Re: [PATCH bpf-next v2 3/6] bpf: Make find_linfo widely available

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 4/8/26 3:13 AM, Kumar Kartikeya Dwivedi wrote:
> Move find_linfo() as bpf_find_linfo() into core.c to allow for its use
> in the verifier in subsequent patches.
> 
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>   include/linux/bpf.h |  1 +
>   kernel/bpf/core.c   | 37 +++++++++++++++++++++++++++++++++++++
>   kernel/bpf/log.c    | 43 +------------------------------------------
>   3 files changed, 39 insertions(+), 42 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index d8fb9d61f5ce..0136a108d083 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3945,6 +3945,7 @@ static inline bool bpf_is_subprog(const struct bpf_prog *prog)
>   	return prog->aux->func_idx != 0;
>   }
>   
> +const struct bpf_line_info *bpf_find_linfo(const struct bpf_prog *prog, u32 insn_off);
>   void bpf_get_linfo_file_line(struct btf *btf, const struct bpf_line_info *linfo,
>   			     const char **filep, const char **linep, int *nump);
>   int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index ada76f997177..066b86e7233c 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -3335,6 +3335,43 @@ void bpf_get_linfo_file_line(struct btf *btf, const struct bpf_line_info *linfo,
>   		*nump = BPF_LINE_INFO_LINE_NUM(linfo->line_col);
>   }
>   
> +const struct bpf_line_info *bpf_find_linfo(const struct bpf_prog *prog, u32 insn_off)
> +{
> +	const struct bpf_line_info *linfo;
> +	u32 nr_linfo;
> +	int l, r, m;
> +
> +	nr_linfo = prog->aux->nr_linfo;
> +	if (!nr_linfo || insn_off >= prog->len)
> +		return NULL;
> +
> +	linfo = prog->aux->linfo;
> +	/* Loop invariant: linfo[l].insn_off <= insns_off.
If you are touching these lines, it's worth updating to kernel style 
comments.
other than that the change looks straightforward, just moving a function 
from one place to another + minor change of the arguments and rename.
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
> +	 * linfo[0].insn_off == 0 which always satisfies above condition.
> +	 * Binary search is searching for rightmost linfo entry that satisfies
> +	 * the above invariant, giving us the desired record that covers given
> +	 * instruction offset.
> +	 */
> +	l = 0;
> +	r = nr_linfo - 1;
> +	while (l < r) {
> +		/* (r - l + 1) / 2 means we break a tie to the right, so if:
> +		 * l=1, r=2, linfo[l].insn_off <= insn_off, linfo[r].insn_off > insn_off,
> +		 * then m=2, we see that linfo[m].insn_off > insn_off, and so
> +		 * r becomes 1 and we exit the loop with correct l==1.
> +		 * If the tie was broken to the left, m=1 would end us up in
> +		 * an endless loop where l and m stay at 1 and r stays at 2.
> +		 */
> +		m = l + (r - l + 1) / 2;
> +		if (linfo[m].insn_off <= insn_off)
> +			l = m;
> +		else
> +			r = m - 1;
> +	}
> +
> +	return &linfo[l];
> +}
> +
>   int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
>   			   const char **linep, int *nump)
>   {
> diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> index c67fbbbd5768..48931d4e5a68 100644
> --- a/kernel/bpf/log.c
> +++ b/kernel/bpf/log.c
> @@ -327,47 +327,6 @@ __printf(2, 3) void bpf_log(struct bpf_verifier_log *log,
>   }
>   EXPORT_SYMBOL_GPL(bpf_log);
>   
> -static const struct bpf_line_info *
> -find_linfo(const struct bpf_verifier_env *env, u32 insn_off)
> -{
> -	const struct bpf_line_info *linfo;
> -	const struct bpf_prog *prog;
> -	u32 nr_linfo;
> -	int l, r, m;
> -
> -	prog = env->prog;
> -	nr_linfo = prog->aux->nr_linfo;
> -
> -	if (!nr_linfo || insn_off >= prog->len)
> -		return NULL;
> -
> -	linfo = prog->aux->linfo;
> -	/* Loop invariant: linfo[l].insn_off <= insns_off.
> -	 * linfo[0].insn_off == 0 which always satisfies above condition.
> -	 * Binary search is searching for rightmost linfo entry that satisfies
> -	 * the above invariant, giving us the desired record that covers given
> -	 * instruction offset.
> -	 */
> -	l = 0;
> -	r = nr_linfo - 1;
> -	while (l < r) {
> -		/* (r - l + 1) / 2 means we break a tie to the right, so if:
> -		 * l=1, r=2, linfo[l].insn_off <= insn_off, linfo[r].insn_off > insn_off,
> -		 * then m=2, we see that linfo[m].insn_off > insn_off, and so
> -		 * r becomes 1 and we exit the loop with correct l==1.
> -		 * If the tie was broken to the left, m=1 would end us up in
> -		 * an endless loop where l and m stay at 1 and r stays at 2.
> -		 */
> -		m = l + (r - l + 1) / 2;
> -		if (linfo[m].insn_off <= insn_off)
> -			l = m;
> -		else
> -			r = m - 1;
> -	}
> -
> -	return &linfo[l];
> -}
> -
>   static const char *ltrim(const char *s)
>   {
>   	while (isspace(*s))
> @@ -388,7 +347,7 @@ __printf(3, 4) void verbose_linfo(struct bpf_verifier_env *env,
>   		return;
>   
>   	prev_linfo = env->prev_linfo;
> -	linfo = find_linfo(env, insn_off);
> +	linfo = bpf_find_linfo(env->prog, insn_off);
>   	if (!linfo || linfo == prev_linfo)
>   		return;
>