pkt rewrite not working

[yonghong-song]

in test2, pkt.rewrite_field is used to rewrite the fields:

state proto::ip {
orig_dip = $ip.dst;
orig_sip = $ip.src;
struct IPKey key = {.dip=orig_dip, .sip=orig_sip};
xlate.lookup(key, xleaf) {};
on_valid(xleaf) {
incr_cksum(@ip.hchecksum, orig_dip, xleaf.xdip);
incr_cksum(@ip.hchecksum, orig_sip, xleaf.xsip);
pkt.rewrite_field($ip.dst, xleaf.xdip);
pkt.rewrite_field($ip.src, xleaf.xsip);
atomic_add(xleaf.xlated_pkts, 1);
}

But actually pkt.rewrite_field is not implemented in bcc.

If you add the following change to bcc,
plumgrid@yhs-plumgrid:~/iovisor/bcc/tests/jit$ git diff
diff --git a/src/cc/codegen_llvm.cc b/src/cc/codegen_llvm.cc
index 6ba9f23..6c7ce28 100644
--- a/src/cc/codegen_llvm.cc
+++ b/src/cc/codegen_llvm.cc
@@ -741,6 +741,8 @@ StatusTuple CodegenLLVM::visit_method_call_expr_node(MethodCallExprNode *n) {
TRY2(emit_table_update(n));
} else if (n->id_->sub_name_ == "delete") {
TRY2(emit_table_delete(n));

• } else {

•  return mkstatus_(n, "unsupported");
  

  }
  } else if (n->id_->name_ == "atomic_add") {
  TRY2(emit_atomic_add(n));

The compilation will fail. Basically, for pkt.rewrite_field, the compiler assumes "pkt" is a map name.
This is not correct.
In codegen_llvm.cc,

StatusTuple CodegenLLVM::visit_packet_expr_node(PacketExprNode *n) {
.....
}

it looks like if PacketExprNode ($ip.dst) is the lvalue of assignment expression,
packet rewrite will be translated. Currently,

assign_expr
: dotted_ident TEQUAL expr
{ $$ = new AssignExprNode(IdentExprNode::Ptr($1), ExprNode::Ptr($3));
parser.set_loc($$, @$); }
| dotted_ident bitop TEQUAL expr
{ $$ = new AssignExprNode(IdentExprNode::Ptr($1), ExprNode::Ptr($4)); $$->bitop_ = BitopExprNode::Ptr($2);
parser.set_loc($$, @$); }
;

It does not support assign lvalue as a packet expr node at this point.

In codegen_llvm.h, there are a lot un-implemented functions like
STATUS_RETURN emit_packet_push_header(MethodCallExprNode* n);
STATUS_RETURN emit_packet_pop_header(MethodCallExprNode* n);
STATUS_RETURN emit_packet_push_vlan(MethodCallExprNode* n);
STATUS_RETURN emit_packet_pop_vlan(MethodCallExprNode* n);
STATUS_RETURN emit_packet_rewrite_field(MethodCallExprNode* n);
.....

Assign to Brenden who can make proper decision about how to support pkt rewrite.