/*
* Kernel execution entry point code.
*
* Copyright (c) 1995-1996 Gary Thomas <gdt@linuxppc.org>
* Initial PowerPC version.
* Copyright (c) 1996 Cort Dougan <cort@cs.nmt.edu>
* Rewritten for PReP
* Copyright (c) 1996 Paul Mackerras <paulus@cs.anu.edu.au>
* Low-level exception handers, MMU support, and rewrite.
* Copyright (c) 1997 Dan Malek <dmalek@jlc.net>
* PowerPC 8xx modifications.
* Copyright (c) 1998-1999 TiVo, Inc.
* PowerPC 403GCX modifications.
* Copyright (c) 1999 Grant Erickson <grant@lcse.umn.edu>
* PowerPC 403GCX/405GP modifications.
* Copyright 2000 MontaVista Software Inc.
* PPC405 modifications
* PowerPC 403GCX/405GP modifications.
* Author: MontaVista Software, Inc.
* frank_rowand@mvista.com or source@mvista.com
* debbie_chu@mvista.com
* Copyright 2002-2005 MontaVista Software, Inc.
* PowerPC 44x support, Matt Porter <mporter@kernel.crashing.org>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version.
*/
#include <asm/processor.h>
#include <asm/page.h>
#include <asm/mmu.h>
#include <asm/pgtable.h>
#include <asm/cputable.h>
#include <asm/thread_info.h>
#include <asm/ppc_asm.h>
#include <asm/asm-offsets.h>
#include "head_booke.h"
/* As with the other PowerPC ports, it is expected that when code
* execution begins here, the following registers contain valid, yet
* optional, information:
*
* r3 - Board info structure pointer (DRAM, frequency, MAC address, etc.)
* r4 - Starting address of the init RAM disk
* r5 - Ending address of the init RAM disk
* r6 - Start of kernel command line string (e.g. "mem=128")
* r7 - End of kernel command line string
*
*/
.section .text.head, "ax"
_ENTRY(_stext);
_ENTRY(_start);
/*
* Reserve a word at a fixed location to store the address
* of abatron_pteptrs
*/
nop
/*
* Save parameters we are passed
*/
mr r31,r3
mr r30,r4
mr r29,r5
mr r28,r6
mr r27,r7
li r24,0 /* CPU number */
/*
* Set up the initial MMU state
*
* We are still executing code at the virtual address
* mappings set by the firmware for the base of RAM.
*
* We first invalidate all TLB entries but the one
* we are running from. We then load the KERNELBASE
* mappings so we can begin to use kernel addresses
* natively and so the interrupt vector locations are
* permanently pinned (necessary since Book E
* implementations always have translation enabled).
*
* TODO: Use the known TLB entry we are running from to
* determine which physical region we are located
* in. This can be used to determine where in RAM
* (on a shared CPU system) or PCI memory space
* (on a DRAMless system) we are located.
* For now, we assume a perfect world which means
* we are located at the base of DRAM (physical 0).
*/
/*
* Search TLB for entry that we are currently using.
* Invalidate all entries but the one we are using.
*/
/* Load our current PID->MMUCR TID and MSR IS->MMUCR STS */
mfspr r3,SPRN_PID /* Get PID */
mfmsr r4 /* Get MSR */
andi. r4,r4,MSR_IS@l /* TS=1? */
beq wmmucr /* If not, leave STS=0 */
oris r3,r3,PPC44x_MMUCR_STS@h /* Set STS=1 */
wmmucr: mtspr SPRN_MMUCR,r3 /* Put MMUCR */
sync
bl invstr /* Find our address */
invstr: mflr r5 /* Make it accessible */
tlbsx r23,0,r5 /* Find entry we are in */
li r4,0 /* Start at TLB entry 0 */
li r3,0 /* Set PAGEID inval value */
1: cmpw r23,r4 /* Is this our entry? */
beq skpinv /* If so, skip the inval */
tlbwe r3,r4,PPC44x_TLB_PAGEID /* If not, inval the entry */
skpinv: addi r4,r4,1 /* Increment */
cmpwi r4,64 /* Are we done? */
bne 1b /* If not, repeat */
isync /* If so, context change */
/*
* Configure and load pinned entry into TLB slot 63.
*/
lis r3,PAGE_OFFSET@h
ori r3,r3,PAGE_OFFSET@l
/* Kernel is at the base of RAM */
li r4, 0 /* Load the kernel physical address */
/* Load the kernel PID = 0 */
li r0,0
mtspr SPRN_PID,r0
sync
/* Initialize MMUCR */
li r5,0
mtspr SPRN_MMUCR,r5
sync
/* pageid fields */
clrrwi r3,r3,10 /* Mask off the effective page number */
ori r3,r3,PPC44x_TLB_VALID | PPC44x_TLB_256M
/* xlat fields */
clrrwi r4,r4,10 /* Mask off the real page number */
/* ERPN is 0 for first 4GB page */
/* attrib fields */
/* Added guarded bit to protect against speculative loads/stores */
li r5,0
ori r5,r5,(PPC44x_TLB_SW | PPC44x_TLB_SR | PPC44x_TLB_SX | PPC44x_TLB_G)
li r0,63 /* TLB slot 63 */
tlbwe r3,r0,PPC44x_TLB_PAGEID /* Load the pageid fields */
tlbwe r4,r0,PPC44x_TLB_XLAT /* Load the translation fields */
tlbwe r5,r0,PPC44x_TLB_ATTRIB /* Load the attrib/access fields */
/* Force context change */
mfmsr r0
mtspr SPRN_SRR1, r0
lis r0,3f@h
ori r0,r0,3f@l
mtspr SPRN_SRR0,r0
sync
rfi
/* If necessary, invalidate original entry we used */
3: cmpwi r23,63
beq 4f
li r6,0
tlbwe r6,r23,PPC44x_TLB_PAGEID
isync
4:
#ifdef CONFIG_PPC_EARLY_DEBUG_44x
/* Add UART mapping for early debug. */
/* pageid fields */
lis r3,PPC44x_EARLY_DEBUG_VIRTADDR@h
ori r3,r3,PPC44x_TLB_VALID|PPC44x_TLB_TS|PPC44x_TLB_64K
/* xlat fields */
lis r4,CONFIG_PPC_EARLY_DEBUG_44x_PHYSLOW@h
ori r4,r4,CONFIG_PPC_EARLY_DEBUG_44x_PHYSHIGH
/* attrib fields */
li r5,(PPC44x_TLB_SW|PPC44x_TLB_SR|PPC44x_TLB_I|PPC44x_TLB_G)
li r0,62 /* TLB slot 0 */
tlbwe r3,r0,PPC44x_TLB_PAGEID
tlbwe r4,r0,PPC44x_TLB_XLAT
tlbwe r5,r0,PPC44x_TLB_ATTRIB
/* Force context change */
isync
#endif /* CONFIG_PPC_EARLY_DEBUG_44x */
/* Establish the interrupt vector offsets */
SET_IVOR(0, CriticalInput);
SET_IVOR(1, MachineCheck);
SET_IVOR(2, DataStorage);
SET_IVOR(3, InstructionStorage);
SET_IVOR(4, ExternalInput);
SET_IVOR(5, Alignment);
SET_IVOR(6, Program);
SET_IVOR(7, FloatingPointUnavailable);
SET_IVOR(8, SystemCall);
SET_IVOR(9, AuxillaryProcessorUnavailable);
SET_IVOR(10, Decrementer);
SET_IVOR(11, FixedIntervalTimer);
SET_IVOR(12, WatchdogTimer);
SET_IVOR(13, DataTLBError);
SET_IVOR(14, InstructionTLBError);
SET_IVOR(15, Debug);
/* Establish the interrupt vector base */
lis r4,interrupt_base@h /* IVPR only uses the high 16-bits */
mtspr SPRN_IVPR,r4
/*
* This is where the main kernel code starts.
*/
/* ptr to current */
lis r2,init_task@h
ori r2,r2,init_task@l
/* ptr to current thread */
addi r4,r2,THREAD /* init task's THREAD */
mtspr SPRN_SPRG3,r4
/* stack */
lis r1,init_thread_union@h
ori r1,r1,init_thread_union@l
li r0,0
stwu r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
bl early_init
/*
* Decide what sort of machine this is and initialize the MMU.
*/
mr r3,r31
mr r4,r30
mr r5,r29
mr r6,r28
mr r7,r27
bl machine_init
bl MMU_init
/* Setup PTE pointers for the Abatron bdiGDB */
lis r6, swapper_pg_dir@h
ori r6, r6, swapper_pg_dir@l
lis r5, abatron_pteptrs@h
ori r5, r5, abatron_pteptrs@l
lis r4, KERNELBASE@h
ori r4, r4, KERNELBASE@l
stw r5, 0(r4) /* Save abatron_pteptrs at a fixed location */
stw r6, 0(r5)
/* Let's move on */
lis r4,start_kernel@h
ori r4,r4,start_kernel@l
lis r3,MSR_KERNEL@h
ori r3,r3,MSR_KERNEL@l
mtspr SPRN_SRR0,r4
mtspr SPRN_SRR1,r3
rfi /* change context and jump to start_kernel */
/*
* Interrupt vector entry code
*
* The Book E MMUs are always on so we don't need to handle
* interrupts in real mode as with previous PPC processors. In
* this case we handle interrupts in the kernel virtual address
* space.
*
* Interrupt vectors are dynamically placed relative to the
* interrupt prefix as determined by the address of interrupt_base.
* The interrupt vectors offsets are programmed using the labels
* for each interrupt vector entry.
*
* Interrupt vectors must be aligned on a 16 byte boundary.
* We align on a 32 byte cache line boundary for good measure.
*/
interrupt_base:
/* Critical Input Interrupt */
CRITICAL_EXCEPTION(0x0100, CriticalInput, unknown_exception)
/* Machine Check Interrupt */
#ifdef CONFIG_440A
MCHECK_EXCEPTION(0x0200, MachineCheck, machine_check_exception)
#else
CRITICAL_EXCEPTION(0x0200, MachineCheck, machine_check_exception)
#endif
/* Data Storage Interrupt */
START_EXCEPTION(DataStorage)
mtspr SPRN_SPRG0, r10 /* Save some working registers */
mtspr SPRN_SPRG1, r11
mtspr SPRN_SPRG4W, r12
mtspr SPRN_SPRG5W, r13
mfcr r11
mtspr SPRN_SPRG7W, r11
/*
* Check if it was a store fault, if not then bail
* because a user tried to access a kernel or
* read-protected page. Otherwise, get the
* offending address and handle it.
*/
mfspr r10, SPRN_ESR
andis. r10, r10, ESR_ST@h
beq 2f
mfspr r10, SPRN_DEAR /* Get faulting address */
/* If we are faulting a kernel address, we have to use the
* kernel page tables.
*/
lis r11, PAGE_OFFSET@h
cmplw r10, r11
blt+ 3f
lis r11, swapper_pg_dir@h
ori r11, r11, swapper_pg_dir@l
mfspr r12,SPRN_MMUCR
rlwinm r12,r12,0,0,23 /* Clear TID */
b 4f
/* Get the PGD for the current thread */
3:
mfspr r11,SPRN_SPRG3
lwz r11,PGDIR(r11)
/* Load PID into MMUCR TID */
mfspr r12,SPRN_MMUCR /* Get MMUCR */
mfspr r13,SPRN_PID /* Get PID */
rlwimi r12,r13,0,24,31 /* Set TID */
4:
mtspr SPRN_MMUCR,r12
rlwinm r12, r10, 13, 19, 29 /* Compute pgdir/pmd offset */
lwzx r11, r12, r11 /* Get pgd/pmd entry */
rlwinm. r12, r11, 0, 0, 20 /* Extract pt base address */
beq 2f /* Bail if no table */
rlwimi r12, r10, 23, 20, 28 /* Compute pte address */
lwz r11, 4(r12) /* Get pte entry */
andi. r13, r11, _PAGE_RW /* Is it writeable? */
beq 2f /* Bail if not */
/* Update 'changed'.
*/
ori r11, r11, _PAGE_DIRTY|_PAGE_ACCESSED|_PAGE_HWWRITE
stw r11, 4(r12) /* Update Linux page table */
li r13, PPC44x_TLB_SR@l /* Set SR */
rlwimi r13, r11, 29, 29, 29 /* SX = _PAGE_HWEXEC */
rlwimi r13, r11, 0, 30, 30 /* SW = _PAGE_RW */
rlwimi r13, r11, 29, 28, 28 /* UR = _PAGE_USER */
rlwimi r12, r11, 31, 26, 26 /* (_PAGE_USER>>1)->r12 */
rlwimi r12, r11, 29, 30, 30 /* (_PAGE_USER>>3)->r12 */
and r12, r12, r11 /* HWEXEC/RW & USER */
rlwimi r13, r12, 0, 26, 26 /* UX = HWEXEC & USER */
rlwimi r13, r12, 3, 27, 27 /* UW = RW & USER */
rlwimi r11,r13,0,26,31 /* Insert static perms */
rlwinm r11,r11,0,20,15 /* Clear U0-U3 */
/* find the TLB index that caused the fault. It has to be here. */
tlbsx r10, 0, r10
tlbwe r11, r10, PPC44x_TLB_ATTRIB /* Write ATTRIB */
/* Done...restore registers and get out of here.
*/
mfspr r11, SPRN_SPRG7R
mtcr r11
mfspr r13, SPRN_SPRG5R
mfspr r12, SPRN_SPRG4R
mfspr r11, SPRN_SPRG1
mfspr r10, SPRN_SPRG0
rfi /* Force context change */
2:
/*
* The bailout. Restore registers to pre-exception conditions
* and call the heavyweights to help us out.
*/
mfspr r11, SPRN_SPRG7R
mtcr r11
mfspr r13, SPRN_SPRG5R
mfspr r12, SPRN_SPRG4R
mfspr r11, SPRN_SPRG1
mfspr r10, SPRN_SPRG0
b data_access
/* Instruction Storage Interrupt */
INSTRUCTION_STORAGE_EXCEPTION
/* External Input Interrupt */
EXCEPTION(0x0500, ExternalInput, do_IRQ, EXC_XFER_LITE)
/* Alignment Interrupt */
ALIGNMENT_EXCEPTION
/* Program Interrupt */
PROGRAM_EXCEPTION
/* Floating Point Unavailable Interrupt */
#ifdef CONFIG_PPC_FPU
FP_UNAVAILABLE_EXCEPTION
#else
EXCEPTION(0x2010, FloatingPointUnavailable, unknown_exception, EXC_XFER_EE)
#endif
/* System Call Interrupt */
START_EXCEPTION(SystemCall)
NORMAL_EXCEPTION_PROLOG
EXC_XFER_EE_LITE(0x0c00, DoSyscall)
/* Auxillary Processor Unavailable Interrupt */
EXCEPTION(0x2020, AuxillaryProcessorUnavailable, unknown_exception, EXC_XFER_EE)
/* Decrementer Interrupt */
DECREMENTER_EXCEPTION
/* Fixed Internal Timer Interrupt */
/* TODO: Add FIT support */
EXCEPTION(0x1010, FixedIntervalTimer, unknown_exception, EXC_XFER_EE)
/* Watchdog Timer Interrupt */
/* TODO: Add watchdog support */
#ifdef CONFIG_BOOKE_WDT
CRITICAL_EXCEPTION(0x1020, WatchdogTimer, WatchdogException)
#else
CRITICAL_EXCEPTION(0x1020, WatchdogTimer, unknown_exception)
#endif
/* Data TLB Error Interrupt */
START_EXCEPTION(DataTLBError)
mtspr SPRN_SPRG0, r10 /* Save some working registers */
mtspr SPRN_SPRG1, r11
mtspr SPRN_SPRG4W, r12
mtspr SPRN_SPRG5W, r13
mfcr r11
mtspr SPRN_SPRG7W, r11
mfspr r10, SPRN_DEAR /* Get faulting address */
/* If we are faulting a kernel address, we have to use the
* kernel page tables.
*/
lis r11, PAGE_OFFSET@h
cmplw r10, r11
blt+ 3f
lis r11, swapper_pg_dir@h
ori r11, r11, swapper_pg_dir@l
mfspr r12,SPRN_MMUCR
rlwinm r12,r12,0,0,23 /* Clear TID */
b 4f
/* Get the PGD for the current thread */
3:
mfspr r11,SPRN_SPRG3
lwz r11,PGDIR(r11)
/* Load PID into MMUCR TID */
mfspr r12,SPRN_MMUCR
mfspr r13,SPRN_PID /* Get PID */
rlwimi r12,r13,0,24,31 /* Set TID */
4:
mtspr SPRN_MMUCR,r12
rlwinm r12, r10, 13, 19, 29 /* Compute pgdir/pmd offset */
lwzx r11, r12, r11 /* Get pgd/pmd entry */
rlwinm. r12, r11, 0, 0, 20 /* Extract pt base address */
beq 2f /* Bail if no table */
rlwimi r12, r10, 23, 20, 28 /* Compute pte address */
lwz r11, 4(r12) /* Get pte entry */
andi. r13, r11, _PAGE_PRESENT /* Is the page present? */
beq 2f /* Bail if not present */
ori r11, r11, _PAGE_ACCESSED
stw r11, 4(r12)
/* Jump to common tlb load */
b finish_tlb_load
2:
/* The bailout. Restore registers to pre-exception conditions
* and call the heavyweights to help us out.
*/
mfspr r11, SPRN_SPRG7R
mtcr r11
mfspr r13, SPRN_SPRG5R
mfspr r12, SPRN_SPRG4R
mfspr r11, SPRN_SPRG1
mfspr r10, SPRN_SPRG0
b data_access
/* Instruction TLB Error Interrupt */
/*
* Nearly the same as above, except we get our
* information from different registers and bailout
* to a different point.
*/
START_EXCEPTION(InstructionTLBError)
mtspr SPRN_SPRG0, r10 /* Save some working registers */
mtspr SPRN_SPRG1, r11
mtspr SPRN_SPRG4W, r12
mtspr SPRN_SPRG5W, r13
mfcr r11
mtspr SPRN_SPRG7W, r11
mfspr r10, SPRN_SRR0 /* Get faulting address */
/* If we are faulting a kernel address, we have to use the
* kernel page tables.
*/
lis r11, PAGE_OFFSET@h
cmplw r10, r11
blt+ 3f
lis r11, swapper_pg_dir@h
ori r11, r11, swapper_pg_dir@l
mfspr r12,SPRN_MMUCR
rlwinm r12,r12,0,0,23 /* Clear TID */
b 4f
/* Get the PGD for the current thread */
3:
mfspr r11,SPRN_SPRG3
lwz r11,PGDIR(r11)
/* Load PID into MMUCR TID */
mfspr r12,SPRN_MMUCR
mfspr r13,SPRN_PID /* Get PID */
rlwimi r12,r13,0,24,31 /* Set TID */
4:
mtspr SPRN_MMUCR,r12
rlwinm r12, r10, 13, 19, 29 /* Compute pgdir/pmd offset */
lwzx r11, r12, r11 /* Get pgd/pmd entry */
rlwinm. r12, r11, 0, 0, 20 /* Extract pt base address */
beq 2f /* Bail if no table */
rlwimi r12, r10, 23, 20, 28 /* Compute pte address */
lwz r11, 4(r12) /* Get pte entry */
andi. r13, r11, _PAGE_PRESENT /* Is the page present? */
beq 2f /* Bail if not present */
ori r11, r11, _PAGE_ACCESSED
stw r11, 4(r12)
/* Jump to common TLB load point */
b finish_tlb_load
2:
/* The bailout. Restore registers to pre-exception conditions
* and call the heavyweights to help us out.
*/
mfspr r11, SPRN_SPRG7R
mtcr r11
mfspr r13, SPRN_SPRG5R
mfspr r12, SPRN_SPRG4R
mfspr r11, SPRN_SPRG1
mfspr r10, SPRN_SPRG0
b InstructionStorage
/* Debug Interrupt */
DEBUG_EXCEPTION
/*
* Local functions
*/
/*
* Data TLB exceptions will bail out to this point
* if they can't resolve the lightweight TLB fault.
*/
data_access:
NORMAL_EXCEPTION_PROLOG
mfspr r5,SPRN_ESR /* Grab the ESR, save it, pass arg3 */
stw r5,_ESR(r11)
mfspr r4,SPRN_DEAR /* Grab the DEAR, save it, pass arg2 */
EXC_XFER_EE_LITE(0x0300, handle_page_fault)
/*
* Both the instruction and data TLB miss get to this
* point to load the TLB.
* r10 - EA of fault
* r11 - available to use
* r12 - Pointer to the 64-bit PTE
* r13 - available to use
* MMUCR - loaded with proper value when we get here
* Upon exit, we reload everything and RFI.
*/
finish_tlb_load:
/*
* We set execute, because we don't have the granularity to
* properly set this at the page level (Linux problem).
* If shared is set, we cause a zero PID->TID load.
* Many of these bits are software only. Bits we don't set
* here we (properly should) assume have the appropriate value.
*/
/* Load the next available TLB index */
lis r13, tlb_44x_index@ha
lwz r13, tlb_44x_index@l(r13)
/* Load the TLB high watermark */
lis r11, tlb_44x_hwater@ha
lwz r11, tlb_44x_hwater@l(r11)
/* Increment, rollover, and store TLB index */
addi r13, r13, 1
cmpw 0, r13, r11 /* reserve entries */
ble 7f
li r13, 0
7:
/* Store the next available TLB index */
lis r11, tlb_44x_index@ha
stw r13, tlb_44x_index@l(r11)
lwz r11, 0(r12) /* Get MS word of PTE */
lwz r12, 4(r12) /* Get LS word of PTE */
rlwimi r11, r12, 0, 0 , 19 /* Insert RPN */
tlbwe r11, r13, PPC44x_TLB_XLAT /* Write XLAT */
/*
* Create PAGEID. This is the faulting address,
* page size, and valid flag.
*/
li r11, PPC44x_TLB_VALID | PPC44x_TLB_4K
rlwimi r10, r11, 0, 20, 31 /* Insert valid and page size */
tlbwe r10, r13, PPC44x_TLB_PAGEID /* Write PAGEID */
li r10, PPC44x_TLB_SR@l /* Set SR */
rlwimi r10, r12, 0, 30, 30 /* Set SW = _PAGE_RW */
rlwimi r10, r12, 29, 29, 29 /* SX = _PAGE_HWEXEC */
rlwimi r10, r12, 29, 28, 28 /* UR = _PAGE_USER */
rlwimi r11, r12, 31, 26, 26 /* (_PAGE_USER>>1)->r12 */
and r11, r12, r11 /* HWEXEC & USER */
rlwimi r10, r11, 0, 26, 26 /* UX = HWEXEC & USER */
rlwimi r12, r10, 0, 26, 31 /* Insert static perms */
rlwinm r12, r12, 0, 20, 15 /* Clear U0-U3 */
tlbwe r12, r13, PPC44x_TLB_ATTRIB /* Write ATTRIB */
/* Done...restore registers and get out of here.
*/
mfspr r11, SPRN_SPRG7R
mtcr r11
mfspr r13, SPRN_SPRG5R
mfspr r12, SPRN_SPRG4R
mfspr r11, SPRN_SPRG1
mfspr r10, SPRN_SPRG0
rfi /* Force context change */
/*
* Global functions
*/
/*
* extern void giveup_altivec(struct task_struct *prev)
*
* The 44x core does not have an AltiVec unit.
*/
_GLOBAL(giveup_altivec)
blr
/*
* extern void giveup_fpu(struct task_struct *prev)
*
* The 44x core does not have an FPU.
*/
#ifndef CONFIG_PPC_FPU
_GLOBAL(giveup_fpu)
blr
#endif
_GLOBAL(set_context)
#ifdef CONFIG_BDI_SWITCH
/* Context switch the PTE pointer for the Abatron BDI2000.
* The PGDIR is the second parameter.
*/
lis r5, abatron_pteptrs@h
ori r5, r5, abatron_pteptrs@l
stw r4, 0x4(r5)
#endif
mtspr SPRN_PID,r3
isync /* Force context change */
blr
/*
* We put a few things here that have to be page-aligned. This stuff
* goes at the beginning of the data segment, which is page-aligned.
*/
.data
.align 12
.globl sdata
sdata:
.globl empty_zero_page
empty_zero_page:
.space 4096
/*
* To support >32-bit physical addresses, we use an 8KB pgdir.
*/
.globl swapper_pg_dir
swapper_pg_dir:
.space 8192
/* Reserved 4k for the critical exception stack & 4k for the machine
* check stack per CPU for kernel mode exceptions */
.section .bss
.align 12
exception_stack_bottom:
.space BOOKE_EXCEPTION_STACK_SIZE
.globl exception_stack_top
exception_stack_top:
/*
* Room for two PTE pointers, usually the kernel and current user pointers
* to their respective root page table.
*/
abatron_pteptrs:
.space 8
