Fix bpf_dins_pkt rewrite in BinaryOperator

Binary operator expressions where the left hand-side expression is a
reference to the packet are replaced by a call to the bpf_dins_pkt
helper. When replacing text, the Clang Rewriter tries to maintain a
list of offsets between the original and the new position of tokens.

Replacing the whole binary operator expression with the call to
bpf_dins_pkt confuses the Rewriter and it is unable to track the new
position of the right hand-side expression. Rewriting the binary
operator expression in two times without rewriting the right
hand-side expression itself solves the issue.

src/cc/frontends/clang/b_frontend_action.cc

@@ -521,7 +521,6 @@ bool BTypeVisitor::VisitBinaryOperator(BinaryOperator *E) {
   if (!E->isAssignmentOp())
     return true;
   Expr *LHS = E->getLHS()->IgnoreImplicit();
-  Expr *RHS = E->getRHS()->IgnoreImplicit();
   if (MemberExpr *Memb = dyn_cast<MemberExpr>(LHS)) {
     if (DeclRefExpr *Base = dyn_cast<DeclRefExpr>(Memb->getBase()->IgnoreImplicit())) {
       if (DeprecatedAttr *A = Base->getDecl()->getAttr<DeprecatedAttr>()) {
@@ -534,10 +533,10 @@ bool BTypeVisitor::VisitBinaryOperator(BinaryOperator *E) {
             uint64_t ofs = C.getFieldOffset(F);
             uint64_t sz = F->isBitField() ? F->getBitWidthValue(C) : C.getTypeSize(F->getType());
             string base = rewriter_.getRewrittenText(expansionRange(Base->getSourceRange()));
-            string rhs = rewriter_.getRewrittenText(expansionRange(RHS->getSourceRange()));
             string text = "bpf_dins_pkt(" + fn_args_[0]->getName().str() + ", (u64)" + base + "+" + to_string(ofs >> 3)
-                + ", " + to_string(ofs & 0x7) + ", " + to_string(sz) + ", " + rhs + ")";
-            rewriter_.ReplaceText(expansionRange(E->getSourceRange()), text);
+                + ", " + to_string(ofs & 0x7) + ", " + to_string(sz) + ",";
+            rewriter_.ReplaceText(expansionRange(SourceRange(E->getLocStart(), E->getOperatorLoc())), text);
+            rewriter_.InsertTextAfterToken(E->getLocEnd(), ")");
           }
         }
       }

tests/python/test_clang.py

@@ -392,5 +392,24 @@ int process(struct xdp_md *ctx) {
         t = b["act"]
         self.assertEquals(len(t), 32);
 
+    def test_bpf_dins_pkt_rewrite(self):
+        text = """
+#include <bcc/proto.h>
+int dns_test(struct __sk_buff *skb) {
+    u8 *cursor = 0;
+    struct ethernet_t *ethernet = cursor_advance(cursor, sizeof(*ethernet));
+    if(ethernet->type == ETH_P_IP) {
+        struct ip_t *ip = cursor_advance(cursor, sizeof(*ip));
+        ip->src = ip->dst;
+        return 0;
+    }
+    return -1;
+}
+        """
+        b = BPF(text=text)
+
 if __name__ == "__main__":
     main()
+
+
+