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
97 ENTRY(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
186 x16:
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
197 xreal: # 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
233 flushit:
234 addr32
235 movw EFLAGS_REGADDR-MYBASE,%ax
236 pushl %eax
237 popfl
238 addr32
239 movw EAX_REGADDR-MYBASE,%ax
240
241 intaddr:
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
275 x32:
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
338 IDT_bios: # BIOS IDT descriptor (real-mode)
339 .word 1023
340 .long 0
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