Brian Davidson <davidson.brian@xxxxxxxxx> wrote:
> Using 'ip6 dscp' in a map lookup does not give expected results. It
> seems to always match the zero value (cs0). It appears in the first
> rule that the byteorder is not being converted between the two bitwise
> operations, which is what happens when using ip6 dscp directly in the
> second rule.
>
> # nft -f - <<EOF
> add table ip6 t
> add chain ip6 t c
> add map ip6 t mapv6 { typeof ip6 dscp : meta mark; }
> EOF
>
> # nft -d netlink add rule ip6 t c meta mark set ip6 dscp map @mapv6
> ip6 t c
> [ payload load 2b @ network header + 0 => reg 1 ]
> [ bitwise reg 1 = ( reg 1 & 0x0000c00f ) ^ 0x00000000 ]
> [ bitwise reg 1 = ( reg 1 >> 0x00000006 ) ]
> [ lookup reg 1 set mapv6 dreg 1 ]
> [ meta set mark with reg 1 ]
>
> # nft -d netlink add rule ip6 t c meta mark set ip6 dscp
> ip6 t c
> [ payload load 2b @ network header + 0 => reg 1 ]
> [ bitwise reg 1 = ( reg 1 & 0x0000c00f ) ^ 0x00000000 ]
> [ byteorder reg 1 = ntoh(reg 1, 2, 2) ]
> [ bitwise reg 1 = ( reg 1 >> 0x00000006 ) ]
> [ meta set mark with reg 1 ]
Uhm. Pablo, any idea why the byte-swap-or-not logic depends
on something *other* than if the mask length is > 8 bit or not?
diff --git a/src/evaluate.c b/src/evaluate.c
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -545,7 +545,7 @@ static void expr_evaluate_bits(struct eval_ctx *ctx, struct expr **exprp)
and->len = masklen;
if (shift) {
- if (ctx->stmt_len > 0 && div_round_up(masklen, BITS_PER_BYTE) > 1) {
+ if (masklen > BITS_PER_BYTE) {
int op = byteorder_conversion_op(expr, BYTEORDER_HOST_ENDIAN);
and = unary_expr_alloc(&expr->location, op, and);
and->len = masklen;
