Fix issue with structure member dereferences

Currently, if a structure member is assigned an external pointer
(pointer to kernel address), the pointer to the structure is marked
as external instead of the structure member. This issue affects all
uses of structures with pointers to external addresses. This commit
fixes it by marking the structure member as external.

src/cc/frontends/clang/b_frontend_action.cc

@@ -105,6 +105,13 @@ class ProbeChecker : public RecursiveASTVisitor<ProbeChecker> {
     }
     return false;
   }
+  bool VisitMemberExpr(MemberExpr *M) {
+    if (ptregs_.find(M->getMemberDecl()) != ptregs_.end()) {
+      needs_probe_ = true;
+      return false;
+    }
+    return true;
+  }
   bool VisitDeclRefExpr(DeclRefExpr *E) {
     if (ptregs_.find(E->getDecl()) != ptregs_.end())
       needs_probe_ = true;
@@ -126,6 +133,10 @@ class ProbeSetter : public RecursiveASTVisitor<ProbeSetter> {
     ptregs_->insert(E->getDecl());
     return true;
   }
+  bool VisitMemberExpr(MemberExpr *M) {
+    ptregs_->insert(M->getMemberDecl());
+    return false;
+  }
  private:
   set<Decl *> *ptregs_;
 };
@@ -231,11 +242,6 @@ bool ProbeVisitor::VisitUnaryOperator(UnaryOperator *E) {
 bool ProbeVisitor::VisitMemberExpr(MemberExpr *E) {
   if (memb_visited_.find(E) != memb_visited_.end()) return true;
 
-  // Checks to see if the expression references something that needs to be run
-  // through bpf_probe_read.
-  if (!ProbeChecker(E, ptregs_).needs_probe())
-    return true;
-
   Expr *base;
   SourceLocation rhs_start, member;
   bool found = false;
@@ -255,6 +261,12 @@ bool ProbeVisitor::VisitMemberExpr(MemberExpr *E) {
     error(base->getLocEnd(), "internal error: MemberLoc is invalid while preparing probe rewrite");
     return false;
   }
+
+  // Checks to see if the expression references something that needs to be run
+  // through bpf_probe_read.
+  if (!ProbeChecker(base, ptregs_).needs_probe())
+    return true;
+
   string rhs = rewriter_.getRewrittenText(expansionRange(SourceRange(rhs_start, E->getLocEnd())));
   string base_type = base->getType()->getPointeeType().getAsString();
   string pre, post;