Re: [PATCH bpf-next v3 1/7] bpf: Allow struct argument in trampoline based programs

[Jiri Olsa <olsajiri@gmail.com>]

On Sat, Aug 27, 2022 at 07:54:43PM -0700, Yonghong Song wrote:

SNIP

> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 903719b89238..4a081bfb4c8a 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -5328,6 +5328,31 @@ static bool is_int_ptr(struct btf *btf, const struct btf_type *t)
>  	return btf_type_is_int(t);
>  }
>  
> +static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto,
> +			   int off)
> +{
> +	const struct btf_param *args;
> +	const struct btf_type *t;
> +	u32 offset = 0, nr_args;
> +	int i;
> +
> +	nr_args = btf_type_vlen(func_proto);
> +	args = (const struct btf_param *)(func_proto + 1);
> +	for (i = 0; i < nr_args; i++) {
> +		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> +		offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
> +		if (off < offset)
> +			return i;
> +	}
> +
> +	t = btf_type_skip_modifiers(btf, func_proto->type, NULL);
> +	offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
> +	if (off < offset)
> +		return nr_args;
> +
> +	return nr_args + 1;
> +}
> +
>  bool btf_ctx_access(int off, int size, enum bpf_access_type type,
>  		    const struct bpf_prog *prog,
>  		    struct bpf_insn_access_aux *info)
> @@ -5347,7 +5372,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
>  			tname, off);
>  		return false;
>  	}
> -	arg = off / 8;
> +	arg = t == NULL ? (off / 8) :  get_ctx_arg_idx(btf, t, off);

is the t == NULL check needed? we relied on t being defined later in the code

jirka

>  	args = (const struct btf_param *)(t + 1);
>  	/* if (t == NULL) Fall back to default BPF prog with
>  	 * MAX_BPF_FUNC_REG_ARGS u64 arguments.
> @@ -5417,7 +5442,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
>  	/* skip modifiers */
>  	while (btf_type_is_modifier(t))
>  		t = btf_type_by_id(btf, t->type);
> -	if (btf_type_is_small_int(t) || btf_is_any_enum(t))
> +	if (btf_type_is_small_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))
>  		/* accessing a scalar */
>  		return true;
>  	if (!btf_type_is_ptr(t)) {
> @@ -5881,7 +5906,7 @@ static int __get_type_size(struct btf *btf, u32 btf_id,
>  	if (btf_type_is_ptr(t))
>  		/* kernel size of pointer. Not BPF's size of pointer*/
>  		return sizeof(void *);
> -	if (btf_type_is_int(t) || btf_is_any_enum(t))
> +	if (btf_type_is_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))
>  		return t->size;
>  	return -EINVAL;

SNIP