Re: [PATCH bpf-next 03/36] bpf: summarize live stack slots in insn_aux_data

[Eduard Zingerman <eddyz87@gmail.com>]

On Sun, 2026-09-27 at 20:26 +0000, bot+bpf-ci@kernel.org wrote:
> > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> > index c6d617581e84..7f31ce5ea6b7 100644
> > --- a/include/linux/bpf_verifier.h
> > +++ b/include/linux/bpf_verifier.h
> > @@ -667,6 +667,7 @@ struct bpf_insn_aux_data {
> >  	 * that this instruction may write to.
> >  	 */
> >  	DECLARE_BITMAP(may_write_mask, MAX_BPF_STACK_SLOTS);
> > +	DECLARE_BITMAP(live_stack_before, MAX_BPF_STACK_SLOTS);
> 
> This isn't a bug, but would a short comment on live_stack_before make it
> clearer what the field holds?  Nearly every neighbouring field like
> live_regs_before and scc has its own comment.

Naming is clear enough.

> 
> >  	int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
> >  	u32 seen; /* this insn was processed by the verifier at env->pass_cnt */
> >  	bool nospec; /* do not execute this instruction speculatively */
> 
> [ ... ]
> 
> > diff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c
> > index c871744ca5a8..b6b7fd479569 100644
> > --- a/kernel/bpf/liveness.c
> > +++ b/kernel/bpf/liveness.c
> > @@ -729,8 +729,9 @@ static void half_spis_to_slots(unsigned long *slots, const unsigned long *mask,
> >  }
> > 
> >  /*
> > - * Precompute, for each instruction, the OR of may_write masks over its top
> > - * frame across all func_instances reaching it, stash it in the insn_aux_data.
> > + * Precompute, for each instruction, the OR of may_write and live_before masks
> > + * over its top frame across all func_instances reaching it, stash them in the
> > + * insn_aux_data.
> >   */
> >  static void compute_may_write_masks(struct bpf_verifier_env *env)
> >  {
> > @@ -746,9 +747,12 @@ static void compute_may_write_masks(struct bpf_verifier_env *env)
> >  		if (!fm)
> >  			continue;
> >  		nbits = frame_mask_bits(fm);
> > -		for (i = 0; i < instance->insn_cnt; i++)
> > +		for (i = 0; i < instance->insn_cnt; i++) {
> >  			half_spis_to_slots(aux[instance->subprog_start + i].may_write_mask,
> >  					   rel_mask(fm, i, FM_MAY_WRITE), nbits);
> > +			half_spis_to_slots(aux[instance->subprog_start + i].live_stack_before,
> > +					   rel_mask(fm, i, FM_LIVE_BEFORE), nbits);
> > +		}
> >  	}
> >  }
> 
> This isn't a bug, but would a more general name for compute_may_write_masks()
> make the function's purpose clearer?  The comment now describes computing both
> may_write and live_before masks, but the name only mentions may_write.

Nope.

> 
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/36346543957