tools/lib/bpf/libbpf.c | 31 ++++++++++++++++++++----------- 1 file changed, 20 insertions(+), 11 deletions(-)
The function prototype of bpf_session_{cookie,is_return} is changed in
the commit 8fe4dc4f6456 ("bpf: change prototype of
bpf_session_{cookie,is_return}"), which is not friendly to the old kernel,
as the libbpf will fail on the compatible checking.
Therefore, let's skip the checking of bpf_session_{cookie,is_return} in
libbpf, and just let the kernel do the checking.
Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
tools/lib/bpf/libbpf.c | 31 ++++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0c8bf0b5cce4..71bdd1c1ac39 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8557,6 +8557,12 @@ static int find_ksym_btf_id(struct bpf_object *obj, const char *ksym_name,
return id;
}
+static bool kfunc_skip_compat_check(const char *name)
+{
+ return name && (strcmp(name, "bpf_session_cookie") == 0 ||
+ strcmp(name, "bpf_session_is_return") == 0);
+}
+
static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj,
struct extern_desc *ext)
{
@@ -8617,12 +8623,13 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
struct module_btf *mod_btf = NULL;
const struct btf_type *kern_func;
struct btf *kern_btf = NULL;
+ const char *kfunc_name;
int ret;
local_func_proto_id = ext->ksym.type_id;
- kfunc_id = find_ksym_btf_id(obj, ext->essent_name ?: ext->name, BTF_KIND_FUNC, &kern_btf,
- &mod_btf);
+ kfunc_name = ext->essent_name ?: ext->name;
+ kfunc_id = find_ksym_btf_id(obj, kfunc_name, BTF_KIND_FUNC, &kern_btf, &mod_btf);
if (kfunc_id < 0) {
if (kfunc_id == -ESRCH && ext->is_weak)
return 0;
@@ -8634,16 +8641,18 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
kern_func = btf__type_by_id(kern_btf, kfunc_id);
kfunc_proto_id = kern_func->type;
- ret = bpf_core_types_are_compat(obj->btf, local_func_proto_id,
- kern_btf, kfunc_proto_id);
- if (ret <= 0) {
- if (ext->is_weak)
- return 0;
+ if (!kfunc_skip_compat_check(kfunc_name)) {
+ ret = bpf_core_types_are_compat(obj->btf, local_func_proto_id,
+ kern_btf, kfunc_proto_id);
+ if (ret <= 0) {
+ if (ext->is_weak)
+ return 0;
- pr_warn("extern (func ksym) '%s': func_proto [%d] incompatible with %s [%d]\n",
- ext->name, local_func_proto_id,
- mod_btf ? mod_btf->name : "vmlinux", kfunc_proto_id);
- return -EINVAL;
+ pr_warn("extern (func ksym) '%s': func_proto [%d] incompatible with %s [%d]\n",
+ ext->name, local_func_proto_id,
+ mod_btf ? mod_btf->name : "vmlinux", kfunc_proto_id);
+ return -EINVAL;
+ }
}
/* set index for module BTF fd in fd_array, if unset */
--
2.53.0On Wed, Feb 11, 2026 at 4:57 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> The function prototype of bpf_session_{cookie,is_return} is changed in
> the commit 8fe4dc4f6456 ("bpf: change prototype of
> bpf_session_{cookie,is_return}"), which is not friendly to the old kernel,
> as the libbpf will fail on the compatible checking.
>
> Therefore, let's skip the checking of bpf_session_{cookie,is_return} in
> libbpf, and just let the kernel do the checking.
>
> Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> ---
> tools/lib/bpf/libbpf.c | 31 ++++++++++++++++++++-----------
> 1 file changed, 20 insertions(+), 11 deletions(-)
>
This is not the way. Use bpf_ksym_exists() check and have custom
legacy bpf_session_cookie___legacy() definition with old prototype.
You can then detect whether
bpf_ksym_exists(bpf_session_cookie___legacy) is true and use the
legacy version, otherwise use the current version.
pw-bot: cr
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 0c8bf0b5cce4..71bdd1c1ac39 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -8557,6 +8557,12 @@ static int find_ksym_btf_id(struct bpf_object *obj, const char *ksym_name,
> return id;
> }
>
> +static bool kfunc_skip_compat_check(const char *name)
> +{
> + return name && (strcmp(name, "bpf_session_cookie") == 0 ||
> + strcmp(name, "bpf_session_is_return") == 0);
> +}
> +
> static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj,
> struct extern_desc *ext)
> {
> @@ -8617,12 +8623,13 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
> struct module_btf *mod_btf = NULL;
> const struct btf_type *kern_func;
> struct btf *kern_btf = NULL;
> + const char *kfunc_name;
> int ret;
>
> local_func_proto_id = ext->ksym.type_id;
>
> - kfunc_id = find_ksym_btf_id(obj, ext->essent_name ?: ext->name, BTF_KIND_FUNC, &kern_btf,
> - &mod_btf);
> + kfunc_name = ext->essent_name ?: ext->name;
> + kfunc_id = find_ksym_btf_id(obj, kfunc_name, BTF_KIND_FUNC, &kern_btf, &mod_btf);
> if (kfunc_id < 0) {
> if (kfunc_id == -ESRCH && ext->is_weak)
> return 0;
> @@ -8634,16 +8641,18 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
> kern_func = btf__type_by_id(kern_btf, kfunc_id);
> kfunc_proto_id = kern_func->type;
>
> - ret = bpf_core_types_are_compat(obj->btf, local_func_proto_id,
> - kern_btf, kfunc_proto_id);
> - if (ret <= 0) {
> - if (ext->is_weak)
> - return 0;
> + if (!kfunc_skip_compat_check(kfunc_name)) {
> + ret = bpf_core_types_are_compat(obj->btf, local_func_proto_id,
> + kern_btf, kfunc_proto_id);
> + if (ret <= 0) {
> + if (ext->is_weak)
> + return 0;
>
> - pr_warn("extern (func ksym) '%s': func_proto [%d] incompatible with %s [%d]\n",
> - ext->name, local_func_proto_id,
> - mod_btf ? mod_btf->name : "vmlinux", kfunc_proto_id);
> - return -EINVAL;
> + pr_warn("extern (func ksym) '%s': func_proto [%d] incompatible with %s [%d]\n",
> + ext->name, local_func_proto_id,
> + mod_btf ? mod_btf->name : "vmlinux", kfunc_proto_id);
> + return -EINVAL;
> + }
> }
>
> /* set index for module BTF fd in fd_array, if unset */
> --
> 2.53.0
>
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