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 #include <bootargs.h>
  19
  20 #define RBX_MUTE        0x10    /* -m */
  21 #define OPT_SET(opt)    (1 << (opt))
  22
  23 /*
  24  * Prototype BTX loader program, written in a couple of hours.  The
  25  * real thing should probably be more flexible, and in C.
  26  */
  27
  28 /*
  29  * Memory locations.
  30  */
  31                 .set MEM_STUB,0x600             # Real mode stub
  32                 .set MEM_ESP,0x1000             # New stack pointer
  33                 .set MEM_TBL,0x5000             # BTX page tables
  34                 .set MEM_ENTRY,0x9010           # BTX entry point
  35                 .set MEM_DATA,start+0x1000      # Data segment
  36 /*
  37  * Segment selectors.
  38  */
  39                 .set SEL_SCODE,0x8              # 4GB code
  40                 .set SEL_SDATA,0x10             # 4GB data
  41                 .set SEL_RCODE,0x18             # 64K code
  42                 .set SEL_RDATA,0x20             # 64K data
  43 /*
  44  * Paging constants.
  45  */
  46                 .set PAG_SIZ,0x1000             # Page size
  47                 .set PAG_ENT,0x4                # Page entry size
  48 /*
  49  * Screen constants.
  50  */
  51                 .set SCR_MAT,0x7                # Mode/attribute
  52                 .set SCR_COL,0x50               # Columns per row
  53                 .set SCR_ROW,0x19               # Rows per screen
  54 /*
  55  * BIOS Data Area locations.
  56  */
  57                 .set BDA_MEM,0x413              # Free memory
  58                 .set BDA_SCR,0x449              # Video mode
  59                 .set BDA_POS,0x450              # Cursor position
  60 /*
  61  * Required by aout gas inadequacy.
  62  */
  63                 .set SIZ_STUB,0x1a              # Size of stub
  64 /*
  65  * We expect to be loaded by boot2 at the origin defined in ./Makefile.
  66  */
  67                 .globl start
  68 /*
  69  * BTX program loader for ELF clients.
  70  */
  71 start:          cld                             # String ops inc
  72                 testl $OPT_SET(RBX_MUTE), 4(%esp) # Check first argument
  73                 setnz muted                     #  for RBX_MUTE, set flag
  74                 movl $m_logo,%esi               # Identify
  75                 call putstr                     #  ourselves
  76                 movzwl BDA_MEM,%eax             # Get base memory
  77                 shll $0xa,%eax                  #  in bytes
  78                 movl %eax,%ebp                  # Base of user stack
  79 #ifdef BTXLDR_VERBOSE
  80                 movl $m_mem,%esi                # Display
  81                 call hexout                     #  amount of
  82                 call putstr                     #  base memory
  83 #endif
  84                 lgdt gdtdesc                    # Load new GDT
  85 /*
  86  * Relocate caller's arguments.
  87  */
  88 #ifdef BTXLDR_VERBOSE
  89                 movl $m_esp,%esi                # Display
  90                 movl %esp,%eax                  #  caller
  91                 call hexout                     #  stack
  92                 call putstr                     #  pointer
  93                 movl $m_args,%esi               # Format string
  94                 leal 0x4(%esp),%ebx             # First argument
  95                 movl $0x6,%ecx                  # Count
  96 start.1:        movl (%ebx),%eax                # Get argument and
  97                 addl $0x4,%ebx                  #  bump pointer
  98                 call hexout                     # Display it
  99                 loop start.1                    # Till done
 100                 call putstr                     # End message
 101 #endif
 102                 movl BA_BOOTINFO+4(%esp),%esi   # Source: bootinfo
 103                 cmpl $0x0, %esi                 # If the bootinfo pointer
 104                 je start_null_bi                #  is null, don't copy it
 105                 movl BI_SIZE(%esi),%ecx         # Allocate space
 106                 subl %ecx,%ebp                  #  for bootinfo
 107                 movl %ebp,%edi                  # Destination
 108                 rep                             # Copy
 109                 movsb                           #  it
 110                 movl %ebp,BA_BOOTINFO+4(%esp)   # Update pointer
 111                 movl %edi,%ebp                  # Restore base pointer
 112 #ifdef BTXLDR_VERBOSE
 113                 movl $m_rel_bi,%esi             # Display
 114                 movl %ebp,%eax                  #  bootinfo
 115                 call hexout                     #  relocation
 116                 call putstr                     #  message
 117 #endif
 118 start_null_bi:  movl $BOOTARGS_SIZE,%ecx        # Fixed size of arguments
 119                 testl $KARGS_FLAGS_EXTARG, BA_BOOTFLAGS+4(%esp) # Check for extra data
 120                 jz start_fixed                  # Skip if the flag is not set
 121                 addl BOOTARGS_SIZE+4(%esp),%ecx # Add size of variable args
 122 start_fixed:    subl $ARGOFF,%ebp               # Place args at fixed offset
 123                 leal 0x4(%esp),%esi             # Source
 124                 movl %ebp,%edi                  # Destination
 125                 rep                             # Copy
 126                 movsb                           #  them
 127 #ifdef BTXLDR_VERBOSE
 128                 movl $m_rel_args,%esi           # Display
 129                 movl %ebp,%eax                  #  argument
 130                 call hexout                     #  relocation
 131                 call putstr                     #  message
 132 #endif
 133 /*
 134  * Set up BTX kernel.
 135  */
 136                 movl $MEM_ESP,%esp              # Set up new stack
 137                 movl $MEM_DATA,%ebx             # Data segment
 138                 movl $m_vers,%esi               # Display BTX
 139                 call putstr                     #  version message
 140                 movb 0x5(%ebx),%al              # Get major version
 141                 addb $'0',%al                   # Display
 142                 call putchr                     #  it
 143                 movb $'.',%al                   # And a
 144                 call putchr                     #  dot
 145                 movb 0x6(%ebx),%al              # Get minor
 146                 xorb %ah,%ah                    #  version
 147                 movb $0xa,%dl                   # Divide
 148                 divb %dl,%al                    #  by 10
 149                 addb $'0',%al                   # Display
 150                 call putchr                     #  tens
 151                 movb %ah,%al                    # Get units
 152                 addb $'0',%al                   # Display
 153                 call putchr                     #  units
 154                 call putstr                     # End message
 155                 movl %ebx,%esi                  # BTX image
 156                 movzwl 0x8(%ebx),%edi           # Compute
 157                 orl $PAG_SIZ/PAG_ENT-1,%edi     #  the
 158                 incl %edi                       #  BTX
 159                 shll $0x2,%edi                  #  load
 160                 addl $MEM_TBL,%edi              #  address
 161                 pushl %edi                      # Save load address
 162                 movzwl 0xa(%ebx),%ecx           # Image size
 163 #ifdef BTXLDR_VERBOSE
 164                 pushl %ecx                      # Save image size
 165 #endif
 166                 rep                             # Relocate
 167                 movsb                           #  BTX
 168                 movl %esi,%ebx                  # Keep place
 169 #ifdef BTXLDR_VERBOSE
 170                 movl $m_rel_btx,%esi            # Restore
 171                 popl %eax                       #  parameters
 172                 call hexout                     #  and
 173 #endif
 174                 popl %ebp                       #  display
 175 #ifdef BTXLDR_VERBOSE
 176                 movl %ebp,%eax                  #  the
 177                 call hexout                     #  relocation
 178                 call putstr                     #  message
 179 #endif
 180                 addl $PAG_SIZ,%ebp              # Display
 181 #ifdef BTXLDR_VERBOSE
 182                 movl $m_base,%esi               #  the
 183                 movl %ebp,%eax                  #  user
 184                 call hexout                     #  base
 185                 call putstr                     #  address
 186 #endif
 187 /*
 188  * Set up ELF-format client program.
 189  */
 190                 cmpl $0x464c457f,(%ebx)         # ELF magic number?
 191                 je start.3                      # Yes
 192                 movl $e_fmt,%esi                # Display error
 193                 call putstr                     #  message
 194 start.2:        jmp start.2                     # Hang
 195 start.3:
 196 #ifdef BTXLDR_VERBOSE
 197                 movl $m_elf,%esi                # Display ELF
 198                 call putstr                     #  message
 199                 movl $m_segs,%esi               # Format string
 200 #endif
 201                 movl $0x2,%edi                  # Segment count
 202                 movl 0x1c(%ebx),%edx            # Get e_phoff
 203                 addl %ebx,%edx                  # To pointer
 204                 movzwl 0x2c(%ebx),%ecx          # Get e_phnum
 205 start.4:        cmpl $0x1,(%edx)                # Is p_type PT_LOAD?
 206                 jne start.6                     # No
 207 #ifdef BTXLDR_VERBOSE
 208                 movl 0x4(%edx),%eax             # Display
 209                 call hexout                     #  p_offset
 210                 movl 0x8(%edx),%eax             # Display
 211                 call hexout                     #  p_vaddr
 212                 movl 0x10(%edx),%eax            # Display
 213                 call hexout                     #  p_filesz
 214                 movl 0x14(%edx),%eax            # Display
 215                 call hexout                     #  p_memsz
 216                 call putstr                     # End message
 217 #endif
 218                 pushl %esi                      # Save
 219                 pushl %edi                      #  working
 220                 pushl %ecx                      #  registers
 221                 movl 0x4(%edx),%esi             # Get p_offset
 222                 addl %ebx,%esi                  #  as pointer
 223                 movl 0x8(%edx),%edi             # Get p_vaddr
 224                 addl %ebp,%edi                  #  as pointer
 225                 movl 0x10(%edx),%ecx            # Get p_filesz
 226                 rep                             # Set up
 227                 movsb                           #  segment
 228                 movl 0x14(%edx),%ecx            # Any bytes
 229                 subl 0x10(%edx),%ecx            #  to zero?
 230                 jz start.5                      # No
 231                 xorb %al,%al                    # Then
 232                 rep                             #  zero
 233                 stosb                           #  them
 234 start.5:        popl %ecx                       # Restore
 235                 popl %edi                       #  working
 236                 popl %esi                       #  registers
 237                 decl %edi                       # Segments to do
 238                 je start.7                      # If none
 239 start.6:        addl $0x20,%edx                 # To next entry
 240                 loop start.4                    # Till done
 241 start.7:
 242 #ifdef BTXLDR_VERBOSE
 243                 movl $m_done,%esi               # Display done
 244                 call putstr                     #  message
 245 #endif
 246                 movl $start.8,%esi              # Real mode stub
 247                 movl $MEM_STUB,%edi             # Destination
 248                 movl $start.9-start.8,%ecx      # Size
 249                 rep                             # Relocate
 250                 movsb                           #  it
 251                 ljmp $SEL_RCODE,$MEM_STUB       # To 16-bit code
 252                 .code16
 253 start.8:        xorw %ax,%ax                    # Data
 254                 movb $SEL_RDATA,%al             #  selector
 255                 movw %ax,%ss                    # Reload SS
 256                 movw %ax,%ds                    # Reset
 257                 movw %ax,%es                    #  other
 258                 movw %ax,%fs                    #  segment
 259                 movw %ax,%gs                    #  limits
 260                 movl %cr0,%eax                  # Switch to
 261                 decw %ax                        #  real
 262                 movl %eax,%cr0                  #  mode
 263                 ljmp $0,$MEM_ENTRY              # Jump to BTX entry point
 264 start.9:
 265                 .code32
 266 /*
 267  * Output message [ESI] followed by EAX in hex.
 268  */
 269 hexout:         pushl %eax                      # Save
 270                 call putstr                     # Display message
 271                 popl %eax                       # Restore
 272                 pushl %esi                      # Save
 273                 pushl %edi                      #  caller's
 274                 movl $buf,%edi                  # Buffer
 275                 pushl %edi                      # Save
 276                 call hex32                      # To hex
 277                 xorb %al,%al                    # Terminate
 278                 stosb                           #  string
 279                 popl %esi                       # Restore
 280 hexout.1:       lodsb                           # Get a char
 281                 cmpb $'0',%al                   # Leading zero?
 282                 je hexout.1                     # Yes
 283                 testb %al,%al                   # End of string?
 284                 jne hexout.2                    # No
 285                 decl %esi                       # Undo
 286 hexout.2:       decl %esi                       # Adjust for inc
 287                 call putstr                     # Display hex
 288                 popl %edi                       # Restore
 289                 popl %esi                       #  caller's
 290                 ret                             # To caller
 291 /*
 292  * Output zero-terminated string [ESI] to the console.
 293  */
 294 putstr.0:       call putchr                     # Output char
 295 putstr:         lodsb                           # Load char
 296                 testb %al,%al                   # End of string?
 297                 jne putstr.0                    # No
 298                 ret                             # To caller
 299 /*
 300  * Output character AL to the console.
 301  */
 302 putchr:         testb $1,muted                  # Check muted
 303                 jnz putchr.5                    #  do a nop
 304                 pusha                           # Save
 305                 xorl %ecx,%ecx                  # Zero for loops
 306                 movb $SCR_MAT,%ah               # Mode/attribute
 307                 movl $BDA_POS,%ebx              # BDA pointer
 308                 movw (%ebx),%dx                 # Cursor position
 309                 movl $0xb8000,%edi              # Regen buffer (color)
 310                 cmpb %ah,BDA_SCR-BDA_POS(%ebx)  # Mono mode?
 311                 jne putchr.1                    # No
 312                 xorw %di,%di                    # Regen buffer (mono)
 313 putchr.1:       cmpb $0xa,%al                   # New line?
 314                 je putchr.2                     # Yes
 315                 xchgl %eax,%ecx                 # Save char
 316                 movb $SCR_COL,%al               # Columns per row
 317                 mulb %dh                        #  * row position
 318                 addb %dl,%al                    #  + column
 319                 adcb $0x0,%ah                   #  position
 320                 shll %eax                       #  * 2
 321                 xchgl %eax,%ecx                 # Swap char, offset
 322                 movw %ax,(%edi,%ecx,1)          # Write attr:char
 323                 incl %edx                       # Bump cursor
 324                 cmpb $SCR_COL,%dl               # Beyond row?
 325                 jb putchr.3                     # No
 326 putchr.2:       xorb %dl,%dl                    # Zero column
 327                 incb %dh                        # Bump row
 328 putchr.3:       cmpb $SCR_ROW,%dh               # Beyond screen?
 329                 jb putchr.4                     # No
 330                 leal 2*SCR_COL(%edi),%esi       # New top line
 331                 movw $(SCR_ROW-1)*SCR_COL/2,%cx # Words to move
 332                 rep                             # Scroll
 333                 movsl                           #  screen
 334                 movb $' ',%al                   # Space
 335                 movb $SCR_COL,%cl               # Columns to clear
 336                 rep                             # Clear
 337                 stosw                           #  line
 338                 movb $SCR_ROW-1,%dh             # Bottom line
 339 putchr.4:       movw %dx,(%ebx)                 # Update position
 340                 popa                            # Restore
 341 putchr.5:       ret                             # To caller
 342 /*
 343  * Convert EAX, AX, or AL to hex, saving the result to [EDI].
 344  */
 345 hex32:          pushl %eax                      # Save
 346                 shrl $0x10,%eax                 # Do upper
 347                 call hex16                      #  16
 348                 popl %eax                       # Restore
 349 hex16:          call hex16.1                    # Do upper 8
 350 hex16.1:        xchgb %ah,%al                   # Save/restore
 351 hex8:           pushl %eax                      # Save
 352                 shrb $0x4,%al                   # Do upper
 353                 call hex8.1                     #  4
 354                 popl %eax                       # Restore
 355 hex8.1:         andb $0xf,%al                   # Get lower 4
 356                 cmpb $0xa,%al                   # Convert
 357                 sbbb $0x69,%al                  #  to hex
 358                 das                             #  digit
 359                 orb $0x20,%al                   # To lower case
 360                 stosb                           # Save char
 361                 ret                             # (Recursive)
 362
 363                 .data
 364                 .p2align 4
 365 /*
 366  * Global descriptor table.
 367  */
 368 gdt:            .word 0x0,0x0,0x0,0x0           # Null entry
 369                 .word 0xffff,0x0,0x9a00,0xcf    # SEL_SCODE
 370                 .word 0xffff,0x0,0x9200,0xcf    # SEL_SDATA
 371                 .word 0xffff,0x0,0x9a00,0x0     # SEL_RCODE
 372                 .word 0xffff,0x0,0x9200,0x0     # SEL_RDATA
 373 gdt.1:
 374 gdtdesc:        .word gdt.1-gdt-1               # Limit
 375                 .long gdt                       # Base
 376 /*
 377  * Messages.
 378  */
 379 m_logo:         .asciz " \nBTX loader 1.00  "
 380 m_vers:         .asciz "BTX version is \0\n"
 381 e_fmt:          .asciz "Error: Client format not supported\n"
 382 #ifdef BTXLDR_VERBOSE
 383 m_mem:          .asciz "Starting in protected mode (base mem=\0)\n"
 384 m_esp:          .asciz "Arguments passed (esp=\0):\n"
 385 m_args:         .asciz"<howto="
 386                 .asciz" bootdev="
 387                 .asciz" junk="
 388                 .asciz" "
 389                 .asciz" "
 390                 .asciz" bootinfo=\0>\n"
 391 m_rel_bi:       .asciz "Relocated bootinfo (size=48) to \0\n"
 392 m_rel_args:     .asciz "Relocated arguments (size=18) to \0\n"
 393 m_rel_btx:      .asciz "Relocated kernel (size=\0) to \0\n"
 394 m_base:         .asciz "Client base address is \0\n"
 395 m_elf:          .asciz "Client format is ELF\n"
 396 m_segs:         .asciz "text segment: offset="
 397                 .asciz " vaddr="
 398                 .asciz " filesz="
 399                 .asciz " memsz=\0\n"
 400                 .asciz "data segment: offset="
 401                 .asciz " vaddr="
 402                 .asciz " filesz="
 403                 .asciz " memsz=\0\n"
 404 m_done:         .asciz "Loading complete\n"
 405 #endif
 406
 407 /*
 408  * Flags
 409  */
 410 muted:          .byte 0x0
 411
 412 /*
 413  * Uninitialized data area.
 414  */
 415 buf:                                            # Scratch buffer