sys/boot/pc98/btx/btx/btx.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 /*
  19  * Memory layout.
  20  */
  21                 .set MEM_BTX,0x1000             # Start of BTX memory
  22                 .set MEM_ESP0,0x1800            # Supervisor stack
  23                 .set MEM_BUF,0x1800             # Scratch buffer
  24                 .set MEM_ESP1,0x1e00            # Link stack
  25                 .set MEM_IDT,0x1e00             # IDT
  26                 .set MEM_TSS,0x1f98             # TSS
  27                 .set MEM_MAP,0x2000             # I/O bit map
  28                 .set MEM_DIR,0x4000             # Page directory
  29                 .set MEM_TBL,0x5000             # Page tables
  30                 .set MEM_ORG,0x9000             # BTX code
  31                 .set MEM_USR,0xa000             # Start of user memory
  32 /*
  33  * Paging control.
  34  */
  35                 .set PAG_SIZ,0x1000             # Page size
  36                 .set PAG_CNT,0x1000             # Pages to map
  37 /*
  38  * Segment selectors.
  39  */
  40                 .set SEL_SCODE,0x8              # Supervisor code
  41                 .set SEL_SDATA,0x10             # Supervisor data
  42                 .set SEL_RCODE,0x18             # Real mode code
  43                 .set SEL_RDATA,0x20             # Real mode data
  44                 .set SEL_UCODE,0x28|3           # User code
  45                 .set SEL_UDATA,0x30|3           # User data
  46                 .set SEL_TSS,0x38               # TSS
  47 /*
  48  * Task state segment fields.
  49  */
  50                 .set TSS_ESP0,0x4               # PL 0 ESP
  51                 .set TSS_SS0,0x8                # PL 0 SS
  52                 .set TSS_ESP1,0xc               # PL 1 ESP
  53                 .set TSS_MAP,0x66               # I/O bit map base
  54 /*
  55  * System calls.
  56  */
  57                 .set SYS_EXIT,0x0               # Exit
  58                 .set SYS_EXEC,0x1               # Exec
  59 /*
  60  * V86 constants.
  61  */
  62                 .set V86_FLG,0x208eff           # V86 flag mask
  63                 .set V86_STK,0x400              # V86 stack allowance
  64 /*
  65  * Dump format control bytes.
  66  */
  67                 .set DMP_X16,0x1                # Word
  68                 .set DMP_X32,0x2                # Long
  69                 .set DMP_MEM,0x4                # Memory
  70                 .set DMP_EOL,0x8                # End of line
  71 /*
  72  * Screen defaults and assumptions.
  73  */
  74                 .set SCR_MAT,0xe1               # Mode/attribute
  75                 .set SCR_COL,0x50               # Columns per row
  76                 .set SCR_ROW,0x19               # Rows per screen
  77 /*
  78  * BIOS Data Area locations.
  79  */
  80                 .set BDA_MEM,0x501              # Free memory
  81                 .set BDA_KEYFLAGS,0x53a         # Keyboard shift-state flags
  82                 .set BDA_POS,0x53e              # Cursor position
  83 /*
  84  * Derivations, for brevity.
  85  */
  86                 .set _ESP0H,MEM_ESP0>>0x8       # Byte 1 of ESP0
  87                 .set _ESP1H,MEM_ESP1>>0x8       # Byte 1 of ESP1
  88                 .set _TSSIO,MEM_MAP-MEM_TSS     # TSS I/O base
  89                 .set _TSSLM,MEM_DIR-MEM_TSS-1   # TSS limit
  90                 .set _IDTLM,MEM_TSS-MEM_IDT-1   # IDT limit
  91 /*
  92  * Code segment.
  93  */
  94                 .globl start
  95                 .code16
  96 start:                                          # Start of code
  97 /*
  98  * BTX header.
  99  */
 100 btx_hdr:        .byte 0xeb                      # Machine ID
 101                 .byte 0xe                       # Header size
 102                 .ascii "BTX"                    # Magic
 103                 .byte 0x1                       # Major version
 104                 .byte 0x1                       # Minor version
 105                 .byte BTX_FLAGS                 # Flags
 106                 .word PAG_CNT-MEM_ORG>>0xc      # Paging control
 107                 .word break-start               # Text size
 108                 .long 0x0                       # Entry address
 109 /*
 110  * Initialization routine.
 111  */
 112 init:           cli                             # Disable interrupts
 113                 xor %ax,%ax                     # Zero/segment
 114                 mov %ax,%ss                     # Set up
 115                 mov $MEM_ESP0,%sp               #  stack
 116                 mov %ax,%es                     # Address
 117                 mov %ax,%ds                     #  data
 118                 pushl $0x2                      # Clear
 119                 popfl                           #  flags
 120 /*
 121  * Initialize memory.
 122  */
 123                 mov $MEM_IDT,%di                # Memory to initialize
 124                 mov $(MEM_ORG-MEM_IDT)/2,%cx    # Words to zero
 125                 push %di                        # Save
 126                 rep                             # Zero-fill
 127                 stosw                           #  memory
 128                 pop %di                         # Restore
 129 /*
 130  * Create IDT.
 131  */
 132                 mov $idtctl,%si                 # Control string
 133 init.1:         lodsb                           # Get entry
 134                 cbw                             #  count
 135                 xchg %ax,%cx                    #  as word
 136                 jcxz init.4                     # If done
 137                 lodsb                           # Get segment
 138                 xchg %ax,%dx                    #  P:DPL:type
 139                 lodsw                           # Get control
 140                 xchg %ax,%bx                    #  set
 141                 lodsw                           # Get handler offset
 142                 mov $SEL_SCODE,%dh              # Segment selector
 143 init.2:         shr %bx                         # Handle this int?
 144                 jnc init.3                      # No
 145                 mov %ax,(%di)                   # Set handler offset
 146                 mov %dh,0x2(%di)                #  and selector
 147                 mov %dl,0x5(%di)                # Set P:DPL:type
 148                 add $0x4,%ax                    # Next handler
 149 init.3:         lea 0x8(%di),%di                # Next entry
 150                 loop init.2                     # Till set done
 151                 jmp init.1                      # Continue
 152 /*
 153  * Initialize TSS.
 154  */
 155 init.4:         movb $_ESP0H,TSS_ESP0+1(%di)    # Set ESP0
 156                 movb $SEL_SDATA,TSS_SS0(%di)    # Set SS0
 157                 movb $_ESP1H,TSS_ESP1+1(%di)    # Set ESP1
 158                 movb $_TSSIO,TSS_MAP(%di)       # Set I/O bit map base
 159 #ifdef PAGING
 160 /*
 161  * Create page directory.
 162  */
 163                 xor %edx,%edx                   # Page
 164                 mov $PAG_SIZ>>0x8,%dh           #  size
 165                 xor %eax,%eax                   # Zero
 166                 mov $MEM_DIR,%di                # Page directory
 167                 mov $PAG_CNT>>0xa,%cl           # Entries
 168                 mov $MEM_TBL|0x7,%ax            # First entry
 169 init.5:         stosl                           # Write entry
 170                 add %dx,%ax                     # To next
 171                 loop init.5                     # Till done
 172 /*
 173  * Create page tables.
 174  */
 175                 mov $MEM_TBL,%di                # Page table
 176                 mov $PAG_CNT>>0x8,%ch           # Entries
 177                 xor %ax,%ax                     # Start address
 178 init.6:         mov $0x7,%al                    # Set U:W:P flags
 179                 cmp btx_hdr+0x8,%cx             # Standard user page?
 180                 jb init.7                       # Yes
 181                 cmp $PAG_CNT-MEM_BTX>>0xc,%cx   # BTX memory?
 182                 jae init.7                      # No or first page
 183                 and $~0x2,%al                   # Clear W flag
 184                 cmp $PAG_CNT-MEM_USR>>0xc,%cx   # User page zero?
 185                 jne init.7                      # No
 186                 testb $0x80,btx_hdr+0x7         # Unmap it?
 187                 jz init.7                       # No
 188                 and $~0x1,%al                   # Clear P flag
 189 init.7:         stosl                           # Set entry
 190                 add %edx,%eax                   # Next address
 191                 loop init.6                     # Till done
 192 #endif
 193 /*
 194  * Bring up the system.
 195  */
 196                 mov $0x2820,%bx                 # Set protected mode
 197                 callw setpic                    #  IRQ offsets
 198                 lidt idtdesc                    # Set IDT
 199 #ifdef PAGING
 200                 xor %eax,%eax                   # Set base
 201                 mov $MEM_DIR>>0x8,%ah           #  of page
 202                 mov %eax,%cr3                   #  directory
 203 #endif
 204                 lgdt gdtdesc                    # Set GDT
 205                 mov %cr0,%eax                   # Switch to protected
 206 #ifdef PAGING
 207                 or $0x80000001,%eax             #  mode and enable paging
 208 #else
 209                 inc %ax                         #  mode
 210 #endif
 211                 mov %eax,%cr0                   #
 212                 ljmp $SEL_SCODE,$init.8         # To 32-bit code
 213                 .code32
 214 init.8:         xorl %ecx,%ecx                  # Zero
 215                 movb $SEL_SDATA,%cl             # To 32-bit
 216                 movw %cx,%ss                    #  stack
 217 /*
 218  * Launch user task.
 219  */
 220                 movb $SEL_TSS,%cl               # Set task
 221                 ltr %cx                         #  register
 222                 movl $MEM_USR,%edx              # User base address
 223                 movzwl %ss:BDA_MEM,%eax         # Get free memory
 224                 andl $0x7,%eax
 225                 incl %eax
 226                 shll $0x11,%eax                 # To bytes
 227                 subl $0x1000,%eax               # Less arg space
 228                 subl %edx,%eax                  # Less base
 229                 movb $SEL_UDATA,%cl             # User data selector
 230                 pushl %ecx                      # Set SS
 231                 pushl %eax                      # Set ESP
 232                 push $0x202                     # Set flags (IF set)
 233                 push $SEL_UCODE                 # Set CS
 234                 pushl btx_hdr+0xc               # Set EIP
 235                 pushl %ecx                      # Set GS
 236                 pushl %ecx                      # Set FS
 237                 pushl %ecx                      # Set DS
 238                 pushl %ecx                      # Set ES
 239                 pushl %edx                      # Set EAX
 240                 movb $0x7,%cl                   # Set remaining
 241 init.9:         push $0x0                       #  general
 242                 loop init.9                     #  registers
 243 #ifdef BTX_SERIAL
 244                 call sio_init                   # setup the serial console
 245 #endif
 246                 popa                            #  and initialize
 247                 popl %es                        # Initialize
 248                 popl %ds                        #  user
 249                 popl %fs                        #  segment
 250                 popl %gs                        #  registers
 251                 iret                            # To user mode
 252 /*
 253  * Exit routine.
 254  */
 255 exit:           cli                             # Disable interrupts
 256                 movl $MEM_ESP0,%esp             # Clear stack
 257 /*
 258  * Turn off paging.
 259  */
 260                 movl %cr0,%eax                  # Get CR0
 261                 andl $~0x80000000,%eax          # Disable
 262                 movl %eax,%cr0                  #  paging
 263                 xorl %ecx,%ecx                  # Zero
 264                 movl %ecx,%cr3                  # Flush TLB
 265 /*
 266  * Restore the GDT in case we caught a kernel trap.
 267  */
 268                 lgdt gdtdesc                    # Set GDT
 269 /*
 270  * To 16 bits.
 271  */
 272                 ljmpw $SEL_RCODE,$exit.1        # Reload CS
 273                 .code16
 274 exit.1:         mov $SEL_RDATA,%cl              # 16-bit selector
 275                 mov %cx,%ss                     # Reload SS
 276                 mov %cx,%ds                     # Load
 277                 mov %cx,%es                     #  remaining
 278                 mov %cx,%fs                     #  segment
 279                 mov %cx,%gs                     #  registers
 280 /*
 281  * To real-address mode.
 282  */
 283                 dec %ax                         # Switch to
 284                 mov %eax,%cr0                   #  real mode
 285                 ljmp $0x0,$exit.2               # Reload CS
 286 exit.2:         xor %ax,%ax                     # Real mode segment
 287                 mov %ax,%ss                     # Reload SS
 288                 mov %ax,%ds                     # Address data
 289                 mov $0x1008,%bx                 # Set real mode
 290                 callw setpic                    #  IRQ offsets
 291                 lidt ivtdesc                    # Set IVT
 292 /*
 293  * Reboot or await reset.
 294  */
 295                 sti                             # Enable interrupts
 296                 testb $0x1,btx_hdr+0x7          # Reboot?
 297 exit.3:         jz exit.3                       # No
 298                 movb $0xa0,%al
 299                 outb %al,$0x35
 300                 movb 0,%al
 301                 outb %al,$0xf0
 302 exit.4:         jmp exit.4
 303 /*
 304  * Set IRQ offsets by reprogramming 8259A PICs.
 305  */
 306 setpic:         in $0x02,%al                    # Save master
 307                 push %ax                        #  IMR
 308                 in $0x0a,%al                    # Save slave
 309                 push %ax                        #  IMR
 310                 movb $0x11,%al                  # ICW1 to
 311                 outb %al,$0x00                  #  master,
 312                 outb %al,$0x08                  #  slave
 313                 movb %bl,%al                    # ICW2 to
 314                 outb %al,$0x02                  #  master
 315                 movb %bh,%al                    # ICW2 to
 316                 outb %al,$0x0a                  #  slave
 317                 movb $0x80,%al                  # ICW3 to
 318                 outb %al,$0x02                  #  master
 319                 movb $0x7,%al                   # ICW3 to
 320                 outb %al,$0x0a                  #  slave
 321                 movb $0x1d,%al                  # ICW4 to
 322                 outb %al,$0x02                  #  master,
 323                 movb $0x9,%al                   # ICW4 to
 324                 outb %al,$0x0a                  #  slave
 325                 pop %ax                         # Restore slave
 326                 outb %al,$0x0a                  #  IMR
 327                 pop %ax                         # Restore master
 328                 outb %al,$0x02                  #  IMR
 329                 retw                            # To caller
 330                 .code32
 331 /*
 332  * Initiate return from V86 mode to user mode.
 333  */
 334 inthlt:         hlt                             # To supervisor mode
 335 /*
 336  * Exception jump table.
 337  */
 338 intx00:         push $0x0                       # Int 0x0: #DE
 339                 jmp ex_noc                      # Divide error
 340                 push $0x1                       # Int 0x1: #DB
 341                 jmp ex_noc                      # Debug
 342                 push $0x3                       # Int 0x3: #BP
 343                 jmp ex_noc                      # Breakpoint
 344                 push $0x4                       # Int 0x4: #OF
 345                 jmp ex_noc                      # Overflow
 346                 push $0x5                       # Int 0x5: #BR
 347                 jmp ex_noc                      # BOUND range exceeded
 348                 push $0x6                       # Int 0x6: #UD
 349                 jmp ex_noc                      # Invalid opcode
 350                 push $0x7                       # Int 0x7: #NM
 351                 jmp ex_noc                      # Device not available
 352                 push $0x8                       # Int 0x8: #DF
 353                 jmp except                      # Double fault
 354                 push $0xa                       # Int 0xa: #TS
 355                 jmp except                      # Invalid TSS
 356                 push $0xb                       # Int 0xb: #NP
 357                 jmp except                      # Segment not present
 358                 push $0xc                       # Int 0xc: #SS
 359                 jmp except                      # Stack segment fault
 360                 push $0xd                       # Int 0xd: #GP
 361                 jmp ex_v86                      # General protection
 362                 push $0xe                       # Int 0xe: #PF
 363                 jmp except                      # Page fault
 364 intx10:         push $0x10                      # Int 0x10: #MF
 365                 jmp ex_noc                      # Floating-point error
 366 /*
 367  * Handle #GP exception.
 368  */
 369 ex_v86:         testb $0x2,0x12(%esp,1)         # V86 mode?
 370                 jz except                       # No
 371                 jmp v86mon                      # To monitor
 372 /*
 373  * Save a zero error code.
 374  */
 375 ex_noc:         pushl (%esp,1)                  # Duplicate int no
 376                 movb $0x0,0x4(%esp,1)           # Fake error code
 377 /*
 378  * Handle exception.
 379  */
 380 except:         cld                             # String ops inc
 381                 pushl %ds                       # Save
 382                 pushl %es                       #  most
 383                 pusha                           #  registers
 384                 movb $0x6,%al                   # Push loop count
 385                 testb $0x2,0x3a(%esp,1)         # V86 mode?
 386                 jnz except.1                    # Yes
 387                 pushl %gs                       # Set GS
 388                 pushl %fs                       # Set FS
 389                 pushl %ds                       # Set DS
 390                 pushl %es                       # Set ES
 391                 movb $0x2,%al                   # Push loop count
 392                 cmpw $SEL_SCODE,0x44(%esp,1)    # Supervisor mode?
 393                 jne except.1                    # No
 394                 pushl %ss                       # Set SS
 395                 leal 0x50(%esp,1),%eax          # Set
 396                 pushl %eax                      #  ESP
 397                 jmp except.2                    # Join common code
 398 except.1:       pushl 0x50(%esp,1)              # Set GS, FS, DS, ES
 399                 decb %al                        #  (if V86 mode), and
 400                 jne except.1                    #  SS, ESP
 401 except.2:       push $SEL_SDATA                 # Set up
 402                 popl %ds                        #  to
 403                 pushl %ds                       #  address
 404                 popl %es                        #  data
 405                 movl %esp,%ebx                  # Stack frame
 406                 movl $dmpfmt,%esi               # Dump format string
 407                 movl $MEM_BUF,%edi              # Buffer
 408                 pushl %eax
 409                 pushl %edx
 410 wait.1:
 411                 inb  $0x60,%al
 412                 testb $0x04,%al
 413                 jz   wait.1
 414                 movb $0xe0,%al
 415                 outb %al,$0x62
 416 wait.2:
 417                 inb  $0x60,%al
 418                 testb $0x01,%al
 419                 jz   wait.2
 420                 xorl %edx,%edx
 421                 inb  $0x62,%al
 422                 movb %al,%dl
 423                 inb  $0x62,%al
 424                 movb %al,%dh
 425                 inb  $0x62,%al
 426                 inb  $0x62,%al
 427                 inb  $0x62,%al
 428                 movl %edx,%eax
 429                 shlw $1,%ax
 430                 movl $BDA_POS,%edx
 431                 movw %ax,(%edx)
 432                 popl  %edx
 433                 popl  %eax
 434                 pushl %edi                      # Dump to
 435                 call dump                       #  buffer
 436                 popl %esi                       #  and
 437                 call putstr                     #  display
 438                 leal 0x18(%esp,1),%esp          # Discard frame
 439                 popa                            # Restore
 440                 popl %es                        #  registers
 441                 popl %ds                        #  saved
 442                 cmpb $0x3,(%esp,1)              # Breakpoint?
 443                 je except.3                     # Yes
 444                 cmpb $0x1,(%esp,1)              # Debug?
 445                 jne except.2a                   # No
 446                 testl $0x100,0x10(%esp,1)       # Trap flag set?
 447                 jnz except.3                    # Yes
 448 except.2a:      jmp exit                        # Exit
 449 except.3:       leal 0x8(%esp,1),%esp           # Discard err, int no
 450                 iret                            # From interrupt
 451 /*
 452  * Return to user mode from V86 mode.
 453  */
 454 intrtn:         cld                             # String ops inc
 455                 pushl %ds                       # Address
 456                 popl %es                        #  data
 457                 leal 0x3c(%ebp),%edx            # V86 Segment registers
 458                 movl MEM_TSS+TSS_ESP1,%esi      # Link stack pointer
 459                 lodsl                           # INT_V86 args pointer
 460                 movl %esi,%ebx                  # Saved exception frame
 461                 testl %eax,%eax                 # INT_V86 args?
 462                 jz intrtn.2                     # No
 463                 movl $MEM_USR,%edi              # User base
 464                 movl 0x1c(%esi),%ebx            # User ESP
 465                 movl %eax,(%edi,%ebx,1)         # Restore to user stack
 466                 leal 0x8(%edi,%eax,1),%edi      # Arg segment registers
 467                 testb $0x4,-0x6(%edi)           # Return flags?
 468                 jz intrtn.1                     # No
 469                 movl 0x30(%ebp),%eax            # Get V86 flags
 470                 movw %ax,0x18(%esi)             # Set user flags
 471 intrtn.1:       leal 0x10(%esi),%ebx            # Saved exception frame
 472                 xchgl %edx,%esi                 # Segment registers
 473                 movb $0x4,%cl                   # Update seg regs
 474                 rep                             #  in INT_V86
 475                 movsl                           #  args
 476 intrtn.2:       xchgl %edx,%esi                 # Segment registers
 477                 leal 0x28(%ebp),%edi            # Set up seg
 478                 movb $0x4,%cl                   #  regs for
 479                 rep                             #  later
 480                 movsl                           #  pop
 481                 xchgl %ebx,%esi                 # Restore exception
 482                 movb $0x5,%cl                   #  frame to
 483                 rep                             #  supervisor
 484                 movsl                           #  stack
 485                 movl %esi,MEM_TSS+TSS_ESP1      # Link stack pointer
 486                 popa                            # Restore
 487                 leal 0x8(%esp,1),%esp           # Discard err, int no
 488                 popl %es                        # Restore
 489                 popl %ds                        #  user
 490                 popl %fs                        #  segment
 491                 popl %gs                        #  registers
 492                 iret                            # To user mode
 493 /*
 494  * V86 monitor.
 495  */
 496 v86mon:         cld                             # String ops inc
 497                 pushl $SEL_SDATA                # Set up for
 498                 popl %ds                        #  flat addressing
 499                 pusha                           # Save registers
 500                 movl %esp,%ebp                  # Address stack frame
 501                 movzwl 0x2c(%ebp),%edi          # Load V86 CS
 502                 shll $0x4,%edi                  # To linear
 503                 movl 0x28(%ebp),%esi            # Load V86 IP
 504                 addl %edi,%esi                  # Code pointer
 505                 xorl %ecx,%ecx                  # Zero
 506                 movb $0x2,%cl                   # 16-bit operands
 507                 xorl %eax,%eax                  # Zero
 508 v86mon.1:       lodsb                           # Get opcode
 509                 cmpb $0x66,%al                  # Operand size prefix?
 510                 jne v86mon.2                    # No
 511                 movb $0x4,%cl                   # 32-bit operands
 512                 jmp v86mon.1                    # Continue
 513 v86mon.2:       cmpb $0xf4,%al                  # HLT?
 514                 jne v86mon.3                    # No
 515                 cmpl $inthlt+0x1,%esi           # Is inthlt?
 516                 jne v86mon.7                    # No (ignore)
 517                 jmp intrtn                      # Return to user mode
 518 v86mon.3:       cmpb $0xf,%al                   # Prefixed instruction?
 519                 jne v86mon.4                    # No
 520                 cmpb $0x09,(%esi)               # Is it a WBINVD?
 521                 je v86wbinvd                    # Yes
 522                 cmpb $0x30,(%esi)               # Is it a WRMSR?
 523                 je v86wrmsr                     # Yes
 524                 cmpb $0x32,(%esi)               # Is it a RDMSR?
 525                 je v86rdmsr                     # Yes
 526                 cmpb $0x20,(%esi)               # Is this a MOV reg,CRx?
 527                 je v86mov                       # Yes
 528 v86mon.4:       cmpb $0xfa,%al                  # CLI?
 529                 je v86cli                       # Yes
 530                 cmpb $0xfb,%al                  # STI?
 531                 je v86sti                       # Yes
 532                 movzwl 0x38(%ebp),%ebx          # Load V86 SS
 533                 shll $0x4,%ebx                  # To offset
 534                 pushl %ebx                      # Save
 535                 addl 0x34(%ebp),%ebx            # Add V86 SP
 536                 movl 0x30(%ebp),%edx            # Load V86 flags
 537                 cmpb $0x9c,%al                  # PUSHF/PUSHFD?
 538                 je v86pushf                     # Yes
 539                 cmpb $0x9d,%al                  # POPF/POPFD?
 540                 je v86popf                      # Yes
 541                 cmpb $0xcd,%al                  # INT imm8?
 542                 je v86intn                      # Yes
 543                 cmpb $0xcf,%al                  # IRET/IRETD?
 544                 je v86iret                      # Yes
 545                 popl %ebx                       # Restore
 546                 popa                            # Restore
 547                 jmp except                      # Handle exception
 548 v86mon.5:       movl %edx,0x30(%ebp)            # Save V86 flags
 549 v86mon.6:       popl %edx                       # V86 SS adjustment
 550                 subl %edx,%ebx                  # Save V86
 551                 movl %ebx,0x34(%ebp)            #  SP
 552 v86mon.7:       subl %edi,%esi                  # From linear
 553                 movl %esi,0x28(%ebp)            # Save V86 IP
 554                 popa                            # Restore
 555                 leal 0x8(%esp,1),%esp           # Discard int no, error
 556                 iret                            # To V86 mode
 557 /*
 558  * Emulate MOV reg,CRx.
 559  */
 560 v86mov:         movb 0x1(%esi),%bl              # Fetch Mod R/M byte
 561                 testb $0x10,%bl                 # Read CR2 or CR3?
 562                 jnz v86mov.1                    # Yes
 563                 movl %cr0,%eax                  # Read CR0
 564                 testb $0x20,%bl                 # Read CR4 instead?
 565                 jz v86mov.2                     # No
 566                 movl %cr4,%eax                  # Read CR4
 567                 jmp v86mov.2
 568 v86mov.1:       movl %cr2,%eax                  # Read CR2
 569                 testb $0x08,%bl                 # Read CR3 instead?
 570                 jz v86mov.2                     # No
 571                 movl %cr3,%eax                  # Read CR3
 572 v86mov.2:       andl $0x7,%ebx                  # Compute offset in
 573                 shl $2,%ebx                     #  frame of destination
 574                 neg %ebx                        #  register
 575                 movl %eax,0x1c(%ebp,%ebx,1)     # Store CR to reg
 576                 incl %esi                       # Adjust IP
 577 /*
 578  * Return from emulating a 0x0f prefixed instruction
 579  */
 580 v86preret:      incl %esi                       # Adjust IP
 581                 jmp v86mon.7                    # Finish up
 582 /*
 583  * Emulate WBINVD
 584  */
 585 v86wbinvd:      wbinvd                          # Write back and invalidate
 586                                                 #  cache
 587                 jmp v86preret                   # Finish up
 588 /*
 589  * Emulate WRMSR
 590  */
 591 v86wrmsr:       movl 0x18(%ebp),%ecx            # Get user's %ecx (MSR to write)
 592                 movl 0x14(%ebp),%edx            # Load the value
 593                 movl 0x1c(%ebp),%eax            #  to write
 594                 wrmsr                           # Write MSR
 595                 jmp v86preret                   # Finish up
 596 /*
 597  * Emulate RDMSR
 598  */
 599 v86rdmsr:       movl 0x18(%ebp),%ecx            # MSR to read
 600                 rdmsr                           # Read the MSR
 601                 movl %eax,0x1c(%ebp)            # Return the value of
 602                 movl %edx,0x14(%ebp)            #  the MSR to the user
 603                 jmp v86preret                   # Finish up
 604 /*
 605  * Emulate CLI.
 606  */
 607 v86cli:         andb $~0x2,0x31(%ebp)           # Clear IF
 608                 jmp v86mon.7                    # Finish up
 609 /*
 610  * Emulate STI.
 611  */
 612 v86sti:         orb $0x2,0x31(%ebp)             # Set IF
 613                 jmp v86mon.7                    # Finish up
 614 /*
 615  * Emulate PUSHF/PUSHFD.
 616  */
 617 v86pushf:       subl %ecx,%ebx                  # Adjust SP
 618                 cmpb $0x4,%cl                   # 32-bit
 619                 je v86pushf.1                   # Yes
 620                 data16                          # 16-bit
 621 v86pushf.1:     movl %edx,(%ebx)                # Save flags
 622                 jmp v86mon.6                    # Finish up
 623 /*
 624  * Emulate IRET/IRETD.
 625  */
 626 v86iret:        movzwl (%ebx),%esi              # Load V86 IP
 627                 movzwl 0x2(%ebx),%edi           # Load V86 CS
 628                 leal 0x4(%ebx),%ebx             # Adjust SP
 629                 movl %edi,0x2c(%ebp)            # Save V86 CS
 630                 xorl %edi,%edi                  # No ESI adjustment
 631 /*
 632  * Emulate POPF/POPFD (and remainder of IRET/IRETD).
 633  */
 634 v86popf:        cmpb $0x4,%cl                   # 32-bit?
 635                 je v86popf.1                    # Yes
 636                 movl %edx,%eax                  # Initialize
 637                 data16                          # 16-bit
 638 v86popf.1:      movl (%ebx),%eax                # Load flags
 639                 addl %ecx,%ebx                  # Adjust SP
 640                 andl $V86_FLG,%eax              # Merge
 641                 andl $~V86_FLG,%edx             #  the
 642                 orl %eax,%edx                   #  flags
 643                 jmp v86mon.5                    # Finish up
 644 /*
 645  * trap int 15, function 87
 646  * reads %es:%si from saved registers on stack to find a GDT containing
 647  * source and destination locations
 648  * reads count of words from saved %cx
 649  * returns success by setting %ah to 0
 650  */
 651 int15_87:       pushl %esi                      # Save
 652                 pushl %edi                      #  registers
 653                 movl 0x3C(%ebp),%edi            # Load ES
 654                 movzwl 0x4(%ebp),%eax           # Load user's SI
 655                 shll $0x4,%edi                  # EDI = (ES << 4) +
 656                 addl %eax,%edi                  #   SI
 657                 movl 0x11(%edi),%eax            # Read base of
 658                 movb 0x17(%edi),%al             #  GDT entry
 659                 ror $8,%eax                     #  for source
 660                 xchgl %eax,%esi                 #  into %esi
 661                 movl 0x19(%edi),%eax            # Read base of
 662                 movb 0x1f(%edi),%al             #  GDT entry for
 663                 ror $8,%eax                     #  destination
 664                 xchgl %eax,%edi                 #  into %edi
 665                 pushl %ds                       # Make:
 666                 popl %es                        # es = ds
 667                 movzwl 0x18(%ebp),%ecx          # Get user's CX
 668                 shll $0x1,%ecx                  # Convert count from words
 669                 rep                             # repeat...
 670                 movsb                           #  perform copy.
 671                 popl %edi                       # Restore
 672                 popl %esi                       #  registers
 673                 movb $0x0,0x1d(%ebp)            # set ah = 0 to indicate
 674                                                 #  success
 675                 andb $0xfe,%dl                  # clear CF
 676                 jmp v86mon.5                    # Finish up
 677
 678 /*
 679  * Reboot the machine by setting the reboot flag and exiting
 680  */
 681 reboot:         orb $0x1,btx_hdr+0x7            # Set the reboot flag
 682                 jmp exit                        # Terminate BTX and reboot
 683
 684 /*
 685  * Emulate INT imm8... also make sure to check if it's int 15/87
 686  */
 687 v86intn:        lodsb                           # Get int no
 688                 cmpb $0x19,%al                  # is it int 19?
 689                 je reboot                       #  yes, reboot the machine
 690                 cmpb $0x15,%al                  # is it int 15?
 691                 jne v86intn.1                   #  no, skip parse
 692                 cmpb $0x87,0x1d(%ebp)           # is it the memcpy subfunction?
 693                 je int15_87                     #  yes
 694                 cmpw $0x4f53,0x1c(%ebp)         # is it the delete key callout?
 695                 jne v86intn.1                   #  no, handle the int normally
 696                 movb BDA_KEYFLAGS,%ch           # get the shift key state
 697                 andb $0x18,%ch                  # mask off just Ctrl and Alt
 698                 cmpb $0x18,%ch                  # are both Ctrl and Alt down?
 699                 je reboot                       # yes, reboot the machine
 700 v86intn.1:      subl %edi,%esi                  # From
 701                 shrl $0x4,%edi                  #  linear
 702                 movw %dx,-0x2(%ebx)             # Save flags
 703                 movw %di,-0x4(%ebx)             # Save CS
 704                 leal -0x6(%ebx),%ebx            # Adjust SP
 705                 movw %si,(%ebx)                 # Save IP
 706                 shll $0x2,%eax                  # Scale
 707                 movzwl (%eax),%esi              # Load IP
 708                 movzwl 0x2(%eax),%edi           # Load CS
 709                 movl %edi,0x2c(%ebp)            # Save CS
 710                 xorl %edi,%edi                  # No ESI adjustment
 711                 andb $~0x1,%dh                  # Clear TF
 712                 jmp v86mon.5                    # Finish up
 713 /*
 714  * Hardware interrupt jump table.
 715  */
 716 intx20:         push $0x8                       # Int 0x20: IRQ0
 717                 jmp int_hw                      # V86 int 0x8
 718                 push $0x9                       # Int 0x21: IRQ1
 719                 jmp int_hw                      # V86 int 0x9
 720                 push $0xa                       # Int 0x22: IRQ2
 721                 jmp int_hw                      # V86 int 0xa
 722                 push $0xb                       # Int 0x23: IRQ3
 723                 jmp int_hw                      # V86 int 0xb
 724                 push $0xc                       # Int 0x24: IRQ4
 725                 jmp int_hw                      # V86 int 0xc
 726                 push $0xd                       # Int 0x25: IRQ5
 727                 jmp int_hw                      # V86 int 0xd
 728                 push $0xe                       # Int 0x26: IRQ6
 729                 jmp int_hw                      # V86 int 0xe
 730                 push $0xf                       # Int 0x27: IRQ7
 731                 jmp int_hw                      # V86 int 0xf
 732                 push $0x10                      # Int 0x28: IRQ8
 733                 jmp int_hw                      # V86 int 0x10
 734                 push $0x11                      # Int 0x29: IRQ9
 735                 jmp int_hw                      # V86 int 0x11
 736                 push $0x12                      # Int 0x2a: IRQ10
 737                 jmp int_hw                      # V86 int 0x12
 738                 push $0x13                      # Int 0x2b: IRQ11
 739                 jmp int_hw                      # V86 int 0x13
 740                 push $0x14                      # Int 0x2c: IRQ12
 741                 jmp int_hw                      # V86 int 0x14
 742                 push $0x15                      # Int 0x2d: IRQ13
 743                 jmp int_hw                      # V86 int 0x15
 744                 push $0x16                      # Int 0x2e: IRQ14
 745                 jmp int_hw                      # V86 int 0x16
 746                 push $0x17                      # Int 0x2f: IRQ15
 747                 jmp int_hw                      # V86 int 0x17
 748 /*
 749  * Reflect hardware interrupts.
 750  */
 751 int_hw:         testb $0x2,0xe(%esp,1)          # V86 mode?
 752                 jz intusr                       # No
 753                 pushl $SEL_SDATA                # Address
 754                 popl %ds                        #  data
 755                 xchgl %eax,(%esp,1)             # Swap EAX, int no
 756                 pushl %ebp                      # Address
 757                 movl %esp,%ebp                  #  stack frame
 758                 pushl %ebx                      # Save
 759                 shll $0x2,%eax                  # Get int
 760                 movl (%eax),%eax                #  vector
 761                 subl $0x6,0x14(%ebp)            # Adjust V86 ESP
 762                 movzwl 0x18(%ebp),%ebx          # V86 SS
 763                 shll $0x4,%ebx                  #  * 0x10
 764                 addl 0x14(%ebp),%ebx            #  + V86 ESP
 765                 xchgw %ax,0x8(%ebp)             # Swap V86 IP
 766                 rorl $0x10,%eax                 # Swap words
 767                 xchgw %ax,0xc(%ebp)             # Swap V86 CS
 768                 roll $0x10,%eax                 # Swap words
 769                 movl %eax,(%ebx)                # CS:IP for IRET
 770                 movl 0x10(%ebp),%eax            # V86 flags
 771                 movw %ax,0x4(%ebx)              # Flags for IRET
 772                 andb $~0x3,0x11(%ebp)           # Clear IF, TF
 773                 popl %ebx                       # Restore
 774                 popl %ebp                       #  saved
 775                 popl %eax                       #  registers
 776                 iret                            # To V86 mode
 777 /*
 778  * Invoke V86 interrupt from user mode, with arguments.
 779  */
 780 intx31:         stc                             # Have btx_v86
 781                 pushl %eax                      # Missing int no
 782 /*
 783  * Invoke V86 interrupt from user mode.
 784  */
 785 intusr:         std                             # String ops dec
 786                 pushl %eax                      # Expand
 787                 pushl %eax                      #  stack
 788                 pushl %eax                      #  frame
 789                 pusha                           # Save
 790                 pushl %gs                       # Save
 791                 movl %esp,%eax                  #  seg regs
 792                 pushl %fs                       #  and
 793                 pushl %ds                       #  point
 794                 pushl %es                       #  to them
 795                 push $SEL_SDATA                 # Set up
 796                 popl %ds                        #  to
 797                 pushl %ds                       #  address
 798                 popl %es                        #  data
 799                 movl $MEM_USR,%ebx              # User base
 800                 movl %ebx,%edx                  #  address
 801                 jc intusr.1                     # If btx_v86
 802                 xorl %edx,%edx                  # Control flags
 803                 xorl %ebp,%ebp                  # btx_v86 pointer
 804 intusr.1:       leal 0x50(%esp,1),%esi          # Base of frame
 805                 pushl %esi                      # Save
 806                 addl -0x4(%esi),%ebx            # User ESP
 807                 movl MEM_TSS+TSS_ESP1,%edi      # Link stack pointer
 808                 leal -0x4(%edi),%edi            # Adjust for push
 809                 xorl %ecx,%ecx                  # Zero
 810                 movb $0x5,%cl                   # Push exception
 811                 rep                             #  frame on
 812                 movsl                           #  link stack
 813                 xchgl %eax,%esi                 # Saved seg regs
 814                 movl 0x40(%esp,1),%eax          # Get int no
 815                 testl %edx,%edx                 # Have btx_v86?
 816                 jz intusr.2                     # No
 817                 movl (%ebx),%ebp                # btx_v86 pointer
 818                 movb $0x4,%cl                   # Count
 819                 addl %ecx,%ebx                  # Adjust for pop
 820                 rep                             # Push saved seg regs
 821                 movsl                           #  on link stack
 822                 addl %ebp,%edx                  # Flatten btx_v86 ptr
 823                 leal 0x14(%edx),%esi            # Seg regs pointer
 824                 movl 0x4(%edx),%eax             # Get int no/address
 825                 movzwl 0x2(%edx),%edx           # Get control flags
 826 intusr.2:       movl %ebp,(%edi)                # Push btx_v86 and
 827                 movl %edi,MEM_TSS+TSS_ESP1      #  save link stack ptr
 828                 popl %edi                       # Base of frame
 829                 xchgl %eax,%ebp                 # Save intno/address
 830                 movl 0x48(%esp,1),%eax          # Get flags
 831                 testb $0x2,%dl                  # Simulate CALLF?
 832                 jnz intusr.3                    # Yes
 833                 decl %ebx                       # Push flags
 834                 decl %ebx                       #  on V86
 835                 movw %ax,(%ebx)                 #  stack
 836 intusr.3:       movb $0x4,%cl                   # Count
 837                 subl %ecx,%ebx                  # Push return address
 838                 movl $inthlt,(%ebx)             #  on V86 stack
 839                 rep                             # Copy seg regs to
 840                 movsl                           #  exception frame
 841                 xchgl %eax,%ecx                 # Save flags
 842                 movl %ebx,%eax                  # User ESP
 843                 subl $V86_STK,%eax              # Less bytes
 844                 ja intusr.4                     #  to
 845                 xorl %eax,%eax                  #  keep
 846 intusr.4:       shrl $0x4,%eax                  # Gives segment
 847                 stosl                           # Set SS
 848                 shll $0x4,%eax                  # To bytes
 849                 xchgl %eax,%ebx                 # Swap
 850                 subl %ebx,%eax                  # Gives offset
 851                 stosl                           # Set ESP
 852                 xchgl %eax,%ecx                 # Get flags
 853                 btsl $0x11,%eax                 # Set VM
 854                 andb $~0x1,%ah                  # Clear TF
 855                 stosl                           # Set EFL
 856                 xchgl %eax,%ebp                 # Get int no/address
 857                 testb $0x1,%dl                  # Address?
 858                 jnz intusr.5                    # Yes
 859                 shll $0x2,%eax                  # Scale
 860                 movl (%eax),%eax                # Load int vector
 861 intusr.5:       movl %eax,%ecx                  # Save
 862                 shrl $0x10,%eax                 # Gives segment
 863                 stosl                           # Set CS
 864                 movw %cx,%ax                    # Restore
 865                 stosl                           # Set EIP
 866                 leal 0x10(%esp,1),%esp          # Discard seg regs
 867                 popa                            # Restore
 868                 iret                            # To V86 mode
 869 /*
 870  * System Call.
 871  */
 872 intx30:         cmpl $SYS_EXEC,%eax             # Exec system call?
 873                 jne intx30.1                    # No
 874                 pushl %ss                       # Set up
 875                 popl %es                        #  all
 876                 pushl %es                       #  segment
 877                 popl %ds                        #  registers
 878                 pushl %ds                       #  for the
 879                 popl %fs                        #  program
 880                 pushl %fs                       #  we're
 881                 popl %gs                        #  invoking
 882                 movl $MEM_USR,%eax              # User base address
 883                 addl 0xc(%esp,1),%eax           # Change to user
 884                 leal 0x4(%eax),%esp             #  stack
 885 #ifdef PAGING
 886                 movl %cr0,%eax                  # Turn
 887                 andl $~0x80000000,%eax          #  off
 888                 movl %eax,%cr0                  #  paging
 889                 xorl %eax,%eax                  # Flush
 890                 movl %eax,%cr3                  #  TLB
 891 #endif
 892                 popl %eax                       # Call
 893                 call *%eax                      #  program
 894 intx30.1:       orb $0x1,%ss:btx_hdr+0x7        # Flag reboot
 895                 jmp exit                        # Exit
 896 /*
 897  * Dump structure [EBX] to [EDI], using format string [ESI].
 898  */
 899 dump.0:         stosb                           # Save char
 900 dump:           lodsb                           # Load char
 901                 testb %al,%al                   # End of string?
 902                 jz dump.10                      # Yes
 903                 testb $0x80,%al                 # Control?
 904                 jz dump.0                       # No
 905                 movb %al,%ch                    # Save control
 906                 movb $'=',%al                   # Append
 907                 stosb                           #  '='
 908                 lodsb                           # Get offset
 909                 pushl %esi                      # Save
 910                 movsbl %al,%esi                 # To
 911                 addl %ebx,%esi                  #  pointer
 912                 testb $DMP_X16,%ch              # Dump word?
 913                 jz dump.1                       # No
 914                 lodsw                           # Get and
 915                 call hex16                      #  dump it
 916 dump.1:         testb $DMP_X32,%ch              # Dump long?
 917                 jz dump.2                       # No
 918                 lodsl                           # Get and
 919                 call hex32                      #  dump it
 920 dump.2:         testb $DMP_MEM,%ch              # Dump memory?
 921                 jz dump.8                       # No
 922                 pushl %ds                       # Save
 923                 testb $0x2,0x52(%ebx)           # V86 mode?
 924                 jnz dump.3                      # Yes
 925                 verr 0x4(%esi)                  # Readable selector?
 926                 jnz dump.3                      # No
 927                 ldsl (%esi),%esi                # Load pointer
 928                 jmp dump.4                      # Join common code
 929 dump.3:         lodsl                           # Set offset
 930                 xchgl %eax,%edx                 # Save
 931                 lodsl                           # Get segment
 932                 shll $0x4,%eax                  #  * 0x10
 933                 addl %edx,%eax                  #  + offset
 934                 xchgl %eax,%esi                 # Set pointer
 935 dump.4:         movb $2,%dl                     # Num lines
 936 dump.4a:        movb $0x10,%cl                  # Bytes to dump
 937 dump.5:         lodsb                           # Get byte and
 938                 call hex8                       #  dump it
 939                 decb %cl                        # Keep count
 940                 jz dump.6a                      # If done
 941                 movb $'-',%al                   # Separator
 942                 cmpb $0x8,%cl                   # Half way?
 943                 je dump.6                       # Yes
 944                 movb $' ',%al                   # Use space
 945 dump.6:         stosb                           # Save separator
 946                 jmp dump.5                      # Continue
 947 dump.6a:        decb %dl                        # Keep count
 948                 jz dump.7                       # If done
 949                 movb $0xa,%al                   # Line feed
 950                 stosb                           # Save one
 951                 movb $7,%cl                     # Leading
 952                 movb $' ',%al                   #  spaces
 953 dump.6b:        stosb                           # Dump
 954                 decb %cl                        #  spaces
 955                 jnz dump.6b
 956                 jmp dump.4a                     # Next line
 957 dump.7:         popl %ds                        # Restore
 958 dump.8:         popl %esi                       # Restore
 959                 movb $0xa,%al                   # Line feed
 960                 testb $DMP_EOL,%ch              # End of line?
 961                 jnz dump.9                      # Yes
 962                 movb $' ',%al                   # Use spaces
 963                 stosb                           # Save one
 964 dump.9:         jmp dump.0                      # Continue
 965 dump.10:        stosb                           # Terminate string
 966                 ret                             # To caller
 967 /*
 968  * Convert EAX, AX, or AL to hex, saving the result to [EDI].
 969  */
 970 hex32:          pushl %eax                      # Save
 971                 shrl $0x10,%eax                 # Do upper
 972                 call hex16                      #  16
 973                 popl %eax                       # Restore
 974 hex16:          call hex16.1                    # Do upper 8
 975 hex16.1:        xchgb %ah,%al                   # Save/restore
 976 hex8:           pushl %eax                      # Save
 977                 shrb $0x4,%al                   # Do upper
 978                 call hex8.1                     #  4
 979                 popl %eax                       # Restore
 980 hex8.1:         andb $0xf,%al                   # Get lower 4
 981                 cmpb $0xa,%al                   # Convert
 982                 sbbb $0x69,%al                  #  to hex
 983                 das                             #  digit
 984                 orb $0x20,%al                   # To lower case
 985                 stosb                           # Save char
 986                 ret                             # (Recursive)
 987 /*
 988  * Output zero-terminated string [ESI] to the console.
 989  */
 990 putstr.0:       call putchr                     # Output char
 991 putstr:         lodsb                           # Load char
 992                 testb %al,%al                   # End of string?
 993                 jnz putstr.0                    # No
 994                 ret                             # To caller
 995 #ifdef BTX_SERIAL
 996                 .set SIO_PRT,SIOPRT             # Base port
 997                 .set SIO_FMT,SIOFMT             # 8N1
 998                 .set SIO_DIV,(115200/SIOSPD)    # 115200 / SPD
 999
1000 /*
1001  * void sio_init(void)
1002  */
1003 sio_init:       movw $SIO_PRT+0x3,%dx           # Data format reg
1004                 movb $SIO_FMT|0x80,%al          # Set format
1005                 outb %al,(%dx)                  #  and DLAB
1006                 pushl %edx                      # Save
1007                 subb $0x3,%dl                   # Divisor latch reg
1008                 movw $SIO_DIV,%ax               # Set
1009                 outw %ax,(%dx)                  #  BPS
1010                 popl %edx                       # Restore
1011                 movb $SIO_FMT,%al               # Clear
1012                 outb %al,(%dx)                  #  DLAB
1013                 incl %edx                       # Modem control reg
1014                 movb $0x3,%al                   # Set RTS,
1015                 outb %al,(%dx)                  #  DTR
1016                 incl %edx                       # Line status reg
1017
1018 /*
1019  * void sio_flush(void)
1020  */
1021 sio_flush.0:    call sio_getc.1                 # Get character
1022 sio_flush:      call sio_ischar                 # Check for character
1023                 jnz sio_flush.0                 # Till none
1024                 ret                             # To caller
1025
1026 /*
1027  * void sio_putc(int c)
1028  */
1029 sio_putc:       movw $SIO_PRT+0x5,%dx           # Line status reg
1030                 xor %ecx,%ecx                   # Timeout
1031                 movb $0x40,%ch                  #  counter
1032 sio_putc.1:     inb (%dx),%al                   # Transmitter
1033                 testb $0x20,%al                 #  buffer empty?
1034                 loopz sio_putc.1                # No
1035                 jz sio_putc.2                   # If timeout
1036                 movb 0x4(%esp,1),%al            # Get character
1037                 subb $0x5,%dl                   # Transmitter hold reg
1038                 outb %al,(%dx)                  # Write character
1039 sio_putc.2:     ret $0x4                        # To caller
1040
1041 /*
1042  * int sio_getc(void)
1043  */
1044 sio_getc:       call sio_ischar                 # Character available?
1045                 jz sio_getc                     # No
1046 sio_getc.1:     subb $0x5,%dl                   # Receiver buffer reg
1047                 inb (%dx),%al                   # Read character
1048                 ret                             # To caller
1049
1050 /*
1051  * int sio_ischar(void)
1052  */
1053 sio_ischar:     movw $SIO_PRT+0x5,%dx           # Line status register
1054                 xorl %eax,%eax                  # Zero
1055                 inb (%dx),%al                   # Received data
1056                 andb $0x1,%al                   #  ready?
1057                 ret                             # To caller
1058
1059 /*
1060  * Output character AL to the serial console.
1061  */
1062 putchr:         pusha                           # Save
1063                 cmpb $10, %al                   # is it a newline?
1064                 jne putchr.1                    #  no?, then leave
1065                 push $13                        # output a carriage
1066                 call sio_putc                   #  return first
1067                 movb $10, %al                   # restore %al
1068 putchr.1:       pushl %eax                      # Push the character
1069                                                 #  onto the stack
1070                 call sio_putc                   # Output the character
1071                 popa                            # Restore
1072                 ret                             # To caller
1073 #else
1074 /*
1075  * Output character AL to the console.
1076  */
1077 putchr:         pusha                           # Save
1078                 xorl %ecx,%ecx                  # Zero for loops
1079                 movb $SCR_MAT,%ah               # Mode/attribute
1080                 movl $BDA_POS,%ebx              # BDA pointer
1081                 movw (%ebx),%dx                 # Cursor position
1082                 movl $0xa0000,%edi
1083 putchr.1:       cmpb $0xa,%al                   # New line?
1084                 je putchr.2                     # Yes
1085                 movw %dx,%cx
1086                 movb %al,(%edi,%ecx,1)          # Write char
1087                 addl $0x2000,%ecx
1088                 movb %ah,(%edi,%ecx,1)          # Write attr
1089                 addw $0x02,%dx
1090                 jmp putchr.3
1091 putchr.2:       movw %dx,%ax
1092                 movb $SCR_COL*2,%dl
1093                 div %dl
1094                 incb %al
1095                 mul %dl
1096                 movw %ax,%dx
1097 putchr.3:       cmpw $SCR_ROW*SCR_COL*2,%dx
1098                 jb putchr.4                     # No
1099                 leal 2*SCR_COL(%edi),%esi       # New top line
1100                 movw $(SCR_ROW-1)*SCR_COL/2,%cx # Words to move
1101                 rep                             # Scroll
1102                 movsl                           #  screen
1103                 movb $0x20,%al                  # Space
1104                 xorb %ah,%ah
1105                 movb $SCR_COL,%cl               # Columns to clear
1106                 rep                             # Clear
1107                 stosw                           #  line
1108                 movw $(SCR_ROW-1)*SCR_COL*2,%dx
1109 putchr.4:       movw %dx,(%ebx)                 # Update position
1110                 popa                            # Restore
1111                 ret                             # To caller
1112 #endif
1113
1114                 .p2align 4
1115 /*
1116  * Global descriptor table.
1117  */
1118 gdt:            .word 0x0,0x0,0x0,0x0           # Null entry
1119                 .word 0xffff,0x0,0x9a00,0xcf    # SEL_SCODE
1120                 .word 0xffff,0x0,0x9200,0xcf    # SEL_SDATA
1121                 .word 0xffff,0x0,0x9a00,0x0     # SEL_RCODE
1122                 .word 0xffff,0x0,0x9200,0x0     # SEL_RDATA
1123                 .word 0xffff,MEM_USR,0xfa00,0xcf# SEL_UCODE
1124                 .word 0xffff,MEM_USR,0xf200,0xcf# SEL_UDATA
1125                 .word _TSSLM,MEM_TSS,0x8900,0x0 # SEL_TSS
1126 gdt.1:
1127 /*
1128  * Pseudo-descriptors.
1129  */
1130 gdtdesc:        .word gdt.1-gdt-1,gdt,0x0       # GDT
1131 idtdesc:        .word _IDTLM,MEM_IDT,0x0        # IDT
1132 ivtdesc:        .word 0x400-0x0-1,0x0,0x0       # IVT
1133 /*
1134  * IDT construction control string.
1135  */
1136 idtctl:         .byte 0x10,  0x8e               # Int 0x0-0xf
1137                 .word 0x7dfb,intx00             #  (exceptions)
1138                 .byte 0x10,  0x8e               # Int 0x10
1139                 .word 0x1,   intx10             #  (exception)
1140                 .byte 0x10,  0x8e               # Int 0x20-0x2f
1141                 .word 0xffff,intx20             #  (hardware)
1142                 .byte 0x1,   0xee               # int 0x30
1143                 .word 0x1,   intx30             #  (system call)
1144                 .byte 0x2,   0xee               # Int 0x31-0x32
1145                 .word 0x1,   intx31             #  (V86, null)
1146                 .byte 0x0                       # End of string
1147 /*
1148  * Dump format string.
1149  */
1150 dmpfmt:         .byte '\n'                      # "\n"
1151                 .ascii "int"                    # "int="
1152                 .byte 0x80|DMP_X32,        0x40 # "00000000  "
1153                 .ascii "err"                    # "err="
1154                 .byte 0x80|DMP_X32,        0x44 # "00000000  "
1155                 .ascii "efl"                    # "efl="
1156                 .byte 0x80|DMP_X32,        0x50 # "00000000  "
1157                 .ascii "eip"                    # "eip="
1158                 .byte 0x80|DMP_X32|DMP_EOL,0x48 # "00000000\n"
1159                 .ascii "eax"                    # "eax="
1160                 .byte 0x80|DMP_X32,        0x34 # "00000000  "
1161                 .ascii "ebx"                    # "ebx="
1162                 .byte 0x80|DMP_X32,        0x28 # "00000000  "
1163                 .ascii "ecx"                    # "ecx="
1164                 .byte 0x80|DMP_X32,        0x30 # "00000000  "
1165                 .ascii "edx"                    # "edx="
1166                 .byte 0x80|DMP_X32|DMP_EOL,0x2c # "00000000\n"
1167                 .ascii "esi"                    # "esi="
1168                 .byte 0x80|DMP_X32,        0x1c # "00000000  "
1169                 .ascii "edi"                    # "edi="
1170                 .byte 0x80|DMP_X32,        0x18 # "00000000  "
1171                 .ascii "ebp"                    # "ebp="
1172                 .byte 0x80|DMP_X32,        0x20 # "00000000  "
1173                 .ascii "esp"                    # "esp="
1174                 .byte 0x80|DMP_X32|DMP_EOL,0x0  # "00000000\n"
1175                 .ascii "cs"                     # "cs="
1176                 .byte 0x80|DMP_X16,        0x4c # "0000  "
1177                 .ascii "ds"                     # "ds="
1178                 .byte 0x80|DMP_X16,        0xc  # "0000  "
1179                 .ascii "es"                     # "es="
1180                 .byte 0x80|DMP_X16,        0x8  # "0000  "
1181                 .ascii "  "                     # "  "
1182                 .ascii "fs"                     # "fs="
1183                 .byte 0x80|DMP_X16,        0x10 # "0000  "
1184                 .ascii "gs"                     # "gs="
1185                 .byte 0x80|DMP_X16,        0x14 # "0000  "
1186                 .ascii "ss"                     # "ss="
1187                 .byte 0x80|DMP_X16|DMP_EOL,0x4  # "0000\n"
1188                 .ascii "cs:eip"                 # "cs:eip="
1189                 .byte 0x80|DMP_MEM|DMP_EOL,0x48 # "00 00 ... 00 00\n"
1190                 .ascii "ss:esp"                 # "ss:esp="
1191                 .byte 0x80|DMP_MEM|DMP_EOL,0x0  # "00 00 ... 00 00\n"
1192                 .asciz "BTX halted\n"           # End
1193 /*
1194  * End of BTX memory.
1195  */
1196                 .p2align 4
1197 break: