 @@ static s32 add_arena_tagged_proto(struct btf *btf, struct kfunc *kfunc)
}
for (i = 0; i < nr_params; i++) {
if (!is_arena_arg(kfunc, i))
t = btf__type_by_id(btf, new_proto_id);
tag_params = btf_params(t);
if (!is_arena_arg(btf, kfunc, &tag_params[i], i))
continue;
t = btf__type_by_id(btf, new_proto_id);
params = btf_params(t);
id = arena_tag_ptr(btf, params[i].type, kfunc);
id = arena_tag_ptr(btf, tag_params[i].type, kfunc);
if (id < 0)
return id;
t = btf__type_by_id(btf, new_proto_id);
params = btf_params(t);
params[i].type = id;
tag_params = btf_params(t);
tag_params[i].type = id;
}
pr_debug("added arena-tagged proto for kfunc %s: %d\n", kfunc->name, new_proto_id);
@ -1403,7 +1437,7 @@ static s32 add_arena_tagged_proto(struct btf *btf, struct kfunc *kfunc)
return new_proto_id;
}
static int process_kfunc_with_arena_flags(struct btf2btf_context *ctx,
static int process_kfunc_with_arena_attrs(struct btf2btf_context *ctx,
struct kfunc *kfunc)
{
struct btf_type *t;
@ -1463,11 +1497,9 @@ static int btf2btf(struct object *obj)
goto out;
}
if (kfunc->flags & (KF_ARENA_RET | KF_ARENA_ARG1 | KF_ARENA_ARG2)) {
err = process_kfunc_with_arena_flags(&ctx, kfunc);
if (err)
goto out;
}
err = process_kfunc_with_arena_attrs(&ctx, kfunc);
if (err)
goto out;
}
err = 0;