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 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 ".print_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):
- .print_strings = 0, .skip_names = 0: (char[6])['h','e','l','l','o',] - .print_strings = 0, .skip_names = 1: ['h','e','l','l','o',] - .print_strings = 1, .skip_names = 0: (char[6])"hello" - .print_strings = 1, .skip_names = 1: "hello"
Here's the string "h\xff", dumped with .compact = 1 and .skip_names = 1:
- .print_strings = 0: ['h',-1,] - .print_strings = 1: "h\xff"
Signed-off-by: Blake Jones blakejones@google.com --- tools/lib/bpf/btf.h | 3 +- tools/lib/bpf/btf_dump.c | 51 ++++++++- .../selftests/bpf/prog_tests/btf_dump.c | 102 ++++++++++++++++++ 3 files changed, 154 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h index 4392451d634b..be8e8e26d245 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 print_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 print_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..a07dd5accdd8 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -75,6 +75,7 @@ struct btf_dump_data { bool is_array_member; bool is_array_terminated; bool is_array_char; + bool print_strings; };
struct btf_dump { @@ -2028,6 +2029,50 @@ 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; + + if (!btf_is_int(skip_mods_and_typedefs(d->btf, array->type, NULL)) || + btf__resolve_size(d->btf, array->type) != 1 || + !d->typed_dump->print_strings) { + pr_warn("unexpected %s() call for array type %u\n", + __func__, array->type); + return -EINVAL; + } + + 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; + + 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 +2100,11 @@ 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->print_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 +2592,7 @@ 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->print_strings = OPTS_GET(opts, print_strings, false);
ret = btf_dump_dump_type_data(d, NULL, t, id, data, 0, 0);
diff --git a/tools/testing/selftests/bpf/prog_tests/btf_dump.c b/tools/testing/selftests/bpf/prog_tests/btf_dump.c index c0a776feec23..70e51943f148 100644 --- a/tools/testing/selftests/bpf/prog_tests/btf_dump.c +++ b/tools/testing/selftests/bpf/prog_tests/btf_dump.c @@ -879,6 +879,106 @@ static void test_btf_dump_var_data(struct btf *btf, struct btf_dump *d, "static int bpf_cgrp_storage_busy = (int)2", 2); }
+/* + * String-like types are generally not named, so they need to be + * found this way rather than via btf__find_by_name(). + */ +static int find_char_array_type(struct btf *btf, int nelems) +{ + const int nr_types = btf__type_cnt(btf); + const int char_type = btf__find_by_name(btf, "char"); + + for (int i = 1; i < nr_types; i++) { + const struct btf_type *t; + const struct btf_array *at; + + t = btf__type_by_id(btf, i); + if (btf_kind(t) != BTF_KIND_ARRAY) + continue; + + at = btf_array(t); + if (at->nelems == nelems && at->type == char_type) + return i; + } + + return -ENOENT; +} + +static int btf_dump_string_data(struct btf *btf, struct btf_dump *d, + char *str, struct btf_dump_type_data_opts *opts, + char *ptr, size_t ptr_sz, + const char *expected_val) +{ + char name[64]; + size_t type_sz; + int type_id; + int ret = 0; + + snprintf(name, sizeof(name), "char[%zu]", ptr_sz); + type_id = find_char_array_type(btf, ptr_sz); + if (!ASSERT_GE(type_id, 0, "find type id")) + return -ENOENT; + type_sz = btf__resolve_size(btf, type_id); + str[0] = '\0'; + ret = btf_dump__dump_type_data(d, type_id, ptr, ptr_sz, opts); + if (type_sz <= ptr_sz) { + if (!ASSERT_EQ(ret, type_sz, "failed/unexpected type_sz")) + return -EINVAL; + } else { + if (!ASSERT_EQ(ret, -E2BIG, "failed to return -E2BIG")) + return -EINVAL; + } + if (!ASSERT_STREQ(str, expected_val, "ensure expected/actual match")) + return -EFAULT; + return 0; +} + +static void test_btf_dump_string_data(struct btf *btf, struct btf_dump *d, + char *str) +{ + DECLARE_LIBBPF_OPTS(btf_dump_type_data_opts, opts); + + opts.compact = true; + opts.emit_zeroes = false; + opts.print_strings = true; + + opts.skip_names = false; + btf_dump_string_data(btf, d, str, &opts, "foo", 4, + "(char[4])"foo""); + + opts.skip_names = true; + btf_dump_string_data(btf, d, str, &opts, "foo", 4, + ""foo""); + + /* This should have no effect. */ + opts.emit_zeroes = false; + btf_dump_string_data(btf, d, str, &opts, "foo", 4, + ""foo""); + + /* This should have no effect. */ + opts.compact = false; + btf_dump_string_data(btf, d, str, &opts, "foo", 4, + ""foo""); + + /* Non-printable characters come out as hex. */ + btf_dump_string_data(btf, d, str, &opts, "fo\xff", 4, + ""fo\xff""); + btf_dump_string_data(btf, d, str, &opts, "fo\x7", 4, + ""fo\x07""); + + /* Should get printed properly even though there's no NUL. */ + char food[4] = { 'f', 'o', 'o', 'd' }; + + btf_dump_string_data(btf, d, str, &opts, food, 4, + ""food""); + + /* The embedded NUL should terminate the string. */ + char embed[4] = { 'f', 'o', '\0', 'd' }; + + btf_dump_string_data(btf, d, str, &opts, embed, 4, + ""fo""); +} + static void test_btf_datasec(struct btf *btf, struct btf_dump *d, char *str, const char *name, const char *expected_val, void *data, size_t data_sz) @@ -970,6 +1070,8 @@ void test_btf_dump() { test_btf_dump_struct_data(btf, d, str); if (test__start_subtest("btf_dump: var_data")) test_btf_dump_var_data(btf, d, str); + if (test__start_subtest("btf_dump: string_data")) + test_btf_dump_string_data(btf, d, str); btf_dump__free(d); btf__free(btf);