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Tue, 20 Jan 2026 00:18:07 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Tue, 20 Jan 2026 09:18:06 +0100 To: Menglong Dong Cc: Menglong Dong , Jiri Olsa , andrii@kernel.org, ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, mattbobrowski@google.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next v3 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW_TP Message-ID: References: <20260119023732.130642-1-dongml2@chinatelecom.cn> <20260119023732.130642-2-dongml2@chinatelecom.cn> <6099572.DvuYhMxLoT@7950hx> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6099572.DvuYhMxLoT@7950hx> On Tue, Jan 20, 2026 at 09:24:46AM +0800, Menglong Dong wrote: > On 2026/1/20 07:37, Jiri Olsa wrote: > > On Mon, Jan 19, 2026 at 10:37:31AM +0800, Menglong Dong 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 > > > --- > > > 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, 30 insertions(+), 6 deletions(-) > > > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > > index faa1ecc1fe9d..4f52342573f0 100644 > > > --- a/kernel/bpf/verifier.c > > > +++ b/kernel/bpf/verifier.c > > > @@ -23316,8 +23316,20 @@ 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); > > > @@ -23369,8 +23381,20 @@ 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 */ > > > > I think we can attach single bpf program to multiple rawtp tracepoints, > > in which case this would not work properly for such program links on > > tracepoints with different nr_args, right? > > Hi, Jiri. As for now, I think we can't do that when I look into > bpf_raw_tp_link_attach(). For the BPF_TRACE_RAW_TP, we specify > a target btf type id when loading the bpf prog. And during > attaching, it seems that we can only attach to that target, which > means that we can't attach to multiple rawtp tracepoint. And > we can't change the target btf id when reattach, too. Right? > > Part of the implement of bpf_raw_tp_link_attach(): > > static int bpf_raw_tp_link_attach(struct bpf_prog *prog, > const char __user *user_tp_name, u64 cookie, > enum bpf_attach_type attach_type) > { > struct bpf_link_primer link_primer; > struct bpf_raw_tp_link *link; > struct bpf_raw_event_map *btp; > const char *tp_name; > char buf[128]; > int err; > > switch (prog->type) { > case BPF_PROG_TYPE_TRACING: > case BPF_PROG_TYPE_EXT: > case BPF_PROG_TYPE_LSM: > if (user_tp_name) > /* The attach point for this category of programs > * should be specified via btf_id during program load. > */ ah there's the name check, ok.. got confused by the max_ctx_offset check in bpf_probe_register thanks, jirka > return -EINVAL; > if (prog->type == BPF_PROG_TYPE_TRACING && > prog->expected_attach_type == BPF_TRACE_RAW_TP) { > tp_name = prog->aux->attach_func_name; > break; > } > [......] > } > [......] > } > > Thanks! > Menglong Dong > > > > > jirka > > > > > > > + 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); > > > + } > > > > > > 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 6e076485bf70..9b1b56851d26 100644 > > > --- a/kernel/trace/bpf_trace.c > > > +++ b/kernel/trace/bpf_trace.c > > > @@ -1734,11 +1734,11 @@ 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: > > > - return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_proto : NULL; > > > + return &bpf_get_func_arg_proto; > > > 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: > > > - return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_cnt_proto : NULL; > > > + return &bpf_get_func_arg_cnt_proto; > > > case BPF_FUNC_get_attach_cookie: > > > if (prog->type == BPF_PROG_TYPE_TRACING && > > > prog->expected_attach_type == BPF_TRACE_RAW_TP) > > > > > > > >