Re: [PATCH] bpf: add diagnostics for rejected memory and map accesses

[Suchit Karunakaran]

On Tue, 22 Sept 2026 at 00:30, Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Mon Sep 21, 2026 at 5:38 PM UTC, Suchit Karunakaran wrote:
> > On Mon, 21 Sept 2026 at 22:35, Alexei Starovoitov
> > <alexei.starovoitov@xxxxxxxxx> wrote:
> > >
> > > On Mon, Sep 21, 2026 at 09:16 PM Suchit Karunakaran <suchitkarunakaran@xxxxxxxxx> wrote:
> > > >                                       verbose(env, "sign extending loads from arena are not supported yet\n");
> > > > +                                     bpf_diag_policy(
> > > > +                                             env, i + delta, "sign-extending arena load",
> > > > +                                             "the current JIT does not support this load instruction for arena memory",
> > > > +                                             "Use a kernel and architecture with JIT support for this arena load.");
> > >
> > > Did you read what AI generated for you?
> > > "Use a kernel and architecture with JIT support for this arena load."
> > > ?!?!
> > >
> > > Please apply human filter to every single line of "your" patches.
> > >
> > > pw-bot: cr
> >
> > Hi Alexei. I'm sorry for the oversight. I somehow misinterpreted it as
> > "Use a kernel and architecture with JIT that supports this arena
> > load." Is the following diagnostic message fine? If yes I'll correct
> > it in v2.
> > bpf_diag_policy(env, i + delta,
> > "sign-extending arena load", "the current JIT backend doesn't
> > implement sign-extending loads from arena memory",
> >  "Use a kernel and architecture where the BPF JIT supports
> > sign-extending loads from arena memory.");
>
> No. That is still wrong. Put yourself in user's shoes.
> How would you react to this message?
>

Hi Alexei, thanks for the review. After some research, I found that
the sign extending load instruction was introduced in BPF ISA V4.
Given that, would the following diagnostic message be more helpful for
users?
bpf_diag_policy(env, i + delta,
"sign-extending load from arena memory",
"the current JIT backend doesn't implement sign-extending loads from
arena memory",
"Recompile the BPF program with Clang's -mcpu=v3 to avoid generating
sign-extending load instructions.");