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