btxldr.S revision 104629
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 16# $FreeBSD: head/sys/boot/i386/btx/btxldr/btxldr.S 104629 2002-10-07 19:12:36Z phk $ 17 18# 19# Prototype BTX loader program, written in a couple of hours. The 20# real thing should probably be more flexible, and in C. 21# 22 23# 24# Memory locations. 25# 26 .set MEM_STUB,0x600 # Real mode stub 27 .set MEM_ESP,0x1000 # New stack pointer 28 .set MEM_TBL,0x5000 # BTX page tables 29 .set MEM_ENTRY,0x9010 # BTX entry point 30 .set MEM_DATA,start+0x1000 # Data segment 31# 32# Segment selectors. 33# 34 .set SEL_SCODE,0x8 # 4GB code 35 .set SEL_SDATA,0x10 # 4GB data 36 .set SEL_RCODE,0x18 # 64K code 37 .set SEL_RDATA,0x20 # 64K data 38# 39# Paging constants. 40# 41 .set PAG_SIZ,0x1000 # Page size 42 .set PAG_ENT,0x4 # Page entry size 43# 44# Screen constants. 45# 46 .set SCR_MAT,0x7 # Mode/attribute 47 .set SCR_COL,0x50 # Columns per row 48 .set SCR_ROW,0x19 # Rows per screen 49# 50# BIOS Data Area locations. 51# 52 .set BDA_MEM,0x413 # Free memory 53 .set BDA_SCR,0x449 # Video mode 54 .set BDA_POS,0x450 # Cursor position 55# 56# Required by aout gas inadequacy. 57# 58 .set SIZ_STUB,0x1a # Size of stub 59# 60# We expect to be loaded by boot2 at the origin defined in ./Makefile. 61# 62 .globl start 63# 64# BTX program loader for ELF clients. 65# 66start: cld # String ops inc 67 movl $m_logo,%esi # Identify 68 call putstr # ourselves 69 movzwl BDA_MEM,%eax # Get base memory 70 shll $0xa,%eax # in bytes 71 movl %eax,%ebp # Base of user stack 72ifdef(`BTXLDR_VERBOSE',` 73 movl $m_mem,%esi # Display 74 call hexout # amount of 75 call putstr # base memory 76') 77 lgdt gdtdesc # Load new GDT 78# 79# Relocate caller's arguments. 80# 81ifdef('BTXLDR_VERBOSE',` 82 movl $m_esp,%esi # Display 83 movl %esp,%eax # caller 84 call hexout # stack 85 call putstr # pointer 86 movl $m_args,%esi # Format string 87 leal 0x4(%esp,1),%ebx # First argument 88 movl $0x6,%ecx # Count 89start.1: movl (%ebx),%eax # Get argument and 90 addl $0x4,%ebx # bump pointer 91 call hexout # Display it 92 loop start.1 # Till done 93 call putstr # End message 94') 95 movl $0x48,%ecx # Allocate space 96 subl %ecx,%ebp # for bootinfo 97 movl 0x18(%esp,1),%esi # Source: bootinfo 98 cmpl $0x0, %esi # If the bootinfo pointer 99 je start_null_bi # is null, don't copy it 100 movl %ebp,%edi # Destination 101 rep # Copy 102 movsb # it 103 movl %ebp,0x18(%esp,1) # Update pointer 104ifdef(`BTXLDR_VERBOSE',` 105 movl $m_rel_bi,%esi # Display 106 movl %ebp,%eax # bootinfo 107 call hexout # relocation 108 call putstr # message 109') 110start_null_bi: movl $0x18,%ecx # Allocate space 111 subl %ecx,%ebp # for arguments 112 leal 0x4(%esp,1),%esi # Source 113 movl %ebp,%edi # Destination 114 rep # Copy 115 movsb # them 116ifdef(`BTXLDR_VERBOSE',` 117 movl $m_rel_args,%esi # Display 118 movl %ebp,%eax # argument 119 call hexout # relocation 120 call putstr # message 121') 122# 123# Set up BTX kernel. 124# 125 movl $MEM_ESP,%esp # Set up new stack 126 movl $MEM_DATA,%ebx # Data segment 127 movl $m_vers,%esi # Display BTX 128 call putstr # version message 129 movb 0x5(%ebx),%al # Get major version 130 addb $'0',%al # Display 131 call putchr # it 132 movb $'.',%al # And a 133 call putchr # dot 134 movb 0x6(%ebx),%al # Get minor 135 xorb %ah,%ah # version 136 movb $0xa,%dl # Divide 137 divb %dl,%al # by 10 138 addb $'0',%al # Display 139 call putchr # tens 140 movb %ah,%al # Get units 141 addb $'0',%al # Display 142 call putchr # units 143 call putstr # End message 144 movl %ebx,%esi # BTX image 145 movzwl 0x8(%ebx),%edi # Compute 146 orl $PAG_SIZ/PAG_ENT-1,%edi # the 147 incl %edi # BTX 148 shll $0x2,%edi # load 149 addl $MEM_TBL,%edi # address 150 pushl %edi # Save load address 151 movzwl 0xa(%ebx),%ecx # Image size 152ifdef(`BTXLDR_VERBOSE',` 153 pushl %ecx # Save image size 154') 155 rep # Relocate 156 movsb # BTX 157 movl %esi,%ebx # Keep place 158ifdef(`BTXLDR_VERBOSE',` 159 movl $m_rel_btx,%esi # Restore 160 popl %eax # parameters 161 call hexout # and 162') 163 popl %ebp # display 164ifdef(`BTXLDR_VERBOSE',` 165 movl %ebp,%eax # the 166 call hexout # relocation 167 call putstr # message 168') 169 addl $PAG_SIZ * 2,%ebp # Display 170ifdef(`BTXLDR_VERBOSE',` 171 movl $m_base,%esi # the 172 movl %ebp,%eax # user 173 call hexout # base 174 call putstr # address 175') 176# 177# Set up ELF-format client program. 178# 179 cmpl $0x464c457f,(%ebx) # ELF magic number? 180 je start.3 # Yes 181 movl $e_fmt,%esi # Display error 182 call putstr # message 183start.2: jmp start.2 # Hang 184start.3: 185ifdef(`BTXLDR_VERBOSE',` 186 movl $m_elf,%esi # Display ELF 187 call putstr # message 188 movl $m_segs,%esi # Format string 189') 190 movl $0x2,%edi # Segment count 191 movl 0x1c(%ebx),%edx # Get e_phoff 192 addl %ebx,%edx # To pointer 193 movzwl 0x2c(%ebx),%ecx # Get e_phnum 194start.4: cmpl $0x1,(%edx) # Is p_type PT_LOAD? 195 jne start.6 # No 196ifdef(`BTXLDR_VERBOSE',` 197 movl 0x4(%edx),%eax # Display 198 call hexout # p_offset 199 movl 0x8(%edx),%eax # Display 200 call hexout # p_vaddr 201 movl 0x10(%edx),%eax # Display 202 call hexout # p_filesz 203 movl 0x14(%edx),%eax # Display 204 call hexout # p_memsz 205 call putstr # End message 206') 207 pushl %esi # Save 208 pushl %edi # working 209 pushl %ecx # registers 210 movl 0x4(%edx),%esi # Get p_offset 211 addl %ebx,%esi # as pointer 212 movl 0x8(%edx),%edi # Get p_vaddr 213 addl %ebp,%edi # as pointer 214 movl 0x10(%edx),%ecx # Get p_filesz 215 rep # Set up 216 movsb # segment 217 movl 0x14(%edx),%ecx # Any bytes 218 subl 0x10(%edx),%ecx # to zero? 219 jz start.5 # No 220 xorb %al,%al # Then 221 rep # zero 222 stosb # them 223start.5: popl %ecx # Restore 224 popl %edi # working 225 popl %esi # registers 226 decl %edi # Segments to do 227 je start.7 # If none 228start.6: addl $0x20,%edx # To next entry 229 loop start.4 # Till done 230start.7: 231ifdef(`BTXLDR_VERBOSE',` 232 movl $m_done,%esi # Display done 233 call putstr # message 234') 235 movl $start.8,%esi # Real mode stub 236 movl $MEM_STUB,%edi # Destination 237 movl $start.9-start.8,%ecx # Size 238 rep # Relocate 239 movsb # it 240 ljmp $SEL_RCODE,$MEM_STUB # To 16-bit code 241 .code16 242start.8: xorw %ax,%ax # Data 243 movb $SEL_RDATA,%al # selector 244 movw %ax,%ss # Reload SS 245 movw %ax,%ds # Reset 246 movw %ax,%es # other 247 movw %ax,%fs # segment 248 movw %ax,%gs # limits 249 movl %cr0,%eax # Switch to 250 decw %ax # real 251 movl %eax,%cr0 # mode 252 ljmp $0,$MEM_ENTRY # Jump to BTX entry point 253start.9: 254 .code32 255# 256# Output message [ESI] followed by EAX in hex. 257# 258hexout: pushl %eax # Save 259 call putstr # Display message 260 popl %eax # Restore 261 pushl %esi # Save 262 pushl %edi # caller's 263 movl $buf,%edi # Buffer 264 pushl %edi # Save 265 call hex32 # To hex 266 xorb %al,%al # Terminate 267 stosb # string 268 popl %esi # Restore 269hexout.1: lodsb # Get a char 270 cmpb $'0',%al # Leading zero? 271 je hexout.1 # Yes 272 testb %al,%al # End of string? 273 jne hexout.2 # No 274 decl %esi # Undo 275hexout.2: decl %esi # Adjust for inc 276 call putstr # Display hex 277 popl %edi # Restore 278 popl %esi # caller's 279 ret # To caller 280# 281# Output zero-terminated string [ESI] to the console. 282# 283putstr.0: call putchr # Output char 284putstr: lodsb # Load char 285 testb %al,%al # End of string? 286 jne putstr.0 # No 287 ret # To caller 288# 289# Output character AL to the console. 290# 291putchr: pusha # Save 292 xorl %ecx,%ecx # Zero for loops 293 movb $SCR_MAT,%ah # Mode/attribute 294 movl $BDA_POS,%ebx # BDA pointer 295 movw (%ebx),%dx # Cursor position 296 movl $0xb8000,%edi # Regen buffer (color) 297 cmpb %ah,BDA_SCR-BDA_POS(%ebx) # Mono mode? 298 jne putchr.1 # No 299 xorw %di,%di # Regen buffer (mono) 300putchr.1: cmpb $0xa,%al # New line? 301 je putchr.2 # Yes 302 xchgl %eax,%ecx # Save char 303 movb $SCR_COL,%al # Columns per row 304 mulb %dh # * row position 305 addb %dl,%al # + column 306 adcb $0x0,%ah # position 307 shll %eax # * 2 308 xchgl %eax,%ecx # Swap char, offset 309 movw %ax,(%edi,%ecx,1) # Write attr:char 310 incl %edx # Bump cursor 311 cmpb $SCR_COL,%dl # Beyond row? 312 jb putchr.3 # No 313putchr.2: xorb %dl,%dl # Zero column 314 incb %dh # Bump row 315putchr.3: cmpb $SCR_ROW,%dh # Beyond screen? 316 jb putchr.4 # No 317 leal 2*SCR_COL(%edi),%esi # New top line 318 movw $(SCR_ROW-1)*SCR_COL/2,%cx # Words to move 319 rep # Scroll 320 movsl # screen 321 movb $' ',%al # Space 322 movb $SCR_COL,%cl # Columns to clear 323 rep # Clear 324 stosw # line 325 movb $SCR_ROW-1,%dh # Bottom line 326putchr.4: movw %dx,(%ebx) # Update position 327 popa # Restore 328 ret # To caller 329# 330# Convert EAX, AX, or AL to hex, saving the result to [EDI]. 331# 332hex32: pushl %eax # Save 333 shrl $0x10,%eax # Do upper 334 call hex16 # 16 335 popl %eax # Restore 336hex16: call hex16.1 # Do upper 8 337hex16.1: xchgb %ah,%al # Save/restore 338hex8: pushl %eax # Save 339 shrb $0x4,%al # Do upper 340 call hex8.1 # 4 341 popl %eax # Restore 342hex8.1: andb $0xf,%al # Get lower 4 343 cmpb $0xa,%al # Convert 344 sbbb $0x69,%al # to hex 345 das # digit 346 orb $0x20,%al # To lower case 347 stosb # Save char 348 ret # (Recursive) 349 350 .data 351 .p2align 4 352# 353# Global descriptor table. 354# 355gdt: .word 0x0,0x0,0x0,0x0 # Null entry 356 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE 357 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA 358 .word 0xffff,0x0,0x9a00,0x0 # SEL_RCODE 359 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA 360gdt.1: 361gdtdesc: .word gdt.1-gdt-1 # Limit 362 .long gdt # Base 363# 364# Messages. 365# 366m_logo: .asciz " \nBTX loader 1.00 " 367m_vers: .asciz "BTX version is \0\n" 368e_fmt: .asciz "Error: Client format not supported\n" 369ifdef(`BTXLDR_VERBOSE',` 370m_mem: .asciz "Starting in protected mode (base mem=\0)\n" 371m_esp: .asciz "Arguments passed (esp=\0):\n" 372m_args: .asciz"<howto=" 373 .asciz" bootdev=" 374 .asciz" junk=" 375 .asciz" " 376 .asciz" " 377 .asciz" bootinfo=\0>\n" 378m_rel_bi: .asciz "Relocated bootinfo (size=48) to \0\n" 379m_rel_args: .asciz "Relocated arguments (size=18) to \0\n" 380m_rel_btx: .asciz "Relocated kernel (size=\0) to \0\n" 381m_base: .asciz "Client base address is \0\n" 382m_elf: .asciz "Client format is ELF\n" 383m_segs: .asciz "text segment: offset=" 384 .asciz " vaddr=" 385 .asciz " filesz=" 386 .asciz " memsz=\0\n" 387 .asciz "data segment: offset=" 388 .asciz " vaddr=" 389 .asciz " filesz=" 390 .asciz " memsz=\0\n" 391m_done: .asciz "Loading complete\n" 392') 393# 394# Uninitialized data area. 395# 396buf: # Scratch buffer 397