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Message-ID: <CAEf4BzZUA+5jsYGN7dA1qEXyZKZvBnESX=8fuJHYmhOVm0_QEQ@mail.gmail.com>
Date: Tue, 20 Jan 2026 16:38:18 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: ast@...nel.org, andrii@...nel.org, yonghong.song@...ux.dev,
daniel@...earbox.net, john.fastabend@...il.com, martin.lau@...ux.dev,
eddyz87@...il.com, song@...nel.org, kpsingh@...nel.org, sdf@...ichev.me,
haoluo@...gle.com, jolsa@...nel.org, mattbobrowski@...gle.com,
rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW_TP
On Mon, Jan 19, 2026 at 11:31 PM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> For now, bpf_get_func_arg() and bpf_get_func_arg_cnt() is not supported by
> the BPF_TRACE_RAW_TP, which is not convenient to get the argument of the
> tracepoint, especially for the case that the position of the arguments in
> a tracepoint can change.
>
> The target tracepoint BTF type id is specified during loading time,
> therefore we can get the function argument count from the function
> prototype instead of the stack.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v4:
> - fix the error of using bpf_get_func_arg() for BPF_TRACE_ITER
>
> v3:
> - remove unnecessary NULL checking for prog->aux->attach_func_proto
>
> v2:
> - for nr_args, skip first 'void *__data' argument in btf_trace_##name
> typedef
> ---
> kernel/bpf/verifier.c | 32 ++++++++++++++++++++++++++++----
> kernel/trace/bpf_trace.c | 4 ++++
> 2 files changed, 32 insertions(+), 4 deletions(-)
>
other than stylistical choices, looks good to me
Acked-by: Andrii Nakryiko <andrii@...nel.org>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9de0ec0c3ed9..0b281b7c41eb 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23323,8 +23323,20 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> /* Implement bpf_get_func_arg inline. */
> if (prog_type == BPF_PROG_TYPE_TRACING &&
> insn->imm == BPF_FUNC_get_func_arg) {
> - /* Load nr_args from ctx - 8 */
> - insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> + if (eatype == BPF_TRACE_RAW_TP) {
> + int nr_args = btf_type_vlen(prog->aux->attach_func_proto);
> +
> + /*
> + * skip first 'void *__data' argument in btf_trace_##name
> + * typedef
> + */
> + nr_args--;
> + /* Save nr_args to reg0 */
> + insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args);
> + } else {
> + /* Load nr_args from ctx - 8 */
> + insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> + }
> insn_buf[1] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6);
> insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3);
> insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1);
> @@ -23376,8 +23388,20 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> /* Implement get_func_arg_cnt inline. */
> if (prog_type == BPF_PROG_TYPE_TRACING &&
> insn->imm == BPF_FUNC_get_func_arg_cnt) {
> - /* Load nr_args from ctx - 8 */
> - insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> + if (eatype == BPF_TRACE_RAW_TP) {
> + int nr_args = btf_type_vlen(prog->aux->attach_func_proto);
> +
> + /*
> + * skip first 'void *__data' argument in btf_trace_##name
> + * typedef
> + */
> + nr_args--;
> + /* Save nr_args to reg0 */
> + insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args);
nit: isn't this just a very verbose way of writing:
int nr_args = btf_type_vlen(prog->aux->attach_func_proto);
/* skip 'void *__data' in btf_trace_##name() and save to reg0 */
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args - 1);
even if you want to preserve nr_args-- for clarity, at least make that
4-line comment into a single-line one, please
> + } else {
> + /* Load nr_args from ctx - 8 */
> + insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> + }
>
> new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1);
> if (!new_prog)
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index f73e08c223b5..0efdad3adcce 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1734,10 +1734,14 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> case BPF_FUNC_d_path:
> return &bpf_d_path_proto;
> case BPF_FUNC_get_func_arg:
> + if (prog->expected_attach_type == BPF_TRACE_RAW_TP)
> + return &bpf_get_func_arg_proto;
> return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_proto : NULL;
> case BPF_FUNC_get_func_ret:
> return bpf_prog_has_trampoline(prog) ? &bpf_get_func_ret_proto : NULL;
> case BPF_FUNC_get_func_arg_cnt:
> + if (prog->expected_attach_type == BPF_TRACE_RAW_TP)
> + return &bpf_get_func_arg_cnt_proto;
> return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_cnt_proto : NULL;
hm, wouldn't "has trampoline or is raw_tp" a more logical grouping?
if (bpf_prog_has_trampoline(prog) || prog->expected_attach_type ==
BPF_TRACE_RAW_TP)
return &bpf_get_func_arg_cnt_proto;
return NULL;
maybe you'll need to wrap that condition, but still, at least no one
has to double check that we return exactly the same prototype in both
cases, no?
> case BPF_FUNC_get_attach_cookie:
> if (prog->type == BPF_PROG_TYPE_TRACING &&
> --
> 2.52.0
>
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