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

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 5ef42f0abed1285476d18a2e4f2b3378d3adad8c..679bf34e3f47f075ef6320e54deaefd347bac016 100644 (file)
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -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