Fix recursive loop in parsing pointer to self struct

Issue occurs in the description visitor class, when the struct used in a
map key is a pointer to self, as in:

struct node;
struct node {
  struct node *next;
};

Avoid this in the desc by using "unsigned long long" for all pointers.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

src/cc/frontends/clang/b_frontend_action.cc

@@ -64,7 +64,10 @@ bool BMapDeclVisitor::VisitRecordDecl(RecordDecl *D) {
   result_ += "\", [";
   for (auto F : D->getDefinition()->fields()) {
     result_ += "[";
-    TraverseDecl(F);
+    if (F->getType()->isPointerType())
+      result_ += "\"unsigned long long\"";
+    else
+      TraverseDecl(F);
     if (F->isBitField())
       result_ += ", " + to_string(F->getBitWidthValue(C));
     result_ += "], ";

tests/cc/test_clang.py

@@ -65,5 +65,26 @@ int foo(void *ctx) {
         self.assertEqual(l.s.a, 5)
         self.assertEqual(l.s.b, 6)
 
+    def test_iosnoop(self):
+        text = """
+#include <linux/blkdev.h>
+#include <uapi/linux/ptrace.h>
+
+struct key_t {
+    struct request *req;
+};
+
+BPF_TABLE("hash", struct key_t, u64, start, 1024);
+int do_request(struct pt_regs *ctx, struct request *req) {
+    struct key_t key = {};
+
+    bpf_trace_printk("traced start %d\\n", req->__data_len);
+
+    return 0;
+}
+"""
+        b = BPF(text=text, debug=0)
+        fn = b.load_func("do_request", BPF.KPROBE)
+
 if __name__ == "__main__":
     main()