diff options
Diffstat (limited to 'arch/i386/boot/head.S')
| -rw-r--r-- | arch/i386/boot/head.S | 349 |
1 files changed, 349 insertions, 0 deletions
diff --git a/arch/i386/boot/head.S b/arch/i386/boot/head.S new file mode 100644 index 000000000..896c62f18 --- /dev/null +++ b/arch/i386/boot/head.S @@ -0,0 +1,349 @@ +/* + * linux/boot/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 %esp,%edi # save stack pointer + andl $0xfffffffc,%esp # align stack to avoid AC fault + 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 + movl $1, %eax # Use the CPUID instruction to + .byte 0x0f, 0xa2 # check the processor type + andl $0xf00, %eax # Set _x86 with the family + shrl $8, %eax # returned. + movl %eax, _x86 + movl %edi,%esp # restore esp + 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 %edi,%esp # restore esp + 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 %edi,%esp # restore esp + 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: + movl $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: movl $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 + +/* 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 */ |