Re: [RFC PATCH bpf-next] bpf: change syscall_nr type to int in struct syscall_tp_t

[Steven Rostedt]

On Fri, 13 Oct 2023 08:01:34 +0200
Artem Savkov <asavkov@xxxxxxxxxx> wrote:

> > But looking at [0] and briefly reading some of the discussions you,
> > Steven, had. I'm just wondering if it would be best to avoid
> > increasing struct trace_entry altogether? It seems like preempt_count
> > is actually a 4-bit field in trace context, so it doesn't seem like we
> > really need to allocate an entire byte for both preempt_count and
> > preempt_lazy_count. Why can't we just combine them and not waste 8
> > extra bytes for each trace event in a ring buffer?
> > 
> >   [0] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/?id=b1773eac3f29cbdcdfd16e0339f1a164066e9f71  
> 
> I agree that avoiding increase in struct trace_entry size would be very
> desirable, but I have no knowledge whether rt developers had reasons to
> do it like this.
> 
> Nevertheless I think the issue with verifier running against a wrong
> struct still needs to be addressed.

Correct. My Ack is based on the current way things are done upstream.
It was just that linux-rt showed the issue, where the code was not as
robust as it should have been. To me this was a correctness issue, not
an issue that had to do with how things are done in linux-rt.

As for the changes in linux-rt, they are not upstream yet. I'll have my
comments on that code when that happens.

-- Steve