【跟我一起读 linux 源码 01】boot

  1 ;
  2 ; SYS_SIZE is the number of clicks (16 bytes) to be loaded.
  3 ; 0x3000 is 0x30000 bytes = 196kB, more than enough for current
  4 ; versions of linux
  5 ;
  6 SYSSIZE = 0x3000
  7 ;
  8 ;    bootsect.s        (C) 1991 Linus Torvalds
  9 ;
 10 ; bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves
 11 ; iself out of the way to address 0x90000, and jumps there.
 12 ;
 13 ; It then loads ‘setup‘ directly after itself (0x90200), and the system
 14 ; at 0x10000, using BIOS interrupts. 
 15 ;
 16 ; NOTE; currently system is at most 8*65536 bytes long. This should be no
 17 ; problem, even in the future. I want to keep it simple. This 512 kB
 18 ; kernel size should be enough, especially as this doesn‘t contain the
 19 ; buffer cache as in minix
 20 ;
 21 ; The loader has been made as simple as possible, and continuos
 22 ; read errors will result in a unbreakable loop. Reboot by hand. It
 23 ; loads pretty fast by getting whole sectors at a time whenever possible.
 24 
 25 .globl begtext, begdata, begbss, endtext, enddata, endbss
 26 .text
 27 begtext:
 28 .data
 29 begdata:
 30 .bss
 31 begbss:
 32 .text
 33 
 34 SETUPLEN = 4                ; nr of setup-sectors
 35 BOOTSEG  = 0x07c0            ; original address of boot-sector
 36 INITSEG  = 0x9000            ; we move boot here - out of the way
 37 SETUPSEG = 0x9020            ; setup starts here
 38 SYSSEG   = 0x1000            ; system loaded at 0x10000 (65536).
 39 ENDSEG   = SYSSEG + SYSSIZE        ; where to stop loading
 40 
 41 ; ROOT_DEV:    0x000 - same type of floppy as boot.
 42 ;        0x301 - first partition on first drive etc
 43 ROOT_DEV = 0x306
 44 
 45 entry start
 46 start:
 47     mov    ax,#BOOTSEG
 48     mov    ds,ax
 49     mov    ax,#INITSEG
 50     mov    es,ax
 51     mov    cx,#256
 52     sub    si,si
 53     sub    di,di
 54     rep
 55     movw
 56     jmpi    go,INITSEG
 57 go:    mov    ax,cs
 58     mov    ds,ax
 59     mov    es,ax
 60 ; put stack at 0x9ff00.
 61     mov    ss,ax
 62     mov    sp,#0xFF00        ; arbitrary value >>512
 63 
 64 ; load the setup-sectors directly after the bootblock.
 65 ; Note that ‘es‘ is already set up.
 66 
 67 load_setup:
 68     mov    dx,#0x0000        ; drive 0, head 0
 69     mov    cx,#0x0002        ; sector 2, track 0
 70     mov    bx,#0x0200        ; address = 512, in INITSEG
 71     mov    ax,#0x0200+SETUPLEN    ; service 2, nr of sectors
 72     int    0x13            ; read it
 73     jnc    ok_load_setup        ; ok - continue
 74     mov    dx,#0x0000
 75     mov    ax,#0x0000        ; reset the diskette
 76     int    0x13
 77     j    load_setup
 78 
 79 ok_load_setup:
 80 
 81 ; Get disk drive parameters, specifically nr of sectors/track
 82 
 83     mov    dl,#0x00
 84     mov    ax,#0x0800        ; AH=8 is get drive parameters
 85     int    0x13
 86     mov    ch,#0x00
 87     seg cs
 88     mov    sectors,cx
 89     mov    ax,#INITSEG
 90     mov    es,ax
 91 
 92 ; Print some inane message
 93 
 94     mov    ah,#0x03        ; read cursor pos
 95     xor    bh,bh
 96     int    0x10
 97     
 98     mov    cx,#24
 99     mov    bx,#0x0007        ; page 0, attribute 7 (normal)
100     mov    bp,#msg1
101     mov    ax,#0x1301        ; write string, move cursor
102     int    0x10
103 
104 ; ok, we‘ve written the message, now
105 ; we want to load the system (at 0x10000)
106 
107     mov    ax,#SYSSEG
108     mov    es,ax        ; segment of 0x010000
109     call    read_it
110     call    kill_motor
111 
112 ; After that we check which root-device to use. If the device is
113 ; defined (!= 0), nothing is done and the given device is used.
114 ; Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending
115 ; on the number of sectors that the BIOS reports currently.
116 
117     seg cs
118     mov    ax,root_dev
119     cmp    ax,#0
120     jne    root_defined
121     seg cs
122     mov    bx,sectors
123     mov    ax,#0x0208        ; /dev/ps0 - 1.2Mb
124     cmp    bx,#15
125     je    root_defined
126     mov    ax,#0x021c        ; /dev/PS0 - 1.44Mb
127     cmp    bx,#18
128     je    root_defined
129 undef_root:
130     jmp undef_root
131 root_defined:
132     seg cs
133     mov    root_dev,ax
134 
135 ; after that (everyting loaded), we jump to
136 ; the setup-routine loaded directly after
137 ; the bootblock:
138 
139     jmpi    0,SETUPSEG
140 
141 ; This routine loads the system at address 0x10000, making sure
142 ; no 64kB boundaries are crossed. We try to load it as fast as
143 ; possible, loading whole tracks whenever we can.
144 ;
145 ; in:    es - starting address segment (normally 0x1000)
146 ;
147 sread:    .word 1+SETUPLEN    ; sectors read of current track
148 head:    .word 0            ; current head
149 track:    .word 0            ; current track
150 
151 read_it:
152     mov ax,es
153     test ax,#0x0fff
154 die:    jne die            ; es must be at 64kB boundary
155     xor bx,bx        ; bx is starting address within segment
156 rp_read:
157     mov ax,es
158     cmp ax,#ENDSEG        ; have we loaded all yet?
159     jb ok1_read
160     ret
161 ok1_read:
162     seg cs
163     mov ax,sectors
164     sub ax,sread
165     mov cx,ax
166     shl cx,#9
167     add cx,bx
168     jnc ok2_read
169     je ok2_read
170     xor ax,ax
171     sub ax,bx
172     shr ax,#9
173 ok2_read:
174     call read_track
175     mov cx,ax
176     add ax,sread
177     seg cs
178     cmp ax,sectors
179     jne ok3_read
180     mov ax,#1
181     sub ax,head
182     jne ok4_read
183     inc track
184 ok4_read:
185     mov head,ax
186     xor ax,ax
187 ok3_read:
188     mov sread,ax
189     shl cx,#9
190     add bx,cx
191     jnc rp_read
192     mov ax,es
193     add ax,#0x1000
194     mov es,ax
195     xor bx,bx
196     jmp rp_read
197 
198 read_track:
199     push ax
200     push bx
201     push cx
202     push dx
203     mov dx,track
204     mov cx,sread
205     inc cx
206     mov ch,dl
207     mov dx,head
208     mov dh,dl
209     mov dl,#0
210     and dx,#0x0100
211     mov ah,#2
212     int 0x13
213     jc bad_rt
214     pop dx
215     pop cx
216     pop bx
217     pop ax
218     ret
219 bad_rt:    mov ax,#0
220     mov dx,#0
221     int 0x13
222     pop dx
223     pop cx
224     pop bx
225     pop ax
226     jmp read_track
227 
228 /*
229  * This procedure turns off the floppy drive motor, so
230  * that we enter the kernel in a known state, and
231  * don‘t have to worry about it later.
232  */
233 kill_motor:
234     push dx
235     mov dx,#0x3f2
236     mov al,#0
237     outb
238     pop dx
239     ret
240 
241 sectors:
242     .word 0
243 
244 msg1:
245     .byte 13,10
246     .ascii "Loading system ..."
247     .byte 13,10,13,10
248 
249 .org 508
250 root_dev:
251     .word ROOT_DEV
252 boot_flag:
253     .word 0xAA55
254 
255 .text
256 endtext:
257 .data
258 enddata:
259 .bss
260 endbss:

  1 ;
  2 ;    setup.s        (C) 1991 Linus Torvalds
  3 ;
  4 ; setup.s is responsible for getting the system data from the BIOS,
  5 ; and putting them into the appropriate places in system memory.
  6 ; both setup.s and system has been loaded by the bootblock.
  7 ;
  8 ; This code asks the bios for memory/disk/other parameters, and
  9 ; puts them in a "safe" place: 0x90000-0x901FF, ie where the
 10 ; boot-block used to be. It is then up to the protected mode
 11 ; system to read them from there before the area is overwritten
 12 ; for buffer-blocks.
 13 ;
 14 
 15 ; NOTE; These had better be the same as in bootsect.s;
 16 
 17 INITSEG  = 0x9000    ; we move boot here - out of the way
 18 SYSSEG   = 0x1000    ; system loaded at 0x10000 (65536).
 19 SETUPSEG = 0x9020    ; this is the current segment
 20 
 21 .globl begtext, begdata, begbss, endtext, enddata, endbss
 22 .text
 23 begtext:
 24 .data
 25 begdata:
 26 .bss
 27 begbss:
 28 .text
 29 
 30 entry start
 31 start:
 32 
 33 ; ok, the read went well so we get current cursor position and save it for
 34 ; posterity.
 35 
 36     mov    ax,#INITSEG    ; this is done in bootsect already, but...
 37     mov    ds,ax
 38     mov    ah,#0x03    ; read cursor pos
 39     xor    bh,bh
 40     int    0x10        ; save it in known place, con_init fetches
 41     mov    [0],dx        ; it from 0x90000.
 42 
 43 ; Get memory size (extended mem, kB)
 44 
 45     mov    ah,#0x88
 46     int    0x15
 47     mov    [2],ax
 48 
 49 ; Get video-card data:
 50 
 51     mov    ah,#0x0f
 52     int    0x10
 53     mov    [4],bx        ; bh = display page
 54     mov    [6],ax        ; al = video mode, ah = window width
 55 
 56 ; check for EGA/VGA and some config parameters
 57 
 58     mov    ah,#0x12
 59     mov    bl,#0x10
 60     int    0x10
 61     mov    [8],ax
 62     mov    [10],bx
 63     mov    [12],cx
 64 
 65 ; Get hd0 data
 66 
 67     mov    ax,#0x0000
 68     mov    ds,ax
 69     lds    si,[4*0x41]
 70     mov    ax,#INITSEG
 71     mov    es,ax
 72     mov    di,#0x0080
 73     mov    cx,#0x10
 74     rep
 75     movsb
 76 
 77 ; Get hd1 data
 78 
 79     mov    ax,#0x0000
 80     mov    ds,ax
 81     lds    si,[4*0x46]
 82     mov    ax,#INITSEG
 83     mov    es,ax
 84     mov    di,#0x0090
 85     mov    cx,#0x10
 86     rep
 87     movsb
 88 
 89 ; Check that there IS a hd1 :-)
 90 
 91     mov    ax,#0x01500
 92     mov    dl,#0x81
 93     int    0x13
 94     jc    no_disk1
 95     cmp    ah,#3
 96     je    is_disk1
 97 no_disk1:
 98     mov    ax,#INITSEG
 99     mov    es,ax
100     mov    di,#0x0090
101     mov    cx,#0x10
102     mov    ax,#0x00
103     rep
104     stosb
105 is_disk1:
106 
107 ; now we want to move to protected mode ...
108 
109     cli            ; no interrupts allowed ;
110 
111 ; first we move the system to it‘s rightful place
112 
113     mov    ax,#0x0000
114     cld            ; ‘direction‘=0, movs moves forward
115 do_move:
116     mov    es,ax        ; destination segment
117     add    ax,#0x1000
118     cmp    ax,#0x9000
119     jz    end_move
120     mov    ds,ax        ; source segment
121     sub    di,di
122     sub    si,si
123     mov     cx,#0x8000
124     rep
125     movsw
126     jmp    do_move
127 
128 ; then we load the segment descriptors
129 
130 end_move:
131     mov    ax,#SETUPSEG    ; right, forgot this at first. didn‘t work :-)
132     mov    ds,ax
133     lidt    idt_48        ; load idt with 0,0
134     lgdt    gdt_48        ; load gdt with whatever appropriate
135 
136 ; that was painless, now we enable A20
137 
138     call    empty_8042
139     mov    al,#0xD1        ; command write
140     out    #0x64,al
141     call    empty_8042
142     mov    al,#0xDF        ; A20 on
143     out    #0x60,al
144     call    empty_8042
145 
146 ; well, that went ok, I hope. Now we have to reprogram the interrupts :-(
147 ; we put them right after the intel-reserved hardware interrupts, at
148 ; int 0x20-0x2F. There they won‘t mess up anything. Sadly IBM really
149 ; messed this up with the original PC, and they haven‘t been able to
150 ; rectify it afterwards. Thus the bios puts interrupts at 0x08-0x0f,
151 ; which is used for the internal hardware interrupts as well. We just
152 ; have to reprogram the 8259‘s, and it isn‘t fun.
153 
154     mov    al,#0x11        ; initialization sequence
155     out    #0x20,al        ; send it to 8259A-1
156     .word    0x00eb,0x00eb        ; jmp $+2, jmp $+2
157     out    #0xA0,al        ; and to 8259A-2
158     .word    0x00eb,0x00eb
159     mov    al,#0x20        ; start of hardware int‘s (0x20)
160     out    #0x21,al
161     .word    0x00eb,0x00eb
162     mov    al,#0x28        ; start of hardware int‘s 2 (0x28)
163     out    #0xA1,al
164     .word    0x00eb,0x00eb
165     mov    al,#0x04        ; 8259-1 is master
166     out    #0x21,al
167     .word    0x00eb,0x00eb
168     mov    al,#0x02        ; 8259-2 is slave
169     out    #0xA1,al
170     .word    0x00eb,0x00eb
171     mov    al,#0x01        ; 8086 mode for both
172     out    #0x21,al
173     .word    0x00eb,0x00eb
174     out    #0xA1,al
175     .word    0x00eb,0x00eb
176     mov    al,#0xFF        ; mask off all interrupts for now
177     out    #0x21,al
178     .word    0x00eb,0x00eb
179     out    #0xA1,al
180 
181 ; well, that certainly wasn‘t fun :-(. Hopefully it works, and we don‘t
182 ; need no steenking BIOS anyway (except for the initial loading :-).
183 ; The BIOS-routine wants lots of unnecessary data, and it‘s less
184 ; "interesting" anyway. This is how REAL programmers do it.
185 ;
186 ; Well, now‘s the time to actually move into protected mode. To make
187 ; things as simple as possible, we do no register set-up or anything,
188 ; we let the gnu-compiled 32-bit programs do that. We just jump to
189 ; absolute address 0x00000, in 32-bit protected mode.
190 
191     mov    ax,#0x0001    ; protected mode (PE) bit
192     lmsw    ax        ; This is it;
193     jmpi    0,8        ; jmp offset 0 of segment 8 (cs)
194 
195 ; This routine checks that the keyboard command queue is empty
196 ; No timeout is used - if this hangs there is something wrong with
197 ; the machine, and we probably couldn‘t proceed anyway.
198 empty_8042:
199     .word    0x00eb,0x00eb
200     in    al,#0x64    ; 8042 status port
201     test    al,#2        ; is input buffer full?
202     jnz    empty_8042    ; yes - loop
203     ret
204 
205 gdt:
206     .word    0,0,0,0        ; dummy
207 
208     .word    0x07FF        ; 8Mb - limit=2047 (2048*4096=8Mb)
209     .word    0x0000        ; base address=0
210     .word    0x9A00        ; code read/exec
211     .word    0x00C0        ; granularity=4096, 386
212 
213     .word    0x07FF        ; 8Mb - limit=2047 (2048*4096=8Mb)
214     .word    0x0000        ; base address=0
215     .word    0x9200        ; data read/write
216     .word    0x00C0        ; granularity=4096, 386
217 
218 idt_48:
219     .word    0            ; idt limit=0
220     .word    0,0            ; idt base=0L
221 
222 gdt_48:
223     .word    0x800        ; gdt limit=2048, 256 GDT entries
224     .word    512+gdt,0x9    ; gdt base = 0X9xxxx
225     
226 .text
227 endtext:
228 .data
229 enddata:
230 .bss
231 endbss:

  1 /*
  2  *  linux/boot/head.s
  3  *
  4  *  (C) 1991  Linus Torvalds
  5  */
  6 
  7 /*
  8  *  head.s contains the 32-bit startup code.
  9  *
 10  * NOTE!!! Startup happens at absolute address 0x00000000, which is also where
 11  * the page directory will exist. The startup code will be overwritten by
 12  * the page directory.
 13  */
 14 .text
 15 .globl _idt,_gdt,_pg_dir,_tmp_floppy_area
 16 _pg_dir:
 17 startup_32:
 18     movl $0x10,%eax
 19     mov %ax,%ds
 20     mov %ax,%es
 21     mov %ax,%fs
 22     mov %ax,%gs
 23     lss _stack_start,%esp
 24     call setup_idt
 25     call setup_gdt
 26     movl $0x10,%eax        # reload all the segment registers
 27     mov %ax,%ds        # after changing gdt. CS was already
 28     mov %ax,%es        # reloaded in ‘setup_gdt‘
 29     mov %ax,%fs
 30     mov %ax,%gs
 31     lss _stack_start,%esp
 32     xorl %eax,%eax
 33 1:    incl %eax        # check that A20 really IS enabled
 34     movl %eax,0x000000    # loop forever if it isn‘t
 35     cmpl %eax,0x100000
 36     je 1b
 37 /*
 38  * NOTE! 486 should set bit 16, to check for write-protect in supervisor
 39  * mode. Then it would be unnecessary with the "verify_area()"-calls.
 40  * 486 users probably want to set the NE (#5) bit also, so as to use
 41  * int 16 for math errors.
 42  */
 43     movl %cr0,%eax        # check math chip
 44     andl $0x80000011,%eax    # Save PG,PE,ET
 45 /* "orl $0x10020,%eax" here for 486 might be good */
 46     orl $2,%eax        # set MP
 47     movl %eax,%cr0
 48     call check_x87
 49     jmp after_page_tables
 50 
 51 /*
 52  * We depend on ET to be correct. This checks for 287/387.
 53  */
 54 check_x87:
 55     fninit
 56     fstsw %ax
 57     cmpb $0,%al
 58     je 1f            /* no coprocessor: have to set bits */
 59     movl %cr0,%eax
 60     xorl $6,%eax        /* reset MP, set EM */
 61     movl %eax,%cr0
 62     ret
 63 .align 2
 64 1:    .byte 0xDB,0xE4        /* fsetpm for 287, ignored by 387 */
 65     ret
 66 
 67 /*
 68  *  setup_idt
 69  *
 70  *  sets up a idt with 256 entries pointing to
 71  *  ignore_int, interrupt gates. It then loads
 72  *  idt. Everything that wants to install itself
 73  *  in the idt-table may do so themselves. Interrupts
 74  *  are enabled elsewhere, when we can be relatively
 75  *  sure everything is ok. This routine will be over-
 76  *  written by the page tables.
 77  */
 78 setup_idt:
 79     lea ignore_int,%edx
 80     movl $0x00080000,%eax
 81     movw %dx,%ax        /* selector = 0x0008 = cs */
 82     movw $0x8E00,%dx    /* interrupt gate - dpl=0, present */
 83 
 84     lea _idt,%edi
 85     mov $256,%ecx
 86 rp_sidt:
 87     movl %eax,(%edi)
 88     movl %edx,4(%edi)
 89     addl $8,%edi
 90     dec %ecx
 91     jne rp_sidt
 92     lidt idt_descr
 93     ret
 94 
 95 /*
 96  *  setup_gdt
 97  *
 98  *  This routines sets up a new gdt and loads it.
 99  *  Only two entries are currently built, the same
100  *  ones that were built in init.s. The routine
101  *  is VERY complicated at two whole lines, so this
102  *  rather long comment is certainly needed :-).
103  *  This routine will beoverwritten by the page tables.
104  */
105 setup_gdt:
106     lgdt gdt_descr
107     ret
108 
109 /*
110  * I put the kernel page tables right after the page directory,
111  * using 4 of them to span 16 Mb of physical memory. People with
112  * more than 16MB will have to expand this.
113  */
114 .org 0x1000
115 pg0:
116 
117 .org 0x2000
118 pg1:
119 
120 .org 0x3000
121 pg2:
122 
123 .org 0x4000
124 pg3:
125 
126 .org 0x5000
127 /*
128  * tmp_floppy_area is used by the floppy-driver when DMA cannot
129  * reach to a buffer-block. It needs to be aligned, so that it isn‘t
130  * on a 64kB border.
131  */
132 _tmp_floppy_area:
133     .fill 1024,1,0
134 
135 after_page_tables:
136     pushl $0        # These are the parameters to main :-)
137     pushl $0
138     pushl $0
139     pushl $L6        # return address for main, if it decides to.
140     pushl $_main
141     jmp setup_paging
142 L6:
143     jmp L6            # main should never return here, but
144                 # just in case, we know what happens.
145 
146 /* This is the default interrupt "handler" :-) */
147 int_msg:
148     .asciz "Unknown interrupt\n\r"
149 .align 2
150 ignore_int:
151     pushl %eax
152     pushl %ecx
153     pushl %edx
154     push %ds
155     push %es
156     push %fs
157     movl $0x10,%eax
158     mov %ax,%ds
159     mov %ax,%es
160     mov %ax,%fs
161     pushl $int_msg
162     call _printk
163     popl %eax
164     pop %fs
165     pop %es
166     pop %ds
167     popl %edx
168     popl %ecx
169     popl %eax
170     iret
171 
172 
173 /*
174  * Setup_paging
175  *
176  * This routine sets up paging by setting the page bit
177  * in cr0. The page tables are set up, identity-mapping
178  * the first 16MB. The pager assumes that no illegal
179  * addresses are produced (ie >4Mb on a 4Mb machine).
180  *
181  * NOTE! Although all physical memory should be identity
182  * mapped by this routine, only the kernel page functions
183  * use the >1Mb addresses directly. All "normal" functions
184  * use just the lower 1Mb, or the local data space, which
185  * will be mapped to some other place - mm keeps track of
186  * that.
187  *
188  * For those with more memory than 16 Mb - tough luck. I‘ve
189  * not got it, why should you :-) The source is here. Change
190  * it. (Seriously - it shouldn‘t be too difficult. Mostly
191  * change some constants etc. I left it at 16Mb, as my machine
192  * even cannot be extended past that (ok, but it was cheap :-)
193  * I‘ve tried to show which constants to change by having
194  * some kind of marker at them (search for "16Mb"), but I
195  * won‘t guarantee that‘s all :-( )
196  */
197 .align 2
198 setup_paging:
199     movl $1024*5,%ecx        /* 5 pages - pg_dir+4 page tables */
200     xorl %eax,%eax
201     xorl %edi,%edi            /* pg_dir is at 0x000 */
202     cld;rep;stosl
203     movl $pg0+7,_pg_dir        /* set present bit/user r/w */
204     movl $pg1+7,_pg_dir+4        /*  --------- " " --------- */
205     movl $pg2+7,_pg_dir+8        /*  --------- " " --------- */
206     movl $pg3+7,_pg_dir+12        /*  --------- " " --------- */
207     movl $pg3+4092,%edi
208     movl $0xfff007,%eax        /*  16Mb - 4096 + 7 (r/w user,p) */
209     std
210 1:    stosl            /* fill pages backwards - more efficient :-) */
211     subl $0x1000,%eax
212     jge 1b
213     xorl %eax,%eax        /* pg_dir is at 0x0000 */
214     movl %eax,%cr3        /* cr3 - page directory start */
215     movl %cr0,%eax
216     orl $0x80000000,%eax
217     movl %eax,%cr0        /* set paging (PG) bit */
218     ret            /* this also flushes prefetch-queue */
219 
220 .align 2
221 .word 0
222 idt_descr:
223     .word 256*8-1        # idt contains 256 entries
224     .long _idt
225 .align 2
226 .word 0
227 gdt_descr:
228     .word 256*8-1        # so does gdt (not that that‘s any
229     .long _gdt        # magic number, but it works for me :^)
230 
231     .align 3
232 _idt:    .fill 256,8,0        # idt is uninitialized
233 
234 _gdt:    .quad 0x0000000000000000    /* NULL descriptor */
235     .quad 0x00c09a0000000fff    /* 16Mb */
236     .quad 0x00c0920000000fff    /* 16Mb */
237     .quad 0x0000000000000000    /* TEMPORARY - don‘t use */
238     .fill 252,8,0            /* space for LDT‘s and TSS‘s etc */