start.S

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/*-
 * Copyright (c) 2002-2018 The UbixOS Project.
 * All rights reserved.
 *
 * This was developed by Christopher W. Olsen for the UbixOS Project.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met:
 *
 * 1) Redistributions of source code must retain the above copyright notice, this list of
 *    conditions, the following disclaimer and the list of authors.
 * 2) Redistributions in binary form must reproduce the above copyright notice, this list of
 *    conditions, the following disclaimer and the list of authors in the documentation and/or
 *    other materials provided with the distribution.
 * 3) Neither the name of the UbixOS Project nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#define BI_VERSION    0x0
#define BI_KERNELNAME 0x4
#define BI_ENDCOMMON  12
#define BI_SIZE       48
#define BOOTINFO_SIZE 135
#define    RB_BOOTINFO     0x80000000      /* have `struct bootinfo *' arg */


.globl _start
.text
.code32
_start:
  movw  $0x1234,0x472
  pushl %ebp
  movl  %esp,%ebp
  pushl $0x00000002
  popfl

  /* Clear the BSS */
  movl  $(_end),%ecx
  movl  $(__bss_start),%edi
  subl  %edi,%ecx
  xorl  %eax,%eax
  cld
  rep
  stosb

  /* Fix Up GS/FS */
  mov %dx,%ax
  mov %ax,%fs
  mov %ax,%gs

  /* Get Boot Args */
  call get_bootargs
 
  /* Load GDT */
  lgdtl (loadGDT)
  mov   $0x10,%eax 
  mov   %eax,%ds
  mov   %eax,%es
  mov   %eax,%fs
  mov   %eax,%gs
  mov   %eax,%ss
  mov   $kStack,%eax
  addl  $0x1000,%eax
  mov   %esp,%edx
  mov   %eax,%esp
  mov   %eax,%ebp 
  mov   $0x18,%ax
  lldt  %ax
  mov   $0x20,%ax
  ltr   %ax
  ljmp  $0x08,$start_next
start_next:
  call vmm_init
  pushl %esp
  mov  %esp,%ebp
  mov  $0xFFFFFFFF,%eax
  mov  %eax, %esp
  pushl $0xDEAD; // Stack
  pushl $0xBEEF; // Marker
  subl  $0xE,%esp;
  call kmain
get_bootargs:
  /*
   * The old style disk boot blocks fake a frame on the stack and
   * did an lret to get here.  The frame on the stack has a return
   * address of 0.
   */

  cmpl    $0,4(%ebp)
  je      old_boot
  
  /*
   * We have some form of return address, so this is either the
   * old diskless netboot code, or the new uniform code.  That can
   * be detected by looking at the 5th argument, if it is 0
   * we are being booted by the new uniform boot code.
   */
  cmpl    $0,24(%ebp)
  je      new_boot

  hlt
new_boot:
  movl    28(%ebp),%ebx           /* &bootinfo.version */
  movl    BI_VERSION(%ebx),%eax
  cmpl    $1,%eax                 /* We only understand version 1 */
  je      1f
  movl    $1,%eax                 /* Return status */
  leave
  /*
   * XXX this returns to our caller's caller (as is required) since
   * we didn't set up a frame and our caller did.
   */
  hlt /* MrO */
  ret
1:
  /*
   * If we have a kernelname copy it in
   */
        movl    BI_KERNELNAME(%ebx),%esi
        cmpl    $0,%esi
        je      2f              /* No kernelname */
        movl    512,%ecx        /* Brute force!!! */
        movl    $_kernelname,%edi
        cmpb    $'/',(%esi)             /* Make sure it starts with a slash */
        je      1f
        movb    $'/',(%edi)
        incl    %edi
        decl    %ecx
1:
        cld
        rep
        movsb

2:
        /*
         * Determine the size of the boot loader's copy of the bootinfo
         * struct.  This is impossible to do properly because old versions
         * of the struct don't contain a size field and there are 2 old
         * versions with the same version number.
         */
        movl    $BI_ENDCOMMON,%ecx      /* prepare for sizeless version */
        testl   $RB_BOOTINFO,8(%ebp)    /* bi_size (and bootinfo) valid? */
        je      got_bi_size             /* no, sizeless version */
        movl    BI_SIZE(%ebx),%ecx
got_bi_size:

        /*
         * Copy the common part of the bootinfo struct
         */
        movl    %ebx,%esi
        movl    $_bootinfo,%edi
        cmpl    $BOOTINFO_SIZE,%ecx
        jbe     got_common_bi_size
        movl    $BOOTINFO_SIZE,%ecx
got_common_bi_size:
        cld
        rep
        movsb
old_boot:
        movl    8(%ebp),%eax
        movl    %eax,(_boothowto)
        movl    12(%ebp),%eax
        movl    %eax,(_bootdev)

        ret

.data
.comm kStack,0x1000