Re: [RFC PATCH v1 06/14] bpf: Adjust frame descriptor pc on instruction patching

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2024-02-01 at 04:21 +0000, Kumar Kartikeya Dwivedi wrote:

[...]

> +static int adjust_subprog_frame_descs_after_remove(struct bpf_verifier_env *env, u32 off, u32 cnt)
> +{
> +	for (int i = 0; i < env->subprog_cnt; i++) {
> +		struct bpf_exception_frame_desc_tab *fdtab = subprog_info(env, i)->fdtab;
> +
> +		if (!fdtab)
> +			continue;
> +		for (int j = 0; j < fdtab->cnt; j++) {
> +			/* Part of a subprog_info whose instructions were removed partially, but the fdtab remained. */
> +			if (fdtab->desc[j]->pc >= off && fdtab->desc[j]->pc < off + cnt) {
> +				void *p = fdtab->desc[j];
> +				if (j < fdtab->cnt - 1)
> +					memmove(fdtab->desc + j, fdtab->desc + j + 1, sizeof(fdtab->desc[0]) * (fdtab->cnt - j - 1));
> +				kfree(p);

Is it necessary to release btf references for desc entries that are removed?
Those that were grabbed by add_used_btf() in gen_exception_frame_desc_iter_entry().

> +				fdtab->cnt--;
> +				j--;
> +			}
> +			if (fdtab->desc[j]->pc >= off + cnt)
> +				fdtab->desc[j]->pc -= cnt;
> +		}
> +	}
> +	return 0;
> +}
> +

[...]