Subject: Re: [linux-next:master 5639/6402] net/ipv4/tcp_output.c:188:3: warning: result of comparison of constant -1 with expression of type 'u8' (aka 'unsigned char') is always false On Wed, May 20, 2020 at 12:09:47AM +0800, kbuild test robot wrote: > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master > head: dfd71d381f7e1aa118e0368774aa05f5c4a48870 > commit: 2b195850128f5bafde177b12489d9fa27962cc1e [5639/6402] tcp: add tp- >dup_ack_counter > config: x86_64-randconfig-r012-20200519 (attached as .config) > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 135b877874fae96b4372c8a3fbfaa8ff44ff86e3) > reproduce: > wget https://raw.githubusercontent.com/intel/lkp- tests/master/sbin/make.cross -O ~/bin/make.cross > chmod +x ~/bin/make.cross > # install x86_64 cross compiling tool for clang build > # apt-get install binutils-x86-64-linux-gnu > git checkout 2b195850128f5bafde177b12489d9fa27962cc1e > # save the attached .config to linux build tree > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 > > If you fix the issue, kindly add following tag as appropriate > Reported-by: kbuild test robot <lkp(a)intel.com&gt; > > All warnings (new ones prefixed by >>, old ones prefixed by <<): > > >> net/ipv4/tcp_output.c:188:3: warning: result of comparison of constant -1 with expression of type 'u8' (aka 'unsigned char') is always false [-Wtautological- constant-out-of-range-compare] > NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED, > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > include/net/ip.h:293:41: note: expanded from macro 'NET_ADD_STATS' > #define NET_ADD_STATS(net, field, adnd) SNMP_ADD_STATS((net)- >mib.net_statistics, field, adnd) > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > include/net/snmp.h:143:4: note: expanded from macro 'SNMP_ADD_STATS' > this_cpu_add(mib->mibs[field], addend) > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > include/linux/percpu-defs.h:509:33: note: expanded from macro 'this_cpu_add' > #define this_cpu_add(pcp, val) __pcpu_size_call(this_cpu_add_, pcp, val) > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all) > <scratch space>:292:1: note: expanded from here > this_cpu_add_8 > ^ > arch/x86/include/asm/percpu.h:492:35: note: expanded from macro 'this_cpu_add_8' > #define this_cpu_add_8(pcp, val) percpu_add_op(volatile, (pcp), val) > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > arch/x86/include/asm/percpu.h:131:31: note: expanded from macro 'percpu_add_op' > ((val) == 1 || (val) == -1)) ? ~~~~~ ^ ~~ > 1 warning generated. This warning is supposed to be disabled under a regular build, is W=1 being turned on (see scripts/Makefile.extrawarn)?

Cheers, Nathan