biostramp.S revision 1.6
1 /* $NetBSD: biostramp.S,v 1.6 1997/10/09 08:55:29 jtc 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 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 /* 40 * biostramp.S: provide a means for NetBSD to call BIOS interrupts 41 * by switching to real mode, calling it, and switching 42 * back to protected & paging mode. 43 */ 44 45 /* 46 * Micro$haft's book on i386/i486 programming says you should do the following 47 * to return to real mode from protected mode: 48 * 49 * 1) disable paging, by jumping to code with identical virtual and physical 50 * addresses, clearing PG in CR0, and zeroing CR3 (PDBR). 51 * 52 * 2) segment descriptors must be byte-granular with limit 64k-1, def32 = 0, 53 * (i.e. 16-bit data accesses and/or 80286 instructions) 54 * CS must be executable; DS,ES,FS,GS should be writable 55 * 56 * 3) disable interrupts, load IDTR with original value (base 0, limit 1023) 57 * 58 * 4) clear PE in CR0, execute FAR jump to load CS. 59 * 60 * 5) load SP, and off you go 61 * 62 */ 63 64 #include "assym.h" 65 66 #include <i386/include/param.h> 67 #include <i386/include/specialreg.h> 68 #include <i386/include/segments.h> 69 #include <i386/include/apmvar.h> 70 #include <i386/include/psl.h> 71 #include <i386/include/asm.h> 72 73 #define addr32 .byte 0x67 74 #define data32 .byte 0x66 75 76 .set MYBASE,NBPG 77 .set MYSCRATCH,NBPG+NBPG 78 .set CR3_ADDR,(MYSCRATCH-4) 79 .set IDTR_SAVE_ADDR,CR3_ADDR-6 80 .set GDTR_SAVE_ADDR,IDTR_SAVE_ADDR-6 81 .set GDTR_LOCAL_ADDR,GDTR_SAVE_ADDR-6 82 .set STACK_PTR_ADDR,GDTR_LOCAL_ADDR-4 83 .set BASE_PTR_ADDR,STACK_PTR_ADDR-4 84 .set FUNCTION_ADDR,(BASE_PTR_ADDR-2) 85 .set GDT_COPY_ADDR,(FUNCTION_ADDR-NGDT*8) 86 .set AX_REGADDR,(GDT_COPY_ADDR-2) 87 .set BX_REGADDR,(AX_REGADDR-2) 88 .set CX_REGADDR,(BX_REGADDR-2) 89 .set DX_REGADDR,(CX_REGADDR-2) 90 .set SI_REGADDR,(DX_REGADDR-2) 91 .set DI_REGADDR,(SI_REGADDR-2) 92 .set FLAGS_REGADDR,(DI_REGADDR-2) 93 .set ENDREGADDR,(FLAGS_REGADDR-2) 94 95 .set REALSTACK,ENDREGADDR-16 # leave a red zone? 96 97 #define COPY_FLAGS (PSL_C|PSL_PF|PSL_AF|PSL_Z|PSL_N|PSL_D|PSL_V) 98 99 /* 100 * do_bios_call(int function, struct apmregs *regs) 101 */ 102 103 ENTRY(do_bios_call) 104 pushl %ebp 105 movl %esp,%ebp /* set up frame ptr */ 106 pushl %esi 107 pushl %edi 108 pushl %ebx 109 pushl %ds 110 pushl %es 111 pushl %fs 112 pushl %gs 113 114 # copy data to where the real-mode hook can handle it 115 movl 8(%ebp),%eax 116 movw %ax,FUNCTION_ADDR 117 movl 12(%ebp),%ebx 118 movw APMREG_AX(%ebx),%ax 119 movw %ax,AX_REGADDR 120 movw APMREG_BX(%ebx),%ax 121 movw %ax,BX_REGADDR 122 movw APMREG_CX(%ebx),%ax 123 movw %ax,CX_REGADDR 124 movw APMREG_DX(%ebx),%ax 125 movw %ax,DX_REGADDR 126 movw APMREG_SI(%ebx),%ax 127 movw %ax,SI_REGADDR 128 movw APMREG_DI(%ebx),%ax 129 movw %ax,DI_REGADDR 130 # merge current flags with certain provided flags 131 movw APMREG_FLAGS(%ebx),%cx 132 pushfl 133 popl %eax 134 andl $~(COPY_FLAGS|PSL_I),%eax 135 andl $COPY_FLAGS,%ecx 136 orl %ecx,%eax 137 movw %ax,FLAGS_REGADDR 138 139 # save flags, disable interrupts, do real mode stuff 140 pushfl 141 142 # save GDT 143 sgdt GDTR_SAVE_ADDR 144 145 # copy the GDT to local area 146 movl GDTR_SAVE_ADDR+2,%esi 147 movl $GDT_COPY_ADDR,%edi 148 movl $(NGDT*8),%ecx 149 cld 150 rep 151 movsb 152 movw $(NGDT*8)-1,GDTR_LOCAL_ADDR 153 movl $GDT_COPY_ADDR,GDTR_LOCAL_ADDR+2 154 155 # install GDT copy 156 lgdt GDTR_LOCAL_ADDR 157 158 cli 159 160 # save IDT 161 sidt IDTR_SAVE_ADDR 162 163 # set up new stack: save old ones, create new segs 164 movl %esp,STACK_PTR_ADDR 165 movl %ebp,BASE_PTR_ADDR 166 movl $REALSTACK,%esp 167 movl $0,%ebp # leave no trace, there is none. 168 169 # save CR3 170 movl %cr3,%eax 171 movl %eax,CR3_ADDR 172 173 # turn off paging 174 movl %cr0,%eax 175 andl $~(CR0_PG),%eax 176 movl %eax,%cr0 177 178 # flush TLB, drop PDBR 179 xorl %eax,%eax 180 movl %eax,%cr3 181 182 ## load 16-bit segment descriptors 183 movw $GSEL(GBIOSDATA_SEL,SEL_KPL),%bx 184 movw %bx,%ds 185 movw %bx,%es 186 movw %bx,%fs 187 movw %bx,%gs 188 189 ljmp $GSEL(GBIOSCODE_SEL,SEL_KPL),$x16+MYBASE 190 191 x16: 192 # turn off protected mode--yikes! 193 mov %cr0,%eax 194 data32 195 and $~CR0_PE,%eax 196 mov %eax,%cr0 197 198 # need inter-segment jump to reload real-mode CS 199 data32 200 ljmp $(MYBASE>>4),$xreal 201 202 xreal: # really in real mode now 203 # set up segment selectors. Note: everything is now relative 204 # to zero-base in this file, except %ss. 205 # data items in our scratch area need to reflect MYADDR 206 xorl %ax,%ax 207 movw %ax,%ss 208 209 movw %cs,%ax 210 movw %ax,%es 211 movw %ax,%fs 212 movw %ax,%gs 213 movw %ax,%ds 214 215 ## load IDT, now that we are here. 216 addr32 217 lidt IDT_bios 218 219 # Don't forget that we're in real mode, with 16-bit default data. 220 # all these movl's are really movw's ! 221 addr32 222 movl DI_REGADDR-MYBASE,%edi 223 addr32 224 movl SI_REGADDR-MYBASE,%esi 225 addr32 226 movl DX_REGADDR-MYBASE,%edx 227 addr32 228 movl CX_REGADDR-MYBASE,%ecx 229 addr32 230 movl BX_REGADDR-MYBASE,%ebx 231 addr32 232 movb FUNCTION_ADDR-MYBASE,%al 233 addr32 234 movb %al,intaddr+1 # self modifying code, yuck. no indirect interrupt instruction! 235 # long jump to flush processor cache to reflect code modification 236 data32 237 ljmp $(MYBASE>>4),$flushit 238 flushit: 239 addr32 240 movl FLAGS_REGADDR-MYBASE,%eax 241 pushl %eax 242 popfl 243 addr32 244 movl AX_REGADDR-MYBASE,%eax 245 246 intaddr: 247 int $0xff 248 249 # save results 250 pushf 251 addr32 252 movl %eax,AX_REGADDR-MYBASE 253 addr32 254 movl %ebx,BX_REGADDR-MYBASE 255 addr32 256 movl %ecx,CX_REGADDR-MYBASE 257 addr32 258 movl %edx,DX_REGADDR-MYBASE 259 addr32 260 movl %esi,SI_REGADDR-MYBASE 261 addr32 262 movl %edi,DI_REGADDR-MYBASE 263 pop %eax 264 addr32 265 movl %eax,FLAGS_REGADDR-MYBASE 266 267 # and return to protected mode 268 cli # just to be sure 269 270 mov %cr0,%eax 271 data32 272 or $CR0_PE,%eax 273 mov %eax,%cr0 274 275 # long jump to 32-bit code segment 276 data32 277 ljmp $GSEL(GCODE_SEL,SEL_KPL),$x32+MYBASE 278 x32: 279 #back in 32-bit mode/protected mode (but not paging yet). 280 # Reload the segment registers & IDT 281 282 movw $GSEL(GDATA_SEL,SEL_KPL),%bx 283 movw %bx,%ds 284 movw %bx,%ss 285 movw %bx,%es 286 287 # reload PDBR 288 movl CR3_ADDR,%eax 289 movl %eax,%cr3 290 movl %cr0,%eax 291 orl $CR0_PG,%eax 292 movl %eax,%cr0 293 294 # reload system copy of GDT 295 lgdt GDTR_SAVE_ADDR 296 297 # restore protected-mode stack 298 movl STACK_PTR_ADDR,%esp 299 movl BASE_PTR_ADDR,%ebp 300 301 #restore protected-mode IDT 302 lidt IDTR_SAVE_ADDR 303 304 # copy back arguments from holding pen 305 306 movl 12(%ebp),%ebx 307 movw AX_REGADDR,%ax 308 movw %ax,APMREG_AX(%ebx) 309 movw BX_REGADDR,%ax 310 movw %ax,APMREG_BX(%ebx) 311 movw CX_REGADDR,%ax 312 movw %ax,APMREG_CX(%ebx) 313 movw DX_REGADDR,%ax 314 movw %ax,APMREG_DX(%ebx) 315 movw SI_REGADDR,%ax 316 movw %ax,APMREG_SI(%ebx) 317 movw DI_REGADDR,%ax 318 movw %ax,APMREG_DI(%ebx) 319 movw FLAGS_REGADDR,%ax 320 movw %ax,APMREG_FLAGS(%ebx) 321 322 # finish up, restore registers, and return 323 popfl 324 popl %gs 325 popl %fs 326 popl %es 327 popl %ds # see above 328 popl %ebx 329 popl %edi 330 popl %esi 331 leave 332 ret 333 334 .align 4 335 IDT_bios: # BIOS IDT descriptor (real-mode) 336 .word 1023 337 .long 0 338
Indexes created Tue Sep 30 11:09:46 GMT 2025