[PATCH bpf-next v1 8/8] bpf: Re-define bpf_stream_vprintk as a magic kfunc

Ihor Solodrai
2025-10-29T19:02:05Z

* void *aux__prog => struct bpf_prog_aux *aux__magic
* Set KF_MAGIC_ARGS flag
* Add relevant symbols to magic_kfuncs list
* Update selftests to use the new signature

bpf_stream_vprintk macro is changed to use bpf_stream_vprintk_impl,
and the extern definition of bpf_stream_vprintk is replaced with _impl
version in bpf_helpers.h

This should help with backwards compatibility, as the API of
bpf_stream_vprintk macro hasn't changed.

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
kernel/bpf/helpers.c | 2 +-
kernel/bpf/stream.c | 9 ++++++---
kernel/bpf/verifier.c | 2 ++
tools/lib/bpf/bpf_helpers.h | 7 ++++---
tools/testing/selftests/bpf/progs/stream_fail.c | 6 +++---
5 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 6a095796433a..418c6b31ccc6 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -4528,7 +4528,7 @@ BTF_ID_FLAGS(func, bpf_strncasestr);
#if defined(CONFIG_BPF_LSM) && defined(CONFIG_CGROUPS)
BTF_ID_FLAGS(func, bpf_cgroup_read_xattr, KF_RCU)
#endif
-BTF_ID_FLAGS(func, bpf_stream_vprintk, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_stream_vprintk, KF_MAGIC_ARGS | KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_task_work_schedule_signal, KF_MAGIC_ARGS | KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_MAGIC_ARGS | KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_dynptr_from_file, KF_TRUSTED_ARGS)
diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
index eb6c5a21c2ef..1a129fff765e 100644
--- a/kernel/bpf/stream.c
+++ b/kernel/bpf/stream.c
@@ -355,19 +355,22 @@ __bpf_kfunc_start_defs();
* Avoid using enum bpf_stream_id so that kfunc users don't have to pull in the
* enum in headers.
*/
-__bpf_kfunc int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args, u32 len__sz, void *aux__prog)
+__bpf_kfunc int bpf_stream_vprintk(int stream_id,
+ const char *fmt__str,
+ const void *args,
+ u32 len__sz,
+ struct bpf_prog_aux *aux__magic)
{
struct bpf_bprintf_data data = {
.get_bin_args = true,
.get_buf = true,
};
- struct bpf_prog_aux *aux = aux__prog;
u32 fmt_size = strlen(fmt__str) + 1;
struct bpf_stream *stream;
u32 data_len = len__sz;
int ret, num_args;

- stream = bpf_stream_get(stream_id, aux);
+ stream = bpf_stream_get(stream_id, aux__magic);
if (!stream)
return -ENOENT;

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ad4af5ddb523..9e38fbee9219 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3273,6 +3273,8 @@ BTF_ID(func, bpf_task_work_schedule_signal)
BTF_ID(func, bpf_task_work_schedule_signal_impl)
BTF_ID(func, bpf_task_work_schedule_resume)
BTF_ID(func, bpf_task_work_schedule_resume_impl)
+BTF_ID(func, bpf_stream_vprintk)
+BTF_ID(func, bpf_stream_vprintk_impl)
BTF_ID_LIST_END(magic_kfuncs)

static s32 magic_kfunc_by_impl(s32 impl_func_id)
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 80c028540656..f41ca993c6d2 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -315,8 +315,9 @@ enum libbpf_tristate {
___param, sizeof(___param)); \
})

-extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args,
- __u32 len__sz, void *aux__prog) __weak __ksym;
+struct bpf_prog_aux;
+extern int bpf_stream_vprintk_impl(int stream_id, const char *fmt__str, const void *args,
+ __u32 len__sz, struct bpf_prog_aux *aux__magic) __weak __ksym;

#define bpf_stream_printk(stream_id, fmt, args...) \
({ \
@@ -328,7 +329,7 @@ extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *a
___bpf_fill(___param, args); \
_Pragma("GCC diagnostic pop") \
\
- bpf_stream_vprintk(stream_id, ___fmt, ___param, sizeof(___param), NULL);\
+ bpf_stream_vprintk_impl(stream_id, ___fmt, ___param, sizeof(___param), NULL);\
})

/* Use __bpf_printk when bpf_printk call has 3 or fewer fmt args
diff --git a/tools/testing/selftests/bpf/progs/stream_fail.c b/tools/testing/selftests/bpf/progs/stream_fail.c
index b4a0d0cc8ec8..8e8249f3521c 100644
--- a/tools/testing/selftests/bpf/progs/stream_fail.c
+++ b/tools/testing/selftests/bpf/progs/stream_fail.c
@@ -10,7 +10,7 @@ SEC("syscall")
__failure __msg("Possibly NULL pointer passed")
int stream_vprintk_null_arg(void *ctx)
{
- bpf_stream_vprintk(BPF_STDOUT, "", NULL, 0, NULL);
+ bpf_stream_vprintk(BPF_STDOUT, "", NULL, 0);
return 0;
}

@@ -18,7 +18,7 @@ SEC("syscall")
__failure __msg("R3 type=scalar expected=")
int stream_vprintk_scalar_arg(void *ctx)
{
- bpf_stream_vprintk(BPF_STDOUT, "", (void *)46, 0, NULL);
+ bpf_stream_vprintk(BPF_STDOUT, "", (void *)46, 0);
return 0;
}

@@ -26,7 +26,7 @@ SEC("syscall")
__failure __msg("arg#1 doesn't point to a const string")
int stream_vprintk_string_arg(void *ctx)
{
- bpf_stream_vprintk(BPF_STDOUT, ctx, NULL, 0, NULL);
+ bpf_stream_vprintk(BPF_STDOUT, ctx, NULL, 0);
return 0;
}

--
2.51.1