[Bug tapsets/18711] Pass 4 failure on RHEL7 for examples netfilter_summary and netfilter_drop

["mcermak at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18711

--- Comment #2 from Martin Cermak <mcermak at redhat dot com> ---
I tested that with 3.10.0-229.el7, STAPCONF_NETFILTER_V313 is defined within
tapset-netfilter.cxx and respective #ifdef branch is effective. Looking at
buildrun.cxx, this is probably because autoconf-netfilter.c compiles fine. I am
not sure how exactly is autoconf compiling it yet. But at the end of the day
netfilter_drop.stp works fine.

With 3.10.0-300.el7, none of STAPCONF_NETFILTER_V41, STAPCONF_NETFILTER_V313 is
defined and thus "LINUX_VERSION_CODE > KERNEL_VERSION(2,6,22)" condition wins.
What fixes the issue for me is following update. Yes, it's not a "fix" but a
dirty hack that makes it work (and probably breaks it all elsewhere):

=======
diff --git a/tapset-netfilter.cxx b/tapset-netfilter.cxx
index 12df8d7..b149be1 100644
--- a/tapset-netfilter.cxx
+++ b/tapset-netfilter.cxx
@@ -279,8 +279,10 @@ netfilter_derived_probe_group::emit_module_decls
(systemtap_session& s)

       s.op->newline() << "#elif LINUX_VERSION_CODE > KERNEL_VERSION(2,6,22)";

-      s.op->newline() << "(unsigned int nf_hooknum, struct sk_buff *nf_skb,
const struct net_device *nf_in, const struct net_device *nf_out, int
(*nf_okfn)(struct sk_buff *))";
+//      s.op->newline() << "(unsigned int nf_hooknum, struct sk_buff *nf_skb,
const struct net_device *nf_in, const struct net_device *nf_out, int
(*nf_okfn)(struct sk_buff *))";
+      s.op->newline() << "(const struct nf_hook_ops *nf_ops, struct sk_buff
*nf_skb, const struct net_device *nf_in, const struct net_device *nf_out, const
struct nf_hook_state *nf_state)";
       s.op->newline() << "{";
+      s.op->newline() << "unsigned int nf_hooknum = nf_ops->hooknum;";

       s.op->newline() << "#else";
=======

I found this by repetitive commenting out various pieces of the code, building
it and running. I wonder how I could put some _stp_warn()-ish debugging outputs
there.

However, my nose says that this will probably require new autoconf .c test
program, adding it to buildrun.cxx where some new STAPCONF_NETFILTER_foo macro
will get defined and add a respective new branch to tapset-netfilter.cxx?
__GENKSYMS__ is still a bit mysterious to me, but I can imagine this being
covered by an autoconf test.

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