linux-kernel - Re: [PATCH v2 1/2] libbpf: add support for printing BTF character arrays as strings

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Message-ID: <aD72CVq-kWr3G4S3@krava>
Date: Tue, 3 Jun 2025 15:18:01 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Blake Jones <blakejones@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Mykola Lysenko <mykolal@...com>,
	Shuah Khan <shuah@...nel.org>,
	Ihor Solodrai <ihor.solodrai@...ux.dev>,
	Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 1/2] libbpf: add support for printing BTF character
 arrays as strings

On Mon, Jun 02, 2025 at 09:48:12PM -0700, Blake Jones wrote:

SNIP

> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> index 460c3e57fadb..336a6646e0fa 100644
> --- a/tools/lib/bpf/btf_dump.c
> +++ b/tools/lib/bpf/btf_dump.c
> @@ -68,6 +68,7 @@ struct btf_dump_data {
>  	bool compact;
>  	bool skip_names;
>  	bool emit_zeroes;
> +	bool emit_strings;
>  	__u8 indent_lvl;	/* base indent level */
>  	char indent_str[BTF_DATA_INDENT_STR_LEN];
>  	/* below are used during iteration */
> @@ -2028,6 +2029,43 @@ static int btf_dump_var_data(struct btf_dump *d,
>  	return btf_dump_dump_type_data(d, NULL, t, type_id, data, 0, 0);
>  }
>  
> +static int btf_dump_string_data(struct btf_dump *d,
> +				const struct btf_type *t,
> +				__u32 id,
> +				const void *data)
> +{
> +	const struct btf_array *array = btf_array(t);
> +	__u32 i;
> +
> +	btf_dump_data_pfx(d);
> +	btf_dump_printf(d, "\"");
> +
> +	for (i = 0; i < array->nelems; i++, data++) {
> +		char c;
> +
> +		if (data >= d->typed_dump->data_end)
> +			return -E2BIG;

curious, is this just string array without null terminating byte?
should we just print " and return 0 instead of E2BIG error ?

thanks,
jirka


> +
> +		c = *(char *)data;
> +		if (c == '\0') {
> +			/*
> +			 * When printing character arrays as strings, NUL bytes
> +			 * are always treated as string terminators; they are
> +			 * never printed.
> +			 */
> +			break;
> +		}
> +		if (isprint(c))
> +			btf_dump_printf(d, "%c", c);
> +		else
> +			btf_dump_printf(d, "\\x%02x", *(__u8 *)data);
> +	}
> +
> +	btf_dump_printf(d, "\"");
> +
> +	return 0;
> +}
> +
>  static int btf_dump_array_data(struct btf_dump *d,
>  			       const struct btf_type *t,
>  			       __u32 id,
> @@ -2055,8 +2093,11 @@ static int btf_dump_array_data(struct btf_dump *d,
>  		 * char arrays, so if size is 1 and element is
>  		 * printable as a char, we'll do that.
>  		 */
> -		if (elem_size == 1)
> +		if (elem_size == 1) {
> +			if (d->typed_dump->emit_strings)
> +				return btf_dump_string_data(d, t, id, data);
>  			d->typed_dump->is_array_char = true;
> +		}
>  	}
>  
>  	/* note that we increment depth before calling btf_dump_print() below;
> @@ -2544,6 +2585,7 @@ int btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
>  	d->typed_dump->compact = OPTS_GET(opts, compact, false);
>  	d->typed_dump->skip_names = OPTS_GET(opts, skip_names, false);
>  	d->typed_dump->emit_zeroes = OPTS_GET(opts, emit_zeroes, false);
> +	d->typed_dump->emit_strings = OPTS_GET(opts, emit_strings, false);
>  
>  	ret = btf_dump_dump_type_data(d, NULL, t, id, data, 0, 0);
>  
> -- 
> 2.49.0.1204.g71687c7c1d-goog
>