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Message-ID: <aElbyWY-cIQNf4wp@krava>
Date: Wed, 11 Jun 2025 12:34:49 +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 v3 1/2] libbpf: add support for printing BTF character
arrays as strings
On Tue, Jun 03, 2025 at 01:37:00PM -0700, Blake Jones wrote:
> The BTF dumper code currently displays arrays of characters as just that -
> arrays, with each character formatted individually. Sometimes this is what
> makes sense, but it's nice to be able to treat that array as a string.
>
> This change adds a special case to the btf_dump functionality to allow
> 0-terminated arrays of single-byte integer values to be printed as
> character strings. Characters for which isprint() returns false are
> printed as hex-escaped values. This is enabled when the new ".emit_strings"
> is set to 1 in the btf_dump_type_data_opts structure.
>
> As an example, here's what it looks like to dump the string "hello" using
> a few different field values for btf_dump_type_data_opts (.compact = 1):
>
> - .emit_strings = 0, .skip_names = 0: (char[6])['h','e','l','l','o',]
> - .emit_strings = 0, .skip_names = 1: ['h','e','l','l','o',]
> - .emit_strings = 1, .skip_names = 0: (char[6])"hello"
> - .emit_strings = 1, .skip_names = 1: "hello"
hi,
could this be used in bpftool map dump? ;-) I checked, but it looks like
bpftool map dump is using something else to dump data.. I admit I haven't
spent much on time that
thanks,
jirka
>
> Here's the string "h\xff", dumped with .compact = 1 and .skip_names = 1:
>
> - .emit_strings = 0: ['h',-1,]
> - .emit_strings = 1: "h\xff"
>
> Signed-off-by: Blake Jones <blakejones@...gle.com>
> ---
> tools/lib/bpf/btf.h | 3 ++-
> tools/lib/bpf/btf_dump.c | 55 +++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 56 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> index 4392451d634b..ccfd905f03df 100644
> --- a/tools/lib/bpf/btf.h
> +++ b/tools/lib/bpf/btf.h
> @@ -326,9 +326,10 @@ struct btf_dump_type_data_opts {
> bool compact; /* no newlines/indentation */
> bool skip_names; /* skip member/type names */
> bool emit_zeroes; /* show 0-valued fields */
> + bool emit_strings; /* print char arrays as strings */
> size_t :0;
> };
> -#define btf_dump_type_data_opts__last_field emit_zeroes
> +#define btf_dump_type_data_opts__last_field emit_strings
>
> LIBBPF_API int
> btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> index 460c3e57fadb..7c2f1f13f958 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 +2029,52 @@ 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);
> + const char *chars = data;
> + __u32 i;
> +
> + /* Make sure it is a NUL-terminated string. */
> + for (i = 0; i < array->nelems; i++) {
> + if ((void *)(chars + i) >= d->typed_dump->data_end)
> + return -E2BIG;
> + if (chars[i] == '\0')
> + break;
> + }
> + if (i == array->nelems) {
> + /* The caller will print this as a regular array. */
> + return -EINVAL;
> + }
> +
> + btf_dump_data_pfx(d);
> + btf_dump_printf(d, "\"");
> +
> + for (i = 0; i < array->nelems; i++) {
> + char c = chars[i];
> +
> + 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)c);
> + }
> +
> + 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 +2102,13 @@ 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 &&
> + btf_dump_string_data(d, t, id, data) == 0) {
> + return 0;
> + }
> d->typed_dump->is_array_char = true;
> + }
> }
>
> /* note that we increment depth before calling btf_dump_print() below;
> @@ -2544,6 +2596,7 @@ 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
>
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