biostramp.S revision 1.3
1 /* $NetBSD: biostramp.S,v 1.3 1996/09/09 18:42:51 mycroft 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 #include "assym.h" 61 #include "apm.h" 62 #if NAPM > 0 63 #include <machine/param.h> 64 #include <machine/specialreg.h> 65 #include <machine/segments.h> 66 #include <machine/apmvar.h> 67 #include <machine/psl.h> 68 #include <machine/asm.h> 69 #define addr32 .byte 0x67 70 #define data32 .byte 0x66 71 72 .set MYBASE,NBPG 73 .set MYSCRATCH,NBPG+NBPG 74 .set CR3_ADDR,(MYSCRATCH-4) 75 .set IDTR_SAVE_ADDR,CR3_ADDR-6 76 .set GDTR_SAVE_ADDR,IDTR_SAVE_ADDR-6 77 .set GDTR_LOCAL_ADDR,GDTR_SAVE_ADDR-6 78 .set STACK_PTR_ADDR,GDTR_LOCAL_ADDR-4 79 .set BASE_PTR_ADDR,STACK_PTR_ADDR-4 80 .set FUNCTION_ADDR,(BASE_PTR_ADDR-2) 81 .set GDT_COPY_ADDR,(FUNCTION_ADDR-NGDT*8) 82 .set AX_REGADDR,(GDT_COPY_ADDR-2) 83 .set BX_REGADDR,(AX_REGADDR-2) 84 .set CX_REGADDR,(BX_REGADDR-2) 85 .set DX_REGADDR,(CX_REGADDR-2) 86 .set SI_REGADDR,(DX_REGADDR-2) 87 .set DI_REGADDR,(SI_REGADDR-2) 88 .set FLAGS_REGADDR,(DI_REGADDR-2) 89 .set ENDREGADDR,(FLAGS_REGADDR-2) 90 91 .set REALSTACK,ENDREGADDR-16 # leave a red zone? 92 93 #define COPY_FLAGS (PSL_C|PSL_PF|PSL_AF|PSL_Z|PSL_N|PSL_D|PSL_V) 94 95 /* 96 * do_bios_call(int function, struct apmregs *regs) 97 */ 98 99 ENTRY(do_bios_call) 100 pushl %ebp 101 movl %esp,%ebp /* set up frame ptr */ 102 pushl %esi 103 pushl %edi 104 pushl %ebx 105 pushl %ds 106 pushl %es 107 pushl %fs 108 pushl %gs 109 110 # copy data to where the real-mode hook can handle it 111 movl 8(%ebp),%eax 112 movw %ax,FUNCTION_ADDR 113 movl 12(%ebp),%ebx 114 movw APMREG_AX(%ebx),%ax 115 movw %ax,AX_REGADDR 116 movw APMREG_BX(%ebx),%ax 117 movw %ax,BX_REGADDR 118 movw APMREG_CX(%ebx),%ax 119 movw %ax,CX_REGADDR 120 movw APMREG_DX(%ebx),%ax 121 movw %ax,DX_REGADDR 122 movw APMREG_SI(%ebx),%ax 123 movw %ax,SI_REGADDR 124 movw APMREG_DI(%ebx),%ax 125 movw %ax,DI_REGADDR 126 # merge current flags with certain provided flags 127 movw APMREG_FLAGS(%ebx),%cx 128 pushfl 129 popl %eax 130 andl $~(COPY_FLAGS|PSL_I),%eax 131 andl $COPY_FLAGS,%ecx 132 orl %ecx,%eax 133 movw %ax,FLAGS_REGADDR 134 135 # save flags, disable interrupts, do real mode stuff 136 pushfl 137 138 # save GDT 139 sgdt GDTR_SAVE_ADDR 140 141 # copy the GDT to local area 142 movl GDTR_SAVE_ADDR+2,%esi 143 movl $GDT_COPY_ADDR,%edi 144 movl $(NGDT*8),%ecx 145 cld 146 rep 147 movsb 148 movw $(NGDT*8)-1,GDTR_LOCAL_ADDR 149 movl $GDT_COPY_ADDR,GDTR_LOCAL_ADDR+2 150 151 # install GDT copy 152 lgdt GDTR_LOCAL_ADDR 153 154 cli 155 156 # save IDT 157 sidt IDTR_SAVE_ADDR 158 159 # set up new stack: save old ones, create new segs 160 movl %esp,STACK_PTR_ADDR 161 movl %ebp,BASE_PTR_ADDR 162 movl $REALSTACK,%esp 163 movl $0,%ebp # leave no trace, there is none. 164 165 # save CR3 166 movl %cr3,%eax 167 movl %eax,CR3_ADDR 168 169 # turn off paging 170 movl %cr0,%eax 171 andl $~(CR0_PG),%eax 172 movl %eax,%cr0 173 174 # flush TLB, drop PDBR 175 xorl %eax,%eax 176 movl %eax,%cr3 177 178 ## load 16-bit segment descriptors 179 movw $GSEL(GBIOSDATA_SEL,SEL_KPL),%bx 180 movw %bx,%ds 181 movw %bx,%es 182 movw %bx,%fs 183 movw %bx,%gs 184 185 ljmp $GSEL(GBIOSCODE_SEL,SEL_KPL),$x16+MYBASE 186 187 x16: 188 # turn off protected mode--yikes! 189 mov %cr0,%eax 190 data32 191 and $~CR0_PE,%eax 192 mov %eax,%cr0 193 194 # need inter-segment jump to reload real-mode CS 195 data32 196 ljmp $(MYBASE>>4),$xreal 197 198 xreal: # really in real mode now 199 # set up segment selectors. Note: everything is now relative 200 # to zero-base in this file, except %ss. 201 # data items in our scratch area need to reflect MYADDR 202 xorl %ax,%ax 203 movw %ax,%ss 204 205 movw %cs,%ax 206 movw %ax,%es 207 movw %ax,%fs 208 movw %ax,%gs 209 movw %ax,%ds 210 211 ## load IDT, now that we are here. 212 addr32 213 lidt IDT_bios 214 215 # Don't forget that we're in real mode, with 16-bit default data. 216 # all these movl's are really movw's ! 217 addr32 218 movl DI_REGADDR-MYBASE,%edi 219 addr32 220 movl SI_REGADDR-MYBASE,%esi 221 addr32 222 movl DX_REGADDR-MYBASE,%edx 223 addr32 224 movl CX_REGADDR-MYBASE,%ecx 225 addr32 226 movl BX_REGADDR-MYBASE,%ebx 227 addr32 228 movb FUNCTION_ADDR-MYBASE,%al 229 addr32 230 movb %al,intaddr+1 # self modifying code, yuck. no indirect interrupt instruction! 231 # long jump to flush processor cache to reflect code modification 232 data32 233 ljmp $(MYBASE>>4),$flushit 234 flushit: 235 addr32 236 movl FLAGS_REGADDR-MYBASE,%eax 237 pushl %eax 238 popfl 239 addr32 240 movl AX_REGADDR-MYBASE,%eax 241 242 intaddr: 243 int $0xff 244 245 # save results 246 pushf 247 addr32 248 movl %eax,AX_REGADDR-MYBASE 249 addr32 250 movl %ebx,BX_REGADDR-MYBASE 251 addr32 252 movl %ecx,CX_REGADDR-MYBASE 253 addr32 254 movl %edx,DX_REGADDR-MYBASE 255 addr32 256 movl %esi,SI_REGADDR-MYBASE 257 addr32 258 movl %edi,DI_REGADDR-MYBASE 259 pop %eax 260 addr32 261 movl %eax,FLAGS_REGADDR-MYBASE 262 263 # and return to protected mode 264 cli # just to be sure 265 266 mov %cr0,%eax 267 data32 268 or $CR0_PE,%eax 269 mov %eax,%cr0 270 271 # long jump to 32-bit code segment 272 data32 273 ljmp $GSEL(GCODE_SEL,SEL_KPL),$x32+MYBASE 274 x32: 275 #back in 32-bit mode/protected mode (but not paging yet). 276 # Reload the segment registers & IDT 277 278 movw $GSEL(GDATA_SEL,SEL_KPL),%bx 279 movw %bx,%ds 280 movw %bx,%ss 281 movw %bx,%es 282 283 # reload PDBR 284 movl CR3_ADDR,%eax 285 movl %eax,%cr3 286 movl %cr0,%eax 287 orl $CR0_PG,%eax 288 movl %eax,%cr0 289 290 # reload system copy of GDT 291 lgdt GDTR_SAVE_ADDR 292 293 # restore protected-mode stack 294 movl STACK_PTR_ADDR,%esp 295 movl BASE_PTR_ADDR,%ebp 296 297 #restore protected-mode IDT 298 lidt IDTR_SAVE_ADDR 299 300 # copy back arguments from holding pen 301 302 movl 12(%ebp),%ebx 303 movw AX_REGADDR,%ax 304 movw %ax,APMREG_AX(%ebx) 305 movw BX_REGADDR,%ax 306 movw %ax,APMREG_BX(%ebx) 307 movw CX_REGADDR,%ax 308 movw %ax,APMREG_CX(%ebx) 309 movw DX_REGADDR,%ax 310 movw %ax,APMREG_DX(%ebx) 311 movw SI_REGADDR,%ax 312 movw %ax,APMREG_SI(%ebx) 313 movw DI_REGADDR,%ax 314 movw %ax,APMREG_DI(%ebx) 315 movw FLAGS_REGADDR,%ax 316 movw %ax,APMREG_FLAGS(%ebx) 317 318 # finish up, restore registers, and return 319 popfl 320 popl %gs 321 popl %fs 322 popl %es 323 popl %ds # see above 324 popl %ebx 325 popl %edi 326 popl %esi 327 leave 328 ret 329 330 .align 4 331 IDT_bios: # BIOS IDT descriptor (real-mode) 332 .word 1023 333 .long 0 334 #endif 335
Indexes created Tue Sep 30 17:09:57 GMT 2025