arch/i386-all/exec/newstackswap.c

   1 /*
   2     Copyright © 1995-2010, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: NewStackSwap() - Call a function with swapped stack.
   6     Lang: english
   7 */
   8
   9 #include <aros/config.h>
  10 #include <aros/debug.h>
  11 #include <exec/tasks.h>
  12 #include <proto/exec.h>
  13
  14 #define _PUSH(sp, val) *--sp = (IPTR)val
  15
  16 AROS_LH3(IPTR, NewStackSwap,
  17         AROS_LHA(struct StackSwapStruct *,  sss, A0),
  18         AROS_LHA(LONG_FUNC, entry, A1),
  19         AROS_LHA(struct StackSwapArgs *, args, A2),
  20         struct ExecBase *, SysBase, 122, Exec)
  21 {
  22     AROS_LIBFUNC_INIT
  23
  24     volatile struct Task *t = FindTask(NULL);
  25     volatile IPTR *sp = sss->stk_Pointer;
  26     volatile APTR splower = t->tc_SPLower;
  27     volatile APTR spupper = t->tc_SPUpper;
  28     IPTR ret;
  29     BYTE i;
  30
  31     /*
  32      * In order to be able to restore the stack after calling the function
  33      * we'll need to store original SP on the new stack. So we reserve a
  34      * location for it.
  35      */
  36     _PUSH(sp, 0);
  37     /* Then put arguments on stack in appropriate order */
  38     for (i = 7; i >= 0; i--)
  39     {
  40         D(bug("[NewStackSwap] Argument %d value 0x%08lX\n", i, args->Args[i]));
  41         _PUSH(sp, args->Args[i]);
  42     }
  43
  44     if (t->tc_Flags & TF_STACKCHK)
  45     {
  46         UBYTE* startfill = sss->stk_Lower;
  47
  48         while (startfill < (UBYTE *)sp)
  49             *startfill++ = 0xE1;
  50     }
  51
  52     /*
  53      * We need to Disable() before changing limits and SP, otherwise
  54      * stack check will fail if we get interrupted in the middle of this
  55      */
  56     D(bug("[NewStackSwap] SP 0x%p, entry point 0x%p\n", sp, entry));
  57     Disable();
  58
  59     /* Change limits. The rest is done in asm below */
  60     t->tc_SPLower = sss->stk_Lower;
  61     t->tc_SPUpper = sss->stk_Upper;
  62
  63     asm volatile(
  64     /* Save original ESP to the location reserved before */
  65     "movl %%esp, 32(%2)\n\t"
  66     /* Actually change the stack */
  67     "movl %2, %%esp\n\t"
  68
  69     /* Enable(). It preserves all registers by convention, so no EAX save/restore.
  70        Note also that we use global SysBase here  because we are running on the new
  71        stack and SysBase is lost. */
  72     "movl SysBase, %%ebx\n\t"
  73     "push %%ebx\n\t"
  74     "call *-84(%%ebx)\n\t"
  75     "pop %%ebx\n\t"
  76
  77     /* Call our function */
  78     "call *%1\n\t"
  79
  80     /* Disable(). Also preserves registers. */
  81     "movl SysBase, %%ebx\n\t"
  82     "push %%ebx\n\t"
  83     "call *-80(%%ebx)\n\t"
  84     "pop %%ebx\n\t"
  85
  86     /* Restore original ESP. Function's return value is in EAX. */
  87     "movl 32(%%esp), %%esp\n\t"
  88     : "=a"(ret)
  89     : "r"(entry), "r"(sp)
  90     : "ebx", "ecx", "edx", "cc");
  91
  92     /* Change limits back and return */
  93     t->tc_SPLower = splower;
  94     t->tc_SPUpper = spupper;
  95     Enable();
  96
  97     D(bug("[NewStackSwap] Returning 0x%08lX\n", ret));
  98     return ret;
  99
 100     AROS_LIBFUNC_EXIT
 101 } /* NewStackSwap() */