Re: [PATCH bpf-next 01/11] bpf: Move insn if/else into do_check_insn()

Eduard Zingerman [off-list ref] writes:

On Thu, 2025-03-13 at 18:21 +0100, Luis Gerhorst wrote:

quoted

+		err = do_check_insn(env, insn, pop_log, &do_print_state, regs, state,
+				    &prev_insn_idx);

- `regs` remains declared in do_check(), while nothing prevents
  pushing its declaration to do_check_insn().
- `state` is `env->cur_state`, so I'd avoid passing it as a parameter
  (just to reduce count);
- `prev_insn_idx` is unused by `do_check_insn`;
- `pop_log` is not used by `do_check_insn`;

Changed for v2, thank you very much.

- given that `insn` is presumed to correspond to `env->insn_idx` in
  many places down the stack not sure about this parameter.

I don't have a strong opinion on this either. Unless someone objects I
will keep it as it matches the other check_*() functions like this.

quoted

+		if (err < 0) {
+			return err;
+		} else if (err == INSN_IDX_MODIFIED) {

Also, I'd get rid of `INSN_IDX_MODIFIED` and move `env->insn_idx++`
into `do_check_insn()`. This would save a few mental cycles when
looking at the code with full patch-set applied:

		} else if (err == INSN_IDX_MODIFIED) {
			continue;
		} else if (err == PROCESS_BPF_EXIT) {
			goto process_bpf_exit;
		}
		WARN_ON_ONCE(err);

		if (state->speculative && cur_aux(env)->nospec_result) {
			... bunch of actions ...
		}

		env->insn_idx++;

One needs to stop for a moment and think why "bunch of actions" is
performed for regular index increment, but not for INSN_IDX_MODIFIED.

That certainly makes it more readable. I changed it for v2.

If we have an instruction that does not simply do `insn_idx++` but
jumps, the `nospec_result` check should never trigger. Otherwise, the
patched nospec might be skipped. Currently, this is satisfied because
`nospec_result` is only used for store-instructions. I will add a
comment and WARN_ON_ONCE to document that for v2.