linux-0.11调试教程，HIST_ENTRY结构中data域的用处

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linux-0.11调试教程，HIST_ENTRY结构中data域的用处

2014年02月10日 ⁄ 综合 ⁄ 共 1482字 ⁄ 字号小中大 ⁄ 评论关闭

HIST_ENTRY结构中data域的使用出现在history.c文件中的replace_history_entry ()函数中。

而replace_history_entry ()函数在readline.c文件中有如下两处调用

char *

readline_internal ()
{

......

    if (entry && rl_undo_list)
      {
   char *temp = savestring (the_line);
   rl_revert_line ();
   entry = replace_history_entry (where_history (), the_line,
                       (HIST_ENTRY *)NULL);
   free_history_entry (entry);

   strcpy (the_line, temp);
   free (temp);
      }
}

/* Perhaps put back the current line if it has changed. */
maybe_replace_line ()
{
HIST_ENTRY *temp = current_history ();

/* If the current line has changed, save the changes. */
if (temp && ((UNDO_LIST *)(temp->data) != rl_undo_list))
    {
      temp = replace_history_entry (where_history (), the_line, rl_undo_list);
      free (temp->line);
      free (temp);
    }

}

下面是在[/root]# abcad ---> [/root]# aabcad之后按下向上方向键时在replace_history_entry
()函数出被截获。

其中参数rl_undo_list的值为0x5d7cc。指向undo_list结构，下面是undo_list结构的定义(readline.h中)：

enum
undo_code { UNDO_DELETE, UNDO_INSERT, UNDO_BEGIN, UNDO_END };

/*
What an element of THE_UNDO_LIST looks like. */
typedef struct undo_list {
struct undo_list *next;
int start, end;       /* Where the change took place. */
char *text;           /* The text to insert, if undoing a delete. */
enum undo_code what;       /* Delete, Insert, Begin, End. */
} UNDO_LIST;

/* The current undo list for RL_LINE_BUFFER. */
extern UNDO_LIST *rl_undo_list;

rl_undo_list->next的值为0x5d78c

rl_undo_list->start的值为1

rl_undo_list->end的值为2

rl_undo_list->text的值为0既NULL

rl_undo_list->what的值为1既UNDO_INSERT