Re: [PATCH net-next v2 2/2] trace: tcp: Add tracepoint for tcp_sendmsg_locked()

[Breno Leitao <leitao@debian.org>]

On Tue, Apr 08, 2025 at 09:16:51AM -0600, David Ahern wrote:
> On 4/8/25 8:27 AM, Breno Leitao wrote:
> > 
> > 	SEC("tracepoint/tcp/tcp_sendmsg_locked")
> 
> Try `raw_tracepoint/tcp/tcp_sendmsg_locked`.
> 
> This is the form I use for my tracepoint based packet capture (not tied
> to this tracepoint, but traces inside our driver) and it works fine.

Thanks. I was not able to get this crashing as well. In fact, the
following program fails to be loaded:

	SEC("raw_tracepoint/tcp/tcp_sendmsg_locked")
	int bpf_tcp_sendmsg_locked(struct bpf_raw_tracepoint_args *ctx)
	{
		void *skb_addr = (void *) ctx->args[0];

		bpf_printk("deref %d\n", *(int *) skb_addr);

		return 0;
	}

libbpf refuses to load it, and drumps:

	libbpf: prog 'bpf_tcp_sendmsg_locked': BPF program load failed: Permission denied
	libbpf: prog 'bpf_tcp_sendmsg_locked': -- BEGIN PROG LOAD LOG --
	0: R1=ctx() R10=fp0
	; void *skb_addr = (void *) ctx->args[0]; @ tcp_sendmsg_locked_bpf.c:18
	0: (79) r1 = *(u64 *)(r1 +0)          ; R1_w=scalar()
	; bpf_printk("deref %d\n", *(int *) skb_addr); @ tcp_sendmsg_locked_bpf.c:20
	1: (61) r3 = *(u32 *)(r1 +0)
	R1 invalid mem access 'scalar'
	processed 2 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
	-- END PROG LOAD LOG --
	libbpf: prog 'bpf_tcp_sendmsg_locked': failed to load: -13
	libbpf: failed to load object 'tcp_sendmsg_locked_bpf.o'
	Failed to load BPF object: -13

> As suggested, you might need to update raw_tp_null_args

Thanks for confirming it. I will update raw_tp_null_args, assuming that
the problem exists but I am failing to reproduce it.

I will send an updated version soon.

Thanks
--breno