176 lines
4.7 KiB
ArmAsm
176 lines
4.7 KiB
ArmAsm
/*
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* head.s contains the 32-bit startup code.
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*
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* NOTE!!! Startup happens at absolute address 0x00000000, which is also where
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* the page directory will exist. The startup code will be overwritten by
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* the page directory.
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*/
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.text
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.globl _idt,_gdt,_pg_dir
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_pg_dir:
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startup_32:
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movl $0x10,%eax
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mov %ax,%ds
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mov %ax,%es
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mov %ax,%fs
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mov %ax,%gs
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lss _stack_start,%esp
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call setup_idt
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call setup_gdt
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movl $0x10,%eax # reload all the segment registers
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mov %ax,%ds # after changing gdt. CS was already
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mov %ax,%es # reloaded in 'setup_gdt'
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mov %ax,%fs
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mov %ax,%gs
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lss _stack_start,%esp
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xorl %eax,%eax
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1: incl %eax # check that A20 really IS enabled
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movl %eax,0x000000
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cmpl %eax,0x100000
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je 1b
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movl %cr0,%eax # check math chip
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andl $0x80000011,%eax # Save PG,ET,PE
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testl $0x10,%eax
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jne 1f # ET is set - 387 is present
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orl $4,%eax # else set emulate bit
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1: movl %eax,%cr0
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jmp after_page_tables
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/*
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* setup_idt
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*
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* sets up a idt with 256 entries pointing to
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* ignore_int, interrupt gates. It then loads
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* idt. Everything that wants to install itself
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* in the idt-table may do so themselves. Interrupts
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* are enabled elsewhere, when we can be relatively
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* sure everything is ok. This routine will be over-
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* written by the page tables.
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*/
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setup_idt:
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lea ignore_int,%edx
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movl $0x00080000,%eax
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movw %dx,%ax /* selector = 0x0008 = cs */
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movw $0x8E00,%dx /* interrupt gate - dpl=0, present */
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lea _idt,%edi
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mov $256,%ecx
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rp_sidt:
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movl %eax,(%edi)
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movl %edx,4(%edi)
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addl $8,%edi
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dec %ecx
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jne rp_sidt
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lidt idt_descr
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ret
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/*
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* setup_gdt
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*
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* This routines sets up a new gdt and loads it.
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* Only two entries are currently built, the same
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* ones that were built in init.s. The routine
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* is VERY complicated at two whole lines, so this
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* rather long comment is certainly needed :-).
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* This routine will beoverwritten by the page tables.
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*/
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setup_gdt:
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lgdt gdt_descr
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ret
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.org 0x1000
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pg0:
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.org 0x2000
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pg1:
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.org 0x3000
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pg2: # This is not used yet, but if you
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# want to expand past 8 Mb, you'll have
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# to use it.
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.org 0x4000
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after_page_tables:
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pushl $0 # These are the parameters to main :-)
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pushl $0
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pushl $0
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pushl $L6 # return address for main, if it decides to.
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pushl $_main
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jmp setup_paging
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L6:
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jmp L6 # main should never return here, but
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# just in case, we know what happens.
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/* This is the default interrupt "handler" :-) */
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.align 2
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ignore_int:
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incb 0xb8000+160 # put something on the screen
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movb $2,0xb8000+161 # so that we know something
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iret # happened
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/*
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* Setup_paging
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*
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* This routine sets up paging by setting the page bit
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* in cr0. The page tables are set up, identity-mapping
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* the first 8MB. The pager assumes that no illegal
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* addresses are produced (ie >4Mb on a 4Mb machine).
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*
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* NOTE! Although all physical memory should be identity
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* mapped by this routine, only the kernel page functions
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* use the >1Mb addresses directly. All "normal" functions
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* use just the lower 1Mb, or the local data space, which
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* will be mapped to some other place - mm keeps track of
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* that.
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*
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* For those with more memory than 8 Mb - tough luck. I've
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* not got it, why should you :-) The source is here. Change
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* it. (Seriously - it shouldn't be too difficult. Mostly
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* change some constants etc. I left it at 8Mb, as my machine
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* even cannot be extended past that (ok, but it was cheap :-)
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* I've tried to show which constants to change by having
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* some kind of marker at them (search for "8Mb"), but I
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* won't guarantee that's all :-( )
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*/
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.align 2
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setup_paging:
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movl $1024*3,%ecx
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xorl %eax,%eax
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xorl %edi,%edi /* pg_dir is at 0x000 */
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cld;rep;stosl
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movl $pg0+7,_pg_dir /* set present bit/user r/w */
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movl $pg1+7,_pg_dir+4 /* --------- " " --------- */
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movl $pg1+4092,%edi
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movl $0x7ff007,%eax /* 8Mb - 4096 + 7 (r/w user,p) */
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std
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1: stosl /* fill pages backwards - more efficient :-) */
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subl $0x1000,%eax
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jge 1b
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xorl %eax,%eax /* pg_dir is at 0x0000 */
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movl %eax,%cr3 /* cr3 - page directory start */
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movl %cr0,%eax
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orl $0x80000000,%eax
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movl %eax,%cr0 /* set paging (PG) bit */
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ret /* this also flushes prefetch-queue */
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.align 2
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.word 0
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idt_descr:
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.word 256*8-1 # idt contains 256 entries
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.long _idt
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.align 2
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.word 0
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gdt_descr:
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.word 256*8-1 # so does gdt (not that that's any
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.long _gdt # magic number, but it works for me :^)
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.align 3
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_idt: .fill 256,8,0 # idt is uninitialized
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_gdt: .quad 0x0000000000000000 /* NULL descriptor */
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.quad 0x00c09a00000007ff /* 8Mb */
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.quad 0x00c09200000007ff /* 8Mb */
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.quad 0x0000000000000000 /* TEMPORARY - don't use */
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.fill 252,8,0 /* space for LDT's and TSS's etc */
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