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 <blakejo...@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);
--
2.49.0.1204.g71687c7c1d-goog
