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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: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211013160902.428340-3-iii@linux.ibm.com
This commit is contained in:
Ilya Leoshkevich 2021-10-13 18:09:00 +02:00 committed by Andrii Nakryiko
parent b16d12f390
commit c9e982b879
1 changed files with 7 additions and 8 deletions
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15
tools/lib/bpf/btf_dump.c
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@ -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