Re: [PATCH RESEND bpf-next v3 2/9] bpf: verifier: refactor check_attach_btf_id()

Andrii Nakryiko [off-list ref] writes:

On Fri, Sep 11, 2020 at 3:00 AM Toke Høiland-Jørgensen [off-list ref] wrote:

quoted

From: Toke Høiland-Jørgensen <redacted>

The check_attach_btf_id() function really does three things:

1. It performs a bunch of checks on the program to ensure that the
   attachment is valid.

2. It stores a bunch of state about the attachment being requested in
   the verifier environment and struct bpf_prog objects.

3. It allocates a trampoline for the attachment.

This patch splits out (1.) and (3.) into separate functions in preparation
for reusing them when the actual attachment is happening (in the
raw_tracepoint_open syscall operation), which will allow tracing programs
to have multiple (compatible) attachments.

No functional change is intended with this patch.

Signed-off-by: Toke Høiland-Jørgensen <redacted>
---

I can't tell if there are any functional changes or not, tbh. The
logic is quite complicated and full of intricate details. I did leave
some suggestions on hopefully simplifying code flow in some places
(and ensuring it's harder to break it on future changes), but I hope
Alexei will give it a very thorough review and check that none of the
subtle details broke.

Yeah, totally agree this is gnarly... :/
Which is also why I chickened out of doing any further changes in an
attempt to simplify the flow, but rather kept as much as the existing
structure as possible (with somewhat mixed results, I suppose).

Let's see what Alexei thinks. I guess I can take another crack at it, in
which case, thank you for the suggestions for simplifying things!

-Toke