Re: [PATCH bpf-next v3 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW_TP

[Menglong Dong <menglong.dong@linux.dev>]

On 2026/1/19 13:11 Yonghong Song <yonghong.song@linux.dev> write:
> 
> On 1/18/26 6:37 PM, 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 <dongml2@chinatelecom.cn>
> > ---
> > 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 */
> > +				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;
> 
> BPF_TRACE_ITER is a tracing attach type. It should not support bpf_get_func_arg() or
> bpf_get_func_arg_cnt().

Ah, my bad, I forgot BPF_TRACE_ITER. I'll fix it in the next version.

Thanks!
Menglong Dong

> 
> >   	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)
> 
> 
>