boot/freeldr/freeldr/arch/i386/linux.S

   1 /*
   2  *  FreeLoader
   3  *  Copyright (C) 1998-2002  Brian Palmer  <brianp@sginet.com>
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; either version 2 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License along
  16  *  with this program; if not, write to the Free Software Foundation, Inc.,
  17  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  */
  19
  20 #include <asm.inc>
  21 #include <arch/pc/x86common.h>
  22 #include <arch/pc/pcbios.h>
  23
  24 EXTERN _DiskStopFloppyMotor:PROC
  25 EXTERN _Relocator16Boot:PROC
  26 EXTERN _FrldrBootDrive:BYTE
  27 EXTERN _FrldrBootPartition:DWORD
  28
  29 .code32
  30
  31 Regs:
  32     .space REGS_SIZE
  33
  34 /*
  35  * VOID __cdecl BootLinuxKernel(
  36  *     IN ULONG KernelSize,
  37  *     IN PVOID KernelCurrentLoadAddress,
  38  *     IN PVOID KernelTargetLoadAddress,
  39  *     IN UCHAR DriveNumber,
  40  *     IN ULONG PartitionNumber);
  41  */
  42 PUBLIC _BootLinuxKernel
  43 _BootLinuxKernel:
  44
  45     /* Stop the floppy drive motor */
  46     call _DiskStopFloppyMotor
  47
  48     /* Set all segment registers to 0x9000 */
  49     mov ax, HEX(9000)
  50     mov word ptr [Regs + REGS_DS], ax
  51     mov word ptr [Regs + REGS_ES], ax
  52     mov word ptr [Regs + REGS_FS], ax
  53     mov word ptr [Regs + REGS_GS], ax
  54
  55     /* Set the boot drive */
  56     xor edx, edx
  57     mov dl, byte ptr [esp + 16]
  58     test dl, dl
  59     jnz set_part
  60     mov dl, byte ptr ds:[_FrldrBootDrive]
  61
  62     /* Set the boot partition */
  63 set_part:
  64     mov eax, dword ptr [esp + 20]
  65     test eax, eax
  66     jnz continue
  67     mov eax, dword ptr ds:[_FrldrBootPartition]
  68 continue:
  69     /* Store the 1-byte truncated partition number in DH */
  70     mov dh, al
  71
  72     mov dword ptr [Regs + REGS_EDX], edx
  73
  74     /*
  75      * Relocate the kernel image to its final destination (can be as low as 0x10000).
  76      * The reason we can overwrite low memory is because this code executes
  77      * between 0000:8000 and 0000:FFFF. That leaves space for 32k of code
  78      * before we start interfering with Linux kernel address space.
  79      */
  80
  81     /* Get KernelSize in ECX */
  82     mov ecx, dword ptr [esp + 4]
  83     test ecx, ecx   // If size is zero, do not perform relocations
  84     jz after_reloc
  85
  86     /* Load the source and target addresses */
  87     mov esi, dword ptr [esp +  8] // HEX(100000) // LINUX_KERNEL_LOAD_ADDRESS
  88     mov edi, dword ptr [esp + 12] // HEX(10000)
  89
  90 //
  91 // FIXME: Support relocating *upwards*, overlapping regions, aligned addresses,
  92 // etc... !! See memmove code.
  93 //
  94     /* Check how we should perform relocation */
  95     cmp edi, esi
  96     je after_reloc  // target == source: do not perform relocations
  97     ja reloc_up     // target  > source: relocate up
  98 //  jb reloc_down   // target  < source: relocate down (default)
  99
 100 reloc_down:
 101     /* Move the kernel down - Start with low addresses and increment them */
 102     cld
 103 #if 0
 104     rep movsb
 105 #else
 106     mov edx, ecx            // Copy the total number of bytes in EDX
 107     and edx, HEX(0FFFFFFFC) // Number of bytes we copy using DWORDs
 108     xor edx, ecx            // Number of remaining bytes to copy after the DWORDs
 109     shr ecx, 2      // Count number of DWORDs
 110     rep movsd       // Move DWORDs
 111     mov ecx, edx    // Count number of remaining bytes
 112     rep movsb       // Move bytes
 113 #endif
 114     jmp after_reloc
 115
 116 reloc_up:
 117     /* Move the kernel up - Start with high addresses and decrement them */
 118     std
 119     add esi, ecx
 120     add edi, ecx
 121     dec esi
 122     dec edi
 123     rep movsb
 124     // jmp after_reloc
 125
 126 after_reloc:
 127
 128     push HEX(0000) // CodePointer
 129     push HEX(9020) // CodeSegment
 130     push HEX(9000) // StackPointer
 131     push HEX(9000) // StackSegment
 132     mov eax, offset Regs
 133     push eax
 134     call _Relocator16Boot
 135
 136     /* We must never get there */
 137     int 3
 138
 139 END