Hi Sami, FYI, the error/warning still remains. tree: https://android.googlesource.com/kernel/common android-4.19-stable head: 30857805a68e99b411410f3c45431b008067abf7 commit: f0723e3bd598d138a44d342818032e89ed2e11a5 [11044/28192] ANDROID: netfilter: nf_nat: remove static from nf_nat_ipv4_fn config: x86_64-rhel-8.3-func compiler: gcc-11 (Debian 11.3.0-8) 11.3.0 reproduce (this is a W=1 build): git remote add android-common https://android.googlesource.com/kernel/common git fetch --no-tags android-common android-4.19-stable git checkout f0723e3bd598d138a44d342818032e89ed2e11a5 # save the config file mkdir build_dir && cp config build_dir/.config make W=1 O=build_dir ARCH=x86_64 olddefconfig make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash drivers/rtc/ drivers/usb/host/ net/ipv4/netfilter/ If you fix the issue, kindly add following tag where applicable | Reported-by: kernel test robot All warnings (new ones prefixed by >>): >> net/ipv4/netfilter/nf_nat_l3proto_ipv4.c:245:1: warning: no previous prototype for 'nf_nat_ipv4_fn' [-Wmissing-prototypes] 245 | nf_nat_ipv4_fn(void *priv, struct sk_buff *skb, | ^~~~~~~~~~~~~~ vim +/nf_nat_ipv4_fn +245 net/ipv4/netfilter/nf_nat_l3proto_ipv4.c c7232c9979cba6 Patrick McHardy 2012-08-26 243 f0723e3bd598d1 Sami Tolvanen 2019-12-06 244 unsigned int 06198b34a3e09e Eric W. Biederman 2015-09-18 @245 nf_nat_ipv4_fn(void *priv, struct sk_buff *skb, 9971a514ed2697 Florian Westphal 2018-05-14 246 const struct nf_hook_state *state) 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 247 { 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 248 struct nf_conn *ct; 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 249 enum ip_conntrack_info ctinfo; 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 250 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 251 ct = nf_ct_get(skb, &ctinfo); 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 252 if (!ct) 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 253 return NF_ACCEPT; 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 254 1f55236bd8dde6 Florian Westphal 2018-05-14 255 if (ctinfo == IP_CT_RELATED || ctinfo == IP_CT_RELATED_REPLY) { 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 256 if (ip_hdr(skb)->protocol == IPPROTO_ICMP) { 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 257 if (!nf_nat_icmp_reply_translation(skb, ct, ctinfo, 082a758f042e1c Eric W. Biederman 2015-09-18 258 state->hook)) 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 259 return NF_DROP; 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 260 else 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 261 return NF_ACCEPT; 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 262 } 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 263 } 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 264 9971a514ed2697 Florian Westphal 2018-05-14 265 return nf_nat_inet_fn(priv, skb, state); 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 266 } 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 267 EXPORT_SYMBOL_GPL(nf_nat_ipv4_fn); 30766f4c2d60dd Pablo Neira Ayuso 2014-08-05 268 :::::: The code at line 245 was first introduced by commit :::::: 06198b34a3e09e06d9aecaa3727e0d37206cea77 netfilter: Pass priv instead of nf_hook_ops to netfilter hooks :::::: TO: Eric W. Biederman :::::: CC: Pablo Neira Ayuso -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests