zboot/piggyback.c

/*
* linux/zBoot/piggyback.c
*
* (C) 1993 Hannu Savolainen
*/

/*
* This program reads the compressed system image from stdin and
* encapsulates it into an object file written to the stdout.
*/
//这个程序读取压缩的system映像文件从标准输入然后压缩后写入标准输出
#include <stdio.h>
#include <unistd.h>
#include <a.out.h>

//主函数
int main(int argc, char *argv[])
{
   int c, n=0, len=0;
   //定义缓冲区
   char tmp_buf[512*1024];

   //可执行文件头
   struct exec obj = {0x00640107};   /* object header */
   //输入的数据和输入的长度
   char string_names[] = {"_input_data\0_input_len\0"};

//标号表，变量名
   struct nlist var_names[2] = /* Symbol table */
       {
           {   /* _input_data   */
               (char *)4, 7, 0, 0, 0
           },
           {   /* _input_len */
               (char *)16, 7, 0, 0, 0
           }
       };

len = 0;
   //从标准输入中读取数据到缓冲区
   while ((n = read(0, &tmp_buf[len], sizeof(tmp_buf)-len+1)) > 0)
          len += n;

//校验读取的长度
   if (n==-1)
   {
       perror("stdin");
       exit(-1);
   }

if (len >= sizeof(tmp_buf))
   {
       fprintf(stderr, "%s: Input too large\n", argv[0]);
       exit(-1);
   }

//输出长度信息
fprintf(stderr, "Compressed size %d.\n", len);

/*
*   Output object header
*/
   //输出对象头
   obj.a_data = len + sizeof(long);
   obj.a_syms = sizeof(var_names);
   write(1, (char *)&obj, sizeof(obj));

/*
*   Output data segment (compressed system & len)
*/
   //输出数据段
   write(1, tmp_buf, len);
   write(1, (char *)&len, sizeof(len));

/*
*   Output symbol table
*/
   //输出符号表
   var_names[1].n_value = len;
   write(1, (char *)&var_names, sizeof(var_names));

/*
*   Output string table
*/
   //输出字符表
   len = sizeof(string_names) + sizeof(len);
   write(1, (char *)&len, sizeof(len));
   write(1, string_names, sizeof(string_names));

exit(0);

}

巴特西

zboot/piggyback.c

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