bionic syscall 添加函数

android： 4.0.4

硬件： nexus

内核： 3.0.8

kernel:

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kernel_src/fs/open.c 添加：
SYSCALL_DEFINE2(mymul,int, x,int,y)     2是参数个数。  宏替换完，函数名为 sys_mymul
{
    int z;
    printk("here is add a log in sys_mymul\n");
    z=x*y;
    return z;
}
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kernel_src/arch/arm/kernel/calls.S
 /*376 */    CALL(sys_mymul)                 函数table：跳转的偏移地址在376
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kernel_src/arch/arm/include/asm/unistd.h
#define __NR_mymul          (__NR_SYSCALL_BASE+376)       
__NR_mymul 在android的bionic内有个文件需要跳转到这个label.
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bionic:
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bionic/libc/include/sys/linux-syscalls.h  声明__NR_mymul在table的偏移。
#define __NR_mymul                          (__NR_SYSCALL_BASE + 376)
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bionic/libc/arch-arm/syscalls/mymul.S： 实现跳转
ENTRY(mymul)
    .save   {r4, r7}
    stmfd   sp!, {r4, r7}
    ldr     r7, =__NR_mymul
    swi     #0
    ldmfd   sp!, {r4, r7}
    movs    r0, r0
    bxpl    lr
    b       __set_syscall_errno
END(mymul)
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bionic/libc/arch-arm/syscalls.mk   把跳转文件添加到会被编译的文件列表呢
syscall_src += arch-arm/syscalls/mymul.S   
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bionic/libc/unistd/open.c 添加如下：
extern int mymul(int,int); //jjd
int Mymul(int x,int y){
printf("bionic.mymul");
    return mymul(x,y);
}
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bionic/libc/include/fcntl.h 添加：
extern int  Mymul(int,int);
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在系统里如果使用到Mymul函数，添加fcntl.h头文件即可。