添加系统调用

概述

本指南介绍如何为 OpenOS 添加新的系统调用。

添加系统调用步骤

1. 定义系统调用号

kernel/src/syscall/mod.rs

/// 系统调用号
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u64)]
pub enum SyscallNumber {
    // 现有系统调用
    Write = 1,
    Read = 2,
    Exit = 3,
    Yield = 4,
    PortCreate = 5,
    Send = 6,
    Receive = 7,

    // 新系统调用
    MyNewSyscall = 8,
}

2. 实现处理函数

kernel/src/syscall/mod.rs

pub fn handle_syscall(
    number: u64,
    arg1: u64,
    arg2: u64,
    arg3: u64,
) -> i64 {
    match number {
        1 => sys_write(arg1, arg2),
        2 => sys_read(arg1, arg2),
        3 => sys_exit(arg1),
        4 => sys_yield(),
        5 => sys_port_create(),
        6 => sys_send(arg1, arg2, arg3),
        7 => sys_receive(arg1, arg2, arg3),

        // 新系统调用
        8 => sys_my_new_syscall(arg1, arg2, arg3),

        _ => -1, // ENOSYS
    }
}

fn sys_my_new_syscall(arg1: u64, arg2: u64, arg3: u64) -> i64 {
    if arg1 == 0 {
        return -1; // EINVAL
    }

    let result = do_something(arg1, arg2, arg3);
    result as i64
}

3. 验证用户态指针

fn validate_user_ptr(ptr: *const u8, len: usize) -> Result<(), Error> {
    if ptr as usize >= 0x800000000000 {
        return Err(Error::InvalidPointer);
    }

    if len > MAX_BUFFER_SIZE {
        return Err(Error::BufferTooLarge);
    }

    if ptr as usize % core::mem::align_of::<u8>() != 0 {
        return Err(Error::UnalignedPointer);
    }

    Ok(())
}

fn read_user_data(ptr: *const u8, len: usize) -> Result<&[u8], Error> {
    validate_user_ptr(ptr, len)?;
    let data = unsafe { core::slice::from_raw_parts(ptr, len) };
    Ok(data)
}

4. 更新系统调用表

kernel/src/syscall/mod.rs

pub const SYSCALL_COUNT: usize = 9;

pub const SYSCALL_NAMES: [&str; SYSCALL_COUNT] = [
    "reserved",
    "write",
    "read",
    "exit",
    "yield",
    "port_create",
    "send",
    "receive",
    "my_new_syscall",
];

5. 添加用户态包装器

; user/syscall.asm

section .text

; my_new_syscall(arg1, arg2, arg3)
global openos_my_new_syscall
openos_my_new_syscall:
    mov rax, 8              ; 系统调用号
    syscall
    ret

6. 添加 C 头文件

sdk/include/openos/syscall.h

#ifndef OPENOS_SYSCALL_H
#define OPENOS_SYSCALL_H

#include <stdint.h>

#define SYS_WRITE           1
#define SYS_READ            2
#define SYS_EXIT            3
#define SYS_YIELD           4
#define SYS_PORT_CREATE     5
#define SYS_SEND            6
#define SYS_RECEIVE         7
#define SYS_MY_NEW_SYSCALL  8

static inline int64_t syscall3(int64_t num, int64_t arg1, int64_t arg2, int64_t arg3) {
    int64_t ret;
    asm volatile ("syscall" : "=a"(ret) : "a"(num), "D"(arg1), "S"(arg2), "d"(arg3) : "rcx", "r11", "memory");
    return ret;
}

static inline int64_t sys_my_new_syscall(uint64_t arg1, uint64_t arg2, uint64_t arg3) {
    return syscall3(SYS_MY_NEW_SYSCALL, arg1, arg2, arg3);
}

#endif

系统调用约定

寄存器使用

寄存器	用途
RAX	系统调用号
RDI	参数 1
RSI	参数 2
RDX	参数 3
R10	参数 4（保留）

返回值

• 成功：返回正值
• 错误：返回负值（高位为 1）

错误处理

标准错误码

pub const EINVAL: i64 = -1;   // 无效参数
pub const ENOENT: i64 = -2;   // 未找到
pub const EPERM: i64 = -3;    // 权限不足
pub const ENOMEM: i64 = -4;   // 内存不足
pub const EBUSY: i64 = -5;    // 资源忙
pub const EPIPE: i64 = -6;    // 管道已关闭
pub const EAGAIN: i64 = -7;   // 会阻塞
pub const ETIME: i64 = -8;    // 超时
pub const EFAULT: i64 = -9;   // 错误指针
pub const ENOSYS: i64 = -10;  // 未知系统调用

安全考虑

参数验证

fn validate_syscall_args(
    number: u64,
    arg1: u64,
    arg2: u64,
    arg3: u64,
) -> Result<(), Error> {
    if number >= SYSCALL_COUNT as u64 {
        return Err(Error::InvalidSyscall);
    }

    if needs_pointer_validation(number, 1) {
        validate_user_ptr(arg1 as *const u8, arg2 as usize)?;
    }

    Ok(())
}

调试系统调用

启用跟踪

pub fn handle_syscall(number: u64, arg1: u64, arg2: u64, arg3: u64) -> i64 {
    serial_println!(
        "[SYSCALL] {}({:#x}, {:#x}, {:#x})",
        SYSCALL_NAMES.get(number as usize).unwrap_or(&"unknown"),
        arg1, arg2, arg3
    );

    let result = match number {
        // ...
    };

    serial_println!("[SYSCALL] → {}", result);

    result
}

相关文档

• 系统调用 ABI - 系统调用约定
• 系统调用参考 - 完整的系统调用接口
• 代码质量 - 代码质量标准