*nux编程的108种奇淫巧计-5(rbp寄存器)

     昨天在家浏览了纽约大学的一个课件，找到一个例子，很有趣，我稍微修改了一下，支持32位和64位环境：如下。

     以后该系列采用这样的模式，首篇只贴代码，续篇进行解释和分析，期间希望读者朋友能自己做实验。

     理解该代码就算对rbp，rsp寄存器以及一些调用有了直接的接触。

     里面有两个奇怪的数字17和23，这是为什么呢？续篇给予解答。

     编译方法：

     64位环境：

       g++ -g  test.cpp -o test_64    //64位代码

       g++ -g  -m32 test.cpp -o test_32        //32位代码

    32位环境：

       g++ -g  test.cpp -o test_32

 

 

 

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/time.h>
       
int     done = 0;

int thread1( void )
{
        printf( "Hello from thread1 /n" );
        while ( !done );
        printf( "/nThread1 is quitting/n" );
        exit(0);
}      
       
int thread2( void )
{      
        printf( "Hello from thread2 /n" );
        while ( !done );
        printf( "/nThread2 is quitting/n" );
        exit(0);
}      

int thread3( void )
{
        printf( "Hello from thread3 /n" );
        while ( !done );
        printf( "/nThread3 is quitting/n" );
        exit(0);
}

int thread4( void )
{
        printf( "Hello from thread4 /n" );
        while ( !done );
        printf( "/nThread4 is quitting/n" );
        exit(0);
}

 

 

typedef int (*THREAD)(void);

THREAD  ready[] = { thread1, thread2, thread3, thread4 };
const int thread_count = sizeof( ready )/sizeof( THREAD );

int     next_thread = 0;        // array-index for 'ready' list

 

void upon_signal( int signum )
{
        unsigned long   *tos;   // this is used for addressing the stack-frame
        #if defined(__i386__)
        asm(" movl %%ebp, %0 " : "=m" (tos) );  // initializes frame-pointer
        tos[17] = (unsigned long)ready[ next_thread ];
        #elif defined(__x86_64__)

        asm(" mov %%rbp, %0 " : "=m" (tos) );   // initializes frame-pointer
        tos[23] = (unsigned long)ready[ next_thread ];
        #endif
        // This was useful during development -- to display the stack elements
        //for (int i = 0; i < 30; i++) printf( "before:tos[%d]=%16X /n", i, tos[i] );

        next_thread = ( 1 + next_thread ) % thread_count;  // "circular" array

        if ( signum == SIGINT ) done = 1;       // to terminate on <CONTROL>-C
}

 

int main( int argc, char **argv )
{
        signal( SIGINT, upon_signal );

        struct itimerval  it;
        it.it_value.tv_sec = 1;
        it.it_value.tv_usec = 0;
        it.it_interval.tv_sec = 0;
        it.it_interval.tv_usec = 200000;
        setitimer( ITIMER_REAL, &it, NULL );
        signal( SIGALRM, upon_signal );

        while ( !done );

        printf( "/nQuitting/n" );
}