Example of macOS sendmsg_x

sendmsg_x.c

// ./usr/include/sys/syscall.h:521:#define	SYS_sendmsg_x      481
// ./kern/syscalls.master:751:480	AUE_NULL	ALL	{ user_ssize_t recvmsg_x(int s, struct msghdr_x *msgp, u_int cnt, int flags); }
#include <sys/syscall.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

// from bsd/sys/socket.h
struct msghdr_x {
    void *msg_name;	/* optional address */
    socklen_t msg_namelen;	/* size of address */
    struct iovec *msg_iov;	/* scatter/gather array */
    int msg_iovlen;	/* # elements in msg_iov */
    void *msg_control;	/* ancillary data, see below */
    socklen_t msg_controllen;	/* ancillary data buffer len */
    int msg_flags;	/* flags on received message */
    size_t msg_datalen;	/* byte length of buffer in msg_iov */
};

int main(int argc, char **argv) {
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    struct sockaddr_in saddr = { };
    saddr.sin_family = AF_INET;
    saddr.sin_port = htons(4433);
    memset(&saddr.sin_addr, 0x08080808, 4); // 8.8.8.8

    int ret = connect(sockfd, (struct sockaddr *)&saddr, sizeof(saddr));

    if (ret < 0) {
        printf("Failed to connect.\n");
        return 1;
    }

    char *buf0 = "AAAAAAAAA";
    char *buf1 = "BBBBBBBBB";

    struct iovec msg_vec0 = { };
    struct iovec msg_vec1 = { };

    msg_vec0.iov_base = buf0;
    msg_vec0.iov_len = strlen(buf0);

    msg_vec1.iov_base = buf1;
    msg_vec1.iov_len = strlen(buf1);

    struct msghdr_x xmsghdr[2] = { };

    xmsghdr[0].msg_iov = &msg_vec0;
    xmsghdr[0].msg_iovlen = 1;
    xmsghdr[1].msg_iov = &msg_vec1;
    xmsghdr[1].msg_iovlen = 1;;

// ./kern/syscalls.master:751:480	AUE_NULL	ALL	{ user_ssize_t recvmsg_x(int s, struct msghdr_x *msgp, u_int cnt, int flags); }
    ret = syscall(SYS_sendmsg_x, sockfd, &xmsghdr, 2, 0);
    printf("ret: %d\n", ret);

    return 0;
}