On Mon, Feb 05, 2024 at 05:09:51PM -0800, Alexei Starovoitov wrote:
> On Fri, Feb 2, 2024 at 8:34 AM Anton Protopopov <aspsk@xxxxxxxxxxxxx> wrote:
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 4def3dde35f6..bdd6be718e82 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1524,6 +1524,13 @@ struct bpf_prog_aux {
> > };
> > /* an array of original indexes for all xlated instructions */
> > u32 *orig_idx;
> > + /* for every xlated instruction point to all generated jited
> > + * instructions, if allocated
> > + */
> > + struct {
> > + u32 off; /* local offset in the jitted code */
> > + u32 len; /* the total len of generated jit code */
> > + } *xlated_to_jit;
>
> Simply put Nack to this approach.
>
> Patches 2 and 3 add an extreme amount of memory overhead.
>
> As we discussed during office hours we need a "pointer to insn" concept
> aka "index on insn".
> The verifier would need to track that such things exist and adjust
> indices of insns when patching affects those indices.
>
> For every static branch there will be one such "pointer to insn".
> Different algorithms can be used to keep them correct.
> The simplest 'lets iterate over all such pointers and update them'
> during patch_insn() may even be ok to start.
>
> Such "pointer to insn" won't add any memory overhead.
> When patch+jit is done all such "pointer to insn" are fixed value.
Ok, thanks for looking, this makes sense.
