1 /* 2 * linux/boot/head.S 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 */ 6
7 /* 8 * head.S contains the 32-bit startup code. 9 */ 10
11 .text
12 .globl _idt,_gdt,
13 .globl _swapper_pg_dir,_pg0
14 .globl _empty_bad_page
15 .globl _empty_bad_page_table
16 .globl _empty_zero_page
17 .globl _tmp_floppy_area,_floppy_track_buffer
18
19 #include <linux/tasks.h>
20 #include <linux/segment.h>
21
22 #define CL_MAGIC_ADDR 0x90020
23 #define CL_MAGIC 0xA33F
24 #define CL_BASE_ADDR 0x90000
25 #define CL_OFFSET 0x90022
26
27 /* 28 * swapper_pg_dir is the main page directory, address 0x00001000 (or at 29 * address 0x00101000 for a compressed boot). 30 */ 31 startup_32:
32 cld
33 movl $(KERNEL_DS),%eax
34 mov %ax,%ds
35 mov %ax,%es
36 mov %ax,%fs
37 mov %ax,%gs
38 lss _stack_start,%esp
39 /* 40 * Clear BSS first so that there are no surprises... 41 */ 42 xorl %eax,%eax
43 movl $__edata,%edi
44 movl $__end,%ecx
45 subl %edi,%ecx
46 cld
47 rep
48 stosb
49 /* 50 * start system 32-bit setup. We need to re-do some of the things done 51 * in 16-bit mode for the "real" operations. 52 */ 53 call setup_idt
54 xorl %eax,%eax
55 1: incl %eax # check that A20 really IS enabled
56 movl %eax,0x000000 # loop forever if it isn't
57 cmpl %eax,0x100000
58 je 1b
59 /* 60 * Initialize eflags. Some BIOS's leave bits like NT set. This would 61 * confuse the debugger if this code is traced. 62 * XXX - best to initialize before switching to protected mode. 63 */ 64 pushl $0
65 popfl
66 /* 67 * Copy bootup parameters out of the way. First 2kB of 68 * _empty_zero_page is for boot parameters, second 2kB 69 * is for the command line. 70 */ 71 movl $0x90000,%esi
72 movl $_empty_zero_page,%edi
73 movl $512,%ecx
74 cld
75 rep
76 movsl
77 xorl %eax,%eax
78 movl $512,%ecx
79 rep
80 stosl
81 cmpw $(CL_MAGIC),CL_MAGIC_ADDR
82 jne 1f
83 movl $_empty_zero_page+2048,%edi
84 movzwl CL_OFFSET,%esi
85 addl $(CL_BASE_ADDR),%esi
86 movl $2048,%ecx
87 rep
88 movsb
89 1:
90 /* check if it is 486 or 386. */ 91 /* 92 * XXX - this does a lot of unnecessary setup. Alignment checks don't 93 * apply at our cpl of 0 and the stack ought to be aligned already, and 94 * we don't need to preserve eflags. 95 */ 96 movl %esp,%edi # save stack pointer
97 andl $0xfffffffc,%esp # align stack to avoid AC fault
98 movl $3,_x86
99 pushfl # push EFLAGS
100 popl %eax # get EFLAGS
101 movl %eax,%ecx # save original EFLAGS
102 xorl $0x40000,%eax # flip AC bit in EFLAGS
103 pushl %eax # copy to EFLAGS
104 popfl # set EFLAGS
105 pushfl # get new EFLAGS
106 popl %eax # put it in eax
107 xorl %ecx,%eax # change in flags
108 andl $0x40000,%eax # check if AC bit changed
109 je is386
110 movl $4,_x86
111 movl %ecx,%eax
112 xorl $0x200000,%eax # check ID flag
113 pushl %eax
114 popfl # if we are on a straight 486DX, SX, or
115 pushfl # 487SX we can't change it
116 popl %eax
117 xorl %ecx,%eax
118 andl $0x200000,%eax
119 je is486
120 isnew: pushl %ecx # restore original EFLAGS
121 popfl
122 movl $1, %eax # Use the CPUID instruction to
123 .byte 0x0f, 0xa2 # check the processor type
124 andl $0xf00, %eax # Set _x86 with the family
125 shrl $8, %eax # returned.
126 movl %eax, _x86
127 movl %edi,%esp # restore esp
128 movl %cr0,%eax # 486+
129 andl $0x80000011,%eax # Save PG,PE,ET
130 orl $0x50022,%eax # set AM, WP, NE and MP
131 jmp 2f
132 is486: pushl %ecx # restore original EFLAGS
133 popfl
134 movl %edi,%esp # restore esp
135 movl %cr0,%eax # 486
136 andl $0x80000011,%eax # Save PG,PE,ET
137 orl $0x50022,%eax # set AM, WP, NE and MP
138 jmp 2f
139 is386: pushl %ecx # restore original EFLAGS
140 popfl
141 movl %edi,%esp # restore esp
142 movl %cr0,%eax # 386
143 andl $0x80000011,%eax # Save PG,PE,ET
144 orl $2,%eax # set MP
145 2: movl %eax,%cr0
146 call check_x87
147 call setup_paging
148 lgdt gdt_descr
149 lidt idt_descr
150 ljmp $(KERNEL_CS),$1f
151 1: movl $(KERNEL_DS),%eax # reload all the segment registers
152 mov %ax,%ds # after changing gdt.
153 mov %ax,%es
154 mov %ax,%fs
155 mov %ax,%gs
156 lss _stack_start,%esp
157 xorl %eax,%eax
158 lldt %ax
159 pushl %eax # These are the parameters to main :-)
160 pushl %eax
161 pushl %eax
162 cld # gcc2 wants the direction flag cleared at all times
163 call _start_kernel
164 L6:
165 jmp L6 # main should never return here, but
166 # just in case, we know what happens. 167
168 /* 169 * We depend on ET to be correct. This checks for 287/387. 170 */ 171 check_x87:
172 movl $0,_hard_math
173 clts
174 fninit
175 fstsw %ax
176 cmpb $0,%al
177 je 1f
178 movl %cr0,%eax /* no coprocessor: have to set bits */ 179 xorl $4,%eax /* set EM */ 180 movl %eax,%cr0
181 ret
182 .align 2
183 1: movl $1,_hard_math
184 .byte 0xDB,0xE4 /* fsetpm for 287, ignored by 387 */ 185 ret
186
187 /* 188 * setup_idt 189 * 190 * sets up a idt with 256 entries pointing to 191 * ignore_int, interrupt gates. It doesn't actually load 192 * idt - that can be done only after paging has been enabled 193 * and the kernel moved to 0xC0000000. Interrupts 194 * are enabled elsewhere, when we can be relatively 195 * sure everything is ok. 196 */ 197 setup_idt:
198 lea ignore_int,%edx
199 movl $(KERNEL_CS << 16),%eax
200 movw %dx,%ax /* selector = 0x0010 = cs */ 201 movw $0x8E00,%dx /* interrupt gate - dpl=0, present */ 202
203 lea _idt,%edi
204 mov $256,%ecx
205 rp_sidt:
206 movl %eax,(%edi)
207 movl %edx,4(%edi)
208 addl $8,%edi
209 dec %ecx
210 jne rp_sidt
211 ret
212
213
214 /* 215 * Setup_paging 216 * 217 * This routine sets up paging by setting the page bit 218 * in cr0. The page tables are set up, identity-mapping 219 * the first 4MB. The rest are initialized later. 220 * 221 * (ref: added support for up to 32mb, 17Apr92) -- Rik Faith 222 * (ref: update, 25Sept92) -- croutons@crunchy.uucp 223 * (ref: 92.10.11 - Linus Torvalds. Corrected 16M limit - no upper memory limit) 224 */ 225 .align 2
226 setup_paging:
227 movl $1024*2,%ecx /* 2 pages - swapper_pg_dir+1 page table */ 228 xorl %eax,%eax
229 movl $_swapper_pg_dir,%edi /* swapper_pg_dir is at 0x1000 */ 230 cld;rep;stosl
231 /* Identity-map the kernel in low 4MB memory for ease of transition */ 232 movl $_pg0+7,_swapper_pg_dir /* set present bit/user r/w */ 233 /* But the real place is at 0xC0000000 */ 234 movl $_pg0+7,_swapper_pg_dir+3072 /* set present bit/user r/w */ 235 movl $_pg0+4092,%edi
236 movl $0x03ff007,%eax /* 4Mb - 4096 + 7 (r/w user,p) */ 237 std
238 1: stosl /* fill the page backwards - more efficient :-) */ 239 subl $0x1000,%eax
240 jge 1b
241 cld
242 movl $_swapper_pg_dir,%eax
243 movl %eax,%cr3 /* cr3 - page directory start */ 244 movl %cr0,%eax
245 orl $0x80000000,%eax
246 movl %eax,%cr0 /* set paging (PG) bit */ 247 ret /* this also flushes the prefetch-queue */ 248
249 /* 250 * page 0 is made non-existent, so that kernel NULL pointer references get 251 * caught. Thus the swapper page directory has been moved to 0x1000 252 * 253 * XXX Actually, the swapper page directory is at 0x1000 plus 1 megabyte, 254 * with the introduction of the compressed boot code. Theoretically, 255 * the original design of overlaying the startup code with the swapper 256 * page directory is still possible --- it would reduce the size of the kernel 257 * by 2-3k. This would be a good thing to do at some point..... 258 */ 259 .org 0x1000
260 _swapper_pg_dir:
261 /* 262 * The page tables are initialized to only 4MB here - the final page 263 * tables are set up later depending on memory size. 264 */ 265 .org 0x2000
266 _pg0:
267
268 .org 0x3000
269 _empty_bad_page:
270
271 .org 0x4000
272 _empty_bad_page_table:
273
274 .org 0x5000
275 _empty_zero_page:
276
277 .org 0x6000
278 /* 279 * tmp_floppy_area is used by the floppy-driver when DMA cannot 280 * reach to a buffer-block. It needs to be aligned, so that it isn't 281 * on a 64kB border. 282 */ 283 _tmp_floppy_area:
284 .fill 1024,1,0
285 /* 286 * floppy_track_buffer is used to buffer one track of floppy data: it 287 * has to be separate from the tmp_floppy area, as otherwise a single- 288 * sector read/write can mess it up. It can contain one full track of 289 * data (18*2*512 bytes). 290 */ 291 _floppy_track_buffer:
292 .fill 512*2*18,1,0
293
294 /* This is the default interrupt "handler" :-) */ 295 int_msg:
296 .asciz "Unknown interrupt\n"
297 .align 2
298 ignore_int:
299 cld
300 pushl %eax
301 pushl %ecx
302 pushl %edx
303 push %ds
304 push %es
305 push %fs
306 movl $(KERNEL_DS),%eax
307 mov %ax,%ds
308 mov %ax,%es
309 mov %ax,%fs
310 pushl $int_msg
311 call _printk
312 popl %eax
313 pop %fs
314 pop %es
315 pop %ds
316 popl %edx
317 popl %ecx
318 popl %eax
319 iret
320
321 /* 322 * The interrupt descriptor table has room for 256 idt's 323 */ 324 .align 4
325 .word 0
326 idt_descr:
327 .word 256*8-1 # idt contains 256 entries
328 .long 0xc0000000+_idt
329
330 .align 4
331 _idt:
332 .fill 256,8,0 # idt is uninitialized
333
334 .align 4
335 .word 0
336 gdt_descr:
337 .word (8+2*NR_TASKS)*8-1
338 .long 0xc0000000+_gdt
339
340 /* 341 * This gdt setup gives the kernel a 1GB address space at virtual 342 * address 0xC0000000 - space enough for expansion, I hope. 343 */ 344 .align 4
345 _gdt:
346 .quad 0x0000000000000000 /* NULL descriptor */ 347 .quad 0x0000000000000000 /* not used */ 348 .quad 0xc0c39a000000ffff /* 0x10 kernel 1GB code at 0xC0000000 */ 349 .quad 0xc0c392000000ffff /* 0x18 kernel 1GB data at 0xC0000000 */ 350 .quad 0x00cbfa000000ffff /* 0x23 user 3GB code at 0x00000000 */ 351 .quad 0x00cbf2000000ffff /* 0x2b user 3GB data at 0x00000000 */ 352 .quad 0x0000000000000000 /* not used */ 353 .quad 0x0000000000000000 /* not used */ 354 .fill 2*NR_TASKS,8,0 /* space for LDT's and TSS's etc */
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