Re: [PATCHv3 bpf-next 3/7] bpf: Add bpf_get_func_ip helper for tracing programs

On Wed, Jul 07, 2021 at 05:06:17PM -0700, Andrii Nakryiko wrote:

On Wed, Jul 7, 2021 at 2:53 PM Jiri Olsa [off-list ref] wrote:

quoted

Adding bpf_get_func_ip helper for BPF_PROG_TYPE_TRACING programs,
specifically for all trampoline attach types.

The trampoline's caller IP address is stored in (ctx - 8) address.
so there's no reason to actually call the helper, but rather fixup
the call instruction and return [ctx - 8] value directly (suggested
by Alexei).

[fixed has_get_func_ip wrong return type]
Reported-by: kernel test robot <redacted>
Reported-by: Dan Carpenter <redacted>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/uapi/linux/bpf.h       |  7 +++++
 kernel/bpf/verifier.c          | 53 ++++++++++++++++++++++++++++++++++
 kernel/trace/bpf_trace.c       | 15 ++++++++++
 tools/include/uapi/linux/bpf.h |  7 +++++
 4 files changed, 82 insertions(+)

[...]

quoted

 static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
                             int *insn_idx_p)
 {

@@ -6225,6 +6256,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
        if (func_id == BPF_FUNC_get_stackid || func_id == BPF_FUNC_get_stack)
                env->prog->call_get_stack = true;

+       if (func_id == BPF_FUNC_get_func_ip) {
+               if (has_get_func_ip(env))

from has_xxx name I'd expect it returns true/false, so this reads
super confusing. check_get_func_ip would be a bit more consistent with
other cases like this (still reads confusing to me, but that's ok)

ok, will change

jirka

quoted

+                       return -ENOTSUPP;
+               env->prog->call_get_func_ip = true;
+       }
+
        if (changes_data)
                clear_all_pkt_pointers(env);
        return 0;

[...]