Re: [PATCH bpf-next v2 01/13] bpf: move linked-scalar flags out of bpf_reg_state->id [NFC]

[Vineet Gupta]

On 9/16/26 5:36 PM, Alexei Starovoitov wrote:
> On Wed, Sep 16, 2026 at 2:24 PM Vineet Gupta<vineet.gupta@xxxxxxxxx> wrote:
> > On 9/16/26 2:02 PM, Alexei Starovoitov wrote:
> > > On Tue Sep 15, 2026 at 1:17 AM UTC, Vineet Gupta wrote:
> > > > Back when I started, keeping it NFC made more sense. But with all the
> > > > nuances discovered in the process, I'm inclined to drop the NFC stance
> > > What is NFC ?
> > non functional change aka refactoring.
> > Like I said when I started I wanted to keep the id / flag breakout
> > purely non functional. But given that splitting it does change one thing
> > (mentioned below) - I'm dropping NFC attribution.
> >
> > > > and make functional changes - there's at least one which is the
> > > > following accepted pre-series and now rejected.
> > > >
> > > >          old {r2.id=A+delta32}         vs cur {r2.id=B+delta64}
> > > that's a red flag, no? The refactoring patch shouldn't have
> > > any changes to selftest and veristat numbers?
> > > Unless I'm missing it again.
> > Yes understood except that it is no longer refactoring.
> NFC is gcc probably lingvo? In kernel people just put in the commit
> log "No functional changes", so it's easier for humans and for AI
> to review patches.
> So pls skip such unusual tags in the future,

Yes keeping kernel's existing conventions makes sense, although LLMs 
understand what NFC is.

> but keep the first patch as "No functional change".

Just to rehash since the meaning of first has moved significantly.

1. Now the first change (patch 1/x and its test 2/x )  is no longer the 
compound id conversion, but coerce_reg_to_size_sx / 
coerce_subreg_to_size_sx change to fix the errno range case, as 
suggested by you. It is a functional change, with following improvement:

   === VERDICT CHANGES: 3 ===
       mov32sx_s8_negative_range     failure -> success
       mov64sx_s32_negative_range    failure -> success
       mov64sx_s8_negative_range     failure -> success

   === total_insns:  0 changed among 1242 both-passing, 0 worse ===
   === total_states: 0 changed among 1242 both-passing, 0 worse ===

2. The second change (3/x and its test 4/x) is accumulating add_const 
deltas (w3 = w0; w3 -=1). This makes the 32-bit link with delta special 
handling of zext unnecessary so its a prereq for the series.

3. I guess you are referring to the patch to convert compound id to 
broken out id + flags (5/x ) is also technically a functional change - 
due to the state comparison behavior improvement that fell out of the 
seemingly mechanical conversion and is clearly called out now. However I 
verified it in isolation (on top of 4 prior of course) and there are no 
veristat or selftest changes with it (just a cosmetic name change due to 
base_id -> id)

   === VERDICT CHANGES: 0 ===
   === total_insns:  0 changed among 1247 both-passing, 0 worse ===
   === total_states: 0 changed among 1247 both-passing, 0 worse ===


I presume that is what you were asking for ?

Thx,
-Vineet