rk3586开发版新增系统调用(Android13)

一、前言

最近想学一下kernel和hal,所以买了一块板子,带了个摄像头和屏幕,1100+,学习投资了。这个Android内核定一个系统调用感觉是真的麻烦，主要是有一层bionic C，一开始不熟悉的时候还是花了点时间去配置。

二、kernel修改

include/uapi/asm-generic/unistd.h
系統调用的定义里增加自己的定义，这里是直接集成到arm64了，我发现arm都没有，简单起见所以后面bionic就直接arm64生成代码了。

#define __NR_hello 449
__SYSCALL(__NR_hello, sys_helloworld)
#undef __NR_syscalls
#define __NR_syscalls 450

然后新增一个目录drivers/char/helloworld，新增以下文件，这里的配置是默认的，后面编译刷入就行，这里我不说明刷入了，只介绍代码流程。

├── Kconfig
├── Makefile
├── mysyscall.c

mysyscall.c

#include <linux/kernel.h>
#include <linux/syscalls.h>



SYSCALL_DEFINE0(helloworld){
	printk("Hello, world my syscall!\n");
    return 0;
}

Makefile

obj-$(CONFIG_helloworld)	+=  mysyscall.o

Kconfig

config helloworld
    bool "helloworld suppore"
    default y
    help
        helloworld

这里配置完成之后需要上一层在char目录下的kConfig和Makefile中引用这里我也贴一下，分别新增

source "drivers/char/helloworld/Kconfig"

obj-y				+= helloworld/

kernel刷入后可以使用命令查看系统调用是否配置在kernel中，这里看到已经有了，第一个就是。

三、bionic修改

进入Android源码目录，今日bionic文件夹，下面的路径都是这里的相对路径了。
新增一个头文件libc/include/sys/myhello.h

/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#pragma once

/**
 * @file sys/sysinfo.h
 * @brief System information.
 */

#include <sys/cdefs.h>
#include <sys/types.h>

__BEGIN_DECLS

/**
 * just direct test
 */
int hello();



__END_DECLS

接下来修改libc/SYSCALLS.TXT
末尾新增

# <sys/myhello.h>
int hello() arm64

在libc/libc.map.txt新增hello，我这里直接在LIBC_P下面增加的，这里随便找的增加的，没有文档介绍，理论上到不要求版本的地方也行。这里的P也就是版本要求了。

LIBC_P { # introduced=P
  global:
    __freading;
    __free_hook;
    __fseterr;
    __fwriting;
    __malloc_hook;
    __memalign_hook;
    __realloc_hook;
    aligned_alloc;
    endhostent;
    endnetent;
    endprotoent;
    epoll_pwait64;
    fexecve;
    fflush_unlocked;
    fgetc_unlocked;
    fgets_unlocked;
    fputc_unlocked;
    fputs_unlocked;
    fread_unlocked;
    fwrite_unlocked;
    getentropy;
    getnetent;
    getprotoent;
    getrandom;
  + hello; #arm64
    ...
   } LIBC_O;

接下来还需要在两个头文件下面增加定义
libc/include/bits/glibc-syscalls.h

#if defined(__NR_hello)
  #define SYS_hello __NR_hello
#endif

libc/kernel/uapi/asm-generic/unistd.h 这里要注意内核里定义的数字要和这里一致，剩下的两个内核里没有的直接注释

// #define __NR_futex_waitv 449
// #define __NR_set_mempolicy_home_node 450

#define __NR_hello 449

到这里修改已经结束，进入bionic目录下面，然后mma即可，这里更新so也介绍一下
进入源码目录rk3568_android13/out/target/product/topeet_rk3568/system/apex/
adb push com.android.runtime /system/apex/ 这样就整体替换了。下面开始编写测试程序

四、测试程序编写

Android源码下随便新建一个目录，添加如下文件

├── Android.bp
└── hello.cpp

Android.bp

cc_binary {
    name: "hello",
    srcs: ["hello.cpp"],
    cflags: ["-Werror"],
    product_specific: true,
}

hello.cpp

#include <cstdio>
#include <sys/myhello.h>

int main()
{
    hello();
    return 0;
}

写完之后make hello，我们把可执行文件push到Android目录下执行即可

topeet_rk3568:/data/local/tmp # ls
hello
topeet_rk3568:/data/local/tmp # ./hello                                                                                    
topeet_rk3568:/data/local/tmp # 

接着查看内核日志 dmesg

可以看到日志已经成功打印，我们自定义的系统调用已经实现