crt.c

Simple Operating Systems （简称SOS）是一个可以运行在X86平台上（包括QEMU

/* Copyright (C) 2005 David Decotigny
   Copyright (C) 2003 Thomas Petazzoni

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
   USA. 
*/


/**
 * @file crt.c
 *
 * The C RunTime environment for the basic support of SOS C user
 * programs
 */

#include <hwcore/swintr.h>
#include <string.h>
#include "crt.h"

/**
 * Starter function !
 */
void _start() __attribute__((noreturn));
void _start()
{
  /* This starter function expects a main() function somewhere */
  extern int main();

  /* Reset the bss section */
  extern char _bbss, _ebss;
  memset(& _bbss, 0x0, (& _ebss) - (& _bbss));

  _sos_exit(main());
}


/*
 * By convention, the USER SOS programs always pass 4 arguments to the
 * kernel syscall handler: in eax/../edx. For less arguments, the
 * unused registers are filled with 0s. For more arguments, the 4th
 * syscall parameter gives the address of the array containing the
 * remaining arguments. In any case, eax corresponds to the syscall
 * IDentifier.
 */


inline
int _sos_syscall3(int id,
		  unsigned int arg1,
		  unsigned int arg2,
		  unsigned int arg3)
{
  int ret;

  asm volatile("movl %1,%%eax \n"
	       "movl %2,%%ebx \n"
	       "movl %3,%%ecx \n"
	       "movl %4,%%edx \n"
	       "int  %5\n"
	       "movl %%eax, %0"
	       :"=g"(ret)
	       :"g"(id),"g"(arg1),"g"(arg2),"g"(arg3)
	        ,"i"(SOS_SWINTR_SOS_SYSCALL)
	       :"eax","ebx","ecx","edx");

  return ret;
}


int _sos_syscall0(int id)
{
  return _sos_syscall3(id, 0, 0, 0);
}


int _sos_syscall1(int id,
	     unsigned int arg1)
{
  return _sos_syscall3(id, arg1, 0, 0);
}


int _sos_syscall2(int id,
		  unsigned int arg1,
		  unsigned int arg2)
{
  return _sos_syscall3(id, arg1, arg2, 0);
}


int _sos_syscall4(int id,
		  unsigned int arg1,
		  unsigned int arg2,
		  unsigned int arg3,
		  unsigned int arg4)
{
  unsigned int args[] = { arg3, arg4 };
  return _sos_syscall3(id, arg1, arg2, (unsigned)args);
}


int _sos_syscall5(int id,
		  unsigned int arg1,
		  unsigned int arg2,
		  unsigned int arg3,
		  unsigned int arg4,
		  unsigned int arg5)
{
  unsigned int args[] = { arg3, arg4, arg5 };
  return _sos_syscall3(id, arg1, arg2, (unsigned)args);
}


int _sos_syscall6(int id,
		  unsigned int arg1,
		  unsigned int arg2,
		  unsigned int arg3,
		  unsigned int arg4,
		  unsigned int arg5,
		  unsigned int arg6)
{
  unsigned int args[] = { arg3, arg4, arg5, arg6 };
  return _sos_syscall3(id, arg1, arg2, (unsigned)args);
}


int _sos_syscall7(int id,
		  unsigned int arg1,
		  unsigned int arg2,
		  unsigned int arg3,
		  unsigned int arg4,
		  unsigned int arg5,
		  unsigned int arg6,
		  unsigned int arg7)
{
  unsigned int args[] = { arg3, arg4, arg5, arg6, arg7 };
  return _sos_syscall3(id, arg1, arg2, (unsigned)args);
}


int _sos_syscall8(int id,
		  unsigned int arg1,
		  unsigned int arg2,
		  unsigned int arg3,
		  unsigned int arg4,
		  unsigned int arg5,
		  unsigned int arg6,
		  unsigned int arg7,
		  unsigned int arg8)
{
  unsigned int args[] = { arg3, arg4, arg5, arg6, arg7, arg8 };
  return _sos_syscall3(id, arg1, arg2, (unsigned)args);
}


void _sos_exit(int status)
{
  _sos_syscall1(SOS_SYSCALL_ID_EXIT, (unsigned)status);
  
  /* Never reached ! */
  for ( ; ; )
    ;
}


int _sos_bochs_write(const char * str, unsigned length)
{
  return _sos_syscall2(SOS_SYSCALL_ID_BOCHS_WRITE,
		       (unsigned)str,
		       length);
}