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一个朋友写的操作系统源码

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00100   ! This is the subroutine called by start386, it shares the same stack with
00101   ! bootmanager, it will continue init the kernel execution environment.
00102   
00103   .sect .text
00104   begtext:
00105   .sect .rom
00106   begrom:
00107   .sect .data
00108   begdata:
00109   .sect .bss
00110   begbss:
00111   
00112   #include "include/stuix/config.h"
00113   #include "include/stuix/const.h"
00114   #include "include/stuix/boot.h"
00115   #include "const.h"
00116   #include "protect.h"
00117   
00118   ! Exported functions
00119   ! Note: in assembly language the .define statement applied to a function name
00120   ! is loosely equivalent to a prototype in C code -- it makes it possible to
00121   ! link to an entity declared in the assembly code but does not create 
00122   ! the entity.
00123   
00124   .define _divide_error
00125   .define _single_step_exception
00126   .define _nmi
00127   .define _breakpoint_exception
00128   .define _overflow
00129   .define _bounds_check
00130   .define _inval_opcode
00131   .define _copr_not_available
00132   .define _double_fault
00133   .define _copr_seg_overrun
00134   .define _inval_tss
00135   .define _segment_not_present
00136   .define _stack_exception
00137   .define _general_protection
00138   .define _page_fault
00139   .define _copr_error
00140   
00141   .define _hwint00
00142   .define _hwint01
00143   .define _hwint02
00144   .define _hwint03
00145   .define _hwint04
00146   .define _hwint05
00147   .define _hwint06
00148   .define _hwint07
00149   .define _hwint08
00150   .define _hwint09
00151   .define _hwint10
00152   .define _hwint11
00153   .define _hwint12
00154   .define _hwint13
00155   .define _hwint14
00156   .define _hwint15
00157   
00158   .define _s_call
00159   .define _savu
00160   .define _retu
00161   .define _aretu
00162   .define _idle
00163   .define _gohome
00164   
00165   ! Imported functions
00166   .extern _cstart
00167   .extern _swtch
00168   .extern _clock_handler
00169   .extern _kbd_hw_int
00170   .extern _trap
00171   .extern _nohandler
00172   
00173   ! Exported variables.
00174   ! Note: when used with a variable the .define does not reserve storage,
00175   ! it makes the name externally visible so it may be linked to.
00176   
00177   .define begbss
00178   .define begdata
00179   
00180   ! Imported variables.
00181   
00182   .extern _runrun             ! schedualing flag
00183   .extern _gdt                ! GDT table
00184   .extern _bm_sp
00185   .extern _usr_ppda_base      ! Page directory physical address
00186   .extern _usr_pagetab_ptr    ! kernel stack pointer at this position
00187   
00188   .sect .text
00189   
00190   !*===========================================================================*
00191   !*                            Stuix                                          *
00192   !*===========================================================================*
00193   
00194   STUIX:
00195   ! Set up a C stack frame on the bootmanager stack, it shares the same stack with
00196   ! boot manager. The stack won't switch until page is enabled.
00197   
00198         push ebp
00199         mov ebp, esp
00200         push esi
00201         push edi
00202         mov (_bm_sp), esp   ! save return address
00203                             ! to start386
00204   
00205   ! Get the boot manager gdtr absolute address, it is used to switch back to real
00206   ! address mode. 
00207   
00208         sgdt (_gdt + PNE_GDT_SELECTOR)  
00209   
00210   ! Copy the bootmanager global descriptor table to the address space of kernel
00211   ! but don't switch over to it until the rest descriptors were all initialized 
00212   ! by Prot_init() and the processor page unit is enabled.
00213   ! FS contains the bootmanager data segment, used to copy first 8 descriptor
00214   ! to the kernel address space for referencing.
00215   
00216         mov esi, BM_GDT_OFFSET  ! 4*3 + 1024
00217         mov ebx, _gdt           ! kernel gdt address
00218         mov ecx, 8*8
00219   copygdt: 
00220   fseg  movb al,(esi)
00221         movb (ebx),al
00222         inc esi
00223         inc ebx
00224         loop copygdt
00225   
00226   ! Locate the kernel image segment information
00227   ! and call C startup code to set up a proper
00228   ! environment to run main()
00229   
00230         mov esi, A_TEXT_OFF
00231   fseg  mov ebx, (esi)
00232         mov esi, A_DATA_OFF
00233   fseg  mov edx, (esi)
00234         mov esi, A_BSS_OFF
00235   fseg  mov eax, (esi)
00236   
00237         push eax
00238         push edx
00239         push ebx
00240         push KERNEL_DATA_SELECTOR
00241         push KERNEL_CODE_SELECTOR
00242         call _cstart    ! cstart(cs, ds, textsize, datasize, bssize)
00243         add esp, 5*4
00244   
00245   ! Enable processor page unit, identity pages is required by the proceesor
00246   ! to guarantees the correctly address referencing during critical section.
00247   ! this makes the machine dependence code extremely hard to understand. Do
00248   ! not try to figure out how it works if you are novice to the architecture
00249   ! of IA-32. if you insist, we recommand you to read <Intel Architecture
00250   ! Software Developer's Manual> volume 3, chapter 9. Also start386.asm need
00251   ! to be grasped, since it highly coorperates with msx686.s
00252   
00253   ! The PDBR aways points to the physical address of current process's PPDA,  
00254   ! the first two page directory entries in PPDA point to the physical address
00255   ! of two kernel tables in contingous 8k space respectly. the thired page
00256   ! directory entry in PPDA point to the usr 4k page table.
00257   
00258   ! As soon as the processor page unit is enabled, don't use long jump, it will
00259   ! cause the processor deed lock, this characteristic was not referred by the
00260   ! Intel document.
00261   
00262         mov eax, (_usr_ppda_base)
00263         mov cr3, eax
00264         mov eax, cr0
00265         or  eax, 0x80000000
00266         mov cr0, eax
00267         jmp csinit
00268   csinit:
00269   
00270   ! we are in identity mapped kernel code and data page now, load our new
00271   ! GDT, IDT, LDT and switch to the new environment to call _main
00272   
00273         lgdt (_gdt + GDT_SELECTOR)
00274         lidt (_gdt + IDT_SELECTOR)
00275    o16  mov ax, LDT_SELECTOR
00276         lldt ax
00277          
00278         jmpf KERNEL_VCODE_SELECTOR:csvinit
00279   csvinit:
00280    o16  mov ax, KERNEL_VDATA_SELECTOR
00281         mov ds, ax
00282         mov ss, ax
00283         mov es, ax
00284         mov fs, ax
00285         mov gs, ax
00286   
00287   ! Load our 0# process kernel stack
00288   
00289         mov esp, (_usr_pagetab_ptr)
00290           
00291   ! Load our first and only task as the requirement of processor
00292    o16  mov ax, KERNEL_TSS_SELECTOR 
00293         ltr ax
00294         push 0     ! set flags to known good state
00295         popf       ! clear nested task and disable interrupt
00296         
00297         call _main
00298   
00299   RING0 = 3        ! Processor code segment RPL
00300   
00301   !*===========================================================================*
00302   !*                        interrupt handlers                                 *
00303   !*===========================================================================*
00304   
00305   !*===========================================================================*
00306   !*                          hwint00 - 07                                     *
00307   !*===========================================================================*
00308   ! Note this is a macro, it looks like a subroutine.
00309   #define hwint_master(irq, handler)       \
00310           cld                     /* set direction flag to a know value     */;\
00311           push 0                  /* padding for error code                 */;\
00312           push irq                /* interrupt irq                          */;\
00313           pushad                  /* save general registers                 */;\
00314           push ds                 /* save ds                                */;\
00315           push es                 /* save es                                */;\
00316           push fs                 /* save fs                                */;\
00317           push gs                 /* save gs                                */;\