On Wed, Jul 29, 2020 at 08:23:56AM +0200, Eelco Chaudron wrote: SNIP > > > > > a patch > > > > > that would nice. > > > > > You can also send it to me before bpf-next opens and I can verify > > > > > it, and > > > > > clean up the self-test so it can be included as well. > > > > > > > > > > > > > hi, > > > > it seems that you cannot exten fentry/fexit programs, > > > > but it's possible to attach fentry/fexit to ext program. > > > > > > > > /* Program extensions can extend all program types > > > > * except fentry/fexit. The reason is the following. > > > > * The fentry/fexit programs are used for performance > > > > * analysis, stats and can be attached to any program > > > > * type except themselves. When extension program is > > > > * replacing XDP function it is necessary to allow > > > > * performance analysis of all functions. Both original > > > > * XDP program and its program extension. Hence > > > > * attaching fentry/fexit to BPF_PROG_TYPE_EXT is > > > > * allowed. If extending of fentry/fexit was allowed it > > > > * would be possible to create long call chain > > > > * fentry->extension->fentry->extension beyond > > > > * reasonable stack size. Hence extending fentry is not > > > > * allowed. > > > > */ > > > > > > > > I changed fexit_bpf2bpf.c test just to do a quick check > > > > and it seems to work: > > > > > > Hi Jiri this is exactly what I’m trying, however when you do this > > > where the > > > first argument is a pointer to some context data which you are > > > accessing > > > it’s failing in the verifier. > > > This is a link to the original email, which has a test patch > > > attached that > > > will show the failure when trying to load/attach the fentry function > > > and > > > access the context: > > > > > > https://lore.kernel.org/bpf/159162546868.10791.12432342618156330247.stgit@ebuild/ > > > > ok, I tried to trace ext program with __sk_buff argument and I can see > > the issue as well.. can't acess the skb argument > > > > patch below fixes it for me, I can access the skb pointer and its data > > via probe read, like: > > > > SEC("fexit/new_get_skb_ifindex") > > int BPF_PROG(fexit_new_get_skb_ifindex, int val, struct __sk_buff *skb, > > int var, int ret) > > { > > __u32 data; > > int err; > > > > bpf_printk("EXIT skb %p", skb); > > bpf_probe_read_kernel(&data, sizeof(data), &skb->data); > > bpf_printk("EXIT ret %d, data %p", err, data); > > return 0; > > } > > > > I think it should fix the xdp_md acess as well > > Excellent patch ;) It works with xdp_md as well, and even better it does not > require the bpf_probe_read_kernel(), so the test_xdp_bpf2bpf.c code just > works. great ;-) will check on xdp_md > > Are you planning to send the patch upstream? yep, I'll add some test for that and send it thanks, jirka
