用uname -a可以看到相应的信息
系统调用一般是定义在usr/include/asm/unistd.h文件中
在64的系统中文件名应该是unistd_64.h,unistd_64.h包含了所有系统嗲用.头几行是这样的:
#ifndef _ASM_X86_UNISTD_64_H
#define _ASM_X86_UNISTD_64_H 1
#define __NR_read 0
#define __NR_write 1
#define __NR_open 2
#define __NR_close 3
#define __NR_stat 4
#define __NR_fstat 5
#define __NR_lstat 6
#define __NR_poll 7
#define __NR_lseek 8
#define __NR_mmap 9
#define __NR_mprotect 10
#define __NR_munmap 11
#define __NR_brk 12
#define __NR_rt_sigaction 13
#define __NR_rt_sigprocmask 14
系统调用的前缀都是__NR_,后面跟着的就是系统调用号.
# man 2 exit.
2 指的是man pages的第二节,也就是系统调用的那一节.记得包含这个数字,因为有些系统调用和在第一节中包含的命令行命令是重名的. exit 想象指定了系统调用的名称.
Name: 系统调用名称
Synopsis: 概括一下系统调用的使用方法
Description: 大致的介绍
Return Value: 系统调用结束后的返回值
| System Call | Description |
|---|---|
| 访问内存 | |
| brk | Change the data segment size. |
| mlock | Disable paging for parts of memory. |
| mlockall | Disable paging for the calling process. |
| mmap Map | files or devices into memory. |
| mprotect | Control allowable accesses to a region of memory. |
| mremap | Remap a virtual memory address. |
| msync | Synchronize the file with a memory map. |
| munlock | Enable paging for parts of memory. |
| munlockall | Enable paging for calling process. |
| munmap | Unmap files or devices from memory. |
| 访问设备 | |
| access | Check permissions for a device. |
| chmod | Change permissions for a device. |
| chown | Change the ownership for a device. |
| close | Close a device file descriptor. |
| dup | Duplicate a device file descriptor. |
| fcntl | Manipulate the file descriptor. |
| fstat | Get the status of a device. |
| ioctl | Control a device’s parameters. |
| link | Assign a new name to a file descriptor. |
| lseek | Reposition the read/write file offset. |
| mknod | Create a new file descriptor for a device. |
| open | Open/create a file descriptor for a device or file. |
| read | Read from a device file descriptor. |
| write | Write to a device file descriptor. |
| 文件系统 | |
| chdir | Change the working directory. |
| chroot | Change the root directory. |
| flock | Apply or remove an advisory lock on an open file. |
| statfs | Get file system statistics. |
| getcwd | Get the current working directory. |
| mkdir | Create a directory. |
| rmdir | Remove a directory. |
| symlink | Make a new name for a file. |
| umask | Set the file creation mask. |
| mount | Mount and unmount file systems. |
| swapon | Start swapping memory to the file system. |
| swapoff | Stop swapping memory to the file system. |
| 进程控制 | |
| acct | Turn process accounting on or off. |
| capget | Get process capabilities. |
| capset | Set process capabilities. |
| clone | Create a child process. |
| execve | Execute a program. |
| exit | Terminate the current process. |
| fork | Create a child process. |
| getgid | Get the group identity. |
| getpgrp | Get/set the process group. |
| getppid | Get process identification. |
| getpriority | Get the program scheduling priority. |
| getuid | Get the user identity. |
| kill | Send a signal to kill a process. |
| nice | Change the process priority. |
| vfork | Create a child process and block the parent. |
在之前的章节,你应该看到了系统调用的例子,与IA-32不同的是64使用的是寄存器的方式调用系统调用.RAX寄存器用来存储系统调用号. 接下来的部分将会展示如何调用系统调用.
系统调用号是唯一标示系统调用的ID.在系统调用之前RAX应该载入相应的系统调用号.一个exit系统调用的例子已经在书中出现过很多次:
movq $60,%rax
movq $0, %rdi
syscall
在之前提到的unistd.h中能够看到#define __NR_exit对应了60这个整数,也就是说将60载入RAX寄存器当中就能正确使用exit这个系统调用.
系统调用需要把参数存到寄存器当中,如果把错误的值存到了错误的寄存器里面的话,可能会导致灾难性的结果.
RAX用来装载系统调用号,RIP,RBP,RSP不能用,因为这些寄存器的值需要保留,不然会影响程序的执行.
系统调用的参数按照下面的顺序给出
| Syscall # | Param 1 | Param 2 | Param 3 | Param 4 | Param 5 | Param 6 | Return Value |
|---|---|---|---|---|---|---|---|
| rax | rdi | rsi | rdx | r10 | r8 | r9 | rax |
如果系统调用需要超过6个参数的话,就要通过内存的指针来传递参数了.
//TODO:前面write的例子写了无数遍以后再补充
系统调用的返回值存在RAX寄存器当中.
有时候返回值会比较复杂,这一节会将如何返回结构体.
sysinfo 系统调用返回的是系统和相应资源的信息.
sysinfo 的参数是一个指向sysinfo结构体的指针,包含了系统所需的信息.
TODO://结构体的详情
我们需要定义一个内存的结构来返回
.section .data
result:
uptime:
.int 0
load1:
.int 0
load5:
.int 0
load15:
.int 0
totalram:
.int 0
freeram:
.int 0
sharedram:
.int 0
bufferram:
.int 0
totalswap:
.int 0
freeswap:
.int 0
totalhigh:
.int 0
memunit:
.int 0
把$Result 传到RDI就能使用该系统调用.
使用strace命令
//TODO:跟踪过程