/opt/grpc-1.2.0 # make -j4make
/opt/grpc-1.2.0 # make
[MAKE]    Generating cache.mk
[C]       Compiling src/core/lib/iomgr/tcp_posix.c
src/core/lib/iomgr/tcp_posix.c: In function 'tcp_do_read':
src/core/lib/iomgr/tcp_posix.c:219:20: error: conversion to 'int' from 'msg_iovlen_type {aka unsigned int}' may change the sign of the result [-Werror=sign-conversion]
   msg.msg_iovlen = tcp->iov_size;
                    ^~~
src/core/lib/iomgr/tcp_posix.c: In function 'tcp_flush':
src/core/lib/iomgr/tcp_posix.c:364:22: error: conversion to 'int' from 'msg_iovlen_type {aka unsigned int}' may change the sign of the result [-Werror=sign-conversion]
     msg.msg_iovlen = iov_size;
                      ^~~~~~~~
cc1: all warnings being treated as errors
make: *** [Makefile:2366: /opt/grpc-1.2.0/objs/opt/src/core/lib/iomgr/tcp_posix.o] Error 1