[ARM] 4665/1: fix __und_usr wrt accessing the undefined insn in user space

[safe/jmp/linux-2.6] / arch / arm / kernel / entry-armv.S

/*
 *  linux/arch/arm/kernel/entry-armv.S
 *
 *  Copyright (C) 1996,1997,1998 Russell King.
 *  ARM700 fix by Matthew Godbolt (linux-user@willothewisp.demon.co.uk)
 *  nommu support by Hyok S. Choi (hyok.choi@samsung.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 *  Low-level vector interface routines
 *
 *  Note:  there is a StrongARM bug in the STMIA rn, {regs}^ instruction that causes
 *  it to save wrong values...  Be aware!
 */

#include <asm/memory.h>
#include <asm/glue.h>
#include <asm/vfpmacros.h>
#include <asm/arch/entry-macro.S>
#include <asm/thread_notify.h>

#include "entry-header.S"

/*
 * Interrupt handling.  Preserves r7, r8, r9
 */
        .macro  irq_handler
        get_irqnr_preamble r5, lr
1:      get_irqnr_and_base r0, r6, r5, lr
        movne   r1, sp
        @
        @ routine called with r0 = irq number, r1 = struct pt_regs *
        @
        adrne   lr, 1b
        bne     asm_do_IRQ

#ifdef CONFIG_SMP
        /*
         * XXX
         *
         * this macro assumes that irqstat (r6) and base (r5) are
         * preserved from get_irqnr_and_base above
         */
        test_for_ipi r0, r6, r5, lr
        movne   r0, sp
        adrne   lr, 1b
        bne     do_IPI

#ifdef CONFIG_LOCAL_TIMERS
        test_for_ltirq r0, r6, r5, lr
        movne   r0, sp
        adrne   lr, 1b
        bne     do_local_timer
#endif
#endif

        .endm

/*
 * Invalid mode handlers
 */
        .macro  inv_entry, reason
        sub     sp, sp, #S_FRAME_SIZE
        stmib   sp, {r1 - lr}
        mov     r1, #\reason
        .endm

__pabt_invalid:
        inv_entry BAD_PREFETCH
        b       common_invalid

__dabt_invalid:
        inv_entry BAD_DATA
        b       common_invalid

__irq_invalid:
        inv_entry BAD_IRQ
        b       common_invalid

__und_invalid:
        inv_entry BAD_UNDEFINSTR

        @
        @ XXX fall through to common_invalid
        @

@
@ common_invalid - generic code for failed exception (re-entrant version of handlers)
@
common_invalid:
        zero_fp

        ldmia   r0, {r4 - r6}
        add     r0, sp, #S_PC           @ here for interlock avoidance
        mov     r7, #-1                 @  ""   ""    ""        ""
        str     r4, [sp]                @ save preserved r0
        stmia   r0, {r5 - r7}           @ lr_<exception>,
                                        @ cpsr_<exception>, "old_r0"

        mov     r0, sp
        b       bad_mode

/*
 * SVC mode handlers
 */

#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5)
#define SPFIX(code...) code
#else
#define SPFIX(code...)
#endif

        .macro  svc_entry
        sub     sp, sp, #S_FRAME_SIZE
 SPFIX( tst     sp, #4          )
 SPFIX( bicne   sp, sp, #4      )
        stmib   sp, {r1 - r12}

        ldmia   r0, {r1 - r3}
        add     r5, sp, #S_SP           @ here for interlock avoidance
        mov     r4, #-1                 @  ""  ""      ""       ""
        add     r0, sp, #S_FRAME_SIZE   @  ""  ""      ""       ""
 SPFIX( addne   r0, r0, #4      )
        str     r1, [sp]                @ save the "real" r0 copied
                                        @ from the exception stack

        mov     r1, lr

        @
        @ We are now ready to fill in the remaining blanks on the stack:
        @
        @  r0 - sp_svc
        @  r1 - lr_svc
        @  r2 - lr_<exception>, already fixed up for correct return/restart
        @  r3 - spsr_<exception>
        @  r4 - orig_r0 (see pt_regs definition in ptrace.h)
        @
        stmia   r5, {r0 - r4}
        .endm

        .align  5
__dabt_svc:
        svc_entry

        @
        @ get ready to re-enable interrupts if appropriate
        @
        mrs     r9, cpsr
        tst     r3, #PSR_I_BIT
        biceq   r9, r9, #PSR_I_BIT

        @
        @ Call the processor-specific abort handler:
        @
        @  r2 - aborted context pc
        @  r3 - aborted context cpsr
        @
        @ The abort handler must return the aborted address in r0, and
        @ the fault status register in r1.  r9 must be preserved.
        @
#ifdef MULTI_ABORT
        ldr     r4, .LCprocfns
        mov     lr, pc
        ldr     pc, [r4]
#else
        bl      CPU_ABORT_HANDLER
#endif

        @
        @ set desired IRQ state, then call main handler
        @
        msr     cpsr_c, r9
        mov     r2, sp
        bl      do_DataAbort

        @
        @ IRQs off again before pulling preserved data off the stack
        @
        disable_irq

        @
        @ restore SPSR and restart the instruction
        @
        ldr     r0, [sp, #S_PSR]
        msr     spsr_cxsf, r0
        ldmia   sp, {r0 - pc}^                  @ load r0 - pc, cpsr

        .align  5
__irq_svc:
        svc_entry

#ifdef CONFIG_TRACE_IRQFLAGS
        bl      trace_hardirqs_off
#endif
#ifdef CONFIG_PREEMPT
        get_thread_info tsk
        ldr     r8, [tsk, #TI_PREEMPT]          @ get preempt count
        add     r7, r8, #1                      @ increment it
        str     r7, [tsk, #TI_PREEMPT]
#endif

        irq_handler
#ifdef CONFIG_PREEMPT
        ldr     r0, [tsk, #TI_FLAGS]            @ get flags
        tst     r0, #_TIF_NEED_RESCHED
        blne    svc_preempt
preempt_return:
        ldr     r0, [tsk, #TI_PREEMPT]          @ read preempt value
        str     r8, [tsk, #TI_PREEMPT]          @ restore preempt count
        teq     r0, r7
        strne   r0, [r0, -r0]                   @ bug()
#endif
        ldr     r0, [sp, #S_PSR]                @ irqs are already disabled
        msr     spsr_cxsf, r0
#ifdef CONFIG_TRACE_IRQFLAGS
        tst     r0, #PSR_I_BIT
        bleq    trace_hardirqs_on
#endif
        ldmia   sp, {r0 - pc}^                  @ load r0 - pc, cpsr

        .ltorg

#ifdef CONFIG_PREEMPT
svc_preempt:
        teq     r8, #0                          @ was preempt count = 0
        ldreq   r6, .LCirq_stat
        movne   pc, lr                          @ no
        ldr     r0, [r6, #4]                    @ local_irq_count
        ldr     r1, [r6, #8]                    @ local_bh_count
        adds    r0, r0, r1
        movne   pc, lr
        mov     r7, #0                          @ preempt_schedule_irq
        str     r7, [tsk, #TI_PREEMPT]          @ expects preempt_count == 0
1:      bl      preempt_schedule_irq            @ irq en/disable is done inside
        ldr     r0, [tsk, #TI_FLAGS]            @ get new tasks TI_FLAGS
        tst     r0, #_TIF_NEED_RESCHED
        beq     preempt_return                  @ go again
        b       1b
#endif

        .align  5
__und_svc:
        svc_entry

        @
        @ call emulation code, which returns using r9 if it has emulated
        @ the instruction, or the more conventional lr if we are to treat
        @ this as a real undefined instruction
        @
        @  r0 - instruction
        @
        ldr     r0, [r2, #-4]
        adr     r9, 1f
        bl      call_fpe

        mov     r0, sp                          @ struct pt_regs *regs
        bl      do_undefinstr

        @
        @ IRQs off again before pulling preserved data off the stack
        @
1:      disable_irq

        @
        @ restore SPSR and restart the instruction
        @
        ldr     lr, [sp, #S_PSR]                @ Get SVC cpsr
        msr     spsr_cxsf, lr
        ldmia   sp, {r0 - pc}^                  @ Restore SVC registers

        .align  5
__pabt_svc:
        svc_entry

        @
        @ re-enable interrupts if appropriate
        @
        mrs     r9, cpsr
        tst     r3, #PSR_I_BIT
        biceq   r9, r9, #PSR_I_BIT
        msr     cpsr_c, r9

        @
        @ set args, then call main handler
        @
        @  r0 - address of faulting instruction
        @  r1 - pointer to registers on stack
        @
        mov     r0, r2                          @ address (pc)
        mov     r1, sp                          @ regs
        bl      do_PrefetchAbort                @ call abort handler

        @
        @ IRQs off again before pulling preserved data off the stack
        @
        disable_irq

        @
        @ restore SPSR and restart the instruction
        @
        ldr     r0, [sp, #S_PSR]
        msr     spsr_cxsf, r0
        ldmia   sp, {r0 - pc}^                  @ load r0 - pc, cpsr

        .align  5
.LCcralign:
        .word   cr_alignment
#ifdef MULTI_ABORT
.LCprocfns:
        .word   processor
#endif
.LCfp:
        .word   fp_enter
#ifdef CONFIG_PREEMPT
.LCirq_stat:
        .word   irq_stat
#endif

/*
 * User mode handlers
 *
 * EABI note: sp_svc is always 64-bit aligned here, so should S_FRAME_SIZE
 */

#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) && (S_FRAME_SIZE & 7)
#error "sizeof(struct pt_regs) must be a multiple of 8"
#endif

        .macro  usr_entry
        sub     sp, sp, #S_FRAME_SIZE
        stmib   sp, {r1 - r12}

        ldmia   r0, {r1 - r3}
        add     r0, sp, #S_PC           @ here for interlock avoidance
        mov     r4, #-1                 @  ""  ""     ""        ""

        str     r1, [sp]                @ save the "real" r0 copied
                                        @ from the exception stack

        @
        @ We are now ready to fill in the remaining blanks on the stack:
        @
        @  r2 - lr_<exception>, already fixed up for correct return/restart
        @  r3 - spsr_<exception>
        @  r4 - orig_r0 (see pt_regs definition in ptrace.h)
        @
        @ Also, separately save sp_usr and lr_usr
        @
        stmia   r0, {r2 - r4}
        stmdb   r0, {sp, lr}^

        @
        @ Enable the alignment trap while in kernel mode
        @
        alignment_trap r0

        @
        @ Clear FP to mark the first stack frame
        @
        zero_fp
        .endm

        .macro  kuser_cmpxchg_check
#if __LINUX_ARM_ARCH__ < 6 && !defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
#ifndef CONFIG_MMU
#warning "NPTL on non MMU needs fixing"
#else
        @ Make sure our user space atomic helper is restarted
        @ if it was interrupted in a critical region.  Here we
        @ perform a quick test inline since it should be false
        @ 99.9999% of the time.  The rest is done out of line.
        cmp     r2, #TASK_SIZE
        blhs    kuser_cmpxchg_fixup
#endif
#endif
        .endm

        .align  5
__dabt_usr:
        usr_entry
        kuser_cmpxchg_check

        @
        @ Call the processor-specific abort handler:
        @
        @  r2 - aborted context pc
        @  r3 - aborted context cpsr
        @
        @ The abort handler must return the aborted address in r0, and
        @ the fault status register in r1.
        @
#ifdef MULTI_ABORT
        ldr     r4, .LCprocfns
        mov     lr, pc
        ldr     pc, [r4]
#else
        bl      CPU_ABORT_HANDLER
#endif

        @
        @ IRQs on, then call the main handler
        @
        enable_irq
        mov     r2, sp
        adr     lr, ret_from_exception
        b       do_DataAbort

        .align  5
__irq_usr:
        usr_entry
        kuser_cmpxchg_check

#ifdef CONFIG_TRACE_IRQFLAGS
        bl      trace_hardirqs_off
#endif
        get_thread_info tsk
#ifdef CONFIG_PREEMPT
        ldr     r8, [tsk, #TI_PREEMPT]          @ get preempt count
        add     r7, r8, #1                      @ increment it
        str     r7, [tsk, #TI_PREEMPT]
#endif

        irq_handler
#ifdef CONFIG_PREEMPT
        ldr     r0, [tsk, #TI_PREEMPT]
        str     r8, [tsk, #TI_PREEMPT]
        teq     r0, r7
        strne   r0, [r0, -r0]
#endif
#ifdef CONFIG_TRACE_IRQFLAGS
        bl      trace_hardirqs_on
#endif

        mov     why, #0
        b       ret_to_user

        .ltorg

        .align  5
__und_usr:
        usr_entry

        tst     r3, #PSR_T_BIT                  @ Thumb mode?
        bne     __und_usr_unknown               @ ignore FP
        sub     r4, r2, #4

        @
        @ fall through to the emulation code, which returns using r9 if
        @ it has emulated the instruction, or the more conventional lr
        @ if we are to treat this as a real undefined instruction
        @
        @  r0 - instruction
        @
        adr     r9, ret_from_exception
        adr     lr, __und_usr_unknown
1:      ldrt    r0, [r4]
        @
        @ fallthrough to call_fpe
        @

/*
 * The out of line fixup for the ldrt above.
 */
        .section .fixup, "ax"
2:      mov     pc, r9
        .previous
        .section __ex_table,"a"
        .long   1b, 2b
        .previous

/*
 * Check whether the instruction is a co-processor instruction.
 * If yes, we need to call the relevant co-processor handler.
 *
 * Note that we don't do a full check here for the co-processor
 * instructions; all instructions with bit 27 set are well
 * defined.  The only instructions that should fault are the
 * co-processor instructions.  However, we have to watch out
 * for the ARM6/ARM7 SWI bug.
 *
 * Emulators may wish to make use of the following registers:
 *  r0  = instruction opcode.
 *  r2  = PC+4
 *  r9  = normal "successful" return address
 *  r10 = this threads thread_info structure.
 *  lr  = unrecognised instruction return address
 */
call_fpe:
        tst     r0, #0x08000000                 @ only CDP/CPRT/LDC/STC have bit 27
#if defined(CONFIG_CPU_ARM610) || defined(CONFIG_CPU_ARM710)
        and     r8, r0, #0x0f000000             @ mask out op-code bits
        teqne   r8, #0x0f000000                 @ SWI (ARM6/7 bug)?
#endif
        moveq   pc, lr
        get_thread_info r10                     @ get current thread
        and     r8, r0, #0x00000f00             @ mask out CP number
        mov     r7, #1
        add     r6, r10, #TI_USED_CP
        strb    r7, [r6, r8, lsr #8]            @ set appropriate used_cp[]
#ifdef CONFIG_IWMMXT
        @ Test if we need to give access to iWMMXt coprocessors
        ldr     r5, [r10, #TI_FLAGS]
        rsbs    r7, r8, #(1 << 8)               @ CP 0 or 1 only
        movcss  r7, r5, lsr #(TIF_USING_IWMMXT + 1)
        bcs     iwmmxt_task_enable
#endif
        add     pc, pc, r8, lsr #6
        mov     r0, r0

        mov     pc, lr                          @ CP#0
        b       do_fpe                          @ CP#1 (FPE)
        b       do_fpe                          @ CP#2 (FPE)
        mov     pc, lr                          @ CP#3
#ifdef CONFIG_CRUNCH
        b       crunch_task_enable              @ CP#4 (MaverickCrunch)
        b       crunch_task_enable              @ CP#5 (MaverickCrunch)
        b       crunch_task_enable              @ CP#6 (MaverickCrunch)
#else
        mov     pc, lr                          @ CP#4
        mov     pc, lr                          @ CP#5
        mov     pc, lr                          @ CP#6
#endif
        mov     pc, lr                          @ CP#7
        mov     pc, lr                          @ CP#8
        mov     pc, lr                          @ CP#9
#ifdef CONFIG_VFP
        b       do_vfp                          @ CP#10 (VFP)
        b       do_vfp                          @ CP#11 (VFP)
#else
        mov     pc, lr                          @ CP#10 (VFP)
        mov     pc, lr                          @ CP#11 (VFP)
#endif
        mov     pc, lr                          @ CP#12
        mov     pc, lr                          @ CP#13
        mov     pc, lr                          @ CP#14 (Debug)
        mov     pc, lr                          @ CP#15 (Control)

do_fpe:
        enable_irq
        ldr     r4, .LCfp
        add     r10, r10, #TI_FPSTATE           @ r10 = workspace
        ldr     pc, [r4]                        @ Call FP module USR entry point

/*
 * The FP module is called with these registers set:
 *  r0  = instruction
 *  r2  = PC+4
 *  r9  = normal "successful" return address
 *  r10 = FP workspace
 *  lr  = unrecognised FP instruction return address
 */

        .data
ENTRY(fp_enter)
        .word   no_fp
        .text

no_fp:  mov     pc, lr

__und_usr_unknown:
        mov     r0, sp
        adr     lr, ret_from_exception
        b       do_undefinstr

        .align  5
__pabt_usr:
        usr_entry

        enable_irq                              @ Enable interrupts
        mov     r0, r2                          @ address (pc)
        mov     r1, sp                          @ regs
        bl      do_PrefetchAbort                @ call abort handler
        /* fall through */
/*
 * This is the return code to user mode for abort handlers
 */
ENTRY(ret_from_exception)
        get_thread_info tsk
        mov     why, #0
        b       ret_to_user

/*
 * Register switch for ARMv3 and ARMv4 processors
 * r0 = previous task_struct, r1 = previous thread_info, r2 = next thread_info
 * previous and next are guaranteed not to be the same.
 */
ENTRY(__switch_to)
        add     ip, r1, #TI_CPU_SAVE
        ldr     r3, [r2, #TI_TP_VALUE]
        stmia   ip!, {r4 - sl, fp, sp, lr}      @ Store most regs on stack
#ifdef CONFIG_MMU
        ldr     r6, [r2, #TI_CPU_DOMAIN]
#endif
#if __LINUX_ARM_ARCH__ >= 6
#ifdef CONFIG_CPU_32v6K
        clrex
#else
        strex   r5, r4, [ip]                    @ Clear exclusive monitor
#endif
#endif
#if defined(CONFIG_HAS_TLS_REG)
        mcr     p15, 0, r3, c13, c0, 3          @ set TLS register
#elif !defined(CONFIG_TLS_REG_EMUL)
        mov     r4, #0xffff0fff
        str     r3, [r4, #-15]                  @ TLS val at 0xffff0ff0
#endif
#ifdef CONFIG_MMU
        mcr     p15, 0, r6, c3, c0, 0           @ Set domain register
#endif
        mov     r5, r0
        add     r4, r2, #TI_CPU_SAVE
        ldr     r0, =thread_notify_head
        mov     r1, #THREAD_NOTIFY_SWITCH
        bl      atomic_notifier_call_chain
        mov     r0, r5
        ldmia   r4, {r4 - sl, fp, sp, pc}       @ Load all regs saved previously

        __INIT

/*
 * User helpers.
 *
 * These are segment of kernel provided user code reachable from user space
 * at a fixed address in kernel memory.  This is used to provide user space
 * with some operations which require kernel help because of unimplemented
 * native feature and/or instructions in many ARM CPUs. The idea is for
 * this code to be executed directly in user mode for best efficiency but
 * which is too intimate with the kernel counter part to be left to user
 * libraries.  In fact this code might even differ from one CPU to another
 * depending on the available  instruction set and restrictions like on
 * SMP systems.  In other words, the kernel reserves the right to change
 * this code as needed without warning. Only the entry points and their
 * results are guaranteed to be stable.
 *
 * Each segment is 32-byte aligned and will be moved to the top of the high
 * vector page.  New segments (if ever needed) must be added in front of
 * existing ones.  This mechanism should be used only for things that are
 * really small and justified, and not be abused freely.
 *
 * User space is expected to implement those things inline when optimizing
 * for a processor that has the necessary native support, but only if such
 * resulting binaries are already to be incompatible with earlier ARM
 * processors due to the use of unsupported instructions other than what
 * is provided here.  In other words don't make binaries unable to run on
 * earlier processors just for the sake of not using these kernel helpers
 * if your compiled code is not going to use the new instructions for other
 * purpose.
 */

        .macro  usr_ret, reg
#ifdef CONFIG_ARM_THUMB
        bx      \reg
#else
        mov     pc, \reg
#endif
        .endm

        .align  5
        .globl  __kuser_helper_start
__kuser_helper_start:

/*
 * Reference prototype:
 *
 *      void __kernel_memory_barrier(void)
 *
 * Input:
 *
 *      lr = return address
 *
 * Output:
 *
 *      none
 *
 * Clobbered:
 *
 *      none
 *
 * Definition and user space usage example:
 *
 *      typedef void (__kernel_dmb_t)(void);
 *      #define __kernel_dmb (*(__kernel_dmb_t *)0xffff0fa0)
 *
 * Apply any needed memory barrier to preserve consistency with data modified
 * manually and __kuser_cmpxchg usage.
 *
 * This could be used as follows:
 *
 * #define __kernel_dmb() \
 *         asm volatile ( "mov r0, #0xffff0fff; mov lr, pc; sub pc, r0, #95" \
 *              : : : "r0", "lr","cc" )
 */

__kuser_memory_barrier:                         @ 0xffff0fa0

#if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_SMP)
        mcr     p15, 0, r0, c7, c10, 5  @ dmb
#endif
        usr_ret lr

        .align  5

/*
 * Reference prototype:
 *
 *      int __kernel_cmpxchg(int oldval, int newval, int *ptr)
 *
 * Input:
 *
 *      r0 = oldval
 *      r1 = newval
 *      r2 = ptr
 *      lr = return address
 *
 * Output:
 *
 *      r0 = returned value (zero or non-zero)
 *      C flag = set if r0 == 0, clear if r0 != 0
 *
 * Clobbered:
 *
 *      r3, ip, flags
 *
 * Definition and user space usage example:
 *
 *      typedef int (__kernel_cmpxchg_t)(int oldval, int newval, int *ptr);
 *      #define __kernel_cmpxchg (*(__kernel_cmpxchg_t *)0xffff0fc0)
 *
 * Atomically store newval in *ptr if *ptr is equal to oldval for user space.
 * Return zero if *ptr was changed or non-zero if no exchange happened.
 * The C flag is also set if *ptr was changed to allow for assembly
 * optimization in the calling code.
 *
 * Notes:
 *
 *    - This routine already includes memory barriers as needed.
 *
 * For example, a user space atomic_add implementation could look like this:
 *
 * #define atomic_add(ptr, val) \
 *      ({ register unsigned int *__ptr asm("r2") = (ptr); \
 *         register unsigned int __result asm("r1"); \
 *         asm volatile ( \
 *             "1: @ atomic_add\n\t" \
 *             "ldr     r0, [r2]\n\t" \
 *             "mov     r3, #0xffff0fff\n\t" \
 *             "add     lr, pc, #4\n\t" \
 *             "add     r1, r0, %2\n\t" \
 *             "add     pc, r3, #(0xffff0fc0 - 0xffff0fff)\n\t" \
 *             "bcc     1b" \
 *             : "=&r" (__result) \
 *             : "r" (__ptr), "rIL" (val) \
 *             : "r0","r3","ip","lr","cc","memory" ); \
 *         __result; })
 */

__kuser_cmpxchg:                                @ 0xffff0fc0

#if defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)

        /*
         * Poor you.  No fast solution possible...
         * The kernel itself must perform the operation.
         * A special ghost syscall is used for that (see traps.c).
         */
        stmfd   sp!, {r7, lr}
        mov     r7, #0xff00             @ 0xfff0 into r7 for EABI
        orr     r7, r7, #0xf0
        swi     #0x9ffff0
        ldmfd   sp!, {r7, pc}

#elif __LINUX_ARM_ARCH__ < 6

#ifdef CONFIG_MMU

        /*
         * The only thing that can break atomicity in this cmpxchg
         * implementation is either an IRQ or a data abort exception
         * causing another process/thread to be scheduled in the middle
         * of the critical sequence.  To prevent this, code is added to
         * the IRQ and data abort exception handlers to set the pc back
         * to the beginning of the critical section if it is found to be
         * within that critical section (see kuser_cmpxchg_fixup).
         */
1:      ldr     r3, [r2]                        @ load current val
        subs    r3, r3, r0                      @ compare with oldval
2:      streq   r1, [r2]                        @ store newval if eq
        rsbs    r0, r3, #0                      @ set return val and C flag
        usr_ret lr

        .text
kuser_cmpxchg_fixup:
        @ Called from kuser_cmpxchg_check macro.
        @ r2 = address of interrupted insn (must be preserved).
        @ sp = saved regs. r7 and r8 are clobbered.
        @ 1b = first critical insn, 2b = last critical insn.
        @ If r2 >= 1b and r2 <= 2b then saved pc_usr is set to 1b.
        mov     r7, #0xffff0fff
        sub     r7, r7, #(0xffff0fff - (0xffff0fc0 + (1b - __kuser_cmpxchg)))
        subs    r8, r2, r7
        rsbcss  r8, r8, #(2b - 1b)
        strcs   r7, [sp, #S_PC]
        mov     pc, lr
        .previous

#else
#warning "NPTL on non MMU needs fixing"
        mov     r0, #-1
        adds    r0, r0, #0
        usr_ret lr
#endif

#else

#ifdef CONFIG_SMP
        mcr     p15, 0, r0, c7, c10, 5  @ dmb
#endif
1:      ldrex   r3, [r2]
        subs    r3, r3, r0
        strexeq r3, r1, [r2]
        teqeq   r3, #1
        beq     1b
        rsbs    r0, r3, #0
        /* beware -- each __kuser slot must be 8 instructions max */
#ifdef CONFIG_SMP
        b       __kuser_memory_barrier
#else
        usr_ret lr
#endif

#endif

        .align  5

/*
 * Reference prototype:
 *
 *      int __kernel_get_tls(void)
 *
 * Input:
 *
 *      lr = return address
 *
 * Output:
 *
 *      r0 = TLS value
 *
 * Clobbered:
 *
 *      none
 *
 * Definition and user space usage example:
 *
 *      typedef int (__kernel_get_tls_t)(void);
 *      #define __kernel_get_tls (*(__kernel_get_tls_t *)0xffff0fe0)
 *
 * Get the TLS value as previously set via the __ARM_NR_set_tls syscall.
 *
 * This could be used as follows:
 *
 * #define __kernel_get_tls() \
 *      ({ register unsigned int __val asm("r0"); \
 *         asm( "mov r0, #0xffff0fff; mov lr, pc; sub pc, r0, #31" \
 *              : "=r" (__val) : : "lr","cc" ); \
 *         __val; })
 */

__kuser_get_tls:                                @ 0xffff0fe0

#if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL)
        ldr     r0, [pc, #(16 - 8)]             @ TLS stored at 0xffff0ff0
#else
        mrc     p15, 0, r0, c13, c0, 3          @ read TLS register
#endif
        usr_ret lr

        .rep    5
        .word   0                       @ pad up to __kuser_helper_version
        .endr

/*
 * Reference declaration:
 *
 *      extern unsigned int __kernel_helper_version;
 *
 * Definition and user space usage example:
 *
 *      #define __kernel_helper_version (*(unsigned int *)0xffff0ffc)
 *
 * User space may read this to determine the curent number of helpers
 * available.
 */

__kuser_helper_version:                         @ 0xffff0ffc
        .word   ((__kuser_helper_end - __kuser_helper_start) >> 5)

        .globl  __kuser_helper_end
__kuser_helper_end:


/*
 * Vector stubs.
 *
 * This code is copied to 0xffff0200 so we can use branches in the
 * vectors, rather than ldr's.  Note that this code must not
 * exceed 0x300 bytes.
 *
 * Common stub entry macro:
 *   Enter in IRQ mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
 *
 * SP points to a minimal amount of processor-private memory, the address
 * of which is copied into r0 for the mode specific abort handler.
 */
        .macro  vector_stub, name, mode, correction=0
        .align  5

vector_\name:
        .if \correction
        sub     lr, lr, #\correction
        .endif

        @
        @ Save r0, lr_<exception> (parent PC) and spsr_<exception>
        @ (parent CPSR)
        @
        stmia   sp, {r0, lr}            @ save r0, lr
        mrs     lr, spsr
        str     lr, [sp, #8]            @ save spsr

        @
        @ Prepare for SVC32 mode.  IRQs remain disabled.
        @
        mrs     r0, cpsr
        eor     r0, r0, #(\mode ^ SVC_MODE)
        msr     spsr_cxsf, r0

        @
        @ the branch table must immediately follow this code
        @
        and     lr, lr, #0x0f
        mov     r0, sp
        ldr     lr, [pc, lr, lsl #2]
        movs    pc, lr                  @ branch to handler in SVC mode
        .endm

        .globl  __stubs_start
__stubs_start:
/*
 * Interrupt dispatcher
 */
        vector_stub     irq, IRQ_MODE, 4

        .long   __irq_usr                       @  0  (USR_26 / USR_32)
        .long   __irq_invalid                   @  1  (FIQ_26 / FIQ_32)
        .long   __irq_invalid                   @  2  (IRQ_26 / IRQ_32)
        .long   __irq_svc                       @  3  (SVC_26 / SVC_32)
        .long   __irq_invalid                   @  4
        .long   __irq_invalid                   @  5
        .long   __irq_invalid                   @  6
        .long   __irq_invalid                   @  7
        .long   __irq_invalid                   @  8
        .long   __irq_invalid                   @  9
        .long   __irq_invalid                   @  a
        .long   __irq_invalid                   @  b
        .long   __irq_invalid                   @  c
        .long   __irq_invalid                   @  d
        .long   __irq_invalid                   @  e
        .long   __irq_invalid                   @  f

/*
 * Data abort dispatcher
 * Enter in ABT mode, spsr = USR CPSR, lr = USR PC
 */
        vector_stub     dabt, ABT_MODE, 8

        .long   __dabt_usr                      @  0  (USR_26 / USR_32)
        .long   __dabt_invalid                  @  1  (FIQ_26 / FIQ_32)
        .long   __dabt_invalid                  @  2  (IRQ_26 / IRQ_32)
        .long   __dabt_svc                      @  3  (SVC_26 / SVC_32)
        .long   __dabt_invalid                  @  4
        .long   __dabt_invalid                  @  5
        .long   __dabt_invalid                  @  6
        .long   __dabt_invalid                  @  7
        .long   __dabt_invalid                  @  8
        .long   __dabt_invalid                  @  9
        .long   __dabt_invalid                  @  a
        .long   __dabt_invalid                  @  b
        .long   __dabt_invalid                  @  c
        .long   __dabt_invalid                  @  d
        .long   __dabt_invalid                  @  e
        .long   __dabt_invalid                  @  f

/*
 * Prefetch abort dispatcher
 * Enter in ABT mode, spsr = USR CPSR, lr = USR PC
 */
        vector_stub     pabt, ABT_MODE, 4

        .long   __pabt_usr                      @  0 (USR_26 / USR_32)
        .long   __pabt_invalid                  @  1 (FIQ_26 / FIQ_32)
        .long   __pabt_invalid                  @  2 (IRQ_26 / IRQ_32)
        .long   __pabt_svc                      @  3 (SVC_26 / SVC_32)
        .long   __pabt_invalid                  @  4
        .long   __pabt_invalid                  @  5
        .long   __pabt_invalid                  @  6
        .long   __pabt_invalid                  @  7
        .long   __pabt_invalid                  @  8
        .long   __pabt_invalid                  @  9
        .long   __pabt_invalid                  @  a
        .long   __pabt_invalid                  @  b
        .long   __pabt_invalid                  @  c
        .long   __pabt_invalid                  @  d
        .long   __pabt_invalid                  @  e
        .long   __pabt_invalid                  @  f

/*
 * Undef instr entry dispatcher
 * Enter in UND mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
 */
        vector_stub     und, UND_MODE

        .long   __und_usr                       @  0 (USR_26 / USR_32)
        .long   __und_invalid                   @  1 (FIQ_26 / FIQ_32)
        .long   __und_invalid                   @  2 (IRQ_26 / IRQ_32)
        .long   __und_svc                       @  3 (SVC_26 / SVC_32)
        .long   __und_invalid                   @  4
        .long   __und_invalid                   @  5
        .long   __und_invalid                   @  6
        .long   __und_invalid                   @  7
        .long   __und_invalid                   @  8
        .long   __und_invalid                   @  9
        .long   __und_invalid                   @  a
        .long   __und_invalid                   @  b
        .long   __und_invalid                   @  c
        .long   __und_invalid                   @  d
        .long   __und_invalid                   @  e
        .long   __und_invalid                   @  f

        .align  5

/*=============================================================================
 * Undefined FIQs
 *-----------------------------------------------------------------------------
 * Enter in FIQ mode, spsr = ANY CPSR, lr = ANY PC
 * MUST PRESERVE SVC SPSR, but need to switch to SVC mode to show our msg.
 * Basically to switch modes, we *HAVE* to clobber one register...  brain
 * damage alert!  I don't think that we can execute any code in here in any
 * other mode than FIQ...  Ok you can switch to another mode, but you can't
 * get out of that mode without clobbering one register.
 */
vector_fiq:
        disable_fiq
        subs    pc, lr, #4

/*=============================================================================
 * Address exception handler
 *-----------------------------------------------------------------------------
 * These aren't too critical.
 * (they're not supposed to happen, and won't happen in 32-bit data mode).
 */

vector_addrexcptn:
        b       vector_addrexcptn

/*
 * We group all the following data together to optimise
 * for CPUs with separate I & D caches.
 */
        .align  5

.LCvswi:
        .word   vector_swi

        .globl  __stubs_end
__stubs_end:

        .equ    stubs_offset, __vectors_start + 0x200 - __stubs_start

        .globl  __vectors_start
__vectors_start:
        swi     SYS_ERROR0
        b       vector_und + stubs_offset
        ldr     pc, .LCvswi + stubs_offset
        b       vector_pabt + stubs_offset
        b       vector_dabt + stubs_offset
        b       vector_addrexcptn + stubs_offset
        b       vector_irq + stubs_offset
        b       vector_fiq + stubs_offset

        .globl  __vectors_end
__vectors_end:

        .data

        .globl  cr_alignment
        .globl  cr_no_alignment
cr_alignment:
        .space  4
cr_no_alignment:
        .space  4