1/* $NetBSD: biostramp.S,v 1.14 2008/04/28 20:23:23 martin Exp $ */ 2 3/*- 4 * Copyright (c) 1996 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by John Kohl. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32/* 33 * biostramp.S: provide a means for NetBSD to call BIOS interrupts 34 * by switching to real mode, calling it, and switching 35 * back to protected & paging mode. 36 */ 37 38/* 39 * Micro$haft's book on i386/i486 programming says you should do the following 40 * to return to real mode from protected mode: 41 * 42 * 1) disable paging, by jumping to code with identical virtual and physical 43 * addresses, clearing PG in CR0, and zeroing CR3 (PDBR). 44 * 45 * 2) segment descriptors must be byte-granular with limit 64k-1, def32 = 0, 46 * (i.e. 16-bit data accesses and/or 80286 instructions) 47 * CS must be executable; DS,ES,FS,GS should be writable 48 * 49 * 3) disable interrupts, load IDTR with original value (base 0, limit 1023) 50 * 51 * 4) clear PE in CR0, execute FAR jump to load CS. 52 * 53 * 5) load SP, and off you go 54 * 55 */ 56 57#include "assym.h" 58 59#include <i386/include/param.h> 60#include <i386/include/specialreg.h> 61#include <i386/include/segments.h> 62#include <i386/include/apmvar.h> 63#include <i386/include/psl.h> 64#include <i386/include/asm.h> 65 66#define addr32 .byte 0x67 67#define data32 .byte 0x66 68 69 .set MYBASE,NBPG 70 .set MYSCRATCH,NBPG*2 71 .set CR3_ADDR,(MYSCRATCH-4) 72 .set IDTR_SAVE_ADDR,CR3_ADDR-6 73 .set GDTR_SAVE_ADDR,IDTR_SAVE_ADDR-6 74 .set GDTR_LOCAL_ADDR,GDTR_SAVE_ADDR-6 75 .set STACK_PTR_ADDR,GDTR_LOCAL_ADDR-4 76 .set BASE_PTR_ADDR,STACK_PTR_ADDR-4 77 .set FUNCTION_ADDR,(BASE_PTR_ADDR-2) 78 .set GDT_COPY_ADDR,(FUNCTION_ADDR-NGDT*8) 79 .set EAX_REGADDR,(GDT_COPY_ADDR-4) 80 .set EBX_REGADDR,(EAX_REGADDR-4) 81 .set ECX_REGADDR,(EBX_REGADDR-4) 82 .set EDX_REGADDR,(ECX_REGADDR-4) 83 .set ESI_REGADDR,(EDX_REGADDR-4) 84 .set EDI_REGADDR,(ESI_REGADDR-4) 85 .set EFLAGS_REGADDR,(EDI_REGADDR-4) 86 .set ES_REGADDR, (EFLAGS_REGADDR-4) 87 .set ENDREGADDR,(ES_REGADDR-4) 88 89 .set REALSTACK,ENDREGADDR-20 # leave a red zone? 90 91#define COPY_FLAGS (PSL_C|PSL_PF|PSL_AF|PSL_Z|PSL_N|PSL_D|PSL_V) 92 93/* 94 * do_bios_call(int function, struct bioscall *regs) 95 */ 96 97ENTRY(do_bios_call) 98 pushl %ebp 99 movl %esp,%ebp /* set up frame ptr */ 100 pushl %esi 101 pushl %edi 102 pushl %ebx 103 pushl %ds 104 pushl %es 105 pushl %fs 106 pushl %gs 107 108 # copy data to where the real-mode hook can handle it 109 movl 8(%ebp),%eax 110 movw %ax,FUNCTION_ADDR 111 movl 12(%ebp),%ebx 112 movl BIOSCALLREG_EAX(%ebx),%eax 113 movl %eax,EAX_REGADDR 114 movl BIOSCALLREG_EBX(%ebx),%eax 115 movl %eax,EBX_REGADDR 116 movl BIOSCALLREG_ECX(%ebx),%eax 117 movl %eax,ECX_REGADDR 118 movl BIOSCALLREG_EDX(%ebx),%eax 119 movl %eax,EDX_REGADDR 120 movl BIOSCALLREG_ESI(%ebx),%eax 121 movl %eax,ESI_REGADDR 122 movl BIOSCALLREG_EDI(%ebx),%eax 123 movl %eax,EDI_REGADDR 124 # merge current flags with certain provided flags 125 movl BIOSCALLREG_EFLAGS(%ebx),%ecx 126 pushfl 127 popl %eax 128 andl $~(COPY_FLAGS|PSL_I),%eax 129 andl $COPY_FLAGS,%ecx 130 orl %ecx,%eax 131 movl %eax,EFLAGS_REGADDR 132 movl $0, ES_REGADDR 133 134 # save flags, disable interrupts, do real mode stuff 135 pushfl 136 137 # save GDT 138 sgdt GDTR_SAVE_ADDR 139 140 # copy the GDT to local area 141 movl GDTR_SAVE_ADDR+2,%esi 142 movl $GDT_COPY_ADDR,%edi 143 movl $(NGDT*8),%ecx 144 cld 145 rep 146 movsb 147 movw $(NGDT*8)-1,GDTR_LOCAL_ADDR 148 movl $GDT_COPY_ADDR,GDTR_LOCAL_ADDR+2 149 150 # install GDT copy 151 lgdt GDTR_LOCAL_ADDR 152 153 cli 154 155 # save IDT 156 sidt IDTR_SAVE_ADDR 157 158 # set up new stack: save old ones, create new segs 159 movl %esp,STACK_PTR_ADDR 160 movl %ebp,BASE_PTR_ADDR 161 movl $REALSTACK,%esp 162 movl $0,%ebp # leave no trace, there is none. 163 164 # save CR3 165 movl %cr3,%eax 166 movl %eax,CR3_ADDR 167 168 # turn off paging 169 movl %cr0,%eax 170 andl $~(CR0_PG),%eax 171 movl %eax,%cr0 172 173 # flush TLB, drop PDBR 174 xorl %eax,%eax 175 movl %eax,%cr3 176 177 ## load 16-bit segment descriptors 178 movw $GSEL(GBIOSDATA_SEL,SEL_KPL),%bx 179 movw %bx,%ds 180 movw %bx,%es 181 movw %bx,%fs 182 movw %bx,%gs 183 184 ljmp $GSEL(GBIOSCODE_SEL,SEL_KPL),$x16+MYBASE 185 186x16: 187 # turn off protected mode--yikes! 188 mov %cr0,%eax 189 data32 190 and $~CR0_PE,%eax 191 mov %eax,%cr0 192 193 # need inter-segment jump to reload real-mode CS 194 data32 195 ljmp $(MYBASE>>4),$xreal 196 197xreal: # really in real mode now 198 # set up segment selectors. Note: everything is now relative 199 # to zero-base in this file, except %ss. 200 # data items in our scratch area need to reflect MYADDR 201 xorl %eax,%eax 202 movw %ax,%ss 203 204 movw %cs,%ax 205 movw %ax,%es 206 movw %ax,%fs 207 movw %ax,%gs 208 movw %ax,%ds 209 210 ## load IDT, now that we are here. 211 addr32 212 lidt IDT_bios 213 214 # Don't forget that we're in real mode, with 16-bit default data. 215 # all these movl's are really movw's, and movw's are movl's! 216 addr32 217 movw EDI_REGADDR-MYBASE,%di 218 addr32 219 movw ESI_REGADDR-MYBASE,%si 220 addr32 221 movw EDX_REGADDR-MYBASE,%dx 222 addr32 223 movw ECX_REGADDR-MYBASE,%cx 224 addr32 225 movw EBX_REGADDR-MYBASE,%bx 226 addr32 227 movb FUNCTION_ADDR-MYBASE,%al 228 addr32 229 movb %al,intaddr+1 # self modifying code, yuck. no indirect interrupt instruction! 230 # long jump to flush processor cache to reflect code modification 231 data32 232 ljmp $(MYBASE>>4),$flushit 233flushit: 234 addr32 235 movw EFLAGS_REGADDR-MYBASE,%ax 236 pushl %eax 237 popfl 238 addr32 239 movw EAX_REGADDR-MYBASE,%ax 240 241intaddr: 242 int $0xff 243 244 # save results 245 pushf 246 addr32 247 movw %ax,EAX_REGADDR-MYBASE 248 addr32 249 movw %bx,EBX_REGADDR-MYBASE 250 addr32 251 movw %cx,ECX_REGADDR-MYBASE 252 addr32 253 movw %dx,EDX_REGADDR-MYBASE 254 addr32 255 movw %si,ESI_REGADDR-MYBASE 256 addr32 257 movw %di,EDI_REGADDR-MYBASE 258 pop %ax 259 addr32 260 movw %ax,EFLAGS_REGADDR-MYBASE 261 addr32 262 movw %es,ES_REGADDR-MYBASE 263 264 # and return to protected mode 265 cli # just to be sure 266 267 mov %cr0,%eax 268 data32 269 or $CR0_PE,%eax 270 mov %eax,%cr0 271 272 # long jump to 32-bit code segment 273 data32 274 ljmp $GSEL(GCODE_SEL,SEL_KPL),$x32+MYBASE 275x32: 276 #back in 32-bit mode/protected mode (but not paging yet). 277 # Reload the segment registers & IDT 278 279 movw $GSEL(GDATA_SEL,SEL_KPL),%bx 280 movw %bx,%ds 281 movw %bx,%ss 282 movw %bx,%es 283 284 # reload PDBR 285 movl CR3_ADDR,%eax 286 movl %eax,%cr3 287 movl %cr0,%eax 288 orl $CR0_PG,%eax 289 movl %eax,%cr0 290 291 # reload system copy of GDT 292 lgdt GDTR_SAVE_ADDR 293 294 # restore protected-mode stack 295 movl STACK_PTR_ADDR,%esp 296 movl BASE_PTR_ADDR,%ebp 297 298 #restore protected-mode IDT 299 lidt IDTR_SAVE_ADDR 300 301 # copy back arguments from holding pen 302 303 movl 12(%ebp),%ebx 304 movl EAX_REGADDR,%eax 305 movl %eax,BIOSCALLREG_EAX(%ebx) 306 movl EBX_REGADDR,%eax 307 movl %eax,BIOSCALLREG_EBX(%ebx) 308 movl ECX_REGADDR,%eax 309 movl %eax,BIOSCALLREG_ECX(%ebx) 310 movl EDX_REGADDR,%eax 311 movl %eax,BIOSCALLREG_EDX(%ebx) 312 movl ESI_REGADDR,%eax 313 movl %eax,BIOSCALLREG_ESI(%ebx) 314 movl EDI_REGADDR,%eax 315 movl %eax,BIOSCALLREG_EDI(%ebx) 316 movl EFLAGS_REGADDR,%eax 317 movl %eax,BIOSCALLREG_EFLAGS(%ebx) 318 movl ES_REGADDR, %eax 319 movl %eax,BIOSCALLREG_ES(%ebx) 320 321 # finish up, restore registers, and return 322 popfl 323 popl %gs 324 popl %fs 325 popl %es 326 popl %ds # see above 327 popl %ebx 328 popl %edi 329 popl %esi 330 leave 331 ret 332 333#ifdef __ELF__ 334 .align 16 335#else 336 .align 4 337#endif 338IDT_bios: # BIOS IDT descriptor (real-mode) 339 .word 1023 340 .long 0 341