Commit c9e982b8 authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Andrii Nakryiko
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libbpf: Fix dumping big-endian bitfields 



On big-endian arches not only bytes, but also bits are numbered in
reverse order (see e.g. S/390 ELF ABI Supplement, but this is also true
for other big-endian arches as well).

Signed-off-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211013160902.428340-3-iii@linux.ibm.com
parent b16d12f3

tools/lib/bpf/btf_dump.c

+7 −8
Original line number Diff line number Diff line
@@ -1562,29 +1562,28 @@ static int btf_dump_get_bitfield_value(struct btf_dump *d, 
				       __u64 *value)

{

	__u16 left_shift_bits, right_shift_bits;

	__u8 nr_copy_bits, nr_copy_bytes;

	const __u8 *bytes = data;

	int sz = t->size;

	__u8 nr_copy_bits;

	__u64 num = 0;

	int i;



	/* Maximum supported bitfield size is 64 bits */

	if (sz > 8) {

		pr_warn("unexpected bitfield size %d\n", sz);

	if (t->size > 8) {

		pr_warn("unexpected bitfield size %d\n", t->size);

		return -EINVAL;

	}



	/* Bitfield value retrieval is done in two steps; first relevant bytes are

	 * stored in num, then we left/right shift num to eliminate irrelevant bits.

	 */

	nr_copy_bits = bit_sz + bits_offset;

	nr_copy_bytes = t->size;

#if __BYTE_ORDER == __LITTLE_ENDIAN

	for (i = nr_copy_bytes - 1; i >= 0; i--)

	for (i = t->size - 1; i >= 0; i--)

		num = num * 256 + bytes[i];

	nr_copy_bits = bit_sz + bits_offset;

#elif __BYTE_ORDER == __BIG_ENDIAN

	for (i = 0; i < nr_copy_bytes; i++)

	for (i = 0; i < t->size; i++)

		num = num * 256 + bytes[i];

	nr_copy_bits = t->size * 8 - bits_offset;

#else

# error "Unrecognized __BYTE_ORDER__"

#endif