bpf: pass the correct accumulator state to the next level

We were mistakenly passing the wrong accumulator state (the state at
the start of the instruction block, not at the end) which was causing
us to generate unnecessary load instructions.

Signed-off-by: Paul Moore <paul@paul-moore.com>

src/gen_bpf.c

@@ -854,6 +854,13 @@ static struct bpf_blk *_gen_bpf_node(struct bpf_state *state,
 			goto node_failure;
 	}
 
+	/* set the accumulator state at the end of the block */
+	/* NOTE: the accumulator end state is very critical when we are
+	 *       assembling the final state; we assume that however we leave
+	 *       this instruction block the accumulator state is represented
+	 *       by blk->acc_end, it must be kept correct */
+	blk->acc_end = *a_state;
+
 	/* check the accumulator against the datum */
 	switch (node->op) {
 	case SCMP_CMP_MASKED_EQ:
@@ -898,7 +905,6 @@ static struct bpf_blk *_gen_bpf_node(struct bpf_state *state,
 		goto node_failure;
 
 	blk->node = node;
-	blk->acc_end = *a_state;
 	return blk;
 
 node_failure:
@@ -953,7 +959,7 @@ static struct bpf_blk *_gen_bpf_chain_lvl_res(struct bpf_state *state,
 		case TGT_PTR_DB:
 			node = (struct db_arg_chain_tree *)i_iter->jt.tgt.db;
 			b_new = _gen_bpf_chain(state, sys, node,
-					       nxt_jump, &blk->acc_start);
+					       nxt_jump, &blk->acc_end);
 			if (b_new == NULL)
 				return NULL;
 			i_iter->jt = _BPF_JMP_HSH(b_new->hash);
@@ -979,7 +985,7 @@ static struct bpf_blk *_gen_bpf_chain_lvl_res(struct bpf_state *state,
 		case TGT_PTR_DB:
 			node = (struct db_arg_chain_tree *)i_iter->jf.tgt.db;
 			b_new = _gen_bpf_chain(state, sys, node,
-					       nxt_jump, &blk->acc_start);
+					       nxt_jump, &blk->acc_end);
 			if (b_new == NULL)
 				return NULL;
 			i_iter->jf = _BPF_JMP_HSH(b_new->hash);