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[mirror_ubuntu-artful-kernel.git] / arch / tile / kernel / intvec_32.S

/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   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, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 *
 * Linux interrupt vectors.
 */

#include <linux/linkage.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <asm/ptrace.h>
#include <asm/thread_info.h>
#include <asm/irqflags.h>
#include <asm/atomic_32.h>
#include <asm/asm-offsets.h>
#include <hv/hypervisor.h>
#include <arch/abi.h>
#include <arch/interrupts.h>
#include <arch/spr_def.h>

#define PTREGS_PTR(reg, ptreg) addli reg, sp, C_ABI_SAVE_AREA_SIZE + (ptreg)

#define PTREGS_OFFSET_SYSCALL PTREGS_OFFSET_REG(TREG_SYSCALL_NR)

        .macro  push_reg reg, ptr=sp, delta=-4
        {
         sw     \ptr, \reg
         addli  \ptr, \ptr, \delta
        }
        .endm

        .macro  pop_reg reg, ptr=sp, delta=4
        {
         lw     \reg, \ptr
         addli  \ptr, \ptr, \delta
        }
        .endm

        .macro  pop_reg_zero reg, zreg, ptr=sp, delta=4
        {
         move   \zreg, zero
         lw     \reg, \ptr
         addi   \ptr, \ptr, \delta
        }
        .endm

        .macro  push_extra_callee_saves reg
        PTREGS_PTR(\reg, PTREGS_OFFSET_REG(51))
        push_reg r51, \reg
        push_reg r50, \reg
        push_reg r49, \reg
        push_reg r48, \reg
        push_reg r47, \reg
        push_reg r46, \reg
        push_reg r45, \reg
        push_reg r44, \reg
        push_reg r43, \reg
        push_reg r42, \reg
        push_reg r41, \reg
        push_reg r40, \reg
        push_reg r39, \reg
        push_reg r38, \reg
        push_reg r37, \reg
        push_reg r36, \reg
        push_reg r35, \reg
        push_reg r34, \reg, PTREGS_OFFSET_BASE - PTREGS_OFFSET_REG(34)
        .endm

        .macro  panic str
        .pushsection .rodata, "a"
1:
        .asciz  "\str"
        .popsection
        {
         moveli r0, lo16(1b)
        }
        {
         auli   r0, r0, ha16(1b)
         jal    panic
        }
        .endm

#ifdef __COLLECT_LINKER_FEEDBACK__
        .pushsection .text.intvec_feedback,"ax"
intvec_feedback:
        .popsection
#endif

        /*
         * Default interrupt handler.
         *
         * vecnum is where we'll put this code.
         * c_routine is the C routine we'll call.
         *
         * The C routine is passed two arguments:
         * - A pointer to the pt_regs state.
         * - The interrupt vector number.
         *
         * The "processing" argument specifies the code for processing
         * the interrupt. Defaults to "handle_interrupt".
         */
        .macro  int_hand vecnum, vecname, c_routine, processing=handle_interrupt
        .org    (\vecnum << 8)
intvec_\vecname:
        .ifc    \vecnum, INT_SWINT_1
        blz     TREG_SYSCALL_NR_NAME, sys_cmpxchg
        .endif

        /* Temporarily save a register so we have somewhere to work. */

        mtspr   SPR_SYSTEM_SAVE_K_1, r0
        mfspr   r0, SPR_EX_CONTEXT_K_1

        /* The cmpxchg code clears sp to force us to reset it here on fault. */
        {
         bz     sp, 2f
         andi   r0, r0, SPR_EX_CONTEXT_1_1__PL_MASK  /* mask off ICS */
        }

        .ifc    \vecnum, INT_DOUBLE_FAULT
        /*
         * For double-faults from user-space, fall through to the normal
         * register save and stack setup path.  Otherwise, it's the
         * hypervisor giving us one last chance to dump diagnostics, and we
         * branch to the kernel_double_fault routine to do so.
         */
        bz      r0, 1f
        j       _kernel_double_fault
1:
        .else
        /*
         * If we're coming from user-space, then set sp to the top of
         * the kernel stack.  Otherwise, assume sp is already valid.
         */
        {
         bnz    r0, 0f
         move   r0, sp
        }
        .endif

        .ifc    \c_routine, do_page_fault
        /*
         * The page_fault handler may be downcalled directly by the
         * hypervisor even when Linux is running and has ICS set.
         *
         * In this case the contents of EX_CONTEXT_K_1 reflect the
         * previous fault and can't be relied on to choose whether or
         * not to reinitialize the stack pointer.  So we add a test
         * to see whether SYSTEM_SAVE_K_2 has the high bit set,
         * and if so we don't reinitialize sp, since we must be coming
         * from Linux.  (In fact the precise case is !(val & ~1),
         * but any Linux PC has to have the high bit set.)
         *
         * Note that the hypervisor *always* sets SYSTEM_SAVE_K_2 for
         * any path that turns into a downcall to one of our TLB handlers.
         */
        mfspr   r0, SPR_SYSTEM_SAVE_K_2
        {
         blz    r0, 0f    /* high bit in S_S_1_2 is for a PC to use */
         move   r0, sp
        }
        .endif

2:
        /*
         * SYSTEM_SAVE_K_0 holds the cpu number in the low bits, and
         * the current stack top in the higher bits.  So we recover
         * our stack top by just masking off the low bits, then
         * point sp at the top aligned address on the actual stack page.
         */
        mfspr   r0, SPR_SYSTEM_SAVE_K_0
        mm      r0, r0, zero, LOG2_NR_CPU_IDS, 31

0:
        /*
         * Align the stack mod 64 so we can properly predict what
         * cache lines we need to write-hint to reduce memory fetch
         * latency as we enter the kernel.  The layout of memory is
         * as follows, with cache line 0 at the lowest VA, and cache
         * line 4 just below the r0 value this "andi" computes.
         * Note that we never write to cache line 4, and we skip
         * cache line 1 for syscalls.
         *
         *    cache line 4: ptregs padding (two words)
         *    cache line 3: r46...lr, pc, ex1, faultnum, orig_r0, flags, pad
         *    cache line 2: r30...r45
         *    cache line 1: r14...r29
         *    cache line 0: 2 x frame, r0..r13
         */
#if STACK_TOP_DELTA != 64
#error STACK_TOP_DELTA must be 64 for assumptions here and in task_pt_regs()
#endif
        andi    r0, r0, -64

        /*
         * Push the first four registers on the stack, so that we can set
         * them to vector-unique values before we jump to the common code.
         *
         * Registers are pushed on the stack as a struct pt_regs,
         * with the sp initially just above the struct, and when we're
         * done, sp points to the base of the struct, minus
         * C_ABI_SAVE_AREA_SIZE, so we can directly jal to C code.
         *
         * This routine saves just the first four registers, plus the
         * stack context so we can do proper backtracing right away,
         * and defers to handle_interrupt to save the rest.
         * The backtracer needs pc, ex1, lr, sp, r52, and faultnum.
         */
        addli   r0, r0, PTREGS_OFFSET_LR - (PTREGS_SIZE + KSTK_PTREGS_GAP)
        wh64    r0    /* cache line 3 */
        {
         sw     r0, lr
         addli  r0, r0, PTREGS_OFFSET_SP - PTREGS_OFFSET_LR
        }
        {
         sw     r0, sp
         addli  sp, r0, PTREGS_OFFSET_REG(52) - PTREGS_OFFSET_SP
        }
        {
         sw     sp, r52
         addli  sp, sp, PTREGS_OFFSET_REG(1) - PTREGS_OFFSET_REG(52)
        }
        wh64    sp    /* cache line 0 */
        {
         sw     sp, r1
         addli  sp, sp, PTREGS_OFFSET_REG(2) - PTREGS_OFFSET_REG(1)
        }
        {
         sw     sp, r2
         addli  sp, sp, PTREGS_OFFSET_REG(3) - PTREGS_OFFSET_REG(2)
        }
        {
         sw     sp, r3
         addli  sp, sp, PTREGS_OFFSET_PC - PTREGS_OFFSET_REG(3)
        }
        mfspr   r0, SPR_EX_CONTEXT_K_0
        .ifc \processing,handle_syscall
        /*
         * Bump the saved PC by one bundle so that when we return, we won't
         * execute the same swint instruction again.  We need to do this while
         * we're in the critical section.
         */
        addi    r0, r0, 8
        .endif
        {
         sw     sp, r0
         addli  sp, sp, PTREGS_OFFSET_EX1 - PTREGS_OFFSET_PC
        }
        mfspr   r0, SPR_EX_CONTEXT_K_1
        {
         sw     sp, r0
         addi   sp, sp, PTREGS_OFFSET_FAULTNUM - PTREGS_OFFSET_EX1
        /*
         * Use r0 for syscalls so it's a temporary; use r1 for interrupts
         * so that it gets passed through unchanged to the handler routine.
         * Note that the .if conditional confusingly spans bundles.
         */
         .ifc \processing,handle_syscall
         movei  r0, \vecnum
        }
        {
         sw     sp, r0
         .else
         movei  r1, \vecnum
        }
        {
         sw     sp, r1
         .endif
         addli  sp, sp, PTREGS_OFFSET_REG(0) - PTREGS_OFFSET_FAULTNUM
        }
        mfspr   r0, SPR_SYSTEM_SAVE_K_1    /* Original r0 */
        {
         sw     sp, r0
         addi   sp, sp, -PTREGS_OFFSET_REG(0) - 4
        }
        {
         sw     sp, zero        /* write zero into "Next SP" frame pointer */
         addi   sp, sp, -4      /* leave SP pointing at bottom of frame */
        }
        .ifc \processing,handle_syscall
        j       handle_syscall
        .else
        /*
         * Capture per-interrupt SPR context to registers.
         * We overload the meaning of r3 on this path such that if its bit 31
         * is set, we have to mask all interrupts including NMIs before
         * clearing the interrupt critical section bit.
         * See discussion below at "finish_interrupt_save".
         */
        .ifc \c_routine, do_page_fault
        mfspr   r2, SPR_SYSTEM_SAVE_K_3   /* address of page fault */
        mfspr   r3, SPR_SYSTEM_SAVE_K_2   /* info about page fault */
        .else
        .ifc \vecnum, INT_DOUBLE_FAULT
        {
         mfspr  r2, SPR_SYSTEM_SAVE_K_2   /* double fault info from HV */
         movei  r3, 0
        }
        .else
        .ifc \c_routine, do_trap
        {
         mfspr  r2, GPV_REASON
         movei  r3, 0
        }
        .else
        .ifc \c_routine, handle_perf_interrupt
        {
         mfspr  r2, PERF_COUNT_STS
         movei  r3, -1   /* not used, but set for consistency */
        }
        .else
        .ifc \c_routine, handle_perf_interrupt
        {
         mfspr  r2, AUX_PERF_COUNT_STS
         movei  r3, -1   /* not used, but set for consistency */
        }
        .else
        movei   r3, 0
        .endif
        .endif
        .endif
        .endif
        .endif
        /* Put function pointer in r0 */
        moveli  r0, lo16(\c_routine)
        {
         auli   r0, r0, ha16(\c_routine)
         j       \processing
        }
        .endif
        ENDPROC(intvec_\vecname)

#ifdef __COLLECT_LINKER_FEEDBACK__
        .pushsection .text.intvec_feedback,"ax"
        .org    (\vecnum << 5)
        FEEDBACK_ENTER_EXPLICIT(intvec_\vecname, .intrpt, 1 << 8)
        jrp     lr
        .popsection
#endif

        .endm


        /*
         * Save the rest of the registers that we didn't save in the actual
         * vector itself.  We can't use r0-r10 inclusive here.
         */
        .macro  finish_interrupt_save, function

        /* If it's a syscall, save a proper orig_r0, otherwise just zero. */
        PTREGS_PTR(r52, PTREGS_OFFSET_ORIG_R0)
        {
         .ifc \function,handle_syscall
         sw     r52, r0
         .else
         sw     r52, zero
         .endif
         PTREGS_PTR(r52, PTREGS_OFFSET_TP)
        }

        /*
         * For ordinary syscalls, we save neither caller- nor callee-
         * save registers, since the syscall invoker doesn't expect the
         * caller-saves to be saved, and the called kernel functions will
         * take care of saving the callee-saves for us.
         *
         * For interrupts we save just the caller-save registers.  Saving
         * them is required (since the "caller" can't save them).  Again,
         * the called kernel functions will restore the callee-save
         * registers for us appropriately.
         *
         * On return, we normally restore nothing special for syscalls,
         * and just the caller-save registers for interrupts.
         *
         * However, there are some important caveats to all this:
         *
         * - We always save a few callee-save registers to give us
         *   some scratchpad registers to carry across function calls.
         *
         * - fork/vfork/etc require us to save all the callee-save
         *   registers, which we do in PTREGS_SYSCALL_ALL_REGS, below.
         *
         * - We always save r0..r5 and r10 for syscalls, since we need
         *   to reload them a bit later for the actual kernel call, and
         *   since we might need them for -ERESTARTNOINTR, etc.
         *
         * - Before invoking a signal handler, we save the unsaved
         *   callee-save registers so they are visible to the
         *   signal handler or any ptracer.
         *
         * - If the unsaved callee-save registers are modified, we set
         *   a bit in pt_regs so we know to reload them from pt_regs
         *   and not just rely on the kernel function unwinding.
         *   (Done for ptrace register writes and SA_SIGINFO handler.)
         */
        {
         sw     r52, tp
         PTREGS_PTR(r52, PTREGS_OFFSET_REG(33))
        }
        wh64    r52    /* cache line 2 */
        push_reg r33, r52
        push_reg r32, r52
        push_reg r31, r52
        .ifc \function,handle_syscall
        push_reg r30, r52, PTREGS_OFFSET_SYSCALL - PTREGS_OFFSET_REG(30)
        push_reg TREG_SYSCALL_NR_NAME, r52, \
          PTREGS_OFFSET_REG(5) - PTREGS_OFFSET_SYSCALL
        .else

        push_reg r30, r52, PTREGS_OFFSET_REG(29) - PTREGS_OFFSET_REG(30)
        wh64    r52    /* cache line 1 */
        push_reg r29, r52
        push_reg r28, r52
        push_reg r27, r52
        push_reg r26, r52
        push_reg r25, r52
        push_reg r24, r52
        push_reg r23, r52
        push_reg r22, r52
        push_reg r21, r52
        push_reg r20, r52
        push_reg r19, r52
        push_reg r18, r52
        push_reg r17, r52
        push_reg r16, r52
        push_reg r15, r52
        push_reg r14, r52
        push_reg r13, r52
        push_reg r12, r52
        push_reg r11, r52
        push_reg r10, r52
        push_reg r9, r52
        push_reg r8, r52
        push_reg r7, r52
        push_reg r6, r52

        .endif

        push_reg r5, r52
        sw      r52, r4

        /* Load tp with our per-cpu offset. */
#ifdef CONFIG_SMP
        {
         mfspr  r20, SPR_SYSTEM_SAVE_K_0
         moveli r21, lo16(__per_cpu_offset)
        }
        {
         auli   r21, r21, ha16(__per_cpu_offset)
         mm     r20, r20, zero, 0, LOG2_NR_CPU_IDS-1
        }
        s2a     r20, r20, r21
        lw      tp, r20
#else
        move    tp, zero
#endif

        /*
         * If we will be returning to the kernel, we will need to
         * reset the interrupt masks to the state they had before.
         * Set DISABLE_IRQ in flags iff we came from PL1 with irqs disabled.
         * We load flags in r32 here so we can jump to .Lrestore_regs
         * directly after do_page_fault_ics() if necessary.
         */
        mfspr   r32, SPR_EX_CONTEXT_K_1
        {
         andi   r32, r32, SPR_EX_CONTEXT_1_1__PL_MASK  /* mask off ICS */
         PTREGS_PTR(r21, PTREGS_OFFSET_FLAGS)
        }
        bzt     r32, 1f       /* zero if from user space */
        IRQS_DISABLED(r32)    /* zero if irqs enabled */
#if PT_FLAGS_DISABLE_IRQ != 1
# error Value of IRQS_DISABLED used to set PT_FLAGS_DISABLE_IRQ; fix
#endif
1:
        .ifnc \function,handle_syscall
        /* Record the fact that we saved the caller-save registers above. */
        ori     r32, r32, PT_FLAGS_CALLER_SAVES
        .endif
        sw      r21, r32

#ifdef __COLLECT_LINKER_FEEDBACK__
        /*
         * Notify the feedback routines that we were in the
         * appropriate fixed interrupt vector area.  Note that we
         * still have ICS set at this point, so we can't invoke any
         * atomic operations or we will panic.  The feedback
         * routines internally preserve r0..r10 and r30 up.
         */
        .ifnc \function,handle_syscall
        shli    r20, r1, 5
        .else
        moveli  r20, INT_SWINT_1 << 5
        .endif
        addli   r20, r20, lo16(intvec_feedback)
        auli    r20, r20, ha16(intvec_feedback)
        jalr    r20

        /* And now notify the feedback routines that we are here. */
        FEEDBACK_ENTER(\function)
#endif

        /*
         * we've captured enough state to the stack (including in
         * particular our EX_CONTEXT state) that we can now release
         * the interrupt critical section and replace it with our
         * standard "interrupts disabled" mask value.  This allows
         * synchronous interrupts (and profile interrupts) to punch
         * through from this point onwards.
         *
         * If bit 31 of r3 is set during a non-NMI interrupt, we know we
         * are on the path where the hypervisor has punched through our
         * ICS with a page fault, so we call out to do_page_fault_ics()
         * to figure out what to do with it.  If the fault was in
         * an atomic op, we unlock the atomic lock, adjust the
         * saved register state a little, and return "zero" in r4,
         * falling through into the normal page-fault interrupt code.
         * If the fault was in a kernel-space atomic operation, then
         * do_page_fault_ics() resolves it itself, returns "one" in r4,
         * and as a result goes directly to restoring registers and iret,
         * without trying to adjust the interrupt masks at all.
         * The do_page_fault_ics() API involves passing and returning
         * a five-word struct (in registers) to avoid writing the
         * save and restore code here.
         */
        .ifc \function,handle_nmi
        IRQ_DISABLE_ALL(r20)
        .else
        .ifnc \function,handle_syscall
        bgezt   r3, 1f
        {
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
         jal    do_page_fault_ics
        }
        FEEDBACK_REENTER(\function)
        bzt     r4, 1f
        j       .Lrestore_regs
1:
        .endif
        IRQ_DISABLE(r20, r21)
        .endif
        mtspr   INTERRUPT_CRITICAL_SECTION, zero

        /*
         * Prepare the first 256 stack bytes to be rapidly accessible
         * without having to fetch the background data.  We don't really
         * know how far to write-hint, but kernel stacks generally
         * aren't that big, and write-hinting here does take some time.
         */
        addi    r52, sp, -64
        {
         wh64   r52
         addi   r52, r52, -64
        }
        {
         wh64   r52
         addi   r52, r52, -64
        }
        {
         wh64   r52
         addi   r52, r52, -64
        }
        wh64    r52

#if defined(CONFIG_TRACE_IRQFLAGS) || defined(CONFIG_CONTEXT_TRACKING)
        .ifnc \function,handle_nmi
        /*
         * We finally have enough state set up to notify the irq
         * tracing code that irqs were disabled on entry to the handler.
         * The TRACE_IRQS_OFF call clobbers registers r0-r29.
         * For syscalls, we already have the register state saved away
         * on the stack, so we don't bother to do any register saves here,
         * and later we pop the registers back off the kernel stack.
         * For interrupt handlers, save r0-r3 in callee-saved registers.
         */
        .ifnc \function,handle_syscall
        { move r30, r0; move r31, r1 }
        { move r32, r2; move r33, r3 }
        .endif
        TRACE_IRQS_OFF
#ifdef CONFIG_CONTEXT_TRACKING
        jal     context_tracking_user_exit
#endif
        .ifnc \function,handle_syscall
        { move r0, r30; move r1, r31 }
        { move r2, r32; move r3, r33 }
        .endif
        .endif
#endif

        .endm

        .macro  check_single_stepping, kind, not_single_stepping
        /*
         * Check for single stepping in user-level priv
         *   kind can be "normal", "ill", or "syscall"
         * At end, if fall-thru
         *   r29: thread_info->step_state
         *   r28: &pt_regs->pc
         *   r27: pt_regs->pc
         *   r26: thread_info->step_state->buffer
         */

        /* Check for single stepping */
        GET_THREAD_INFO(r29)
        {
         /* Get pointer to field holding step state */
         addi   r29, r29, THREAD_INFO_STEP_STATE_OFFSET

         /* Get pointer to EX1 in register state */
         PTREGS_PTR(r27, PTREGS_OFFSET_EX1)
        }
        {
         /* Get pointer to field holding PC */
         PTREGS_PTR(r28, PTREGS_OFFSET_PC)

         /* Load the pointer to the step state */
         lw     r29, r29
        }
        /* Load EX1 */
        lw      r27, r27
        {
         /* Points to flags */
         addi   r23, r29, SINGLESTEP_STATE_FLAGS_OFFSET

         /* No single stepping if there is no step state structure */
         bzt    r29, \not_single_stepping
        }
        {
         /* mask off ICS and any other high bits */
         andi   r27, r27, SPR_EX_CONTEXT_1_1__PL_MASK

         /* Load pointer to single step instruction buffer */
         lw     r26, r29
        }
        /* Check priv state */
        bnz     r27, \not_single_stepping

        /* Get flags */
        lw      r22, r23
        {
         /* Branch if single-step mode not enabled */
         bbnst  r22, \not_single_stepping

         /* Clear enabled flag */
         andi   r22, r22, ~SINGLESTEP_STATE_MASK_IS_ENABLED
        }
        .ifc \kind,normal
        {
         /* Load PC */
         lw     r27, r28

         /* Point to the entry containing the original PC */
         addi   r24, r29, SINGLESTEP_STATE_ORIG_PC_OFFSET
        }
        {
         /* Disable single stepping flag */
         sw     r23, r22
        }
        {
         /* Get the original pc */
         lw     r24, r24

         /* See if the PC is at the start of the single step buffer */
         seq    r25, r26, r27
        }
        /*
         * NOTE: it is really expected that the PC be in the single step buffer
         *       at this point
         */
        bzt     r25, \not_single_stepping

        /* Restore the original PC */
        sw      r28, r24
        .else
        .ifc \kind,syscall
        {
         /* Load PC */
         lw     r27, r28

         /* Point to the entry containing the next PC */
         addi   r24, r29, SINGLESTEP_STATE_NEXT_PC_OFFSET
        }
        {
         /* Increment the stopped PC by the bundle size */
         addi   r26, r26, 8

         /* Disable single stepping flag */
         sw     r23, r22
        }
        {
         /* Get the next pc */
         lw     r24, r24

         /*
          * See if the PC is one bundle past the start of the
          * single step buffer
          */
         seq    r25, r26, r27
        }
        {
         /*
          * NOTE: it is really expected that the PC be in the
          * single step buffer at this point
          */
         bzt    r25, \not_single_stepping
        }
        /* Set to the next PC */
        sw      r28, r24
        .else
        {
         /* Point to 3rd bundle in buffer */
         addi   r25, r26, 16

         /* Load PC */
         lw      r27, r28
        }
        {
         /* Disable single stepping flag */
         sw      r23, r22

         /* See if the PC is in the single step buffer */
         slte_u  r24, r26, r27
        }
        {
         slte_u r25, r27, r25

         /*
          * NOTE: it is really expected that the PC be in the
          * single step buffer at this point
          */
         bzt    r24, \not_single_stepping
        }
        bzt     r25, \not_single_stepping
        .endif
        .endif
        .endm

        /*
         * Redispatch a downcall.
         */
        .macro  dc_dispatch vecnum, vecname
        .org    (\vecnum << 8)
intvec_\vecname:
        j       _hv_downcall_dispatch
        ENDPROC(intvec_\vecname)
        .endm

        /*
         * Common code for most interrupts.  The C function we're eventually
         * going to is in r0, and the faultnum is in r1; the original
         * values for those registers are on the stack.
         */
        .pushsection .text.handle_interrupt,"ax"
handle_interrupt:
        finish_interrupt_save handle_interrupt

        /*
         * Check for if we are single stepping in user level. If so, then
         * we need to restore the PC.
         */

        check_single_stepping normal, .Ldispatch_interrupt
.Ldispatch_interrupt:

        /* Jump to the C routine; it should enable irqs as soon as possible. */
        {
         jalr   r0
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
        }
        FEEDBACK_REENTER(handle_interrupt)
        {
         movei  r30, 0   /* not an NMI */
         j      interrupt_return
        }
        STD_ENDPROC(handle_interrupt)

/*
 * This routine takes a boolean in r30 indicating if this is an NMI.
 * If so, we also expect a boolean in r31 indicating whether to
 * re-enable the oprofile interrupts.
 *
 * Note that .Lresume_userspace is jumped to directly in several
 * places, and we need to make sure r30 is set correctly in those
 * callers as well.
 */
STD_ENTRY(interrupt_return)
        /* If we're resuming to kernel space, don't check thread flags. */
        {
         bnz    r30, .Lrestore_all  /* NMIs don't special-case user-space */
         PTREGS_PTR(r29, PTREGS_OFFSET_EX1)
        }
        lw      r29, r29
        andi    r29, r29, SPR_EX_CONTEXT_1_1__PL_MASK  /* mask off ICS */
        bzt     r29, .Lresume_userspace

#ifdef CONFIG_PREEMPT
        /* Returning to kernel space. Check if we need preemption. */
        GET_THREAD_INFO(r29)
        addli   r28, r29, THREAD_INFO_FLAGS_OFFSET
        {
         lw     r28, r28
         addli  r29, r29, THREAD_INFO_PREEMPT_COUNT_OFFSET
        }
        {
         andi   r28, r28, _TIF_NEED_RESCHED
         lw     r29, r29
        }
        bzt     r28, 1f
        bnz     r29, 1f
        /* Disable interrupts explicitly for preemption. */
        IRQ_DISABLE(r20,r21)
        TRACE_IRQS_OFF
        jal     preempt_schedule_irq
        FEEDBACK_REENTER(interrupt_return)
1:
#endif

        /* If we're resuming to _cpu_idle_nap, bump PC forward by 8. */
        {
         PTREGS_PTR(r29, PTREGS_OFFSET_PC)
         moveli r27, lo16(_cpu_idle_nap)
        }
        {
         lw     r28, r29
         auli   r27, r27, ha16(_cpu_idle_nap)
        }
        {
         seq    r27, r27, r28
        }
        {
         bbns   r27, .Lrestore_all
         addi   r28, r28, 8
        }
        sw      r29, r28
        j       .Lrestore_all

.Lresume_userspace:
        FEEDBACK_REENTER(interrupt_return)

        /*
         * Disable interrupts so as to make sure we don't
         * miss an interrupt that sets any of the thread flags (like
         * need_resched or sigpending) between sampling and the iret.
         * Routines like schedule() or do_signal() may re-enable
         * interrupts before returning.
         */
        IRQ_DISABLE(r20, r21)
        TRACE_IRQS_OFF  /* Note: clobbers registers r0-r29 */

        /*
         * See if there are any work items (including single-shot items)
         * to do.  If so, save the callee-save registers to pt_regs
         * and then dispatch to C code.
         */
        GET_THREAD_INFO(r21)
        {
         addi   r22, r21, THREAD_INFO_FLAGS_OFFSET
         moveli r20, lo16(_TIF_ALLWORK_MASK)
        }
        {
         lw     r22, r22
         auli   r20, r20, ha16(_TIF_ALLWORK_MASK)
        }
        and     r1, r22, r20
        {
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
         bzt    r1, .Lrestore_all
        }
        push_extra_callee_saves r0
        jal     prepare_exit_to_usermode

        /*
         * In the NMI case we
         * omit the call to single_process_check_nohz, which normally checks
         * to see if we should start or stop the scheduler tick, because
         * we can't call arbitrary Linux code from an NMI context.
         * We always call the homecache TLB deferral code to re-trigger
         * the deferral mechanism.
         *
         * The other chunk of responsibility this code has is to reset the
         * interrupt masks appropriately to reset irqs and NMIs.  We have
         * to call TRACE_IRQS_OFF and TRACE_IRQS_ON to support all the
         * lockdep-type stuff, but we can't set ICS until afterwards, since
         * ICS can only be used in very tight chunks of code to avoid
         * tripping over various assertions that it is off.
         *
         * (There is what looks like a window of vulnerability here since
         * we might take a profile interrupt between the two SPR writes
         * that set the mask, but since we write the low SPR word first,
         * and our interrupt entry code checks the low SPR word, any
         * profile interrupt will actually disable interrupts in both SPRs
         * before returning, which is OK.)
         */
.Lrestore_all:
        PTREGS_PTR(r0, PTREGS_OFFSET_EX1)
        {
         lw     r0, r0
         PTREGS_PTR(r32, PTREGS_OFFSET_FLAGS)
        }
        {
         andi   r0, r0, SPR_EX_CONTEXT_1_1__PL_MASK
         lw     r32, r32
        }
        bnz    r0, 1f
        j       2f
#if PT_FLAGS_DISABLE_IRQ != 1
# error Assuming PT_FLAGS_DISABLE_IRQ == 1 so we can use bbnst below
#endif
1:      bbnst   r32, 2f
        IRQ_DISABLE(r20,r21)
        TRACE_IRQS_OFF
        movei   r0, 1
        mtspr   INTERRUPT_CRITICAL_SECTION, r0
        bzt     r30, .Lrestore_regs
        j       3f
2:      TRACE_IRQS_ON
        movei   r0, 1
        mtspr   INTERRUPT_CRITICAL_SECTION, r0
        IRQ_ENABLE(r20, r21)
        bzt     r30, .Lrestore_regs
3:

        /* We are relying on INT_PERF_COUNT at 33, and AUX_PERF_COUNT at 48 */
        {
         moveli r0, lo16(1 << (INT_PERF_COUNT - 32))
         bz     r31, .Lrestore_regs
        }
        auli    r0, r0, ha16(1 << (INT_AUX_PERF_COUNT - 32))
        mtspr   SPR_INTERRUPT_MASK_RESET_K_1, r0

        /*
         * We now commit to returning from this interrupt, since we will be
         * doing things like setting EX_CONTEXT SPRs and unwinding the stack
         * frame.  No calls should be made to any other code after this point.
         * This code should only be entered with ICS set.
         * r32 must still be set to ptregs.flags.
         * We launch loads to each cache line separately first, so we can
         * get some parallelism out of the memory subsystem.
         * We start zeroing caller-saved registers throughout, since
         * that will save some cycles if this turns out to be a syscall.
         */
.Lrestore_regs:
        FEEDBACK_REENTER(interrupt_return)   /* called from elsewhere */

        /*
         * Rotate so we have one high bit and one low bit to test.
         * - low bit says whether to restore all the callee-saved registers,
         *   or just r30-r33, and r52 up.
         * - high bit (i.e. sign bit) says whether to restore all the
         *   caller-saved registers, or just r0.
         */
#if PT_FLAGS_CALLER_SAVES != 2 || PT_FLAGS_RESTORE_REGS != 4
# error Rotate trick does not work :-)
#endif
        {
         rli    r20, r32, 30
         PTREGS_PTR(sp, PTREGS_OFFSET_REG(0))
        }

        /*
         * Load cache lines 0, 2, and 3 in that order, then use
         * the last loaded value, which makes it likely that the other
         * cache lines have also loaded, at which point we should be
         * able to safely read all the remaining words on those cache
         * lines without waiting for the memory subsystem.
         */
        pop_reg_zero r0, r28, sp, PTREGS_OFFSET_REG(30) - PTREGS_OFFSET_REG(0)
        pop_reg_zero r30, r2, sp, PTREGS_OFFSET_PC - PTREGS_OFFSET_REG(30)
        pop_reg_zero r21, r3, sp, PTREGS_OFFSET_EX1 - PTREGS_OFFSET_PC
        pop_reg_zero lr, r4, sp, PTREGS_OFFSET_REG(52) - PTREGS_OFFSET_EX1
        {
         mtspr  SPR_EX_CONTEXT_K_0, r21
         move   r5, zero
        }
        {
         mtspr  SPR_EX_CONTEXT_K_1, lr
         andi   lr, lr, SPR_EX_CONTEXT_1_1__PL_MASK  /* mask off ICS */
        }

        /* Restore callee-saveds that we actually use. */
        pop_reg_zero r52, r6, sp, PTREGS_OFFSET_REG(31) - PTREGS_OFFSET_REG(52)
        pop_reg_zero r31, r7
        pop_reg_zero r32, r8
        pop_reg_zero r33, r9, sp, PTREGS_OFFSET_REG(29) - PTREGS_OFFSET_REG(33)

        /*
         * If we modified other callee-saveds, restore them now.
         * This is rare, but could be via ptrace or signal handler.
         */
        {
         move   r10, zero
         bbs    r20, .Lrestore_callees
        }
.Lcontinue_restore_regs:

        /* Check if we're returning from a syscall. */
        {
         move   r11, zero
         blzt   r20, 1f  /* no, so go restore callee-save registers */
        }

        /*
         * Check if we're returning to userspace.
         * Note that if we're not, we don't worry about zeroing everything.
         */
        {
         addli  sp, sp, PTREGS_OFFSET_LR - PTREGS_OFFSET_REG(29)
         bnz    lr, .Lkernel_return
        }

        /*
         * On return from syscall, we've restored r0 from pt_regs, but we
         * clear the remainder of the caller-saved registers.  We could
         * restore the syscall arguments, but there's not much point,
         * and it ensures user programs aren't trying to use the
         * caller-saves if we clear them, as well as avoiding leaking
         * kernel pointers into userspace.
         */
        pop_reg_zero lr, r12, sp, PTREGS_OFFSET_TP - PTREGS_OFFSET_LR
        pop_reg_zero tp, r13, sp, PTREGS_OFFSET_SP - PTREGS_OFFSET_TP
        {
         lw     sp, sp
         move   r14, zero
         move   r15, zero
        }
        { move r16, zero; move r17, zero }
        { move r18, zero; move r19, zero }
        { move r20, zero; move r21, zero }
        { move r22, zero; move r23, zero }
        { move r24, zero; move r25, zero }
        { move r26, zero; move r27, zero }

        /* Set r1 to errno if we are returning an error, otherwise zero. */
        {
         moveli r29, 4096
         sub    r1, zero, r0
        }
        slt_u   r29, r1, r29
        {
         mnz    r1, r29, r1
         move   r29, zero
        }
        iret

        /*
         * Not a syscall, so restore caller-saved registers.
         * First kick off a load for cache line 1, which we're touching
         * for the first time here.
         */
        .align 64
1:      pop_reg r29, sp, PTREGS_OFFSET_REG(1) - PTREGS_OFFSET_REG(29)
        pop_reg r1
        pop_reg r2
        pop_reg r3
        pop_reg r4
        pop_reg r5
        pop_reg r6
        pop_reg r7
        pop_reg r8
        pop_reg r9
        pop_reg r10
        pop_reg r11
        pop_reg r12
        pop_reg r13
        pop_reg r14
        pop_reg r15
        pop_reg r16
        pop_reg r17
        pop_reg r18
        pop_reg r19
        pop_reg r20
        pop_reg r21
        pop_reg r22
        pop_reg r23
        pop_reg r24
        pop_reg r25
        pop_reg r26
        pop_reg r27
        pop_reg r28, sp, PTREGS_OFFSET_LR - PTREGS_OFFSET_REG(28)
        /* r29 already restored above */
        bnz     lr, .Lkernel_return
        pop_reg lr, sp, PTREGS_OFFSET_TP - PTREGS_OFFSET_LR
        pop_reg tp, sp, PTREGS_OFFSET_SP - PTREGS_OFFSET_TP
        lw      sp, sp
        iret

        /*
         * We can't restore tp when in kernel mode, since a thread might
         * have migrated from another cpu and brought a stale tp value.
         */
.Lkernel_return:
        pop_reg lr, sp, PTREGS_OFFSET_SP - PTREGS_OFFSET_LR
        lw      sp, sp
        iret

        /* Restore callee-saved registers from r34 to r51. */
.Lrestore_callees:
        addli  sp, sp, PTREGS_OFFSET_REG(34) - PTREGS_OFFSET_REG(29)
        pop_reg r34
        pop_reg r35
        pop_reg r36
        pop_reg r37
        pop_reg r38
        pop_reg r39
        pop_reg r40
        pop_reg r41
        pop_reg r42
        pop_reg r43
        pop_reg r44
        pop_reg r45
        pop_reg r46
        pop_reg r47
        pop_reg r48
        pop_reg r49
        pop_reg r50
        pop_reg r51, sp, PTREGS_OFFSET_REG(29) - PTREGS_OFFSET_REG(51)
        j .Lcontinue_restore_regs
        STD_ENDPROC(interrupt_return)

        /*
         * Some interrupts don't check for single stepping
         */
        .pushsection .text.handle_interrupt_no_single_step,"ax"
handle_interrupt_no_single_step:
        finish_interrupt_save handle_interrupt_no_single_step
        {
         jalr   r0
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
        }
        FEEDBACK_REENTER(handle_interrupt_no_single_step)
        {
         movei  r30, 0   /* not an NMI */
         j      interrupt_return
        }
        STD_ENDPROC(handle_interrupt_no_single_step)

        /*
         * "NMI" interrupts mask ALL interrupts before calling the
         * handler, and don't check thread flags, etc., on the way
         * back out.  In general, the only things we do here for NMIs
         * are the register save/restore, fixing the PC if we were
         * doing single step, and the dataplane kernel-TLB management.
         * We don't (for example) deal with start/stop of the sched tick.
         */
        .pushsection .text.handle_nmi,"ax"
handle_nmi:
        finish_interrupt_save handle_nmi
        check_single_stepping normal, .Ldispatch_nmi
.Ldispatch_nmi:
        {
         jalr   r0
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
        }
        FEEDBACK_REENTER(handle_nmi)
        {
         movei  r30, 1
         seq    r31, r0, zero
        }
        j       interrupt_return
        STD_ENDPROC(handle_nmi)

        /*
         * Parallel code for syscalls to handle_interrupt.
         */
        .pushsection .text.handle_syscall,"ax"
handle_syscall:
        finish_interrupt_save handle_syscall

        /*
         * Check for if we are single stepping in user level. If so, then
         * we need to restore the PC.
         */
        check_single_stepping syscall, .Ldispatch_syscall
.Ldispatch_syscall:

        /* Enable irqs. */
        TRACE_IRQS_ON
        IRQ_ENABLE(r20, r21)

        /* Bump the counter for syscalls made on this tile. */
        moveli  r20, lo16(irq_stat + IRQ_CPUSTAT_SYSCALL_COUNT_OFFSET)
        auli    r20, r20, ha16(irq_stat + IRQ_CPUSTAT_SYSCALL_COUNT_OFFSET)
        add     r20, r20, tp
        lw      r21, r20
        addi    r21, r21, 1
        {
         sw     r20, r21
         GET_THREAD_INFO(r31)
        }

        /* Trace syscalls, if requested. */
        addi    r31, r31, THREAD_INFO_FLAGS_OFFSET
        lw      r30, r31
        andi    r30, r30, _TIF_SYSCALL_TRACE
        bzt     r30, .Lrestore_syscall_regs
        {
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
         jal    do_syscall_trace_enter
        }
        FEEDBACK_REENTER(handle_syscall)
        blz     r0, .Lsyscall_sigreturn_skip

        /*
         * We always reload our registers from the stack at this
         * point.  They might be valid, if we didn't build with
         * TRACE_IRQFLAGS, and this isn't a dataplane tile, and we're not
         * doing syscall tracing, but there are enough cases now that it
         * seems simplest just to do the reload unconditionally.
         */
.Lrestore_syscall_regs:
        PTREGS_PTR(r11, PTREGS_OFFSET_REG(0))
        pop_reg r0, r11
        pop_reg r1, r11
        pop_reg r2, r11
        pop_reg r3, r11
        pop_reg r4, r11
        pop_reg r5, r11, PTREGS_OFFSET_SYSCALL - PTREGS_OFFSET_REG(5)
        pop_reg TREG_SYSCALL_NR_NAME, r11

        /* Ensure that the syscall number is within the legal range. */
        moveli  r21, __NR_syscalls
        {
         slt_u  r21, TREG_SYSCALL_NR_NAME, r21
         moveli r20, lo16(sys_call_table)
        }
        {
         bbns   r21, .Linvalid_syscall
         auli   r20, r20, ha16(sys_call_table)
        }
        s2a     r20, TREG_SYSCALL_NR_NAME, r20
        lw      r20, r20

        /* Jump to syscall handler. */
        jalr    r20
.Lhandle_syscall_link: /* value of "lr" after "jalr r20" above */

        /*
         * Write our r0 onto the stack so it gets restored instead
         * of whatever the user had there before.
         */
        PTREGS_PTR(r29, PTREGS_OFFSET_REG(0))
        sw      r29, r0

.Lsyscall_sigreturn_skip:
        FEEDBACK_REENTER(handle_syscall)

        /* Do syscall trace again, if requested. */
        lw      r30, r31
        andi    r30, r30, _TIF_SYSCALL_TRACE
        bzt     r30, 1f
        {
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
         jal    do_syscall_trace_exit
        }
        FEEDBACK_REENTER(handle_syscall)
1:      {
         movei  r30, 0               /* not an NMI */
         j      .Lresume_userspace   /* jump into middle of interrupt_return */
        }

.Linvalid_syscall:
        /* Report an invalid syscall back to the user program */
        {
         PTREGS_PTR(r29, PTREGS_OFFSET_REG(0))
         movei  r28, -ENOSYS
        }
        sw      r29, r28
        {
         movei  r30, 0               /* not an NMI */
         j      .Lresume_userspace   /* jump into middle of interrupt_return */
        }
        STD_ENDPROC(handle_syscall)

        /* Return the address for oprofile to suppress in backtraces. */
STD_ENTRY_SECTION(handle_syscall_link_address, .text.handle_syscall)
        lnk     r0
        {
         addli  r0, r0, .Lhandle_syscall_link - .
         jrp    lr
        }
        STD_ENDPROC(handle_syscall_link_address)

STD_ENTRY(ret_from_fork)
        jal     sim_notify_fork
        jal     schedule_tail
        FEEDBACK_REENTER(ret_from_fork)
        {
         movei  r30, 0               /* not an NMI */
         j      .Lresume_userspace   /* jump into middle of interrupt_return */
        }
        STD_ENDPROC(ret_from_fork)

STD_ENTRY(ret_from_kernel_thread)
        jal     sim_notify_fork
        jal     schedule_tail
        FEEDBACK_REENTER(ret_from_fork)
        {
         move   r0, r31
         jalr   r30
        }
        FEEDBACK_REENTER(ret_from_kernel_thread)
        {
         movei  r30, 0               /* not an NMI */
         j      interrupt_return
        }
        STD_ENDPROC(ret_from_kernel_thread)

        /*
         * Code for ill interrupt.
         */
        .pushsection .text.handle_ill,"ax"
handle_ill:
        finish_interrupt_save handle_ill

        /*
         * Check for if we are single stepping in user level. If so, then
         * we need to restore the PC.
         */
        check_single_stepping ill, .Ldispatch_normal_ill

        {
         /* See if the PC is the 1st bundle in the buffer */
         seq    r25, r27, r26

         /* Point to the 2nd bundle in the buffer */
         addi   r26, r26, 8
        }
        {
         /* Point to the original pc */
         addi   r24, r29, SINGLESTEP_STATE_ORIG_PC_OFFSET

         /* Branch if the PC is the 1st bundle in the buffer */
         bnz    r25, 3f
        }
        {
         /* See if the PC is the 2nd bundle of the buffer */
         seq    r25, r27, r26

         /* Set PC to next instruction */
         addi   r24, r29, SINGLESTEP_STATE_NEXT_PC_OFFSET
        }
        {
         /* Point to flags */
         addi   r25, r29, SINGLESTEP_STATE_FLAGS_OFFSET

         /* Branch if PC is in the second bundle */
         bz     r25, 2f
        }
        /* Load flags */
        lw      r25, r25
        {
         /*
          * Get the offset for the register to restore
          * Note: the lower bound is 2, so we have implicit scaling by 4.
          *  No multiplication of the register number by the size of a register
          *  is needed.
          */
         mm     r27, r25, zero, SINGLESTEP_STATE_TARGET_LB, \
                SINGLESTEP_STATE_TARGET_UB

         /* Mask Rewrite_LR */
         andi   r25, r25, SINGLESTEP_STATE_MASK_UPDATE
        }
        {
         addi   r29, r29, SINGLESTEP_STATE_UPDATE_VALUE_OFFSET

         /* Don't rewrite temp register */
         bz     r25, 3f
        }
        {
         /* Get the temp value */
         lw     r29, r29

         /* Point to where the register is stored */
         add    r27, r27, sp
        }

        /* Add in the C ABI save area size to the register offset */
        addi    r27, r27, C_ABI_SAVE_AREA_SIZE

        /* Restore the user's register with the temp value */
        sw      r27, r29
        j       3f

2:
        /* Must be in the third bundle */
        addi    r24, r29, SINGLESTEP_STATE_BRANCH_NEXT_PC_OFFSET

3:
        /* set PC and continue */
        lw      r26, r24
        {
         sw     r28, r26
         GET_THREAD_INFO(r0)
        }

        /*
         * Clear TIF_SINGLESTEP to prevent recursion if we execute an ill.
         * The normal non-arch flow redundantly clears TIF_SINGLESTEP, but we
         * need to clear it here and can't really impose on all other arches.
         * So what's another write between friends?
         */

        addi    r1, r0, THREAD_INFO_FLAGS_OFFSET
        {
         lw     r2, r1
         addi   r0, r0, THREAD_INFO_TASK_OFFSET  /* currently a no-op */
        }
        andi    r2, r2, ~_TIF_SINGLESTEP
        sw      r1, r2

        /* Issue a sigtrap */
        {
         lw     r0, r0          /* indirect thru thread_info to get task_info*/
         addi   r1, sp, C_ABI_SAVE_AREA_SIZE  /* put ptregs pointer into r1 */
        }

        jal     send_sigtrap    /* issue a SIGTRAP */
        FEEDBACK_REENTER(handle_ill)
        {
         movei  r30, 0               /* not an NMI */
         j      .Lresume_userspace   /* jump into middle of interrupt_return */
        }

.Ldispatch_normal_ill:
        {
         jalr   r0
         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
        }
        FEEDBACK_REENTER(handle_ill)
        {
         movei  r30, 0   /* not an NMI */
         j      interrupt_return
        }
        STD_ENDPROC(handle_ill)

/* Various stub interrupt handlers and syscall handlers */

STD_ENTRY_LOCAL(_kernel_double_fault)
        mfspr   r1, SPR_EX_CONTEXT_K_0
        move    r2, lr
        move    r3, sp
        move    r4, r52
        addi    sp, sp, -C_ABI_SAVE_AREA_SIZE
        j       kernel_double_fault
        STD_ENDPROC(_kernel_double_fault)

STD_ENTRY_LOCAL(bad_intr)
        mfspr   r2, SPR_EX_CONTEXT_K_0
        panic   "Unhandled interrupt %#x: PC %#lx"
        STD_ENDPROC(bad_intr)

/*
 * Special-case sigreturn to not write r0 to the stack on return.
 * This is technically more efficient, but it also avoids difficulties
 * in the 64-bit OS when handling 32-bit compat code, since we must not
 * sign-extend r0 for the sigreturn return-value case.
 */
#define PTREGS_SYSCALL_SIGRETURN(x, reg)                \
        STD_ENTRY(_##x);                                \
        addli   lr, lr, .Lsyscall_sigreturn_skip - .Lhandle_syscall_link; \
        {                                               \
         PTREGS_PTR(reg, PTREGS_OFFSET_BASE);           \
         j      x                                       \
        };                                              \
        STD_ENDPROC(_##x)

PTREGS_SYSCALL_SIGRETURN(sys_rt_sigreturn, r0)

/* Save additional callee-saves to pt_regs and jump to standard function. */
STD_ENTRY(_sys_clone)
        push_extra_callee_saves r4
        j       sys_clone
        STD_ENDPROC(_sys_clone)

/*
 * This entrypoint is taken for the cmpxchg and atomic_update fast
 * swints.  We may wish to generalize it to other fast swints at some
 * point, but for now there are just two very similar ones, which
 * makes it faster.
 *
 * The fast swint code is designed to have a small footprint.  It does
 * not save or restore any GPRs, counting on the caller-save registers
 * to be available to it on entry.  It does not modify any callee-save
 * registers (including "lr").  It does not check what PL it is being
 * called at, so you'd better not call it other than at PL0.
 * The <atomic.h> wrapper assumes it only clobbers r20-r29, so if
 * it ever is necessary to use more registers, be aware.
 *
 * It does not use the stack, but since it might be re-interrupted by
 * a page fault which would assume the stack was valid, it does
 * save/restore the stack pointer and zero it out to make sure it gets reset.
 * Since we always keep interrupts disabled, the hypervisor won't
 * clobber our EX_CONTEXT_K_x registers, so we don't save/restore them
 * (other than to advance the PC on return).
 *
 * We have to manually validate the user vs kernel address range
 * (since at PL1 we can read/write both), and for performance reasons
 * we don't allow cmpxchg on the fc000000 memory region, since we only
 * validate that the user address is below PAGE_OFFSET.
 *
 * We place it in the __HEAD section to ensure it is relatively
 * near to the intvec_SWINT_1 code (reachable by a conditional branch).
 *
 * Our use of ATOMIC_LOCK_REG here must match do_page_fault_ics().
 *
 * As we do in lib/atomic_asm_32.S, we bypass a store if the value we
 * would store is the same as the value we just loaded.
 */
        __HEAD
        .align 64
        /* Align much later jump on the start of a cache line. */
        nop
#if PAGE_SIZE >= 0x10000
        nop
#endif
ENTRY(sys_cmpxchg)

        /*
         * Save "sp" and set it zero for any possible page fault.
         *
         * HACK: We want to both zero sp and check r0's alignment,
         * so we do both at once. If "sp" becomes nonzero we
         * know r0 is unaligned and branch to the error handler that
         * restores sp, so this is OK.
         *
         * ICS is disabled right now so having a garbage but nonzero
         * sp is OK, since we won't execute any faulting instructions
         * when it is nonzero.
         */
        {
         move   r27, sp
         andi   sp, r0, 3
        }

        /*
         * Get the lock address in ATOMIC_LOCK_REG, and also validate that the
         * address is less than PAGE_OFFSET, since that won't trap at PL1.
         * We only use bits less than PAGE_SHIFT to avoid having to worry
         * about aliasing among multiple mappings of the same physical page,
         * and we ignore the low 3 bits so we have one lock that covers
         * both a cmpxchg64() and a cmpxchg() on either its low or high word.
         * NOTE: this must match __atomic_hashed_lock() in lib/atomic_32.c.
         */

#if (PAGE_OFFSET & 0xffff) != 0
# error Code here assumes PAGE_OFFSET can be loaded with just hi16()
#endif

        {
         /* Check for unaligned input. */
         bnz    sp, .Lcmpxchg_badaddr
         auli   r23, zero, hi16(PAGE_OFFSET)  /* hugepage-aligned */
        }
        {
         /*
          * Slide bits into position for 'mm'. We want to ignore
          * the low 3 bits of r0, and consider only the next
          * ATOMIC_HASH_SHIFT bits.
          * Because of C pointer arithmetic, we want to compute this:
          *
          * ((char*)atomic_locks +
          *  (((r0 >> 3) & ((1 << ATOMIC_HASH_SHIFT) - 1)) << 2))
          *
          * Instead of two shifts we just ">> 1", and use 'mm'
          * to ignore the low and high bits we don't want.
          */
         shri   r25, r0, 1

         slt_u  r23, r0, r23

         /*
          * Ensure that the TLB is loaded before we take out the lock.
          * This will start fetching the value all the way into our L1
          * as well (and if it gets modified before we grab the lock,
          * it will be invalidated from our cache before we reload it).
          */
         lw     r26, r0
        }
        {
         auli   r21, zero, ha16(atomic_locks)

         bbns   r23, .Lcmpxchg_badaddr
        }
#if PAGE_SIZE < 0x10000
        /* atomic_locks is page-aligned so for big pages we don't need this. */
        addli   r21, r21, lo16(atomic_locks)
#endif
        {
         /*
          * Insert the hash bits into the page-aligned pointer.
          * ATOMIC_HASH_SHIFT is so big that we don't actually hash
          * the unmasked address bits, as that may cause unnecessary
          * collisions.
          */
         mm     ATOMIC_LOCK_REG_NAME, r25, r21, 2, (ATOMIC_HASH_SHIFT + 2) - 1

         seqi   r23, TREG_SYSCALL_NR_NAME, __NR_FAST_cmpxchg64
        }
        {
         /* Branch away at this point if we're doing a 64-bit cmpxchg. */
         bbs    r23, .Lcmpxchg64
         andi   r23, r0, 7       /* Precompute alignment for cmpxchg64. */
        }
        {
         /*
          * We very carefully align the code that actually runs with
          * the lock held (twelve bundles) so that we know it is all in
          * the icache when we start.  This instruction (the jump) is
          * at the start of the first cache line, address zero mod 64;
          * we jump to the very end of the second cache line to get that
          * line loaded in the icache, then fall through to issue the tns
          * in the third cache line, at which point it's all cached.
          * Note that is for performance, not correctness.
          */
         j      .Lcmpxchg32_tns
        }

/* Symbol for do_page_fault_ics() to use to compare against the PC. */
.global __sys_cmpxchg_grab_lock
__sys_cmpxchg_grab_lock:

        /*
         * Perform the actual cmpxchg or atomic_update.
         */
.Ldo_cmpxchg32:
        {
         lw     r21, r0
         seqi   r23, TREG_SYSCALL_NR_NAME, __NR_FAST_atomic_update
         move   r24, r2
        }
        {
         seq    r22, r21, r1     /* See if cmpxchg matches. */
         and    r25, r21, r1     /* If atomic_update, compute (*mem & mask) */
        }
        {
         or     r22, r22, r23    /* Skip compare branch for atomic_update. */
         add    r25, r25, r2     /* Compute (*mem & mask) + addend. */
        }
        {
         mvnz   r24, r23, r25    /* Use atomic_update value if appropriate. */
         bbns   r22, .Lcmpxchg32_nostore
        }
        seq     r22, r24, r21    /* Are we storing the value we loaded? */
        bbs     r22, .Lcmpxchg32_nostore
        sw      r0, r24

        /* The following instruction is the start of the second cache line. */
        /* Do slow mtspr here so the following "mf" waits less. */
        {
         move   sp, r27
         mtspr  SPR_EX_CONTEXT_K_0, r28
        }
        mf

        {
         move   r0, r21
         sw     ATOMIC_LOCK_REG_NAME, zero
        }
        iret

        /* Duplicated code here in the case where we don't overlap "mf" */
.Lcmpxchg32_nostore:
        {
         move   r0, r21
         sw     ATOMIC_LOCK_REG_NAME, zero
        }
        {
         move   sp, r27
         mtspr  SPR_EX_CONTEXT_K_0, r28
        }
        iret

        /*
         * The locking code is the same for 32-bit cmpxchg/atomic_update,
         * and for 64-bit cmpxchg.  We provide it as a macro and put
         * it into both versions.  We can't share the code literally
         * since it depends on having the right branch-back address.
         */
        .macro  cmpxchg_lock, bitwidth

        /* Lock; if we succeed, jump back up to the read-modify-write. */
#ifdef CONFIG_SMP
        tns     r21, ATOMIC_LOCK_REG_NAME
#else
        /*
         * Non-SMP preserves all the lock infrastructure, to keep the
         * code simpler for the interesting (SMP) case.  However, we do
         * one small optimization here and in atomic_asm.S, which is
         * to fake out acquiring the actual lock in the atomic_lock table.
         */
        movei   r21, 0
#endif

        /* Issue the slow SPR here while the tns result is in flight. */
        mfspr   r28, SPR_EX_CONTEXT_K_0

        {
         addi   r28, r28, 8    /* return to the instruction after the swint1 */
         bzt    r21, .Ldo_cmpxchg\bitwidth
        }
        /*
         * The preceding instruction is the last thing that must be
         * hot in the icache before we do the "tns" above.
         */

#ifdef CONFIG_SMP
        /*
         * We failed to acquire the tns lock on our first try.  Now use
         * bounded exponential backoff to retry, like __atomic_spinlock().
         */
        {
         moveli r23, 2048       /* maximum backoff time in cycles */
         moveli r25, 32         /* starting backoff time in cycles */
        }
1:      mfspr   r26, CYCLE_LOW  /* get start point for this backoff */
2:      mfspr   r22, CYCLE_LOW  /* test to see if we've backed off enough */
        sub     r22, r22, r26
        slt     r22, r22, r25
        bbst    r22, 2b
        {
         shli   r25, r25, 1     /* double the backoff; retry the tns */
         tns    r21, ATOMIC_LOCK_REG_NAME
        }
        slt     r26, r23, r25   /* is the proposed backoff too big? */
        {
         mvnz   r25, r26, r23
         bzt    r21, .Ldo_cmpxchg\bitwidth
        }
        j       1b
#endif /* CONFIG_SMP */
        .endm

.Lcmpxchg32_tns:
        /*
         * This is the last instruction on the second cache line.
         * The nop here loads the second line, then we fall through
         * to the tns to load the third line before we take the lock.
         */
        nop
        cmpxchg_lock 32

        /*
         * This code is invoked from sys_cmpxchg after most of the
         * preconditions have been checked.  We still need to check
         * that r0 is 8-byte aligned, since if it's not we won't
         * actually be atomic.  However, ATOMIC_LOCK_REG has the atomic
         * lock pointer and r27/r28 have the saved SP/PC.
         * r23 is holding "r0 & 7" so we can test for alignment.
         * The compare value is in r2/r3; the new value is in r4/r5.
         * On return, we must put the old value in r0/r1.
         */
        .align 64
.Lcmpxchg64:
        {
         bzt     r23, .Lcmpxchg64_tns
        }
        j       .Lcmpxchg_badaddr

.Ldo_cmpxchg64:
        {
         lw     r21, r0
         addi   r25, r0, 4
        }
        {
         lw     r1, r25
        }
        seq     r26, r21, r2
        {
         bz     r26, .Lcmpxchg64_mismatch
         seq    r26, r1, r3
        }
        {
         bz     r26, .Lcmpxchg64_mismatch
        }
        sw      r0, r4
        sw      r25, r5

        /*
         * The 32-bit path provides optimized "match" and "mismatch"
         * iret paths, but we don't have enough bundles in this cache line
         * to do that, so we just make even the "mismatch" path do an "mf".
         */
.Lcmpxchg64_mismatch:
        {
         move   sp, r27
         mtspr  SPR_EX_CONTEXT_K_0, r28
        }
        mf
        {
         move   r0, r21
         sw     ATOMIC_LOCK_REG_NAME, zero
        }
        iret

.Lcmpxchg64_tns:
        cmpxchg_lock 64


        /*
         * Reset sp and revector to sys_cmpxchg_badaddr(), which will
         * just raise the appropriate signal and exit.  Doing it this
         * way means we don't have to duplicate the code in intvec.S's
         * int_hand macro that locates the top of the stack.
         */
.Lcmpxchg_badaddr:
        {
         moveli TREG_SYSCALL_NR_NAME, __NR_cmpxchg_badaddr
         move   sp, r27
        }
        j       intvec_SWINT_1
        ENDPROC(sys_cmpxchg)
        ENTRY(__sys_cmpxchg_end)


/* The single-step support may need to read all the registers. */
int_unalign:
        push_extra_callee_saves r0
        j       do_trap

/* Include .intrpt array of interrupt vectors */
        .section ".intrpt", "ax"

#ifndef CONFIG_USE_PMC
#define handle_perf_interrupt bad_intr
#endif

#ifndef CONFIG_HARDWALL
#define do_hardwall_trap bad_intr
#endif

        int_hand     INT_ITLB_MISS, ITLB_MISS, \
                     do_page_fault, handle_interrupt_no_single_step
        int_hand     INT_MEM_ERROR, MEM_ERROR, bad_intr
        int_hand     INT_ILL, ILL, do_trap, handle_ill
        int_hand     INT_GPV, GPV, do_trap
        int_hand     INT_SN_ACCESS, SN_ACCESS, do_trap
        int_hand     INT_IDN_ACCESS, IDN_ACCESS, do_trap
        int_hand     INT_UDN_ACCESS, UDN_ACCESS, do_trap
        int_hand     INT_IDN_REFILL, IDN_REFILL, bad_intr
        int_hand     INT_UDN_REFILL, UDN_REFILL, bad_intr
        int_hand     INT_IDN_COMPLETE, IDN_COMPLETE, bad_intr
        int_hand     INT_UDN_COMPLETE, UDN_COMPLETE, bad_intr
        int_hand     INT_SWINT_3, SWINT_3, do_trap
        int_hand     INT_SWINT_2, SWINT_2, do_trap
        int_hand     INT_SWINT_1, SWINT_1, SYSCALL, handle_syscall
        int_hand     INT_SWINT_0, SWINT_0, do_trap
        int_hand     INT_UNALIGN_DATA, UNALIGN_DATA, int_unalign
        int_hand     INT_DTLB_MISS, DTLB_MISS, do_page_fault
        int_hand     INT_DTLB_ACCESS, DTLB_ACCESS, do_page_fault
        int_hand     INT_DMATLB_MISS, DMATLB_MISS, do_page_fault
        int_hand     INT_DMATLB_ACCESS, DMATLB_ACCESS, do_page_fault
        int_hand     INT_SNITLB_MISS, SNITLB_MISS, do_page_fault
        int_hand     INT_SN_NOTIFY, SN_NOTIFY, bad_intr
        int_hand     INT_SN_FIREWALL, SN_FIREWALL, do_hardwall_trap
        int_hand     INT_IDN_FIREWALL, IDN_FIREWALL, bad_intr
        int_hand     INT_UDN_FIREWALL, UDN_FIREWALL, do_hardwall_trap
        int_hand     INT_TILE_TIMER, TILE_TIMER, do_timer_interrupt
        int_hand     INT_IDN_TIMER, IDN_TIMER, bad_intr
        int_hand     INT_UDN_TIMER, UDN_TIMER, bad_intr
        int_hand     INT_DMA_NOTIFY, DMA_NOTIFY, bad_intr
        int_hand     INT_IDN_CA, IDN_CA, bad_intr
        int_hand     INT_UDN_CA, UDN_CA, bad_intr
        int_hand     INT_IDN_AVAIL, IDN_AVAIL, bad_intr
        int_hand     INT_UDN_AVAIL, UDN_AVAIL, bad_intr
        int_hand     INT_PERF_COUNT, PERF_COUNT, \
                     handle_perf_interrupt, handle_nmi
        int_hand     INT_INTCTRL_3, INTCTRL_3, bad_intr
#if CONFIG_KERNEL_PL == 2
        dc_dispatch  INT_INTCTRL_2, INTCTRL_2
        int_hand     INT_INTCTRL_1, INTCTRL_1, bad_intr
#else
        int_hand     INT_INTCTRL_2, INTCTRL_2, bad_intr
        dc_dispatch  INT_INTCTRL_1, INTCTRL_1
#endif
        int_hand     INT_INTCTRL_0, INTCTRL_0, bad_intr
        int_hand     INT_MESSAGE_RCV_DWNCL, MESSAGE_RCV_DWNCL, \
                     hv_message_intr
        int_hand     INT_DEV_INTR_DWNCL, DEV_INTR_DWNCL, \
                     tile_dev_intr
        int_hand     INT_I_ASID, I_ASID, bad_intr
        int_hand     INT_D_ASID, D_ASID, bad_intr
        int_hand     INT_DMATLB_MISS_DWNCL, DMATLB_MISS_DWNCL, \
                     do_page_fault
        int_hand     INT_SNITLB_MISS_DWNCL, SNITLB_MISS_DWNCL, \
                     do_page_fault
        int_hand     INT_DMATLB_ACCESS_DWNCL, DMATLB_ACCESS_DWNCL, \
                     do_page_fault
        int_hand     INT_SN_CPL, SN_CPL, bad_intr
        int_hand     INT_DOUBLE_FAULT, DOUBLE_FAULT, do_trap
        int_hand     INT_AUX_PERF_COUNT, AUX_PERF_COUNT, \
                     handle_perf_interrupt, handle_nmi

        /* Synthetic interrupt delivered only by the simulator */
        int_hand     INT_BREAKPOINT, BREAKPOINT, do_breakpoint