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Text File | 1995-01-02 | 8.6 KB | 363 lines

/* * linux/arch/i386/head.S * * Copyright (C) 1991, 1992 Linus Torvalds */ /* * head.S contains the 32-bit startup code. */ .text .globl _idt,_gdt, .globl _swapper_pg_dir,_pg0 .globl _empty_bad_page .globl _empty_bad_page_table .globl _empty_zero_page .globl _floppy_track_buffer #define __ASSEMBLY__ #include <linux/tasks.h> #include <linux/fd.h> #include <asm/segment.h> #define CL_MAGIC_ADDR 0x90020 #define CL_MAGIC 0xA33F #define CL_BASE_ADDR 0x90000 #define CL_OFFSET 0x90022 /* * swapper_pg_dir is the main page directory, address 0x00001000 (or at * address 0x00101000 for a compressed boot). */ startup_32: cld movl $(KERNEL_DS),%eax mov %ax,%ds mov %ax,%es mov %ax,%fs mov %ax,%gs lss stack_start,%esp /* * Clear BSS first so that there are no surprises... */ xorl %eax,%eax movl $__edata,%edi movl $__end,%ecx subl %edi,%ecx cld rep stosb /* * start system 32-bit setup. We need to re-do some of the things done * in 16-bit mode for the "real" operations. */ call setup_idt xorl %eax,%eax 1: incl %eax # check that A20 really IS enabled movl %eax,0x000000 # loop forever if it isn't cmpl %eax,0x100000 je 1b /* * Initialize eflags. Some BIOS's leave bits like NT set. This would * confuse the debugger if this code is traced. * XXX - best to initialize before switching to protected mode. */ pushl $0 popfl /* * Copy bootup parameters out of the way. First 2kB of * _empty_zero_page is for boot parameters, second 2kB * is for the command line. */ movl $0x90000,%esi movl $_empty_zero_page,%edi movl $512,%ecx cld rep movsl xorl %eax,%eax movl $512,%ecx rep stosl cmpw $(CL_MAGIC),CL_MAGIC_ADDR jne 1f movl $_empty_zero_page+2048,%edi movzwl CL_OFFSET,%esi addl $(CL_BASE_ADDR),%esi movl $2048,%ecx rep movsb 1: /* check if it is 486 or 386. */ /* * XXX - this does a lot of unnecessary setup. Alignment checks don't * apply at our cpl of 0 and the stack ought to be aligned already, and * we don't need to preserve eflags. */ movl $3,_x86 pushfl # push EFLAGS popl %eax # get EFLAGS movl %eax,%ecx # save original EFLAGS xorl $0x40000,%eax # flip AC bit in EFLAGS pushl %eax # copy to EFLAGS popfl # set EFLAGS pushfl # get new EFLAGS popl %eax # put it in eax xorl %ecx,%eax # change in flags andl $0x40000,%eax # check if AC bit changed je is386 movl $4,_x86 movl %ecx,%eax xorl $0x200000,%eax # check ID flag pushl %eax popfl # if we are on a straight 486DX, SX, or pushfl # 487SX we can't change it popl %eax xorl %ecx,%eax andl $0x200000,%eax je is486 isnew: pushl %ecx # restore original EFLAGS popfl /* get processor type */ movl $1, %eax # Use the CPUID instruction to .byte 0x0f, 0xa2 # check the processor type movb %al, %cl # save reg for future use andb $0x0f,%ah # mask processor family movb %ah, _x86 andb $0xf0, %eax # mask model shrb $4, %al movb %al, _x86_model andb $0x0f, %cl # mask mask revision movb %cl, _x86_mask movl %edx, _x86_capability /* get vendor info */ xorl %eax, %eax # call CPUID with 0 -> return vendor ID .byte 0x0f, 0xa2 # CPUID movl %ebx, _x86_vendor_id # lo 4 chars movl %edx, _x86_vendor_id+4 # next 4 chars movl %ecx, _x86_vendor_id+8 # last 4 chars movl %cr0,%eax # 486+ andl $0x80000011,%eax # Save PG,PE,ET orl $0x50022,%eax # set AM, WP, NE and MP jmp 2f is486: pushl %ecx # restore original EFLAGS popfl movl %cr0,%eax # 486 andl $0x80000011,%eax # Save PG,PE,ET orl $0x50022,%eax # set AM, WP, NE and MP jmp 2f is386: pushl %ecx # restore original EFLAGS popfl movl %cr0,%eax # 386 andl $0x80000011,%eax # Save PG,PE,ET orl $2,%eax # set MP 2: movl %eax,%cr0 call check_x87 call setup_paging lgdt gdt_descr lidt idt_descr ljmp $(KERNEL_CS),$1f 1: movl $(KERNEL_DS),%eax # reload all the segment registers mov %ax,%ds # after changing gdt. mov %ax,%es mov %ax,%fs mov %ax,%gs lss stack_start,%esp xorl %eax,%eax lldt %ax pushl %eax # These are the parameters to main :-) pushl %eax pushl %eax cld # gcc2 wants the direction flag cleared at all times call _start_kernel L6: jmp L6 # main should never return here, but # just in case, we know what happens. /* * We depend on ET to be correct. This checks for 287/387. */ check_x87: movb $0,_hard_math clts fninit fstsw %ax cmpb $0,%al je 1f movl %cr0,%eax /* no coprocessor: have to set bits */ xorl $4,%eax /* set EM */ movl %eax,%cr0 ret .align 2 1: movb $1,_hard_math .byte 0xDB,0xE4 /* fsetpm for 287, ignored by 387 */ ret /* * setup_idt * * sets up a idt with 256 entries pointing to * ignore_int, interrupt gates. It doesn't actually load * idt - that can be done only after paging has been enabled * and the kernel moved to 0xC0000000. Interrupts * are enabled elsewhere, when we can be relatively * sure everything is ok. */ setup_idt: lea ignore_int,%edx movl $(KERNEL_CS << 16),%eax movw %dx,%ax /* selector = 0x0010 = cs */ movw $0x8E00,%dx /* interrupt gate - dpl=0, present */ lea _idt,%edi mov $256,%ecx rp_sidt: movl %eax,(%edi) movl %edx,4(%edi) addl $8,%edi dec %ecx jne rp_sidt ret /* * Setup_paging * * This routine sets up paging by setting the page bit * in cr0. The page tables are set up, identity-mapping * the first 4MB. The rest are initialized later. * * (ref: added support for up to 32mb, 17Apr92) -- Rik Faith * (ref: update, 25Sept92) -- croutons@crunchy.uucp * (ref: 92.10.11 - Linus Torvalds. Corrected 16M limit - no upper memory limit) */ .align 2 setup_paging: movl $1024*2,%ecx /* 2 pages - swapper_pg_dir+1 page table */ xorl %eax,%eax movl $_swapper_pg_dir,%edi /* swapper_pg_dir is at 0x1000 */ cld;rep;stosl /* Identity-map the kernel in low 4MB memory for ease of transition */ movl $_pg0+7,_swapper_pg_dir /* set present bit/user r/w */ /* But the real place is at 0xC0000000 */ movl $_pg0+7,_swapper_pg_dir+3072 /* set present bit/user r/w */ movl $_pg0+4092,%edi movl $0x03ff007,%eax /* 4Mb - 4096 + 7 (r/w user,p) */ std 1: stosl /* fill the page backwards - more efficient :-) */ subl $0x1000,%eax jge 1b cld movl $_swapper_pg_dir,%eax movl %eax,%cr3 /* cr3 - page directory start */ movl %cr0,%eax orl $0x80000000,%eax movl %eax,%cr0 /* set paging (PG) bit */ ret /* this also flushes the prefetch-queue */ /* * page 0 is made non-existent, so that kernel NULL pointer references get * caught. Thus the swapper page directory has been moved to 0x1000 * * XXX Actually, the swapper page directory is at 0x1000 plus 1 megabyte, * with the introduction of the compressed boot code. Theoretically, * the original design of overlaying the startup code with the swapper * page directory is still possible --- it would reduce the size of the kernel * by 2-3k. This would be a good thing to do at some point..... */ .org 0x1000 _swapper_pg_dir: /* * The page tables are initialized to only 4MB here - the final page * tables are set up later depending on memory size. */ .org 0x2000 _pg0: .org 0x3000 _empty_bad_page: .org 0x4000 _empty_bad_page_table: .org 0x5000 _empty_zero_page: .org 0x6000 /* * floppy_track_buffer is used to buffer one track of floppy data: it * has to be separate from the tmp_floppy area, as otherwise a single- * sector read/write can mess it up. It can contain one full cylinder (sic) of * data (36*2*512 bytes). */ _floppy_track_buffer: .fill 512*2*MAX_BUFFER_SECTORS,1,0 stack_start: .long _init_user_stack+4096 .long KERNEL_DS /* This is the default interrupt "handler" :-) */ int_msg: .asciz "Unknown interrupt\n" .align 2 ignore_int: cld pushl %eax pushl %ecx pushl %edx push %ds push %es push %fs movl $(KERNEL_DS),%eax mov %ax,%ds mov %ax,%es mov %ax,%fs pushl $int_msg call _printk popl %eax pop %fs pop %es pop %ds popl %edx popl %ecx popl %eax iret /* * The interrupt descriptor table has room for 256 idt's */ .align 4 .word 0 idt_descr: .word 256*8-1 # idt contains 256 entries .long 0xc0000000+_idt .align 4 _idt: .fill 256,8,0 # idt is uninitialized .align 4 .word 0 gdt_descr: .word (8+2*NR_TASKS)*8-1 .long 0xc0000000+_gdt /* * This gdt setup gives the kernel a 1GB address space at virtual * address 0xC0000000 - space enough for expansion, I hope. */ .align 4 _gdt: .quad 0x0000000000000000 /* NULL descriptor */ .quad 0x0000000000000000 /* not used */ .quad 0xc0c39a000000ffff /* 0x10 kernel 1GB code at 0xC0000000 */ .quad 0xc0c392000000ffff /* 0x18 kernel 1GB data at 0xC0000000 */ .quad 0x00cbfa000000ffff /* 0x23 user 3GB code at 0x00000000 */ .quad 0x00cbf2000000ffff /* 0x2b user 3GB data at 0x00000000 */ .quad 0x0000000000000000 /* not used */ .quad 0x0000000000000000 /* not used */ .fill 2*NR_TASKS,8,0 /* space for LDT's and TSS's etc */