/*
 * DOS upper memory management.
 *
 * Copyright 2002 Jukka Heinonen
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */

#include "dosexe.h"
#include "wine/debug.h"

WINE_DEFAULT_DEBUG_CHANNEL(dosmem);

/*
 * Wine DOS memory layout above 640k:
 *
 *   a0000 - affff : VGA graphics         (vga.c)
 *   b0000 - bffff : Monochrome text      (unused)
 *   b8000 - bffff : VGA text             (vga.c)
 *   c0000 - cffff : EMS frame            (int67.c)
 *   d0000 - effff : Free memory for UMBs (himem.c)
 *   f0000 - fffff : BIOS stuff           (msdos/dosmem.c)
 *  100000 -10ffff : High memory area     (unused)
 */

/*
 * Table of real mode segments and protected mode selectors 
 * for code stubs and other miscellaneous storage.
 */
struct DPMI_segments *DOSVM_dpmi_segments = NULL;

/*
 * First and last address available for upper memory blocks.
 */
#define DOSVM_UMB_BOTTOM 0xd0000
#define DOSVM_UMB_TOP    0xeffff

/*
 * First free address for upper memory blocks.
 */
static DWORD DOSVM_umb_free = DOSVM_UMB_BOTTOM;


/***********************************************************************
 *           DOSVM_AllocUMB
 *
 * Allocate upper memory block (UMB) from upper memory.
 * Returned pointer is aligned to 16-byte (paragraph) boundary.
 *
 * This routine is only for allocating static storage for 
 * Wine internal uses. Allocated memory can be accessed from
 * real mode, memory is taken from area already mapped and reserved
 * by Wine and the allocation has very little memory and speed
 * overhead. Use of this routine also preserves precious DOS
 * conventional memory.
 */
static LPVOID DOSVM_AllocUMB( DWORD size )
{
  LPVOID ptr = (LPVOID)DOSVM_umb_free;
  
  size = ((size + 15) >> 4) << 4;
  
  if(DOSVM_umb_free + size - 1 > DOSVM_UMB_TOP) {
    ERR("Out of upper memory area.\n");
    return 0;
  }

  DOSVM_umb_free += size;
  return ptr;
}


/**********************************************************************
 *          alloc_selector
 *
 * Allocate a selector corresponding to a real mode address.
 * size must be < 64k.
 */
static WORD alloc_selector( void *base, DWORD size, unsigned char flags )
{
    WORD sel = wine_ldt_alloc_entries( 1 );

    if (sel)
    {
        LDT_ENTRY entry;
        wine_ldt_set_base( &entry, base );
        wine_ldt_set_limit( &entry, size - 1 );
        wine_ldt_set_flags( &entry, flags );
        wine_ldt_set_entry( sel, &entry );
    }
    return sel;
}


/***********************************************************************
 *           DOSVM_AllocCodeUMB
 *
 * Allocate upper memory block for storing code stubs.
 * Initializes real mode segment and 16-bit protected mode selector 
 * for the allocated code block.
 *
 * FIXME: should allocate a single PM selector for the whole UMB range.
 */
static LPVOID DOSVM_AllocCodeUMB( DWORD size, WORD *segment, WORD *selector )
{
  LPVOID ptr = DOSVM_AllocUMB( size );
  
  if (segment)
    *segment = (DWORD)ptr >> 4;

  if (selector)
    *selector = alloc_selector( ptr, size, WINE_LDT_FLAGS_CODE );

  return ptr;
}


/***********************************************************************
 *           DOSVM_AllocDataUMB
 *
 * Allocate upper memory block for storing data.
 * Initializes real mode segment and 16-bit protected mode selector 
 * for the allocated data block.
 */
LPVOID DOSVM_AllocDataUMB( DWORD size, WORD *segment, WORD *selector )
{
  LPVOID ptr = DOSVM_AllocUMB( size );
  
  if (segment)
    *segment = (DWORD)ptr >> 4;

  if (selector)
    *selector = alloc_selector( ptr, size, WINE_LDT_FLAGS_DATA );

  return ptr;
}


/***********************************************************************
 *           DOSVM_InitSegments
 *
 * Initializes DOSVM_dpmi_segments. Allocates required memory and
 * sets up segments and selectors for accessing the memory.
 */
void DOSVM_InitSegments( void )
{
    LPSTR ptr;
    int   i;

    static const char wrap_code[]={
     0xCD,0x31, /* int $0x31 */
     0xCB       /* lret */
    };

    static const char enter_xms[]=
    {
        /* XMS hookable entry point */
        0xEB,0x03,           /* jmp entry */
        0x90,0x90,0x90,      /* nop;nop;nop */
                             /* entry: */
        /* real entry point */
        /* for simplicity, we'll just use the same hook as DPMI below */
        0xCD,0x31,           /* int $0x31 */
        0xCB                 /* lret */
    };

    static const char enter_pm[]=
    {
        0x50,                /* pushw %ax */
        0x52,                /* pushw %dx */
        0x55,                /* pushw %bp */
        0x89,0xE5,           /* movw %sp,%bp */
        /* get return CS */
        0x8B,0x56,0x08,      /* movw 8(%bp),%dx */
        /* just call int 31 here to get into protected mode... */
        /* it'll check whether it was called from dpmi_seg... */
        0xCD,0x31,           /* int $0x31 */
        /* we are now in the context of a 16-bit relay call */
        /* need to fixup our stack;
         * 16-bit relay return address will be lost, 
         * but we won't worry quite yet 
         */
        0x8E,0xD0,           /* movw %ax,%ss */
        0x66,0x0F,0xB7,0xE5, /* movzwl %bp,%esp */
        /* set return CS */
        0x89,0x56,0x08,      /* movw %dx,8(%bp) */
        0x5D,                /* popw %bp */
        0x5A,                /* popw %dx */
        0x58,                /* popw %ax */
        0xfb,                /* sti, enable and check virtual interrupts */
        0xCB                 /* lret */
    };

    static const char relay[]=
    {
        0xca, 0x04, 0x00, /* 16-bit far return and pop 4 bytes (relay void* arg) */
        0xcd, 0x31,       /* int 31 */
        0xfb, 0x66, 0xcb  /* sti and 32-bit far return */
    };

    /*
     * Allocate pointer array.
     */
    DOSVM_dpmi_segments = DOSVM_AllocUMB( sizeof(struct DPMI_segments) );

    /*
     * RM / offset 0: Exit from real mode.
     * RM / offset 2: Points to lret opcode.
     */
    ptr = DOSVM_AllocCodeUMB( sizeof(wrap_code),
                              &DOSVM_dpmi_segments->wrap_seg, 0 );
    memcpy( ptr, wrap_code, sizeof(wrap_code) );

    /*
     * RM / offset 0: XMS driver entry.
     */
    ptr = DOSVM_AllocCodeUMB( sizeof(enter_xms), 
                              &DOSVM_dpmi_segments->xms_seg, 0 );
    memcpy( ptr, enter_xms, sizeof(enter_xms) );

    /*
     * RM / offset 0: Switch to DPMI.
     * PM / offset 8: DPMI raw mode switch.
     */
    ptr = DOSVM_AllocCodeUMB( sizeof(enter_pm), 
                              &DOSVM_dpmi_segments->dpmi_seg,
                              &DOSVM_dpmi_segments->dpmi_sel );
    memcpy( ptr, enter_pm, sizeof(enter_pm) );

    /*
     * PM / offset N*6: Interrupt N in DPMI32.
     */
    ptr = DOSVM_AllocCodeUMB( 6 * 256,
                              0, &DOSVM_dpmi_segments->int48_sel );
    for(i=0; i<256; i++) {
        /*
         * Each 32-bit interrupt handler is 6 bytes:
         * 0xCD,<i>            = int <i> (nested 16-bit interrupt)
         * 0x66,0xCA,0x04,0x00 = ret 4   (32-bit far return and pop 4 bytes / eflags)
         */
        ptr[i * 6 + 0] = 0xCD;
        ptr[i * 6 + 1] = i;
        ptr[i * 6 + 2] = 0x66;
        ptr[i * 6 + 3] = 0xCA;
        ptr[i * 6 + 4] = 0x04;
        ptr[i * 6 + 5] = 0x00;
    }

    /*
     * PM / offset N*5: Interrupt N in 16-bit protected mode.
     */
    ptr = DOSVM_AllocCodeUMB( 5 * 256,
                              0, &DOSVM_dpmi_segments->int16_sel );
    for(i=0; i<256; i++) {
        /*
         * Each 16-bit interrupt handler is 5 bytes:
         * 0xCD,<i>       = int <i> (interrupt)
         * 0xCA,0x02,0x00 = ret 2   (16-bit far return and pop 2 bytes / eflags)
         */
        ptr[i * 5 + 0] = 0xCD;
        ptr[i * 5 + 1] = i;
        ptr[i * 5 + 2] = 0xCA;
        ptr[i * 5 + 3] = 0x02;
        ptr[i * 5 + 4] = 0x00;
    }

    /*
     * PM / offset 0: Stub where __wine_call_from_16_regs returns.
     * PM / offset 3: Stub which swaps back to 32-bit application code/stack.
     * PM / offset 5: Stub which enables interrupts
     */
    ptr = DOSVM_AllocCodeUMB( sizeof(relay), 
                              0,  &DOSVM_dpmi_segments->relay_code_sel);
    memcpy( ptr, relay, sizeof(relay) );

    /*
     * Space for 16-bit stack used by relay code.
     */
    ptr = DOSVM_AllocDataUMB( DOSVM_RELAY_DATA_SIZE, 
                              0, &DOSVM_dpmi_segments->relay_data_sel);
    memset( ptr, 0, DOSVM_RELAY_DATA_SIZE );

    /*
     * As we store code in UMB we should make sure it is executable
     */
    VirtualProtect((void *)DOSVM_UMB_BOTTOM, DOSVM_UMB_TOP - DOSVM_UMB_BOTTOM, PAGE_EXECUTE_READWRITE, NULL);
}