非阻塞tcp客户端程序集

Question

我正在尝试为交换数据创建一个tcp客户端。客户端应首先发送消息。如果消息正确，并且用户已获得财产授权，系统将回复消息“确认”，确认会话已成功绑定。

    ;; yasm -g dwarf2 -f elf64 -a x86 message.asm -o msg.o
    ;; ld -o msg msg.o
    segment .bss

listen_socket:  resq 1
read_fdset: resb 2  

    segment .data

packet istruc message
    at message.length_mes,          dw  0x2800
        at message.message_id,          dw  0x0100
        at message.scheme_id,           dw  0x0100
        at message.version,     dw  0x0100
        at message.timestamp,           dq  0
        at message.keeepaliveinterval,  dd  0xe8030000
        at message.credentials,         dq  0
        at message.ext,             dw  0
iend

pop_sa istruc sockaddr_in
        at sockaddr_in.sin_family,  dw 2             ; AF_INET
        at sockaddr_in.sin_port,    dw 0x2823        ; port 9000
        at sockaddr_in.sin_addr,    dd 0xf4e8d05b    ; 91.208.232.244
        at sockaddr_in.sin_zero,    dd 0, 0
iend
sockaddr_in_len     equ $ - pop_sa


timeval: ;struct
        tv_sec  dq 0
        tv_usec dq 0

timeout: ;struct
        to_sec  dq 0
        to_usec dq 5000

buffer      times 512 db 0x0

    segment .text
    global _start

_start:

struc message
    .length_mes             resw 1
    .message_id             resw 1
    .scheme_id              resw 1
    .version                resw 1
    .timestamp              resq 1
    .keeepaliveinterval         resd 1
    .credentials            resq 2
    .ext                    resw 1
endstruc

 struc sockaddr_in
    .sin_family resw 1
    .sin_port   resw 1
    .sin_addr   resd 1
    .sin_zero   resb 8
 endstruc

    mov rsi, timeval    ;   struct timespec *tp
    mov rdi, 0      ;   const clockid_t which_clock - CLOCK_REALTIME
    mov rax, 228        ;   SYS_CLOCK_GETTIME
    syscall
    mov r8, qword [tv_sec]
    mov r9, qword [tv_usec]
    imul r8, 1000000000
    sub r8, r9
    mov qword [packet + message.timestamp], r8

    mov rdi, 2      ; AF_INET
    mov rsi, 1      ; SOCK_STREAM
    mov rdx, 6      ; PROTO_TCP
    mov rax, 41     ; SYS_SOCKET
    syscall

    cmp rax, 0
    jl exit
    mov [listen_socket], rax

    xor rdx, rdx
    mov rsi, 3      ;F_GETFL
    mov rdi, [listen_socket]
    mov rax, 72     ;SYS_FCNTL
    syscall         ;return 2

    mov rdx, rax 
    or rdx, 2048
    mov rsi, 4      ;F_SETFL
    mov rdi, [listen_socket]
    mov rax, 72     ;SYS_FCNTL
    syscall         ; return 0

    mov rsi, pop_sa     ;
    mov rdx, sockaddr_in_len    ;
    mov rdi, [listen_socket]
    mov rax, 42     ; SYS_CONNECT
    syscall         ; return -115

    xor r9, r9
    xor r8, r8
    xor r10, r10
    mov rdx, 40
    mov rsi, packet
    mov rdi, [listen_socket]
    mov rax, 44     ; SYS_SENDTO
    syscall         ; return 40 - length message

rec:    

    mov r8, timeout
    mov r10, 0
    mov rdx, 0
    bts [read_fdset], rdi
    mov rsi, read_fdset
    inc rdi
    mov rax, 23     ;SYS_SELECT
    syscall         ; return 1

    xor r9, r9
    xor r8, r8
    xor r10, r10
    mov rdx, 512
    mov rsi, buffer
    mov rdi, [listen_socket]
    mov rax, 45     ; SYS_RECVFROM
    syscall         ; return 0

    cmp rax, 0
    jne exit

     jmp rec

exit:   
    mov rdi, 0
    mov rax, 60     ;   SYS_EXIT
    syscall

recvfrom return 0。代码有什么问题？