bash 源码分析

• 下载解压 bash-3.2

• 编译bash

export LFS=/my/soft/mylfs
tar xvf $LFS/sources/bash-3.2.tar.gz -C $LFS/sources/
cd $LFS/sources/bash-3.2/
 
patch -Np1 -i ../bash-3.2-fixes-.patch
 
./configure --prefix=$LFS/builds --without-bash-malloc
make
make install

• 常用的调用堆栈

在读取命令之前执行一些命令，如PS1的打印
bash [C/C++ Application]
bash [] [cores: ]
Thread #  [core: ] (Suspended : Step)
execute_builtin_or_function() at execute_cmd.c:, 0x42bf86
execute_simple_command() at execute_cmd.c:, 0x42bf86
execute_command_internal() at execute_cmd.c: 0x42952e
parse_and_execute() at evalstring.c: 0x45dc63
execute_variable_command() at parse.y:, 0x41e157
parse_command() at eval.c: 0x41b1c2
read_command() at eval.c: 0x41b2a6
reader_loop() at eval.c: 0x41b4e4
main() at shell.c: 0x41ac53
gdb (7.2)

执行用户输入命令的堆栈
bash [C/C++ Application]
bash [] [cores: ]
Thread #  [core: ] (Suspended : Step)
cd_builtin() at cd.def: 0x45a830
execute_builtin() at execute_cmd.c:, 0x4283d1
execute_builtin_or_function() at execute_cmd.c:, 0x42bf60
execute_simple_command() at execute_cmd.c:, 0x42bf60
execute_command_internal() at execute_cmd.c: 0x42952e
execute_command() at execute_cmd.c: 0x429ffe
reader_loop() at eval.c: 0x41b412
main() at shell.c: 0x41ac53
gdb (7.2)

execute_builtin_or_function 方法有一个分支，分为执行内建命令和执行函数
if (builtin)
result = execute_builtin (builtin, words, flags, );
else
result = execute_function (var, words, flags, fds_to_close, , );
 
如果是执行函数，如何找到执行的函数呢？
func = find_function (words->word->word);
 
/* Return the pointer to the function implementing builtin command NAME. */
sh_builtin_func_t *
find_shell_builtin (name)
char *name;
{
current_builtin = builtin_address_internal (name, );
return (current_builtin ? current_builtin->function : (sh_builtin_func_t *)NULL);
}

• 执行内置命令的方法如下：

static int
execute_builtin (builtin, words, flags, subshell)
     sh_builtin_func_t *builtin;
     WORD_LIST *words;
     int flags, subshell;
{
  int old_e_flag, result, eval_unwind;
  int isbltinenv;
 
  old_e_flag = exit_immediately_on_error;
  /* The eval builtin calls parse_and_execute, which does not know about
     the setting of flags, and always calls the execution functions with
     flags that will exit the shell on an error if -e is set.  If the
     eval builtin is being called, and we're supposed to ignore the exit
     value of the command, we turn the -e flag off ourselves, then
     restore it when the command completes. */
  if (subshell ==  && builtin == eval_builtin && (flags & CMD_IGNORE_RETURN))
    {
      begin_unwind_frame ("eval_builtin");
      unwind_protect_int (exit_immediately_on_error);
      exit_immediately_on_error = ;
      eval_unwind = ;
    }
  else
    eval_unwind = ;
 
  /* The temporary environment for a builtin is supposed to apply to
     all commands executed by that builtin.  Currently, this is a
     problem only with the `unset', `source' and `eval' builtins. */
 
  isbltinenv = (builtin == source_builtin || builtin == eval_builtin || builtin == unset_builtin);
 
  if (isbltinenv)
    {
      if (subshell == )
    begin_unwind_frame ("builtin_env");
 
      if (temporary_env)
    {
      push_scope (VC_BLTNENV, temporary_env);
      if (subshell == )
        add_unwind_protect (pop_scope, (flags & CMD_COMMAND_BUILTIN) ?  : "");
          temporary_env = (HASH_TABLE *)NULL;
    }
    }
 
  /* `return' does a longjmp() back to a saved environment in execute_function.
     If a variable assignment list preceded the command, and the shell is
     running in POSIX mode, we need to merge that into the shell_variables
     table, since `return' is a POSIX special builtin. */
  if (posixly_correct && subshell ==  && builtin == return_builtin && temporary_env)
    {
      begin_unwind_frame ("return_temp_env");
      add_unwind_protect (merge_temporary_env, (char *)NULL);
    }
 
/*
执行执行的语句，会调用不同的内置方法执行具体的命令，如cd命令会执行cd.def中的cd_builtin方法，内置方法的文件都在builtins目录下
*/
  result = ((*builtin) (words->next));
 
  /* This shouldn't happen, but in case `return' comes back instead of
     longjmp'ing, we need to unwind. */
  if (posixly_correct && subshell ==  && builtin == return_builtin && temporary_env)
    discard_unwind_frame ("return_temp_env");
 
  if (subshell ==  && isbltinenv)
    run_unwind_frame ("builtin_env");
 
  if (eval_unwind)
    {
      exit_immediately_on_error += old_e_flag;
      discard_unwind_frame ("eval_builtin");
    }
 
  return (result);
}