Message-ID:	<20000914025420.6116.qmail@sina.com>
From:	computerboy <computerboy AT sina DOT com>
To:	djgpp AT delorie DOT com
Subject:	how hook int 21h from protect mode!
Date:	Thu Sep 14 02:54:20 2000
X-Mailer:	SinaMail 3.0Beta (FireToad)
X-Priority:	3
Reply-To:	djgpp AT delorie DOT com

hi, please help me , I'm new for djgpp, I want hook real mode int 21h at protect mode , I use a source from mailing list - test.c, but 
my pc hung, call_dos() seem reenter! can u give a simple and  complete code for hook 21h!

Very thinks 


 >/***START test.c ***/
 >#include <dpmi.h>
 >#include <go32.h>
 >#include <crt0.h>
 >#include <stdlib.h>
 >
 >int _crt0_startup_flags = _CRT0_FLAG_LOCK_MEMORY;
 >
 >_go32_dpmi_seginfo  old_int21_vector;
 >_go32_dpmi_registers  my_int21_regs;
 >_go32_dpmi_seginfo  my_int21_info;
 >
 >/*
 > * My int 21h handler
 > */
 >static
 >void call_dos(_go32_dpmi_registers *r)
 >{
 > r->x.cs = old_int21_vector.rm_segment;
 > r->x.ip = old_int21_vector.rm_offset;
 > _go32_dpmi_simulate_fcall_iret(r);
 >}
 >
 >int grab_dos() {
 >    _go32_dpmi_get_real_mode_interrupt_vector(0x21, &old_int21_vector);
 >    my_int21_info.pm_offset = (int) call_dos;
 >
 >if(_go32_dpmi_allocate_real_mode_callback_iret(&my_int21_info,&my_int21_regs)
 >
 >        || _go32_dpmi_set_real_mode_interrupt_vector(0x21,
 >&my_int21_info) )
 >    {
 >        return 1;
 >    }
 >    return 0;
 >}
 >
 >void release_dos(void)
 >{
 > _go32_dpmi_set_real_mode_interrupt_vector(0x21, &old_int21_vector);
 > _go32_dpmi_free_real_mode_callback(&my_int21_info);
 >}
 >
 >int main()
 >{
 > if( grab_dos() == 0 ) {
 >  system("dir");
 >  release_dos();
 > }
 > return 0;
 >}
 >
 >/*** END test.c ***/

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