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.
