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c1fb6816fb
linux-next/arch/powerpc/kernel/head_64.S
Michael Neuling c1fb6816fb powerpc: Add relocation on exception vector handlers 
POWER8/v2.07 allows exceptions to be taken with the MMU still on.

A new set of exception vectors is added at 0xc000_0000_0000_4xxx.  When the HW
takes us here, MSR IR/DR will be set already and we no longer need a costly
RFID to turn the MMU back on again.

The original 0x0 based exception vectors remain for when the HW can't leave the
MMU on.  Examples of this are when we can't trust the current MMU mappings,
like when we are changing from guest to hypervisor (HV 0 -> 1) or when the MMU
was off already.  In these cases the HW will take us to the original 0x0 based
exception vectors with the MMU off as before.

This uses the new macros added previously too implement these new execption
vectors at 0xc000_0000_0000_4xxx.  We exit these exception vectors using
mflr/blr (rather than mtspr SSR0/RFID), since we don't need the costly MMU
switch anymore.

This moves the __end_interrupts marker down past these new 0x4000 vectors since
they will need to be copied down to 0x0 when the kernel is not at 0x0.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-11-15 15:08:05 +11:00

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/*
* PowerPC version
* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
*
* Rewritten by Cort Dougan (cort@cs.nmt.edu) for PReP
* Copyright (C) 1996 Cort Dougan <cort@cs.nmt.edu>
* Adapted for Power Macintosh by Paul Mackerras.
* Low-level exception handlers and MMU support
* rewritten by Paul Mackerras.
* Copyright (C) 1996 Paul Mackerras.
*
* Adapted for 64bit PowerPC by Dave Engebretsen, Peter Bergner, and
* Mike Corrigan {engebret|bergner|mikejc}@us.ibm.com
*
* This file contains the entry point for the 64-bit kernel along
* with some early initialization code common to all 64-bit powerpc
* variants.
*
* 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 <linux/threads.h>
#include <asm/reg.h>
#include <asm/page.h>
#include <asm/mmu.h>
#include <asm/ppc_asm.h>
#include <asm/asm-offsets.h>
#include <asm/bug.h>
#include <asm/cputable.h>
#include <asm/setup.h>
#include <asm/hvcall.h>
#include <asm/thread_info.h>
#include <asm/firmware.h>
#include <asm/page_64.h>
#include <asm/irqflags.h>
#include <asm/kvm_book3s_asm.h>
#include <asm/ptrace.h>
#include <asm/hw_irq.h>
/* The physical memory is laid out such that the secondary processor
* spin code sits at 0x0000...0x00ff. On server, the vectors follow
* using the layout described in exceptions-64s.S
*/
/*
* Entering into this code we make the following assumptions:
*
* For pSeries or server processors:
* 1. The MMU is off & open firmware is running in real mode.
* 2. The kernel is entered at __start
* -or- For OPAL entry:
* 1. The MMU is off, processor in HV mode, primary CPU enters at 0
* with device-tree in gpr3. We also get OPAL base in r8 and
* entry in r9 for debugging purposes
* 2. Secondary processors enter at 0x60 with PIR in gpr3
*
* For Book3E processors:
* 1. The MMU is on running in AS0 in a state defined in ePAPR
* 2. The kernel is entered at __start
*/
.text
.globl _stext
_stext:
_GLOBAL(__start)
/* NOP this out unconditionally */
BEGIN_FTR_SECTION
b .__start_initialization_multiplatform
END_FTR_SECTION(0, 1)
/* Catch branch to 0 in real mode */
trap
/* Secondary processors spin on this value until it becomes nonzero.
* When it does it contains the real address of the descriptor
* of the function that the cpu should jump to to continue
* initialization.
*/
.globl __secondary_hold_spinloop
__secondary_hold_spinloop:
.llong 0x0
/* Secondary processors write this value with their cpu # */
/* after they enter the spin loop immediately below. */
.globl __secondary_hold_acknowledge
__secondary_hold_acknowledge:
.llong 0x0
#ifdef CONFIG_RELOCATABLE
/* This flag is set to 1 by a loader if the kernel should run
* at the loaded address instead of the linked address. This
* is used by kexec-tools to keep the the kdump kernel in the
* crash_kernel region. The loader is responsible for
* observing the alignment requirement.
*/
/* Do not move this variable as kexec-tools knows about it. */
. = 0x5c
.globl __run_at_load
__run_at_load:
.long 0x72756e30 /* "run0" -- relocate to 0 by default */
#endif
. = 0x60
/*
* The following code is used to hold secondary processors
* in a spin loop after they have entered the kernel, but
* before the bulk of the kernel has been relocated. This code
* is relocated to physical address 0x60 before prom_init is run.
* All of it must fit below the first exception vector at 0x100.
* Use .globl here not _GLOBAL because we want __secondary_hold
* to be the actual text address, not a descriptor.
*/
.globl __secondary_hold
__secondary_hold:
#ifndef CONFIG_PPC_BOOK3E
mfmsr r24
ori r24,r24,MSR_RI
mtmsrd r24 /* RI on */
#endif
/* Grab our physical cpu number */
mr r24,r3
/* Tell the master cpu we're here */
/* Relocation is off & we are located at an address less */
/* than 0x100, so only need to grab low order offset. */
std r24,__secondary_hold_acknowledge-_stext(0)
sync
/* All secondary cpus wait here until told to start. */
100: ld r4,__secondary_hold_spinloop-_stext(0)
cmpdi 0,r4,0
beq 100b
#if defined(CONFIG_SMP) || defined(CONFIG_KEXEC)
ld r4,0(r4) /* deref function descriptor */
mtctr r4
mr r3,r24
li r4,0
/* Make sure that patched code is visible */
isync
bctr
#else
BUG_OPCODE
#endif
/* This value is used to mark exception frames on the stack. */
.section ".toc","aw"
exception_marker:
.tc ID_72656773_68657265[TC],0x7265677368657265
.text
/*
* On server, we include the exception vectors code here as it
* relies on absolute addressing which is only possible within
* this compilation unit
*/
#ifdef CONFIG_PPC_BOOK3S
#include "exceptions-64s.S"
#endif
_GLOBAL(generic_secondary_thread_init)
mr r24,r3
/* turn on 64-bit mode */
bl .enable_64b_mode
/* get a valid TOC pointer, wherever we're mapped at */
bl .relative_toc
#ifdef CONFIG_PPC_BOOK3E
/* Book3E initialization */
mr r3,r24
bl .book3e_secondary_thread_init
#endif
b generic_secondary_common_init
/*
* On pSeries and most other platforms, secondary processors spin
* in the following code.
* At entry, r3 = this processor's number (physical cpu id)
*
* On Book3E, r4 = 1 to indicate that the initial TLB entry for
* this core already exists (setup via some other mechanism such
* as SCOM before entry).
*/
_GLOBAL(generic_secondary_smp_init)
mr r24,r3
mr r25,r4
/* turn on 64-bit mode */
bl .enable_64b_mode
/* get a valid TOC pointer, wherever we're mapped at */
bl .relative_toc
#ifdef CONFIG_PPC_BOOK3E
/* Book3E initialization */
mr r3,r24
mr r4,r25
bl .book3e_secondary_core_init
#endif
generic_secondary_common_init:
/* Set up a paca value for this processor. Since we have the
* physical cpu id in r24, we need to search the pacas to find
* which logical id maps to our physical one.
*/
LOAD_REG_ADDR(r13, paca) /* Load paca pointer */
ld r13,0(r13) /* Get base vaddr of paca array */
#ifndef CONFIG_SMP
addi r13,r13,PACA_SIZE /* know r13 if used accidentally */
b .kexec_wait /* wait for next kernel if !SMP */
#else
LOAD_REG_ADDR(r7, nr_cpu_ids) /* Load nr_cpu_ids address */
lwz r7,0(r7) /* also the max paca allocated */
li r5,0 /* logical cpu id */
1: lhz r6,PACAHWCPUID(r13) /* Load HW procid from paca */
cmpw r6,r24 /* Compare to our id */
beq 2f
addi r13,r13,PACA_SIZE /* Loop to next PACA on miss */
addi r5,r5,1
cmpw r5,r7 /* Check if more pacas exist */
blt 1b
mr r3,r24 /* not found, copy phys to r3 */
b .kexec_wait /* next kernel might do better */
2: SET_PACA(r13)
#ifdef CONFIG_PPC_BOOK3E
addi r12,r13,PACA_EXTLB /* and TLB exc frame in another */
mtspr SPRN_SPRG_TLB_EXFRAME,r12
#endif
/* From now on, r24 is expected to be logical cpuid */
mr r24,r5
/* See if we need to call a cpu state restore handler */
LOAD_REG_ADDR(r23, cur_cpu_spec)
ld r23,0(r23)
ld r23,CPU_SPEC_RESTORE(r23)
cmpdi 0,r23,0
beq 3f
ld r23,0(r23)
mtctr r23
bctrl
3: LOAD_REG_ADDR(r3, spinning_secondaries) /* Decrement spinning_secondaries */
lwarx r4,0,r3
subi r4,r4,1
stwcx. r4,0,r3
bne 3b
isync
4: HMT_LOW
lbz r23,PACAPROCSTART(r13) /* Test if this processor should */
/* start. */
cmpwi 0,r23,0
beq 4b /* Loop until told to go */
sync /* order paca.run and cur_cpu_spec */
isync /* In case code patching happened */
/* Create a temp kernel stack for use before relocation is on. */
ld r1,PACAEMERGSP(r13)
subi r1,r1,STACK_FRAME_OVERHEAD
b __secondary_start
#endif /* SMP */
/*
* Turn the MMU off.
* Assumes we're mapped EA == RA if the MMU is on.
*/
#ifdef CONFIG_PPC_BOOK3S
_STATIC(__mmu_off)
mfmsr r3
andi. r0,r3,MSR_IR|MSR_DR
beqlr
mflr r4
andc r3,r3,r0
mtspr SPRN_SRR0,r4
mtspr SPRN_SRR1,r3
sync
rfid
b . /* prevent speculative execution */
#endif
/*
* Here is our main kernel entry point. We support currently 2 kind of entries
* depending on the value of r5.
*
* r5 != NULL -> OF entry, we go to prom_init, "legacy" parameter content
* in r3...r7
*
* r5 == NULL -> kexec style entry. r3 is a physical pointer to the
* DT block, r4 is a physical pointer to the kernel itself
*
*/
_GLOBAL(__start_initialization_multiplatform)
/* Make sure we are running in 64 bits mode */
bl .enable_64b_mode
/* Get TOC pointer (current runtime address) */
bl .relative_toc
/* find out where we are now */
bcl 20,31,$+4
0: mflr r26 /* r26 = runtime addr here */
addis r26,r26,(_stext - 0b)@ha
addi r26,r26,(_stext - 0b)@l /* current runtime base addr */
/*
* Are we booted from a PROM Of-type client-interface ?
*/
cmpldi cr0,r5,0
beq 1f
b .__boot_from_prom /* yes -> prom */
1:
/* Save parameters */
mr r31,r3
mr r30,r4
#ifdef CONFIG_PPC_EARLY_DEBUG_OPAL
/* Save OPAL entry */
mr r28,r8
mr r29,r9
#endif
#ifdef CONFIG_PPC_BOOK3E
bl .start_initialization_book3e
b .__after_prom_start
#else
/* Setup some critical 970 SPRs before switching MMU off */
mfspr r0,SPRN_PVR
srwi r0,r0,16
cmpwi r0,0x39 /* 970 */
beq 1f
cmpwi r0,0x3c /* 970FX */
beq 1f
cmpwi r0,0x44 /* 970MP */
beq 1f
cmpwi r0,0x45 /* 970GX */
bne 2f
1: bl .__cpu_preinit_ppc970
2:
/* Switch off MMU if not already off */
bl .__mmu_off
b .__after_prom_start
#endif /* CONFIG_PPC_BOOK3E */
_INIT_STATIC(__boot_from_prom)
#ifdef CONFIG_PPC_OF_BOOT_TRAMPOLINE
/* Save parameters */
mr r31,r3
mr r30,r4
mr r29,r5
mr r28,r6
mr r27,r7
/*
* Align the stack to 16-byte boundary
* Depending on the size and layout of the ELF sections in the initial
* boot binary, the stack pointer may be unaligned on PowerMac
*/
rldicr r1,r1,0,59
#ifdef CONFIG_RELOCATABLE
/* Relocate code for where we are now */
mr r3,r26
bl .relocate
#endif
/* Restore parameters */
mr r3,r31
mr r4,r30
mr r5,r29
mr r6,r28
mr r7,r27
/* Do all of the interaction with OF client interface */
mr r8,r26
bl .prom_init
#endif /* #CONFIG_PPC_OF_BOOT_TRAMPOLINE */
/* We never return. We also hit that trap if trying to boot
* from OF while CONFIG_PPC_OF_BOOT_TRAMPOLINE isn't selected */
trap
_STATIC(__after_prom_start)
#ifdef CONFIG_RELOCATABLE
/* process relocations for the final address of the kernel */
lis r25,PAGE_OFFSET@highest /* compute virtual base of kernel */
sldi r25,r25,32
lwz r7,__run_at_load-_stext(r26)
cmplwi cr0,r7,1 /* flagged to stay where we are ? */
bne 1f
add r25,r25,r26
1: mr r3,r25
bl .relocate
#endif
/*
* We need to run with _stext at physical address PHYSICAL_START.
* This will leave some code in the first 256B of
* real memory, which are reserved for software use.
*
* Note: This process overwrites the OF exception vectors.
*/
li r3,0 /* target addr */
#ifdef CONFIG_PPC_BOOK3E
tovirt(r3,r3) /* on booke, we already run at PAGE_OFFSET */
#endif
mr. r4,r26 /* In some cases the loader may */
beq 9f /* have already put us at zero */
li r6,0x100 /* Start offset, the first 0x100 */
/* bytes were copied earlier. */
#ifdef CONFIG_PPC_BOOK3E
tovirt(r6,r6) /* on booke, we already run at PAGE_OFFSET */
#endif
#ifdef CONFIG_RELOCATABLE
/*
* Check if the kernel has to be running as relocatable kernel based on the
* variable __run_at_load, if it is set the kernel is treated as relocatable
* kernel, otherwise it will be moved to PHYSICAL_START
*/
lwz r7,__run_at_load-_stext(r26)
cmplwi cr0,r7,1
bne 3f
/* just copy interrupts */
LOAD_REG_IMMEDIATE(r5, __end_interrupts - _stext)
b 5f
3:
#endif
lis r5,(copy_to_here - _stext)@ha
addi r5,r5,(copy_to_here - _stext)@l /* # bytes of memory to copy */
bl .copy_and_flush /* copy the first n bytes */
/* this includes the code being */
/* executed here. */
addis r8,r3,(4f - _stext)@ha /* Jump to the copy of this code */
addi r8,r8,(4f - _stext)@l /* that we just made */
mtctr r8
bctr
p_end: .llong _end - _stext
4: /* Now copy the rest of the kernel up to _end */
addis r5,r26,(p_end - _stext)@ha
ld r5,(p_end - _stext)@l(r5) /* get _end */
5: bl .copy_and_flush /* copy the rest */
9: b .start_here_multiplatform
/*
* Copy routine used to copy the kernel to start at physical address 0
* and flush and invalidate the caches as needed.
* r3 = dest addr, r4 = source addr, r5 = copy limit, r6 = start offset
* on exit, r3, r4, r5 are unchanged, r6 is updated to be >= r5.
*
* Note: this routine *only* clobbers r0, r6 and lr
*/
_GLOBAL(copy_and_flush)
addi r5,r5,-8
addi r6,r6,-8
4: li r0,8 /* Use the smallest common */
/* denominator cache line */
/* size. This results in */
/* extra cache line flushes */
/* but operation is correct. */
/* Can't get cache line size */
/* from NACA as it is being */
/* moved too. */
mtctr r0 /* put # words/line in ctr */
3: addi r6,r6,8 /* copy a cache line */
ldx r0,r6,r4
stdx r0,r6,r3
bdnz 3b
dcbst r6,r3 /* write it to memory */
sync
icbi r6,r3 /* flush the icache line */
cmpld 0,r6,r5
blt 4b
sync
addi r5,r5,8
addi r6,r6,8
blr
.align 8
copy_to_here:
#ifdef CONFIG_SMP
#ifdef CONFIG_PPC_PMAC
/*
* On PowerMac, secondary processors starts from the reset vector, which
* is temporarily turned into a call to one of the functions below.
*/
.section ".text";
.align 2 ;
.globl __secondary_start_pmac_0
__secondary_start_pmac_0:
/* NB the entries for cpus 0, 1, 2 must each occupy 8 bytes. */
li r24,0
b 1f
li r24,1
b 1f
li r24,2
b 1f
li r24,3
1:
_GLOBAL(pmac_secondary_start)
/* turn on 64-bit mode */
bl .enable_64b_mode
li r0,0
mfspr r3,SPRN_HID4
rldimi r3,r0,40,23 /* clear bit 23 (rm_ci) */
sync
mtspr SPRN_HID4,r3
isync
sync
slbia
/* get TOC pointer (real address) */
bl .relative_toc
/* Copy some CPU settings from CPU 0 */
bl .__restore_cpu_ppc970
/* pSeries do that early though I don't think we really need it */
mfmsr r3
ori r3,r3,MSR_RI
mtmsrd r3 /* RI on */
/* Set up a paca value for this processor. */
LOAD_REG_ADDR(r4,paca) /* Load paca pointer */
ld r4,0(r4) /* Get base vaddr of paca array */
mulli r13,r24,PACA_SIZE /* Calculate vaddr of right paca */
add r13,r13,r4 /* for this processor. */
SET_PACA(r13) /* Save vaddr of paca in an SPRG*/
/* Mark interrupts soft and hard disabled (they might be enabled
* in the PACA when doing hotplug)
*/
li r0,0
stb r0,PACASOFTIRQEN(r13)
li r0,PACA_IRQ_HARD_DIS
stb r0,PACAIRQHAPPENED(r13)
/* Create a temp kernel stack for use before relocation is on. */
ld r1,PACAEMERGSP(r13)
subi r1,r1,STACK_FRAME_OVERHEAD
b __secondary_start
#endif /* CONFIG_PPC_PMAC */
/*
* This function is called after the master CPU has released the
* secondary processors. The execution environment is relocation off.
* The paca for this processor has the following fields initialized at
* this point:
* 1. Processor number
* 2. Segment table pointer (virtual address)
* On entry the following are set:
* r1 = stack pointer (real addr of temp stack)
* r24 = cpu# (in Linux terms)
* r13 = paca virtual address
* SPRG_PACA = paca virtual address
*/
.section ".text";
.align 2 ;
.globl __secondary_start
__secondary_start:
/* Set thread priority to MEDIUM */
HMT_MEDIUM
/* Initialize the kernel stack */
LOAD_REG_ADDR(r3, current_set)
sldi r28,r24,3 /* get current_set[cpu#] */
ldx r14,r3,r28
addi r14,r14,THREAD_SIZE-STACK_FRAME_OVERHEAD
std r14,PACAKSAVE(r13)
/* Do early setup for that CPU (stab, slb, hash table pointer) */
bl .early_setup_secondary
/*
* setup the new stack pointer, but *don't* use this until
* translation is on.
*/
mr r1, r14
/* Clear backchain so we get nice backtraces */
li r7,0
mtlr r7
/* Mark interrupts soft and hard disabled (they might be enabled
* in the PACA when doing hotplug)
*/
stb r7,PACASOFTIRQEN(r13)
li r0,PACA_IRQ_HARD_DIS
stb r0,PACAIRQHAPPENED(r13)
/* enable MMU and jump to start_secondary */
LOAD_REG_ADDR(r3, .start_secondary_prolog)
LOAD_REG_IMMEDIATE(r4, MSR_KERNEL)
mtspr SPRN_SRR0,r3
mtspr SPRN_SRR1,r4
RFI
b . /* prevent speculative execution */
/*
* Running with relocation on at this point. All we want to do is
* zero the stack back-chain pointer and get the TOC virtual address
* before going into C code.
*/
_GLOBAL(start_secondary_prolog)
ld r2,PACATOC(r13)
li r3,0
std r3,0(r1) /* Zero the stack frame pointer */
bl .start_secondary
b .
/*
* Reset stack pointer and call start_secondary
* to continue with online operation when woken up
* from cede in cpu offline.
*/
_GLOBAL(start_secondary_resume)
ld r1,PACAKSAVE(r13) /* Reload kernel stack pointer */
li r3,0
std r3,0(r1) /* Zero the stack frame pointer */
bl .start_secondary
b .
#endif
/*
* This subroutine clobbers r11 and r12
*/
_GLOBAL(enable_64b_mode)
mfmsr r11 /* grab the current MSR */
#ifdef CONFIG_PPC_BOOK3E
oris r11,r11,0x8000 /* CM bit set, we'll set ICM later */
mtmsr r11
#else /* CONFIG_PPC_BOOK3E */
li r12,(MSR_64BIT | MSR_ISF)@highest
sldi r12,r12,48
or r11,r11,r12
mtmsrd r11
isync
#endif
blr
/*
* This puts the TOC pointer into r2, offset by 0x8000 (as expected
* by the toolchain). It computes the correct value for wherever we
* are running at the moment, using position-independent code.
*/
_GLOBAL(relative_toc)
mflr r0
bcl 20,31,$+4
0: mflr r11
ld r2,(p_toc - 0b)(r11)
add r2,r2,r11
mtlr r0
blr
p_toc: .llong __toc_start + 0x8000 - 0b
/*
* This is where the main kernel code starts.
*/
_INIT_STATIC(start_here_multiplatform)
/* set up the TOC (real address) */
bl .relative_toc
/* Clear out the BSS. It may have been done in prom_init,
* already but that's irrelevant since prom_init will soon
* be detached from the kernel completely. Besides, we need
* to clear it now for kexec-style entry.
*/
LOAD_REG_ADDR(r11,__bss_stop)
LOAD_REG_ADDR(r8,__bss_start)
sub r11,r11,r8 /* bss size */
addi r11,r11,7 /* round up to an even double word */
srdi. r11,r11,3 /* shift right by 3 */
beq 4f
addi r8,r8,-8
li r0,0
mtctr r11 /* zero this many doublewords */
3: stdu r0,8(r8)
bdnz 3b
4:
#ifdef CONFIG_PPC_EARLY_DEBUG_OPAL
/* Setup OPAL entry */
LOAD_REG_ADDR(r11, opal)
std r28,0(r11);
std r29,8(r11);
#endif
#ifndef CONFIG_PPC_BOOK3E
mfmsr r6
ori r6,r6,MSR_RI
mtmsrd r6 /* RI on */
#endif
#ifdef CONFIG_RELOCATABLE
/* Save the physical address we're running at in kernstart_addr */
LOAD_REG_ADDR(r4, kernstart_addr)
clrldi r0,r25,2
std r0,0(r4)
#endif
/* The following gets the stack set up with the regs */
/* pointing to the real addr of the kernel stack. This is */
/* all done to support the C function call below which sets */
/* up the htab. This is done because we have relocated the */
/* kernel but are still running in real mode. */
LOAD_REG_ADDR(r3,init_thread_union)
/* set up a stack pointer */
addi r1,r3,THREAD_SIZE
li r0,0
stdu r0,-STACK_FRAME_OVERHEAD(r1)
/* Do very early kernel initializations, including initial hash table,
* stab and slb setup before we turn on relocation. */
/* Restore parameters passed from prom_init/kexec */
mr r3,r31
bl .early_setup /* also sets r13 and SPRG_PACA */
LOAD_REG_ADDR(r3, .start_here_common)
ld r4,PACAKMSR(r13)
mtspr SPRN_SRR0,r3
mtspr SPRN_SRR1,r4
RFI
b . /* prevent speculative execution */
/* This is where all platforms converge execution */
_INIT_GLOBAL(start_here_common)
/* relocation is on at this point */
std r1,PACAKSAVE(r13)
/* Load the TOC (virtual address) */
ld r2,PACATOC(r13)
/* Do more system initializations in virtual mode */
bl .setup_system
/* Mark interrupts soft and hard disabled (they might be enabled
* in the PACA when doing hotplug)
*/
li r0,0
stb r0,PACASOFTIRQEN(r13)
li r0,PACA_IRQ_HARD_DIS
stb r0,PACAIRQHAPPENED(r13)
/* Generic kernel entry */
bl .start_kernel
/* Not reached */
BUG_OPCODE
/*
* We put a few things here that have to be page-aligned.
* This stuff goes at the beginning of the bss, which is page-aligned.
*/
.section ".bss"
.align PAGE_SHIFT
.globl empty_zero_page
empty_zero_page:
.space PAGE_SIZE
.globl swapper_pg_dir
swapper_pg_dir:
.space PGD_TABLE_SIZE
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