sys/boot/i386/btx/btxldr/btxldr.S

   1 /*
   2  * Copyright (c) 1998 Robert Nordier
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms are freely
   6  * permitted provided that the above copyright notice and this
   7  * paragraph and the following disclaimer are duplicated in all
   8  * such forms.
   9  *
  10  * This software is provided "AS IS" and without any express or
  11  * implied warranties, including, without limitation, the implied
  12  * warranties of merchantability and fitness for a particular
  13  * purpose.
  14  *
  15  * $FreeBSD$
  16  */
  17
  18 #define RBX_MUTE        0x10    /* -m */
  19 #define OPT_SET(opt)    (1 << (opt))
  20
  21 /*
  22  * Prototype BTX loader program, written in a couple of hours.  The
  23  * real thing should probably be more flexible, and in C.
  24  */
  25
  26 /*
  27  * Memory locations.
  28  */
  29                 .set MEM_STUB,0x600             # Real mode stub
  30                 .set MEM_ESP,0x1000             # New stack pointer
  31                 .set MEM_TBL,0x5000             # BTX page tables
  32                 .set MEM_ENTRY,0x9010           # BTX entry point
  33                 .set MEM_DATA,start+0x1000      # Data segment
  34 /*
  35  * Segment selectors.
  36  */
  37                 .set SEL_SCODE,0x8              # 4GB code
  38                 .set SEL_SDATA,0x10             # 4GB data
  39                 .set SEL_RCODE,0x18             # 64K code
  40                 .set SEL_RDATA,0x20             # 64K data
  41 /*
  42  * Paging constants.
  43  */
  44                 .set PAG_SIZ,0x1000             # Page size
  45                 .set PAG_ENT,0x4                # Page entry size
  46 /*
  47  * Screen constants.
  48  */
  49                 .set SCR_MAT,0x7                # Mode/attribute
  50                 .set SCR_COL,0x50               # Columns per row
  51                 .set SCR_ROW,0x19               # Rows per screen
  52 /*
  53  * BIOS Data Area locations.
  54  */
  55                 .set BDA_MEM,0x413              # Free memory
  56                 .set BDA_SCR,0x449              # Video mode
  57                 .set BDA_POS,0x450              # Cursor position
  58 /*
  59  * Required by aout gas inadequacy.
  60  */
  61                 .set SIZ_STUB,0x1a              # Size of stub
  62 /*
  63  * We expect to be loaded by boot2 at the origin defined in ./Makefile.
  64  */
  65                 .globl start
  66 /*
  67  * BTX program loader for ELF clients.
  68  */
  69 start:          cld                             # String ops inc
  70                 testl $OPT_SET(RBX_MUTE), 4(%esp) # Check first argument
  71                 setnz muted                     #  for RBX_MUTE, set flag
  72                 movl $m_logo,%esi               # Identify
  73                 call putstr                     #  ourselves
  74                 movzwl BDA_MEM,%eax             # Get base memory
  75                 shll $0xa,%eax                  #  in bytes
  76                 movl %eax,%ebp                  # Base of user stack
  77 #ifdef BTXLDR_VERBOSE
  78                 movl $m_mem,%esi                # Display
  79                 call hexout                     #  amount of
  80                 call putstr                     #  base memory
  81 #endif
  82                 lgdt gdtdesc                    # Load new GDT
  83 /*
  84  * Relocate caller's arguments.
  85  */
  86 #ifdef BTXLDR_VERBOSE
  87                 movl $m_esp,%esi                # Display
  88                 movl %esp,%eax                  #  caller
  89                 call hexout                     #  stack
  90                 call putstr                     #  pointer
  91                 movl $m_args,%esi               # Format string
  92                 leal 0x4(%esp,1),%ebx           # First argument
  93                 movl $0x6,%ecx                  # Count
  94 start.1:        movl (%ebx),%eax                # Get argument and
  95                 addl $0x4,%ebx                  #  bump pointer
  96                 call hexout                     # Display it
  97                 loop start.1                    # Till done
  98                 call putstr                     # End message
  99 #endif
 100                 movl $0x48,%ecx                 # Allocate space
 101                 subl %ecx,%ebp                  #  for bootinfo
 102                 movl 0x18(%esp,1),%esi          # Source: bootinfo
 103                 cmpl $0x0, %esi                 # If the bootinfo pointer
 104                 je start_null_bi                #  is null, don't copy it
 105                 movl %ebp,%edi                  # Destination
 106                 rep                             # Copy
 107                 movsb                           #  it
 108                 movl %ebp,0x18(%esp,1)          # Update pointer
 109 #ifdef BTXLDR_VERBOSE
 110                 movl $m_rel_bi,%esi             # Display
 111                 movl %ebp,%eax                  #  bootinfo
 112                 call hexout                     #  relocation
 113                 call putstr                     #  message
 114 #endif
 115 start_null_bi:  movl $0x18,%ecx                 # Allocate space
 116                 subl %ecx,%ebp                  #  for arguments
 117                 leal 0x4(%esp,1),%esi           # Source
 118                 movl %ebp,%edi                  # Destination
 119                 rep                             # Copy
 120                 movsb                           #  them
 121 #ifdef BTXLDR_VERBOSE
 122                 movl $m_rel_args,%esi           # Display
 123                 movl %ebp,%eax                  #  argument
 124                 call hexout                     #  relocation
 125                 call putstr                     #  message
 126 #endif
 127 /*
 128  * Set up BTX kernel.
 129  */
 130                 movl $MEM_ESP,%esp              # Set up new stack
 131                 movl $MEM_DATA,%ebx             # Data segment
 132                 movl $m_vers,%esi               # Display BTX
 133                 call putstr                     #  version message
 134                 movb 0x5(%ebx),%al              # Get major version
 135                 addb $'0',%al                   # Display
 136                 call putchr                     #  it
 137                 movb $'.',%al                   # And a
 138                 call putchr                     #  dot
 139                 movb 0x6(%ebx),%al              # Get minor
 140                 xorb %ah,%ah                    #  version
 141                 movb $0xa,%dl                   # Divide
 142                 divb %dl,%al                    #  by 10
 143                 addb $'0',%al                   # Display
 144                 call putchr                     #  tens
 145                 movb %ah,%al                    # Get units
 146                 addb $'0',%al                   # Display
 147                 call putchr                     #  units
 148                 call putstr                     # End message
 149                 movl %ebx,%esi                  # BTX image
 150                 movzwl 0x8(%ebx),%edi           # Compute
 151                 orl $PAG_SIZ/PAG_ENT-1,%edi     #  the
 152                 incl %edi                       #  BTX
 153                 shll $0x2,%edi                  #  load
 154                 addl $MEM_TBL,%edi              #  address
 155                 pushl %edi                      # Save load address
 156                 movzwl 0xa(%ebx),%ecx           # Image size
 157 #ifdef BTXLDR_VERBOSE
 158                 pushl %ecx                      # Save image size
 159 #endif
 160                 rep                             # Relocate
 161                 movsb                           #  BTX
 162                 movl %esi,%ebx                  # Keep place
 163 #ifdef BTXLDR_VERBOSE
 164                 movl $m_rel_btx,%esi            # Restore
 165                 popl %eax                       #  parameters
 166                 call hexout                     #  and
 167 #endif
 168                 popl %ebp                       #  display
 169 #ifdef BTXLDR_VERBOSE
 170                 movl %ebp,%eax                  #  the
 171                 call hexout                     #  relocation
 172                 call putstr                     #  message
 173 #endif
 174                 addl $PAG_SIZ,%ebp              # Display
 175 #ifdef BTXLDR_VERBOSE
 176                 movl $m_base,%esi               #  the
 177                 movl %ebp,%eax                  #  user
 178                 call hexout                     #  base
 179                 call putstr                     #  address
 180 #endif
 181 /*
 182  * Set up ELF-format client program.
 183  */
 184                 cmpl $0x464c457f,(%ebx)         # ELF magic number?
 185                 je start.3                      # Yes
 186                 movl $e_fmt,%esi                # Display error
 187                 call putstr                     #  message
 188 start.2:        jmp start.2                     # Hang
 189 start.3:
 190 #ifdef BTXLDR_VERBOSE
 191                 movl $m_elf,%esi                # Display ELF
 192                 call putstr                     #  message
 193                 movl $m_segs,%esi               # Format string
 194 #endif
 195                 movl $0x2,%edi                  # Segment count
 196                 movl 0x1c(%ebx),%edx            # Get e_phoff
 197                 addl %ebx,%edx                  # To pointer
 198                 movzwl 0x2c(%ebx),%ecx          # Get e_phnum
 199 start.4:        cmpl $0x1,(%edx)                # Is p_type PT_LOAD?
 200                 jne start.6                     # No
 201 #ifdef BTXLDR_VERBOSE
 202                 movl 0x4(%edx),%eax             # Display
 203                 call hexout                     #  p_offset
 204                 movl 0x8(%edx),%eax             # Display
 205                 call hexout                     #  p_vaddr
 206                 movl 0x10(%edx),%eax            # Display
 207                 call hexout                     #  p_filesz
 208                 movl 0x14(%edx),%eax            # Display
 209                 call hexout                     #  p_memsz
 210                 call putstr                     # End message
 211 #endif
 212                 pushl %esi                      # Save
 213                 pushl %edi                      #  working
 214                 pushl %ecx                      #  registers
 215                 movl 0x4(%edx),%esi             # Get p_offset
 216                 addl %ebx,%esi                  #  as pointer
 217                 movl 0x8(%edx),%edi             # Get p_vaddr
 218                 addl %ebp,%edi                  #  as pointer
 219                 movl 0x10(%edx),%ecx            # Get p_filesz
 220                 rep                             # Set up
 221                 movsb                           #  segment
 222                 movl 0x14(%edx),%ecx            # Any bytes
 223                 subl 0x10(%edx),%ecx            #  to zero?
 224                 jz start.5                      # No
 225                 xorb %al,%al                    # Then
 226                 rep                             #  zero
 227                 stosb                           #  them
 228 start.5:        popl %ecx                       # Restore
 229                 popl %edi                       #  working
 230                 popl %esi                       #  registers
 231                 decl %edi                       # Segments to do
 232                 je start.7                      # If none
 233 start.6:        addl $0x20,%edx                 # To next entry
 234                 loop start.4                    # Till done
 235 start.7:
 236 #ifdef BTXLDR_VERBOSE
 237                 movl $m_done,%esi               # Display done
 238                 call putstr                     #  message
 239 #endif
 240                 movl $start.8,%esi              # Real mode stub
 241                 movl $MEM_STUB,%edi             # Destination
 242                 movl $start.9-start.8,%ecx      # Size
 243                 rep                             # Relocate
 244                 movsb                           #  it
 245                 ljmp $SEL_RCODE,$MEM_STUB       # To 16-bit code
 246                 .code16
 247 start.8:        xorw %ax,%ax                    # Data
 248                 movb $SEL_RDATA,%al             #  selector
 249                 movw %ax,%ss                    # Reload SS
 250                 movw %ax,%ds                    # Reset
 251                 movw %ax,%es                    #  other
 252                 movw %ax,%fs                    #  segment
 253                 movw %ax,%gs                    #  limits
 254                 movl %cr0,%eax                  # Switch to
 255                 decw %ax                        #  real
 256                 movl %eax,%cr0                  #  mode
 257                 ljmp $0,$MEM_ENTRY              # Jump to BTX entry point
 258 start.9:
 259                 .code32
 260 /*
 261  * Output message [ESI] followed by EAX in hex.
 262  */
 263 hexout:         pushl %eax                      # Save
 264                 call putstr                     # Display message
 265                 popl %eax                       # Restore
 266                 pushl %esi                      # Save
 267                 pushl %edi                      #  caller's
 268                 movl $buf,%edi                  # Buffer
 269                 pushl %edi                      # Save
 270                 call hex32                      # To hex
 271                 xorb %al,%al                    # Terminate
 272                 stosb                           #  string
 273                 popl %esi                       # Restore
 274 hexout.1:       lodsb                           # Get a char
 275                 cmpb $'0',%al                   # Leading zero?
 276                 je hexout.1                     # Yes
 277                 testb %al,%al                   # End of string?
 278                 jne hexout.2                    # No
 279                 decl %esi                       # Undo
 280 hexout.2:       decl %esi                       # Adjust for inc
 281                 call putstr                     # Display hex
 282                 popl %edi                       # Restore
 283                 popl %esi                       #  caller's
 284                 ret                             # To caller
 285 /*
 286  * Output zero-terminated string [ESI] to the console.
 287  */
 288 putstr.0:       call putchr                     # Output char
 289 putstr:         lodsb                           # Load char
 290                 testb %al,%al                   # End of string?
 291                 jne putstr.0                    # No
 292                 ret                             # To caller
 293 /*
 294  * Output character AL to the console.
 295  */
 296 putchr:         testb $1,muted                  # Check muted
 297                 jnz putchr.5                    #  do a nop
 298                 pusha                           # Save
 299                 xorl %ecx,%ecx                  # Zero for loops
 300                 movb $SCR_MAT,%ah               # Mode/attribute
 301                 movl $BDA_POS,%ebx              # BDA pointer
 302                 movw (%ebx),%dx                 # Cursor position
 303                 movl $0xb8000,%edi              # Regen buffer (color)
 304                 cmpb %ah,BDA_SCR-BDA_POS(%ebx)  # Mono mode?
 305                 jne putchr.1                    # No
 306                 xorw %di,%di                    # Regen buffer (mono)
 307 putchr.1:       cmpb $0xa,%al                   # New line?
 308                 je putchr.2                     # Yes
 309                 xchgl %eax,%ecx                 # Save char
 310                 movb $SCR_COL,%al               # Columns per row
 311                 mulb %dh                        #  * row position
 312                 addb %dl,%al                    #  + column
 313                 adcb $0x0,%ah                   #  position
 314                 shll %eax                       #  * 2
 315                 xchgl %eax,%ecx                 # Swap char, offset
 316                 movw %ax,(%edi,%ecx,1)          # Write attr:char
 317                 incl %edx                       # Bump cursor
 318                 cmpb $SCR_COL,%dl               # Beyond row?
 319                 jb putchr.3                     # No
 320 putchr.2:       xorb %dl,%dl                    # Zero column
 321                 incb %dh                        # Bump row
 322 putchr.3:       cmpb $SCR_ROW,%dh               # Beyond screen?
 323                 jb putchr.4                     # No
 324                 leal 2*SCR_COL(%edi),%esi       # New top line
 325                 movw $(SCR_ROW-1)*SCR_COL/2,%cx # Words to move
 326                 rep                             # Scroll
 327                 movsl                           #  screen
 328                 movb $' ',%al                   # Space
 329                 movb $SCR_COL,%cl               # Columns to clear
 330                 rep                             # Clear
 331                 stosw                           #  line
 332                 movb $SCR_ROW-1,%dh             # Bottom line
 333 putchr.4:       movw %dx,(%ebx)                 # Update position
 334                 popa                            # Restore
 335 putchr.5:       ret                             # To caller
 336 /*
 337  * Convert EAX, AX, or AL to hex, saving the result to [EDI].
 338  */
 339 hex32:          pushl %eax                      # Save
 340                 shrl $0x10,%eax                 # Do upper
 341                 call hex16                      #  16
 342                 popl %eax                       # Restore
 343 hex16:          call hex16.1                    # Do upper 8
 344 hex16.1:        xchgb %ah,%al                   # Save/restore
 345 hex8:           pushl %eax                      # Save
 346                 shrb $0x4,%al                   # Do upper
 347                 call hex8.1                     #  4
 348                 popl %eax                       # Restore
 349 hex8.1:         andb $0xf,%al                   # Get lower 4
 350                 cmpb $0xa,%al                   # Convert
 351                 sbbb $0x69,%al                  #  to hex
 352                 das                             #  digit
 353                 orb $0x20,%al                   # To lower case
 354                 stosb                           # Save char
 355                 ret                             # (Recursive)
 356
 357                 .data
 358                 .p2align 4
 359 /*
 360  * Global descriptor table.
 361  */
 362 gdt:            .word 0x0,0x0,0x0,0x0           # Null entry
 363                 .word 0xffff,0x0,0x9a00,0xcf    # SEL_SCODE
 364                 .word 0xffff,0x0,0x9200,0xcf    # SEL_SDATA
 365                 .word 0xffff,0x0,0x9a00,0x0     # SEL_RCODE
 366                 .word 0xffff,0x0,0x9200,0x0     # SEL_RDATA
 367 gdt.1:
 368 gdtdesc:        .word gdt.1-gdt-1               # Limit
 369                 .long gdt                       # Base
 370 /*
 371  * Messages.
 372  */
 373 m_logo:         .asciz " \nBTX loader 1.00  "
 374 m_vers:         .asciz "BTX version is \0\n"
 375 e_fmt:          .asciz "Error: Client format not supported\n"
 376 #ifdef BTXLDR_VERBOSE
 377 m_mem:          .asciz "Starting in protected mode (base mem=\0)\n"
 378 m_esp:          .asciz "Arguments passed (esp=\0):\n"
 379 m_args:         .asciz"<howto="
 380                 .asciz" bootdev="
 381                 .asciz" junk="
 382                 .asciz" "
 383                 .asciz" "
 384                 .asciz" bootinfo=\0>\n"
 385 m_rel_bi:       .asciz "Relocated bootinfo (size=48) to \0\n"
 386 m_rel_args:     .asciz "Relocated arguments (size=18) to \0\n"
 387 m_rel_btx:      .asciz "Relocated kernel (size=\0) to \0\n"
 388 m_base:         .asciz "Client base address is \0\n"
 389 m_elf:          .asciz "Client format is ELF\n"
 390 m_segs:         .asciz "text segment: offset="
 391                 .asciz " vaddr="
 392                 .asciz " filesz="
 393                 .asciz " memsz=\0\n"
 394                 .asciz "data segment: offset="
 395                 .asciz " vaddr="
 396                 .asciz " filesz="
 397                 .asciz " memsz=\0\n"
 398 m_done:         .asciz "Loading complete\n"
 399 #endif
 400
 401 /*
 402  * Flags
 403  */
 404 muted:          .byte 0x0
 405
 406 /*
 407  * Uninitialized data area.
 408  */
 409 buf:                                            # Scratch buffer