linux-kernel - Re: [PATCH bpf-next v10 07/13] btf: Verify BTF Sorting

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Message-ID: <1a9c0b5c22b2ecd8a8df531b1ed9441ab926415b.camel@gmail.com>
Date: Thu, 18 Dec 2025 13:43:02 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Donglin Peng <dolinux.peng@...il.com>, ast@...nel.org, 
	andrii.nakryiko@...il.com
Cc: zhangxiaoqin@...omi.com, ihor.solodrai@...ux.dev, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, pengdonglin
	 <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCH bpf-next v10 07/13] btf: Verify BTF Sorting

On Thu, 2025-12-18 at 19:30 +0800, Donglin Peng wrote:
> From: pengdonglin <pengdonglin@...omi.com>
> 
> This patch checks whether the BTF is sorted by name in ascending order.
> If sorted, binary search will be used when looking up types.
> 
> Specifically, vmlinux and kernel module BTFs are always sorted during
> the build phase with anonymous types placed before named types, so we
> only need to identify the starting ID of named types.
> 
> Cc: Eduard Zingerman <eddyz87@...il.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: Alan Maguire <alan.maguire@...cle.com>
> Cc: Ihor Solodrai <ihor.solodrai@...ux.dev>
> Cc: Xiaoqin Zhang <zhangxiaoqin@...omi.com>
> Signed-off-by: pengdonglin <pengdonglin@...omi.com>
> ---

Lgtm, but please take a look at a few nits.

>  kernel/bpf/btf.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
> 
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 0394f0c8ef74..a9e2345558c0 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -550,6 +550,60 @@ u32 btf_nr_types(const struct btf *btf)
>  	return total;
>  }
>  
> +/*
> + * Assuming that types are sorted by name in ascending order.
> + */
> +static int btf_compare_type_names(u32 *a, u32 *b, const struct btf *btf)

Nit: no need for 'a' and 'b' to be pointers.

> +{
> +	const struct btf_type *ta = btf_type_by_id(btf, *a);
> +	const struct btf_type *tb = btf_type_by_id(btf, *b);
> +	const char *na, *nb;
> +
> +	na = btf_name_by_offset(btf, ta->name_off);
> +	nb = btf_name_by_offset(btf, tb->name_off);
> +	return strcmp(na, nb);
> +}
> +
> +/* Note that vmlinux and kernel module BTFs are always sorted
> + * during the building phase.
> + */
> +static void btf_check_sorted(struct btf *btf)
> +{
> +	const struct btf_type *t;
> +	u32 sorted_start_id;
> +	u32 i, n, k;
> +
> +	if (btf_is_kernel(btf) && !btf_is_module(btf)) {
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Nit: there is a btf_is_vmlinux() helper, which does the same thing.

> +		for (i = btf_start_id(btf); i < n; i++) {
> +			t = btf_type_by_id(btf, i);
> +			if (t->name_off) {
> +				btf->sorted_start_id = i;
> +				return;
> +			}
> +		}

Nit: return here?

> +	}
> +
> +	if (btf->nr_types < 2)
> +		return;
> +
> +	sorted_start_id = 0;
> +	n = btf_nr_types(btf);
> +	for (i = btf_start_id(btf); i < n; i++) {
> +		k = i + 1;
> +		if (k < n && btf_compare_type_names(&i, &k, btf) > 0)
> +			return;
> +
> +		if (sorted_start_id == 0) {
> +			t = btf_type_by_id(btf, i);
> +			if (t->name_off)
> +				sorted_start_id = i;
> +		}
> +	}
> +
> +	if (sorted_start_id)
> +		btf->sorted_start_id = sorted_start_id;
> +}
> +
>  static s32 btf_find_by_name_bsearch(const struct btf *btf, const char *name,
>  				    s32 start_id, s32 end_id)
>  {
> @@ -6296,6 +6350,7 @@ static struct btf *btf_parse_base(struct btf_verifier_env *env, const char *name
>  	if (err)
>  		goto errout;
>  
> +	btf_check_sorted(btf);
>  	refcount_set(&btf->refcnt, 1);
>  
>  	return btf;
> @@ -6430,6 +6485,7 @@ static struct btf *btf_parse_module(const char *module_name, const void *data,
>  	}
>  
>  	btf_verifier_env_free(env);
> +	btf_check_sorted(btf);
>  	refcount_set(&btf->refcnt, 1);
>  	return btf;
>