prevent rewriting for array element type

Fix issue iovisor#2352.
Corresponding llvm bug: https://bugs.llvm.org/show_bug.cgi?id=41918.

If the element type is array type, the rewriter may generate code like
  addr = ({ typeof(__u8 [16]) _val; __builtin_memset(&_val, 0, sizeof(_val));
            bpf_probe_read(&_val, sizeof(_val), (u64)&daddr->s6_addr); _val; })
for something like
  addr = daddr->s6_addr;
where s6_addr is an array.

The above code has an issue then as addr is pointing to some data
which is out of scope, which meaning compiler is free to use the space.

Let us disable such transformation until we find a good solution.

Signed-off-by: Yonghong Song <[email protected]>

src/cc/frontends/clang/b_frontend_action.cc

@@ -490,6 +490,10 @@ bool ProbeVisitor::VisitMemberExpr(MemberExpr *E) {
  if (!ProbeChecker(base, ptregs_, track_helpers_).needs_probe())
  return true;
 
+ // If the base is an array, we will skip rewriting. See issue #2352.
+ if (E->getType()->isArrayType())
+ return true;
+
  string rhs = rewriter_.getRewrittenText(expansionRange(SourceRange(rhs_start, GET_ENDLOC(E))));
  string base_type = base->getType()->getPointeeType().getAsString();
  string pre, post;
@@ -509,6 +513,10 @@ bool ProbeVisitor::VisitArraySubscriptExpr(ArraySubscriptExpr *E) {
  if (is_addrof_)
  return true;
 
+ // If the base is an array, we will skip rewriting. See issue #2352.
+ if (E->getType()->isArrayType())
+ return true;
+
  if (!rewriter_.isRewritable(GET_BEGINLOC(E)))
  return true;
 

tools/tcptop.py

@@ -112,10 +112,10 @@ def range_check(string):
 
  } else if (family == AF_INET6) {
  struct ipv6_key_t ipv6_key = {.pid = pid};
- __builtin_memcpy(&ipv6_key.saddr,
- sk->__sk_common.skc_v6_rcv_saddr.in6_u.u6_addr32, sizeof(ipv6_key.saddr));
- __builtin_memcpy(&ipv6_key.daddr,
- sk->__sk_common.skc_v6_daddr.in6_u.u6_addr32, sizeof(ipv6_key.daddr));
+ bpf_probe_read(&ipv6_key.saddr, sizeof(ipv6_key.saddr),
+ &sk->__sk_common.skc_v6_rcv_saddr.in6_u.u6_addr32);
+ bpf_probe_read(&ipv6_key.daddr, sizeof(ipv6_key.daddr),
+ &sk->__sk_common.skc_v6_daddr.in6_u.u6_addr32);
  ipv6_key.lport = sk->__sk_common.skc_num;
  dport = sk->__sk_common.skc_dport;
  ipv6_key.dport = ntohs(dport);
@@ -153,10 +153,10 @@ def range_check(string):
 
  } else if (family == AF_INET6) {
  struct ipv6_key_t ipv6_key = {.pid = pid};
- __builtin_memcpy(&ipv6_key.saddr,
- sk->__sk_common.skc_v6_rcv_saddr.in6_u.u6_addr32, sizeof(ipv6_key.saddr));
- __builtin_memcpy(&ipv6_key.daddr,
- sk->__sk_common.skc_v6_daddr.in6_u.u6_addr32, sizeof(ipv6_key.daddr));
+ bpf_probe_read(&ipv6_key.saddr, sizeof(ipv6_key.saddr),
+ &sk->__sk_common.skc_v6_rcv_saddr.in6_u.u6_addr32);
+ bpf_probe_read(&ipv6_key.daddr, sizeof(ipv6_key.daddr),
+ &sk->__sk_common.skc_v6_daddr.in6_u.u6_addr32);
  ipv6_key.lport = sk->__sk_common.skc_num;
  dport = sk->__sk_common.skc_dport;
  ipv6_key.dport = ntohs(dport);