Merge branch 'libbpf: BTF dumper support for typed data'

Alan Maguire says:

====================

Add a libbpf dumper function that supports dumping a representation
of data passed in using the BTF id associated with the data in a
manner similar to the bpf_snprintf_btf helper.

Default output format is identical to that dumped by bpf_snprintf_btf()
(bar using tabs instead of spaces for indentation, but the indent string
can be customized also); for example, a "struct sk_buff" representation
would look like this:

(struct sk_buff){
        (union){
                (struct){
                        .next = (struct sk_buff *)0xffffffffffffffff,
                        .prev = (struct sk_buff *)0xffffffffffffffff,
                        (union){
                                .dev = (struct net_device *)0xffffffffffffffff,
                                .dev_scratch = (long unsigned int)18446744073709551615,
                        },
        },
...

Patch 1 implements the dump functionality in a manner similar
to that in kernel/bpf/btf.c, but with a view to fitting into
libbpf more naturally.  For example, rather than using flags,
boolean dump options are used to control output.  In addition,
rather than combining checks for display (such as is this
field zero?) and actual display - as is done for the kernel
code - the code is organized to separate zero and overflow
checks from type display.

Patch 2 adds ASSERT_STRNEQ() for use in the following BTF dumper
tests.

Patch 3 consists of selftests that utilize a dump printf function
to snprintf the dump output to a string for comparison with
expected output.  Tests deliberately mirror those in
snprintf_btf helper test to keep output consistent, but
also cover overflow handling, var/section display.

Changes since v5 [1]
 - readjust dump options to avoid unnecessary padding (Andrii, patch 1).
 - tidied up bitfield data checking/retrieval using Andrii's suggestions.
   Removed code where we adjust data pointer prior to calling bitfield
   functions as this adjustment is not needed, provided we use the type
   size as the number of bytes to iterate over when retrieving the
   full value we apply bit shifting operations to retrieve the bitfield
   value.  With these chances, the *_int_bits() functions were no longer needed
   (Andrii, patch 1).
 - coalesced the "is zero" checking for ints, floats and pointers
   into btf_dump_base_type_check_zero(), using a memcmp() of the
   size of the data.  This can be derived from t->size for ints
   and floats, and pointer size is retrieved from dump's ptr_sz
   field (Andrii, patch 1).
 - Added alignment-aware handling for int, enum, float retrieval.
   Packed data structures can force ints, enums and floats to be
   aligned on different boundaries; for example, the

struct p {
        char f1;
        int f2;
} __attribute__((packed));

   ...will have the int f2 field offset at byte 1, rather than at
   byte 4 for an unpacked structure.  The problem is directly
   dereferencing that as an int is problematic on some platforms.
   For ints and enums, we can reuse bitfield retrieval to get the
   value for display, while for floats we use a local union of the
   floating-point types and memcpy into it, ensuring we can then
   dereference pointers into that union which will have safe alignment
   (Andrii, patch 1).
 - added comments to explain why we increment depth prior to displaying
   opening parens, and decrement it prior to displaying closing parens
   for structs, unions and arrays.  The reason is that we don't want
   to have a trailing newline when displaying a type.  The logic that
   handles this says "don't show a newline when the depth we're at is 0".
   For this to work for opening parens then we need to bump depth before
   showing opening parens + newline, and when we close out structure
   we need to show closing parens after reducing depth so that we don't
   append a newline to a top-level structure. So as a result we have

struct foo {\n
 struct bar {\n
 }\n
}

 - silently truncate provided indent string with strncat() if > 31 bytes
   (Andrii, patch 1).
 - fixed ASSERT_STRNEQ() macro to show only n bytes of string
   (Andrii, patch 2).
 - fixed strncat() of type data string to avoid stack corruption
   (Andrii, patch 3).
 - removed early returns from dump type tests (Andrii, patch 3).
 - have tests explicitly specify prefix (enum, struct, union)
   (Andrii, patch 3).
 - switch from CHECK() to ASSERT_* where possible (Andrii, patch 3).

Changes since v4 [2]
- Andrii kindly provided code to unify emitting a prepended cast
  (for example "(int)") with existing code, and this had the nice
  benefit of adding array indices in type specifications (Andrii,
  patches 1, 3)
- Fixed indent_str option to make it a const char *, stored in a
  fixed-length buffer internally (Andrii, patch 1)
- Reworked bit shift logic to minimize endian-specific interactions,
  and use same macros as found elsewhere in libbpf to determine endianness
  (Andrii, patch 1)
- Fixed type emitting to ensure that a trailing '\n' is not displayed;
  newlines are added during struct/array display, but for a single type
  the last character is no longer a newline (Andrii, patches 1, 3)
- Added support for ASSERT_STRNEQ() macro (Andrii, patch 2)
- Split tests into subtests for int, char, enum etc rather than one
  "dump type data" subtest (Andrii, patch 3)
- Made better use of ASSERT* macros (Andrii, patch 3)
- Got rid of some other TEST_* macros that were unneeded (Andrii, patch 3)
- Switched to using "struct fs_context" to verify enum bitfield values
  (Andrii, patch 3)

Changes since v3 [3]
- Retained separation of emitting of type name cast prefixing
  type values from existing functionality such as btf_dump_emit_type_chain()
  since initial code-shared version had so many exceptions it became
  hard to read.  For example, we don't emit a type name if the type
  to be displayed is an array member, we also always emit "forward"
  definitions for structs/unions that aren't really forward definitions
  (we just want a "struct foo" output for "(struct foo){.bar = ...".
  We also always ignore modifiers const/volatile/restrict as they
  clutter output when emitting large types.
- Added configurable 4-char indent string option; defaults to tab
  (Andrii)
- Added support for BTF_KIND_FLOAT and associated tests (Andrii)
- Added support for BTF_KIND_FUNC_PROTO function pointers to
  improve output of "ops" structures; for example:

(struct file_operations){
        .owner = (struct module *)0xffffffffffffffff,
        .llseek = (loff_t(*)(struct file *, loff_t, int))0xffffffffffffffff,
        ...
  Added associated test also (Andrii)
- Added handling for enum bitfields and associated test (Andrii)
- Allocation of "struct btf_dump_data" done on-demand (Andrii)
- Removed ".field = " output from function emitting type name and
  into caller (Andrii)
- Removed BTF_INT_OFFSET() support (Andrii)
- Use libbpf_err() to set errno for error cases (Andrii)
- btf_dump_dump_type_data() returns size written, which is used
  when returning successfully from btf_dump__dump_type_data()
  (Andrii)

Changes since v2 [4]
- Renamed function to btf_dump__dump_type_data, reorganized
  arguments such that opts are last (Andrii)
- Modified code to separate questions about display such
  as have we overflowed?/is this field zero? from actual
  display of typed data, such that we ask those questions
  separately from the code that actually displays typed data
  (Andrii)
- Reworked code to handle overflow - where we do not provide
  enough data for the type we wish to display - by returning
  -E2BIG and attempting to present as much data as possible.
  Such a mode of operation allows for tracers which retrieve
  partial data (such as first 1024 bytes of a
  "struct task_struct" say), and want to display that partial
  data, while also knowing that it is not the full type.
 Such tracers can then denote this (perhaps via "..." or
  similar).
- Explored reusing existing type emit functions, such as
  passing in a type id stack with a single type id to
  btf_dump_emit_type_chain() to support the display of
  typed data where a "cast" is prepended to the data to
  denote its type; "(int)1", "(struct foo){", etc.
  However the task of emitting a
  ".field_name = (typecast)" did not match well with model
  of walking the stack to display innermost types first
  and made the resultant code harder to read.  Added a
  dedicated btf_dump_emit_type_name() function instead which
  is only ~70 lines (Andrii)
- Various cleanups around bitfield macros, unneeded member
  iteration macros, avoiding compiler complaints when
  displaying int da ta by casting to long long, etc (Andrii)
- Use DECLARE_LIBBPF_OPTS() in defining opts for tests (Andrii)
- Added more type tests, overflow tests, var tests and
  section tests.

Changes since RFC [5]
- The initial approach explored was to share the kernel code
  with libbpf using #defines to paper over the different needs;
  however it makes more sense to try and fit in with libbpf
  code style for maintenance.  A comment in the code points at
  the implementation in kernel/bpf/btf.c and notes that any
  issues found in it should be fixed there or vice versa;
  mirroring the tests should help with this also
  (Andrii)

[1] https://lore.kernel.org/bpf/1624092968-5598-1-git-send-email-alan.maguire@oracle.com/
[2] https://lore.kernel.org/bpf/CAEf4BzYtbnphCkhz0epMKE4zWfvSOiMpu+-SXp9hadsrRApuZw@mail.gmail.com/T/
[3] https://lore.kernel.org/bpf/1622131170-8260-1-git-send-email-alan.maguire@oracle.com/
[4] https://lore.kernel.org/bpf/1610921764-7526-1-git-send-email-alan.maguire@oracle.com/
[5] https://lore.kernel.org/bpf/1610386373-24162-1-git-send-email-alan.maguire@oracle.com/
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

1 files changed, 598 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_dump.c b/tools/testing/selftests/bpf/prog_tests/btf_dump.c
index 1b90e684ff13..0b4ba53b5961 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_dump.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_dump.c
@@ -232,7 +232,576 @@ err_out:
 	btf__free(btf);
 }
 
+#define STRSIZE				4096
+
+static void btf_dump_snprintf(void *ctx, const char *fmt, va_list args)
+{
+	char *s = ctx, new[STRSIZE];
+
+	vsnprintf(new, STRSIZE, fmt, args);
+	if (strlen(s) < STRSIZE)
+		strncat(s, new, STRSIZE - strlen(s) - 1);
+}
+
+static int btf_dump_data(struct btf *btf, struct btf_dump *d,
+			 char *name, char *prefix, __u64 flags, void *ptr,
+			 size_t ptr_sz, char *str, const char *expected_val)
+{
+	DECLARE_LIBBPF_OPTS(btf_dump_type_data_opts, opts);
+	size_t type_sz;
+	__s32 type_id;
+	int ret = 0;
+
+	if (flags & BTF_F_COMPACT)
+		opts.compact = true;
+	if (flags & BTF_F_NONAME)
+		opts.skip_names = true;
+	if (flags & BTF_F_ZERO)
+		opts.emit_zeroes = true;
+	if (prefix) {
+		ASSERT_STRNEQ(name, prefix, strlen(prefix),
+			      "verify prefix match");
+		name += strlen(prefix) + 1;
+	}
+	type_id = btf__find_by_name(btf, name);
+	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;
+}
+
+#define TEST_BTF_DUMP_DATA(_b, _d, _prefix, _str, _type, _flags,	\
+			   _expected, ...)				\
+	do {								\
+		char __ptrtype[64] = #_type;				\
+		char *_ptrtype = (char *)__ptrtype;			\
+		_type _ptrdata = __VA_ARGS__;				\
+		void *_ptr = &_ptrdata;					\
+									\
+		(void) btf_dump_data(_b, _d, _ptrtype, _prefix, _flags,	\
+				     _ptr, sizeof(_type), _str,		\
+				     _expected);			\
+	} while (0)
+
+/* Use where expected data string matches its stringified declaration */
+#define TEST_BTF_DUMP_DATA_C(_b, _d, _prefix,  _str, _type, _flags,	\
+			     ...)					\
+	TEST_BTF_DUMP_DATA(_b, _d, _prefix, _str, _type, _flags,	\
+			   "(" #_type ")" #__VA_ARGS__,	__VA_ARGS__)
+
+/* overflow test; pass typesize < expected type size, ensure E2BIG returned */
+#define TEST_BTF_DUMP_DATA_OVER(_b, _d, _prefix, _str, _type, _type_sz,	\
+				_expected, ...)				\
+	do {								\
+		char __ptrtype[64] = #_type;				\
+		char *_ptrtype = (char *)__ptrtype;			\
+		_type _ptrdata = __VA_ARGS__;				\
+		void *_ptr = &_ptrdata;					\
+									\
+		(void) btf_dump_data(_b, _d, _ptrtype, _prefix, 0,	\
+				     _ptr, _type_sz, _str, _expected);	\
+	} while (0)
+
+#define TEST_BTF_DUMP_VAR(_b, _d, _prefix, _str, _var, _type, _flags,	\
+			  _expected, ...)				\
+	do {								\
+		_type _ptrdata = __VA_ARGS__;				\
+		void *_ptr = &_ptrdata;					\
+									\
+		(void) btf_dump_data(_b, _d, _var, _prefix, _flags,	\
+				     _ptr, sizeof(_type), _str,		\
+				     _expected);			\
+	} while (0)
+
+static void test_btf_dump_int_data(struct btf *btf, struct btf_dump *d,
+				   char *str)
+{
+	/* simple int */
+	TEST_BTF_DUMP_DATA_C(btf, d, NULL, str, int, BTF_F_COMPACT, 1234);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int, BTF_F_COMPACT | BTF_F_NONAME,
+			   "1234", 1234);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int, 0, "(int)1234", 1234);
+
+	/* zero value should be printed at toplevel */
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int, BTF_F_COMPACT, "(int)0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int, BTF_F_COMPACT | BTF_F_NONAME,
+			   "0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int, BTF_F_COMPACT | BTF_F_ZERO,
+			   "(int)0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int,
+			   BTF_F_COMPACT | BTF_F_NONAME | BTF_F_ZERO,
+			   "0", 0);
+	TEST_BTF_DUMP_DATA_C(btf, d, NULL, str, int, BTF_F_COMPACT, -4567);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int, BTF_F_COMPACT | BTF_F_NONAME,
+			   "-4567", -4567);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, int, 0, "(int)-4567", -4567);
+
+	TEST_BTF_DUMP_DATA_OVER(btf, d, NULL, str, int, sizeof(int)-1, "", 1);
+}
+
+static void test_btf_dump_float_data(struct btf *btf, struct btf_dump *d,
+				     char *str)
+{
+	float t1 = 1.234567;
+	float t2 = -1.234567;
+	float t3 = 0.0;
+	double t4 = 5.678912;
+	double t5 = -5.678912;
+	double t6 = 0.0;
+	long double t7 = 9.876543;
+	long double t8 = -9.876543;
+	long double t9 = 0.0;
+
+	/* since the kernel does not likely have any float types in its BTF, we
+	 * will need to add some of various sizes.
+	 */
+
+	ASSERT_GT(btf__add_float(btf, "test_float", 4), 0, "add float");
+	ASSERT_OK(btf_dump_data(btf, d, "test_float", NULL, 0, &t1, 4, str,
+				"(test_float)1.234567"), "dump float");
+	ASSERT_OK(btf_dump_data(btf, d, "test_float", NULL, 0, &t2, 4, str,
+				"(test_float)-1.234567"), "dump float");
+	ASSERT_OK(btf_dump_data(btf, d, "test_float", NULL, 0, &t3, 4, str,
+				"(test_float)0.000000"), "dump float");
+
+	ASSERT_GT(btf__add_float(btf, "test_double", 8), 0, "add_double");
+	ASSERT_OK(btf_dump_data(btf, d, "test_double", NULL, 0, &t4, 8, str,
+		  "(test_double)5.678912"), "dump double");
+	ASSERT_OK(btf_dump_data(btf, d, "test_double", NULL, 0, &t5, 8, str,
+		  "(test_double)-5.678912"), "dump double");
+	ASSERT_OK(btf_dump_data(btf, d, "test_double", NULL, 0, &t6, 8, str,
+				"(test_double)0.000000"), "dump double");
+
+	ASSERT_GT(btf__add_float(btf, "test_long_double", 16), 0, "add long double");
+	ASSERT_OK(btf_dump_data(btf, d, "test_long_double", NULL, 0, &t7, 16,
+				str, "(test_long_double)9.876543"),
+				"dump long_double");
+	ASSERT_OK(btf_dump_data(btf, d, "test_long_double", NULL, 0, &t8, 16,
+				str, "(test_long_double)-9.876543"),
+				"dump long_double");
+	ASSERT_OK(btf_dump_data(btf, d, "test_long_double", NULL, 0, &t9, 16,
+				str, "(test_long_double)0.000000"),
+				"dump long_double");
+}
+
+static void test_btf_dump_char_data(struct btf *btf, struct btf_dump *d,
+				    char *str)
+{
+	/* simple char */
+	TEST_BTF_DUMP_DATA_C(btf, d, NULL, str, char, BTF_F_COMPACT, 100);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, char, BTF_F_COMPACT | BTF_F_NONAME,
+			   "100", 100);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, char, 0, "(char)100", 100);
+	/* zero value should be printed at toplevel */
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, char, BTF_F_COMPACT,
+			   "(char)0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, char, BTF_F_COMPACT | BTF_F_NONAME,
+			   "0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, char, BTF_F_COMPACT | BTF_F_ZERO,
+			   "(char)0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, char, BTF_F_COMPACT | BTF_F_NONAME | BTF_F_ZERO,
+			   "0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, char, 0, "(char)0", 0);
+
+	TEST_BTF_DUMP_DATA_OVER(btf, d, NULL, str, char, sizeof(char)-1, "", 100);
+}
+
+static void test_btf_dump_typedef_data(struct btf *btf, struct btf_dump *d,
+				       char *str)
+{
+	/* simple typedef */
+	TEST_BTF_DUMP_DATA_C(btf, d, NULL, str, uint64_t, BTF_F_COMPACT, 100);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, u64, BTF_F_COMPACT | BTF_F_NONAME,
+			   "1", 1);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, u64, 0, "(u64)1", 1);
+	/* zero value should be printed at toplevel */
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, u64, BTF_F_COMPACT, "(u64)0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, u64, BTF_F_COMPACT | BTF_F_NONAME,
+			   "0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, u64, BTF_F_COMPACT | BTF_F_ZERO,
+			   "(u64)0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, u64,
+			   BTF_F_COMPACT | BTF_F_NONAME | BTF_F_ZERO,
+			   "0", 0);
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, u64, 0, "(u64)0", 0);
+
+	/* typedef struct */
+	TEST_BTF_DUMP_DATA_C(btf, d, NULL, str, atomic_t, BTF_F_COMPACT,
+			     {.counter = (int)1,});
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t, BTF_F_COMPACT | BTF_F_NONAME,
+			   "{1,}", { .counter = 1 });
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t, 0,
+"(atomic_t){\n"
+"	.counter = (int)1,\n"
+"}",
+			   {.counter = 1,});
+	/* typedef with 0 value should be printed at toplevel */
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t, BTF_F_COMPACT, "(atomic_t){}",
+			   {.counter = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t, BTF_F_COMPACT | BTF_F_NONAME,
+			   "{}", {.counter = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t, 0,
+"(atomic_t){\n"
+"}",
+			   {.counter = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t, BTF_F_COMPACT | BTF_F_ZERO,
+			   "(atomic_t){.counter = (int)0,}",
+			   {.counter = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t,
+			   BTF_F_COMPACT | BTF_F_NONAME | BTF_F_ZERO,
+			   "{0,}", {.counter = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, NULL, str, atomic_t, BTF_F_ZERO,
+"(atomic_t){\n"
+"	.counter = (int)0,\n"
+"}",
+			   { .counter = 0,});
+
+	/* overflow should show type but not value since it overflows */
+	TEST_BTF_DUMP_DATA_OVER(btf, d, NULL, str, atomic_t, sizeof(atomic_t)-1,
+				"(atomic_t){\n", { .counter = 1});
+}
+
+static void test_btf_dump_enum_data(struct btf *btf, struct btf_dump *d,
+				    char *str)
+{
+	/* enum where enum value does (and does not) exist */
+	TEST_BTF_DUMP_DATA_C(btf, d, "enum", str, enum bpf_cmd, BTF_F_COMPACT,
+			     BPF_MAP_CREATE);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd, BTF_F_COMPACT,
+			   "(enum bpf_cmd)BPF_MAP_CREATE", 0);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "BPF_MAP_CREATE",
+			   BPF_MAP_CREATE);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd, 0,
+			   "(enum bpf_cmd)BPF_MAP_CREATE",
+			   BPF_MAP_CREATE);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd,
+			   BTF_F_COMPACT | BTF_F_NONAME | BTF_F_ZERO,
+			   "BPF_MAP_CREATE", 0);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd,
+			   BTF_F_COMPACT | BTF_F_ZERO,
+			   "(enum bpf_cmd)BPF_MAP_CREATE",
+			   BPF_MAP_CREATE);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd,
+			   BTF_F_COMPACT | BTF_F_NONAME | BTF_F_ZERO,
+			   "BPF_MAP_CREATE", BPF_MAP_CREATE);
+	TEST_BTF_DUMP_DATA_C(btf, d, "enum", str, enum bpf_cmd, BTF_F_COMPACT, 2000);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "2000", 2000);
+	TEST_BTF_DUMP_DATA(btf, d, "enum", str, enum bpf_cmd, 0,
+			   "(enum bpf_cmd)2000", 2000);
+
+	TEST_BTF_DUMP_DATA_OVER(btf, d, "enum", str, enum bpf_cmd,
+				sizeof(enum bpf_cmd) - 1, "", BPF_MAP_CREATE);
+}
+
+static void test_btf_dump_struct_data(struct btf *btf, struct btf_dump *d,
+				      char *str)
+{
+	DECLARE_LIBBPF_OPTS(btf_dump_type_data_opts, opts);
+	char zero_data[512] = { };
+	char type_data[512];
+	void *fops = type_data;
+	void *skb = type_data;
+	size_t type_sz;
+	__s32 type_id;
+	char *cmpstr;
+	int ret;
+
+	memset(type_data, 255, sizeof(type_data));
+
+	/* simple struct */
+	TEST_BTF_DUMP_DATA_C(btf, d, "struct", str, struct btf_enum, BTF_F_COMPACT,
+			     {.name_off = (__u32)3,.val = (__s32)-1,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "{3,-1,}",
+			   { .name_off = 3, .val = -1,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum, 0,
+"(struct btf_enum){\n"
+"	.name_off = (__u32)3,\n"
+"	.val = (__s32)-1,\n"
+"}",
+			   { .name_off = 3, .val = -1,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "{-1,}",
+			   { .name_off = 0, .val = -1,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum,
+			   BTF_F_COMPACT | BTF_F_NONAME | BTF_F_ZERO,
+			   "{0,-1,}",
+			   { .name_off = 0, .val = -1,});
+	/* empty struct should be printed */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum, BTF_F_COMPACT,
+			   "(struct btf_enum){}",
+			   { .name_off = 0, .val = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "{}",
+			   { .name_off = 0, .val = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum, 0,
+"(struct btf_enum){\n"
+"}",
+			   { .name_off = 0, .val = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum,
+			   BTF_F_COMPACT | BTF_F_ZERO,
+			   "(struct btf_enum){.name_off = (__u32)0,.val = (__s32)0,}",
+			   { .name_off = 0, .val = 0,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct btf_enum,
+			   BTF_F_ZERO,
+"(struct btf_enum){\n"
+"	.name_off = (__u32)0,\n"
+"	.val = (__s32)0,\n"
+"}",
+			   { .name_off = 0, .val = 0,});
+
+	/* struct with pointers */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct list_head, BTF_F_COMPACT,
+			   "(struct list_head){.next = (struct list_head *)0x1,}",
+			   { .next = (struct list_head *)1 });
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct list_head, 0,
+"(struct list_head){\n"
+"	.next = (struct list_head *)0x1,\n"
+"}",
+			   { .next = (struct list_head *)1 });
+	/* NULL pointer should not be displayed */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct list_head, BTF_F_COMPACT,
+			   "(struct list_head){}",
+			   { .next = (struct list_head *)0 });
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct list_head, 0,
+"(struct list_head){\n"
+"}",
+			   { .next = (struct list_head *)0 });
+
+	/* struct with function pointers */
+	type_id = btf__find_by_name(btf, "file_operations");
+	if (ASSERT_GT(type_id, 0, "find type id")) {
+		type_sz = btf__resolve_size(btf, type_id);
+		str[0] = '\0';
+
+		ret = btf_dump__dump_type_data(d, type_id, fops, type_sz, &opts);
+		ASSERT_EQ(ret, type_sz,
+			  "unexpected return value dumping file_operations");
+		cmpstr =
+"(struct file_operations){\n"
+"	.owner = (struct module *)0xffffffffffffffff,\n"
+"	.llseek = (loff_t (*)(struct file *, loff_t, int))0xffffffffffffffff,";
+
+		ASSERT_STRNEQ(str, cmpstr, strlen(cmpstr), "file_operations");
+	}
+
+	/* struct with char array */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_prog_info, BTF_F_COMPACT,
+			   "(struct bpf_prog_info){.name = (char[16])['f','o','o',],}",
+			   { .name = "foo",});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_prog_info,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "{['f','o','o',],}",
+			   {.name = "foo",});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_prog_info, 0,
+"(struct bpf_prog_info){\n"
+"	.name = (char[16])[\n"
+"		'f',\n"
+"		'o',\n"
+"		'o',\n"
+"	],\n"
+"}",
+			   {.name = "foo",});
+	/* leading null char means do not display string */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_prog_info, BTF_F_COMPACT,
+			   "(struct bpf_prog_info){}",
+			   {.name = {'\0', 'f', 'o', 'o'}});
+	/* handle non-printable characters */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_prog_info, BTF_F_COMPACT,
+			   "(struct bpf_prog_info){.name = (char[16])[1,2,3,],}",
+			   { .name = {1, 2, 3, 0}});
+
+	/* struct with non-char array */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct __sk_buff, BTF_F_COMPACT,
+			   "(struct __sk_buff){.cb = (__u32[5])[1,2,3,4,5,],}",
+			   { .cb = {1, 2, 3, 4, 5,},});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct __sk_buff,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "{[1,2,3,4,5,],}",
+			   { .cb = { 1, 2, 3, 4, 5},});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct __sk_buff, 0,
+"(struct __sk_buff){\n"
+"	.cb = (__u32[5])[\n"
+"		1,\n"
+"		2,\n"
+"		3,\n"
+"		4,\n"
+"		5,\n"
+"	],\n"
+"}",
+			   { .cb = { 1, 2, 3, 4, 5},});
+	/* For non-char, arrays, show non-zero values only */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct __sk_buff, BTF_F_COMPACT,
+			   "(struct __sk_buff){.cb = (__u32[5])[0,0,1,0,0,],}",
+			   { .cb = { 0, 0, 1, 0, 0},});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct __sk_buff, 0,
+"(struct __sk_buff){\n"
+"	.cb = (__u32[5])[\n"
+"		0,\n"
+"		0,\n"
+"		1,\n"
+"		0,\n"
+"		0,\n"
+"	],\n"
+"}",
+			   { .cb = { 0, 0, 1, 0, 0},});
+
+	/* struct with bitfields */
+	TEST_BTF_DUMP_DATA_C(btf, d, "struct", str, struct bpf_insn, BTF_F_COMPACT,
+		{.code = (__u8)1,.dst_reg = (__u8)0x2,.src_reg = (__u8)0x3,.off = (__s16)4,.imm = (__s32)5,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_insn,
+			   BTF_F_COMPACT | BTF_F_NONAME,
+			   "{1,0x2,0x3,4,5,}",
+			   { .code = 1, .dst_reg = 0x2, .src_reg = 0x3, .off = 4,
+			     .imm = 5,});
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_insn, 0,
+"(struct bpf_insn){\n"
+"	.code = (__u8)1,\n"
+"	.dst_reg = (__u8)0x2,\n"
+"	.src_reg = (__u8)0x3,\n"
+"	.off = (__s16)4,\n"
+"	.imm = (__s32)5,\n"
+"}",
+			   {.code = 1, .dst_reg = 2, .src_reg = 3, .off = 4, .imm = 5});
+
+	/* zeroed bitfields should not be displayed */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_insn, BTF_F_COMPACT,
+			   "(struct bpf_insn){.dst_reg = (__u8)0x1,}",
+			   { .code = 0, .dst_reg = 1});
+
+	/* struct with enum bitfield */
+	type_id = btf__find_by_name(btf, "fs_context");
+	if (ASSERT_GT(type_id,  0, "find fs_context")) {
+		type_sz = btf__resolve_size(btf, type_id);
+		str[0] = '\0';
+
+		opts.emit_zeroes = true;
+		ret = btf_dump__dump_type_data(d, type_id, zero_data, type_sz, &opts);
+		ASSERT_EQ(ret, type_sz,
+			  "unexpected return value dumping fs_context");
+
+		ASSERT_NEQ(strstr(str, "FS_CONTEXT_FOR_MOUNT"), NULL,
+				  "bitfield value not present");
+	}
+
+	/* struct with nested anon union */
+	TEST_BTF_DUMP_DATA(btf, d, "struct", str, struct bpf_sock_ops, BTF_F_COMPACT,
+			   "(struct bpf_sock_ops){.op = (__u32)1,(union){.args = (__u32[4])[1,2,3,4,],.reply = (__u32)1,.replylong = (__u32[4])[1,2,3,4,],},}",
+			   { .op = 1, .args = { 1, 2, 3, 4}});
+
+	/* union with nested struct */
+	TEST_BTF_DUMP_DATA(btf, d, "union", str, union bpf_iter_link_info, BTF_F_COMPACT,
+			   "(union bpf_iter_link_info){.map = (struct){.map_fd = (__u32)1,},}",
+			   { .map = { .map_fd = 1 }});
+
+	/* struct skb with nested structs/unions; because type output is so
+	 * complex, we don't do a string comparison, just verify we return
+	 * the type size as the amount of data displayed.
+	 */
+	type_id = btf__find_by_name(btf, "sk_buff");
+	if (ASSERT_GT(type_id, 0, "find struct sk_buff")) {
+		type_sz = btf__resolve_size(btf, type_id);
+		str[0] = '\0';
+
+		ret = btf_dump__dump_type_data(d, type_id, skb, type_sz, &opts);
+		ASSERT_EQ(ret, type_sz,
+			  "unexpected return value dumping sk_buff");
+	}
+
+	/* overflow bpf_sock_ops struct with final element nonzero/zero.
+	 * Regardless of the value of the final field, we don't have all the
+	 * data we need to display it, so we should trigger an overflow.
+	 * In other words oveflow checking should trump "is field zero?"
+	 * checks because if we've overflowed, it shouldn't matter what the
+	 * field is - we can't trust its value so shouldn't display it.
+	 */
+	TEST_BTF_DUMP_DATA_OVER(btf, d, "struct", str, struct bpf_sock_ops,
+				sizeof(struct bpf_sock_ops) - 1,
+				"(struct bpf_sock_ops){\n\t.op = (__u32)1,\n",
+				{ .op = 1, .skb_tcp_flags = 2});
+	TEST_BTF_DUMP_DATA_OVER(btf, d, "struct", str, struct bpf_sock_ops,
+				sizeof(struct bpf_sock_ops) - 1,
+				"(struct bpf_sock_ops){\n\t.op = (__u32)1,\n",
+				{ .op = 1, .skb_tcp_flags = 0});
+}
+
+static void test_btf_dump_var_data(struct btf *btf, struct btf_dump *d,
+				   char *str)
+{
+	TEST_BTF_DUMP_VAR(btf, d, NULL, str, "cpu_number", int, BTF_F_COMPACT,
+			  "int cpu_number = (int)100", 100);
+	TEST_BTF_DUMP_VAR(btf, d, NULL, str, "cpu_profile_flip", int, BTF_F_COMPACT,
+			  "static int cpu_profile_flip = (int)2", 2);
+}
+
+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)
+{
+	DECLARE_LIBBPF_OPTS(btf_dump_type_data_opts, opts);
+	int ret = 0, cmp;
+	size_t secsize;
+	__s32 type_id;
+
+	opts.compact = true;
+
+	type_id = btf__find_by_name(btf, name);
+	if (!ASSERT_GT(type_id, 0, "find type id"))
+		return;
+
+	secsize = btf__resolve_size(btf, type_id);
+	ASSERT_EQ(secsize,  0, "verify section size");
+
+	str[0] = '\0';
+	ret = btf_dump__dump_type_data(d, type_id, data, data_sz, &opts);
+	ASSERT_EQ(ret, 0, "unexpected return value");
+
+	cmp = strcmp(str, expected_val);
+	ASSERT_EQ(cmp, 0, "ensure expected/actual match");
+}
+
+static void test_btf_dump_datasec_data(char *str)
+{
+	struct btf *btf = btf__parse("xdping_kern.o", NULL);
+	struct btf_dump_opts opts = { .ctx = str };
+	char license[4] = "GPL";
+	struct btf_dump *d;
+
+	if (!ASSERT_OK_PTR(btf, "xdping_kern.o BTF not found"))
+		return;
+
+	d = btf_dump__new(btf, NULL, &opts, btf_dump_snprintf);
+	if (!ASSERT_OK_PTR(d, "could not create BTF dump"))
+		return;
+
+	test_btf_datasec(btf, d, str, "license",
+			 "SEC(\"license\") char[4] _license = (char[4])['G','P','L',];",
+			 license, sizeof(license));
+}
+
 void test_btf_dump() {
+	char str[STRSIZE];
+	struct btf_dump_opts opts = { .ctx = str };
+	struct btf_dump *d;
+	struct btf *btf;
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(btf_dump_test_cases); i++) {
@@ -245,4 +814,33 @@ void test_btf_dump() {
 	}
 	if (test__start_subtest("btf_dump: incremental"))
 		test_btf_dump_incremental();
+
+	btf = libbpf_find_kernel_btf();
+	if (!ASSERT_OK_PTR(btf, "no kernel BTF found"))
+		return;
+
+	d = btf_dump__new(btf, NULL, &opts, btf_dump_snprintf);
+	if (!ASSERT_OK_PTR(d, "could not create BTF dump"))
+		return;
+
+	/* Verify type display for various types. */
+	if (test__start_subtest("btf_dump: int_data"))
+		test_btf_dump_int_data(btf, d, str);
+	if (test__start_subtest("btf_dump: float_data"))
+		test_btf_dump_float_data(btf, d, str);
+	if (test__start_subtest("btf_dump: char_data"))
+		test_btf_dump_char_data(btf, d, str);
+	if (test__start_subtest("btf_dump: typedef_data"))
+		test_btf_dump_typedef_data(btf, d, str);
+	if (test__start_subtest("btf_dump: enum_data"))
+		test_btf_dump_enum_data(btf, d, str);
+	if (test__start_subtest("btf_dump: struct_data"))
+		test_btf_dump_struct_data(btf, d, str);
+	if (test__start_subtest("btf_dump: var_data"))
+		test_btf_dump_var_data(btf, d, str);
+	btf_dump__free(d);
+	btf__free(btf);
+
+	if (test__start_subtest("btf_dump: datasec_data"))
+		test_btf_dump_datasec_data(str);
 }