biostramp.S revision 1.1
1 /* $NetBSD: biostramp.S,v 1.1 1996/09/08 15:36:53 jtk Exp $ */ 2 /*- 3 * Copyright (c) 1996 John T. Kohl. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR 22 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 23 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 24 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, 25 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 26 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 27 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 29 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 30 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 31 * POSSIBILITY OF SUCH DAMAGE. 32 * 33 */ 34 35 /* 36 * biostramp.S: provide a means for NetBSD to call BIOS interrupts 37 * by switching to real mode, calling it, and switching 38 * back to protected & paging mode. 39 */ 40 41 /* 42 * Micro$haft's book on i386/i486 programming says you should do the following 43 * to return to real mode from protected mode: 44 * 45 * 1) disable paging, by jumping to code with identical virtual and physical 46 * addresses, clearing PG in CR0, and zeroing CR3 (PDBR). 47 * 48 * 2) segment descriptors must be byte-granular with limit 64k-1, def32 = 0, 49 * (i.e. 16-bit data accesses and/or 80286 instructions) 50 * CS must be executable; DS,ES,FS,GS should be writable 51 * 52 * 3) disable interrupts, load IDTR with original value (base 0, limit 1023) 53 * 54 * 4) clear PE in CR0, execute FAR jump to load CS. 55 * 56 * 5) load SP, and off you go 57 * 58 */ 59 60 #define ASM 61 #define _LOCORE 62 63 #define addr32 .byte 0x67 64 #define data32 .byte 0x66 65 66 /* these from locore.s: */ 67 #define ALIGN_TEXT .align 2,0x90 /* 4-byte boundaries, NOP-filled */ 68 #define ENTRY(name) .globl _ ## name; ALIGN_TEXT; _ ## name: 69 70 #include "assym.h" 71 #include <machine/param.h> 72 #include <machine/specialreg.h> 73 #include <machine/segments.h> 74 #include <machine/apmvar.h> 75 #include <machine/psl.h> 76 77 .set MYBASE,NBPG 78 .set MYSCRATCH,NBPG+NBPG 79 .set CR3_ADDR,(MYSCRATCH-4) 80 .set IDTR_SAVE_ADDR,CR3_ADDR-6 81 .set GDTR_SAVE_ADDR,IDTR_SAVE_ADDR-6 82 .set GDTR_LOCAL_ADDR,GDTR_SAVE_ADDR-6 83 .set STACK_PTR_ADDR,GDTR_LOCAL_ADDR-4 84 .set BASE_PTR_ADDR,STACK_PTR_ADDR-4 85 .set FUNCTION_ADDR,(BASE_PTR_ADDR-2) 86 .set GDT_COPY_ADDR,(FUNCTION_ADDR-NGDT*8) 87 .set AX_REGADDR,(GDT_COPY_ADDR-2) 88 .set BX_REGADDR,(AX_REGADDR-2) 89 .set CX_REGADDR,(BX_REGADDR-2) 90 .set DX_REGADDR,(CX_REGADDR-2) 91 .set SI_REGADDR,(DX_REGADDR-2) 92 .set DI_REGADDR,(SI_REGADDR-2) 93 .set FLAGS_REGADDR,(DI_REGADDR-2) 94 .set ENDREGADDR,(FLAGS_REGADDR-2) 95 96 .set REALSTACK,ENDREGADDR-16 # leave a red zone? 97 98 #define COPY_FLAGS (PSL_C|PSL_PF|PSL_AF|PSL_Z|PSL_N|PSL_D|PSL_V) 99 100 /* 101 * do_bios_call(int function, struct apmregs *regs) 102 */ 103 104 ENTRY(do_bios_call) 105 pushl %ebp 106 movl %esp,%ebp /* set up frame ptr */ 107 pushl %esi 108 pushl %edi 109 pushl %ebx 110 pushl %ds 111 pushl %es 112 pushl %fs 113 pushl %gs 114 115 # copy data to where the real-mode hook can handle it 116 movl 8(%ebp),%eax 117 movw %ax,FUNCTION_ADDR 118 movl 12(%ebp),%ebx 119 movw APMREG_AX(%ebx),%ax 120 movw %ax,AX_REGADDR 121 movw APMREG_BX(%ebx),%ax 122 movw %ax,BX_REGADDR 123 movw APMREG_CX(%ebx),%ax 124 movw %ax,CX_REGADDR 125 movw APMREG_DX(%ebx),%ax 126 movw %ax,DX_REGADDR 127 movw APMREG_SI(%ebx),%ax 128 movw %ax,SI_REGADDR 129 movw APMREG_DI(%ebx),%ax 130 movw %ax,DI_REGADDR 131 # merge current flags with certain provided flags 132 movw APMREG_FLAGS(%ebx),%cx 133 pushfl 134 popl %eax 135 andl $~(COPY_FLAGS|PSL_I),%eax 136 andl $COPY_FLAGS,%ecx 137 orl %ecx,%eax 138 movw %ax,FLAGS_REGADDR 139 140 # save flags, disable interrupts, do real mode stuff 141 pushfl 142 143 # save GDT 144 sgdt GDTR_SAVE_ADDR 145 146 # copy the GDT to local area 147 movl GDTR_SAVE_ADDR+2,%esi 148 movl $GDT_COPY_ADDR,%edi 149 movl $(NGDT*8),%ecx 150 cld 151 rep 152 movsb 153 movw $(NGDT*8)-1,GDTR_LOCAL_ADDR 154 movl $GDT_COPY_ADDR,GDTR_LOCAL_ADDR+2 155 156 # install GDT copy 157 lgdt GDTR_LOCAL_ADDR 158 159 cli 160 161 # save IDT 162 sidt IDTR_SAVE_ADDR 163 164 # set up new stack: save old ones, create new segs 165 movl %esp,STACK_PTR_ADDR 166 movl %ebp,BASE_PTR_ADDR 167 movl $REALSTACK,%esp 168 movl $0,%ebp # leave no trace, there is none. 169 170 # save CR3 171 movl %cr3,%eax 172 movl %eax,CR3_ADDR 173 174 # turn off paging 175 movl %cr0,%eax 176 andl $~(CR0_PG),%eax 177 movl %eax,%cr0 178 179 # flush TLB, drop PDBR 180 xorl %eax,%eax 181 movl %eax,%cr3 182 183 ## load 16-bit segment descriptors 184 movw $GSEL(GBIOSDATA_SEL,SEL_KPL),%bx 185 movw %bx,%ds 186 movw %bx,%es 187 movw %bx,%fs 188 movw %bx,%gs 189 190 ljmp $GSEL(GBIOSCODE_SEL,SEL_KPL),$x16+MYBASE 191 192 x16: 193 # turn off protected mode--yikes! 194 mov %cr0,%eax 195 data32 196 and $~CR0_PE,%eax 197 mov %eax,%cr0 198 199 # need inter-segment jump to reload real-mode CS 200 data32 201 ljmp $(MYBASE>>4),$xreal 202 203 xreal: # really in real mode now 204 # set up segment selectors. Note: everything is now relative 205 # to zero-base in this file, except %ss. 206 # data items in our scratch area need to reflect MYADDR 207 xorl %ax,%ax 208 movw %ax,%ss 209 210 movw %cs,%ax 211 movw %ax,%es 212 movw %ax,%fs 213 movw %ax,%gs 214 movw %ax,%ds 215 216 ## load IDT, now that we are here. 217 addr32 218 lidt IDT_bios 219 220 # Don't forget that we're in real mode, with 16-bit default data. 221 # all these movl's are really movw's ! 222 addr32 223 movl DI_REGADDR-MYBASE,%edi 224 addr32 225 movl SI_REGADDR-MYBASE,%esi 226 addr32 227 movl DX_REGADDR-MYBASE,%edx 228 addr32 229 movl CX_REGADDR-MYBASE,%ecx 230 addr32 231 movl BX_REGADDR-MYBASE,%ebx 232 addr32 233 movb FUNCTION_ADDR-MYBASE,%al 234 addr32 235 movb %al,intaddr+1 # self modifying code, yuck. no indirect interrupt instruction! 236 # long jump to flush processor cache to reflect code modification 237 data32 238 ljmp $(MYBASE>>4),$flushit 239 flushit: 240 addr32 241 movl FLAGS_REGADDR-MYBASE,%eax 242 pushl %eax 243 popfl 244 addr32 245 movl AX_REGADDR-MYBASE,%eax 246 247 intaddr: 248 int $0xff 249 250 # save results 251 pushf 252 addr32 253 movl %eax,AX_REGADDR-MYBASE 254 addr32 255 movl %ebx,BX_REGADDR-MYBASE 256 addr32 257 movl %ecx,CX_REGADDR-MYBASE 258 addr32 259 movl %edx,DX_REGADDR-MYBASE 260 addr32 261 movl %esi,SI_REGADDR-MYBASE 262 addr32 263 movl %edi,DI_REGADDR-MYBASE 264 pop %eax 265 addr32 266 movl %eax,FLAGS_REGADDR-MYBASE 267 268 # and return to protected mode 269 cli # just to be sure 270 271 mov %cr0,%eax 272 data32 273 or $CR0_PE,%eax 274 mov %eax,%cr0 275 276 # long jump to 32-bit code segment 277 data32 278 ljmp $GSEL(GCODE_SEL,SEL_KPL),$x32+MYBASE 279 x32: 280 #back in 32-bit mode/protected mode (but not paging yet). 281 # Reload the segment registers & IDT 282 283 movw $GSEL(GDATA_SEL,SEL_KPL),%bx 284 movw %bx,%ds 285 movw %bx,%ss 286 movw %bx,%es 287 288 # reload PDBR 289 movl CR3_ADDR,%eax 290 movl %eax,%cr3 291 movl %cr0,%eax 292 orl $CR0_PG,%eax 293 movl %eax,%cr0 294 295 # reload system copy of GDT 296 lgdt GDTR_SAVE_ADDR 297 298 # restore protected-mode stack 299 movl STACK_PTR_ADDR,%esp 300 movl BASE_PTR_ADDR,%ebp 301 302 #restore protected-mode IDT 303 lidt IDTR_SAVE_ADDR 304 305 # copy back arguments from holding pen 306 307 movl 12(%ebp),%ebx 308 movw AX_REGADDR,%ax 309 movw %ax,APMREG_AX(%ebx) 310 movw BX_REGADDR,%ax 311 movw %ax,APMREG_BX(%ebx) 312 movw CX_REGADDR,%ax 313 movw %ax,APMREG_CX(%ebx) 314 movw DX_REGADDR,%ax 315 movw %ax,APMREG_DX(%ebx) 316 movw SI_REGADDR,%ax 317 movw %ax,APMREG_SI(%ebx) 318 movw DI_REGADDR,%ax 319 movw %ax,APMREG_DI(%ebx) 320 movw FLAGS_REGADDR,%ax 321 movw %ax,APMREG_FLAGS(%ebx) 322 323 # finish up, restore registers, and return 324 popfl 325 popl %gs 326 popl %fs 327 popl %es 328 popl %ds # see above 329 popl %ebx 330 popl %edi 331 popl %esi 332 leave 333 ret 334 335 .align 4 336 IDT_bios: # BIOS IDT descriptor (real-mode) 337 .word 1023 338 .long 0 339
Indexes created Tue Sep 30 17:09:57 GMT 2025