一、socket()......
推荐链接 见证又一......
一、socket()库函数到系统调用,再到内核
1、Linux运行的C库是glibc;
2、socket()调用如下:
1) socket()->__socket():glibc-2.3.6/sysdept/generic/socket.c (weak_alias(name1, name2))
2) __socket():glibc-2.3.6/sysdept/unix/sysv/linux/i386/socket.S
3) ENTER_KERNEL:
C代码
movl $SYS_ify(socketcall), %eax /* System call number in %eax. */
/* Use ## so `socket' is a separate token that might be #define'd. */
movl $P(SOCKOP_,socket), %ebx /* Subcode is first arg to syscall. */
lea 4(%esp), %ecx /* Address of args is 2nd arg. */
/* Do the system call trap. */
ENTER_KERNEL
movl $SYS_ify(socketcall), %eax /* System call number in %eax. */
/* Use ## so `socket' is a separate token that might be #define'd. */
movl $P(SOCKOP_,socket), %ebx /* Subcode is first arg to syscall. */
lea 4(%esp), %ecx /* Address of args is 2nd arg. */
/* Do the system call trap. */
ENTER_KERNEL这里,
SYS_ify宏定义为:glibc-2.3.6/sysdept/unix/sysv/linux/i386/Sysdept.h
C代码
#define SYS_ify(syscall_name) __NR_##syscall_name;
#define SYS_ify(syscall_name) __NR_##syscall_name;P宏定义为:glibc-2.3.6/sysdept/unix/sysv/linux/i386/socket.S
C代码
#define P(a, b) P2(a, b)
#define P2(a, b) a##b
#define P(a, b) P2(a, b)
#define P2(a, b) a##b其中,##为连接符号;
C代码
#define __NR_socketcall 102
#define __NR_socketcall 102SOCKOP_socket:glibc-2.3.6/sysdept/unix/sysv/linux/Socketcall.h
C代码
#define SOCKOP_socket 1
#define SOCKOP_socket 1因此,中断号是102,子中断号是1;
4) int 0x80进入内核:glibc-2.3.6/sysdept/unix/sysv/linux/i386/Sysdept.h:
C代码
# define ENTER_KERNEL int $0x80
# define ENTER_KERNEL int $0x805) system_call中断入口:kernel/arch/x86/kernel/entry_32.S:
C代码
syscall_call:
call *sys_call_table(,%eax,4)
syscall_call:
call *sys_call_table(,%eax,4)
6) 进入中断向量表:kernel/arch/x86/kernel/syscall_table_32.S中的102号中断:
C代码
.long sys_socketcall
.long sys_socketcall
7) 进入sys_socketcall()函数,根据子中断号以决定走哪个分支:kernel/net/Socket.c:
C代码
switch (call) {
case SYS_SOCKET:
break;
case SYS_BIND:
…...
switch (call) {
case SYS_SOCKET:
break;
case SYS_BIND:
…...
二、socket其他库函数(bind, accept...)
1、对于其他库函数,都是引用上面提到的glibc-2.3.6/sysdept/unix/sysv/linux/i386/socket.S来实现的,如
a) bind.S:
C代码
#define socket bind
#define NARGS 3
#define NO_WEAK_ALIAS 1
#include <socket.S>
weak_alias (bind, __bind)
#define socket bind
#define NARGS 3
#define NO_WEAK_ALIAS 1
#include <socket.S>
weak_alias (bind, __bind)b) accept.S:
C代码
#define socket accept
#define __socket __libc_accept
#define NARGS 3
#define NEED_CANCELLATION
#include <socket.S>
libc_hidden_def (accept)
#define socket accept
#define __socket __libc_accept
#define NARGS 3
#define NEED_CANCELLATION
#include <socket.S>
libc_hidden_def (accept)在各个库函数调用中,设置不同的参数,如socket(用于设置子中断号), NARGS(系统调用的参数个数)等,最终由
C代码
movl $P(SOCKOP_,socket), %ebx /* Subcode is first arg to syscall. */
movl $P(SOCKOP_,socket), %ebx /* Subcode is first arg to syscall. */来生成最终的子中断号,然后放到ebx寄存器中;
2、所有socket系统调用的子中断号参见glibc-2.3.6/sysdept/unix/sysv/linux/Socketcall.h:
C代码
#define SOCKOP_socket 1
#define SOCKOP_bind 2
#define SOCKOP_connect 3
#define SOCKOP_listen 4
#define SOCKOP_accept 5
#define SOCKOP_getsockname 6
#define SOCKOP_getpeername 7
#define SOCKOP_socketpair 8
#define SOCKOP_send 9
#define SOCKOP_recv 10
#define SOCKOP_sendto 11
#define SOCKOP_recvfrom 12
#define SOCKOP_shutdown 13
#define SOCKOP_setsockopt 14
#define SOCKOP_getsockopt 15
#define SOCKOP_sendmsg 16
#define SOCKOP_recvmsg 17
#define SOCKOP_socket 1
#define SOCKOP_bind 2
#define SOCKOP_connect 3
#define SOCKOP_listen 4
#define SOCKOP_accept 5
#define SOCKOP_getsockname 6
#define SOCKOP_getpeername 7
#define SOCKOP_socketpair 8
#define SOCKOP_send 9
#define SOCKOP_recv 10
#define SOCKOP_sendto 11
#define SOCKOP_recvfrom 12
#define SOCKOP_shutdown 13
#define SOCKOP_setsockopt 14
#define SOCKOP_getsockopt 15
#define SOCKOP_sendmsg 16
#define SOCKOP_recvmsg 17
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