Commit 87c9c79a authored by Blake Jones's avatar Blake Jones Committed by Andrii Nakryiko
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libbpf: Add support for printing BTF character arrays as strings 



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"

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: default avatarBlake Jones <blakejones@google.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250603203701.520541-1-blakejones@google.com
parent 97744b49

tools/lib/bpf/btf.h

+2 −1
Original line number Diff line number Diff line
@@ -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,

tools/lib/bpf/btf_dump.c

+54 −1
Original line number Diff line number Diff line
@@ -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,
@@ -2055,9 +2102,14 @@ 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;

	 * this is intentional.  btf_dump_data_newline() will not print a
@@ -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);