xnu-4570.41.2.tar.gz

[apple/xnu.git] / osfmk / x86_64 / idt64.s

/*
 * Copyright (c) 2010 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
#include <i386/asm.h>
#include <assym.s>
#include <debug.h>
#include <i386/eflags.h>
#include <i386/rtclock_asm.h>
#include <i386/trap.h>
#define _ARCH_I386_ASM_HELP_H_  /* Prevent inclusion of user header */
#include <mach/i386/syscall_sw.h>
#include <i386/postcode.h>
#include <i386/proc_reg.h>
#include <mach/exception_types.h>

#if DEBUG
#define DEBUG_IDT64             1       
#endif

/*
 * This is the low-level trap and interrupt handling code associated with
 * the IDT. It also includes system call handlers for sysenter/syscall.
 * The IDT itself is defined in mp_desc.c.
 *
 * Code here is structured as follows:
 *
 * stubs        Code called directly from an IDT vector.
 *              All entry points have the "idt64_" prefix and they are built
 *              using macros expanded by the inclusion of idt_table.h.
 *              This code performs vector-dependent identification and jumps
 *              into the dispatch code.
 *
 * dispatch     The dispatch code is responsible for saving the thread state
 *              (which is either 64-bit or 32-bit) and then jumping to the
 *              class handler identified by the stub.
 *
 * returns      Code to restore state and return to the previous context.
 *
 * handlers     There are several classes of handlers:
 *   interrupt  - asynchronous events typically from external devices
 *   trap       - synchronous events due to thread execution
 *   syscall    - synchronous system call request
 *   fatal      - fatal traps
 */
/*
 * Indices of handlers for each exception type.
 */
#define HNDL_ALLINTRS           0
#define HNDL_ALLTRAPS           1
#define HNDL_SYSENTER           2
#define HNDL_SYSCALL            3
#define HNDL_UNIX_SCALL         4
#define HNDL_MACH_SCALL         5
#define HNDL_MDEP_SCALL         6
#define HNDL_DOUBLE_FAULT       7
#define HNDL_MACHINE_CHECK      8

/* Begin double-mapped descriptor section */
        
.section        __HIB, __desc
.globl EXT(idt64_hndl_table0)
EXT(idt64_hndl_table0):
        .quad EXT(ks_dispatch)
        .quad EXT(ks_64bit_return)
        .quad 0 /* Populated with CPU shadow displacement*/
        .quad EXT(ks_return)

EXT(idt64_hndl_table1):
        .quad   EXT(hndl_allintrs)
        .quad   EXT(hndl_alltraps)
        .quad   EXT(hndl_sysenter)
        .quad   EXT(hndl_syscall)
        .quad   EXT(hndl_unix_scall)
        .quad   EXT(hndl_mach_scall)
        .quad   EXT(hndl_mdep_scall)
        .quad   EXT(hndl_double_fault)
        .quad   EXT(hndl_machine_check)
.text


/* The wrapper for all non-special traps/interrupts */
/* Everything up to PUSH_FUNCTION is just to output 
 * the interrupt number out to the postcode display
 */
#if DEBUG_IDT64
#define IDT_ENTRY_WRAPPER(n, f)                  \
        push    %rax                            ;\
        POSTCODE2(0x6400+n)                     ;\
        pop     %rax                            ;\
        pushq   $(f)                            ;\
        pushq   $(n)                            ;\
        jmp L_dispatch
#else
#define IDT_ENTRY_WRAPPER(n, f)                  \
        pushq   $(f)                            ;\
        pushq   $(n)                            ;\
        jmp L_dispatch
#endif

/* A trap that comes with an error code already on the stack */
#define TRAP_ERR(n, f)                           \
        Entry(f)                                ;\
        IDT_ENTRY_WRAPPER(n, HNDL_ALLTRAPS)

/* A normal trap */
#define TRAP(n, f)                               \
        Entry(f)                                ;\
        pushq   $0                              ;\
        IDT_ENTRY_WRAPPER(n, HNDL_ALLTRAPS)

#define USER_TRAP TRAP

/* An interrupt */
#define INTERRUPT(n)                            \
        Entry(_intr_ ## n)                      ;\
        pushq   $0                              ;\
        IDT_ENTRY_WRAPPER(n, HNDL_ALLINTRS)

/* A trap with a special-case handler, hence we don't need to define anything */
#define TRAP_SPC(n, f)
#define TRAP_IST1(n, f)
#define TRAP_IST2(n, f)
#define USER_TRAP_SPC(n, f)

/* Begin double-mapped text section */
.section __HIB, __text
/* Generate all the stubs */
#include "idt_table.h"

Entry(idt64_page_fault)
        pushq   $(HNDL_ALLTRAPS)
        push    $(T_PAGE_FAULT)
        jmp     L_dispatch

Entry(idt64_debug)
        push    $0                      /* error code */
        pushq   $(HNDL_ALLTRAPS)
        pushq   $(T_DEBUG)
        jmp     L_dispatch
/*
 * Legacy interrupt gate System call handlers.
 * These are entered via a syscall interrupt. The system call number in %rax
 * is saved to the error code slot in the stack frame. We then branch to the
 * common state saving code.
 */

#ifndef UNIX_INT
#error NO UNIX INT!!!
#endif
Entry(idt64_unix_scall)
        pushq   %rax                    /* save system call number */
        pushq   $(HNDL_UNIX_SCALL)
        pushq   $(UNIX_INT)
        jmp     L_dispatch
        
Entry(idt64_mach_scall)
        pushq   %rax                    /* save system call number */
        pushq   $(HNDL_MACH_SCALL)
        pushq   $(MACH_INT)
        jmp     L_dispatch
        
Entry(idt64_mdep_scall)
        pushq   %rax                    /* save system call number */
        pushq   $(HNDL_MDEP_SCALL)
        pushq   $(MACHDEP_INT)
        jmp     L_dispatch

/*
 * For GP/NP/SS faults, we use the IST1 stack.
 * For faults from user-space, we have to copy the machine state to the
 * PCB stack and then dispatch as normal.
 * For faults in kernel-space, we need to scrub for kernel exit faults and
 * treat these as user-space faults. But for all other kernel-space faults
 * we continue to run on the IST1 stack and we dispatch to handle the fault
 * as fatal.
 */
Entry(idt64_gen_prot)
        pushq   $(HNDL_ALLTRAPS)
        pushq   $(T_GENERAL_PROTECTION)
        jmp     L_dispatch

Entry(idt64_stack_fault)
        pushq   $(HNDL_ALLTRAPS)
        pushq   $(T_STACK_FAULT)
        jmp     L_dispatch

Entry(idt64_segnp)
        pushq   $(HNDL_ALLTRAPS)
        pushq   $(T_SEGMENT_NOT_PRESENT)
        jmp     L_dispatch

/*
 * Fatal exception handlers:
 */
Entry(idt64_db_task_dbl_fault)
        pushq   $(HNDL_DOUBLE_FAULT)
        pushq   $(T_DOUBLE_FAULT)
        jmp     L_dispatch

Entry(idt64_db_task_stk_fault)
        pushq   $(HNDL_DOUBLE_FAULT)
        pushq   $(T_STACK_FAULT)
        jmp     L_dispatch

Entry(idt64_mc)
        push    $(0)                    /* Error */
        pushq   $(HNDL_MACHINE_CHECK)
        pushq   $(T_MACHINE_CHECK)
        jmp     L_dispatch

/*
 * NMI
 * This may or may not be fatal but extreme care is required
 * because it may fall when control was already in another trampoline.
 *
 * We get here on IST2 stack which is used for NMIs only.
 */
Entry(idt64_nmi)
        push    %rax                            /* save RAX to ISF64_ERR */
        push    %rcx                            /* save RCX to ISF64_TRAPFN */
        push    %rdx                            /* save RDX to ISF64_TRAPNO */
        jmp     L_dispatch

Entry(idt64_double_fault)
        pushq   $(HNDL_DOUBLE_FAULT)
        pushq   $(T_DOUBLE_FAULT)
        jmp     L_dispatch

Entry(hi64_syscall)
Entry(idt64_syscall)
        swapgs
     /* Use RAX as a temporary by shifting its contents into R11[32:63]
      * The systemcall number is defined to be a 32-bit quantity, as is
      * RFLAGS.
      */
        shlq    $32, %rax
        or      %rax, %r11
.globl EXT(dblsyscall_patch_point)
EXT(dblsyscall_patch_point):
//      movabsq $0x12345678ABCDEFFFULL, %rax
     /* Generate offset to the double-mapped per-CPU data shadow
      * into RAX
      */
        leaq    EXT(idt64_hndl_table0)(%rip), %rax
        mov     16(%rax), %rax
        mov     %rsp, %gs:CPU_UBER_TMP(%rax)  /* save user stack */
        mov     %gs:CPU_ESTACK(%rax), %rsp  /* switch stack to per-cpu estack */
        sub     $(ISF64_SIZE), %rsp

        /*
         * Synthesize an ISF frame on the exception stack
         */
        movl    $(USER_DS), ISF64_SS(%rsp)
        mov     %rcx, ISF64_RIP(%rsp)           /* rip */

        mov     %gs:CPU_UBER_TMP(%rax), %rcx
        mov     %rcx, ISF64_RSP(%rsp)           /* user stack --changed */

        mov     %r11, %rax
        shrq    $32, %rax               /* Restore RAX */
        mov     %r11d, %r11d            /* Clear r11[32:63] */

        mov     %r11, ISF64_RFLAGS(%rsp)        /* rflags */
        movl    $(SYSCALL_CS), ISF64_CS(%rsp)   /* cs - a pseudo-segment */
        mov     %rax, ISF64_ERR(%rsp)           /* err/rax - syscall code */
        movq    $(HNDL_SYSCALL), ISF64_TRAPFN(%rsp)
        movq    $(T_SYSCALL), ISF64_TRAPNO(%rsp)        /* trapno */
        swapgs
        jmp     L_dispatch                      /* this can only be 64-bit */

Entry(hi64_sysenter)
Entry(idt64_sysenter)
        /* Synthesize an interrupt stack frame onto the
         * exception stack.
         */
        push    $(USER_DS)              /* ss */
        push    %rcx                    /* uesp */
        pushf                           /* flags */
        /*
         * Clear, among others, the Nested Task (NT) flags bit;
         * this is zeroed by INT, but not by SYSENTER.
         */
        push    $0
        popf
        push    $(SYSENTER_CS)          /* cs */ 
L_sysenter_continue:
        push    %rdx                    /* eip */
        push    %rax                    /* err/eax - syscall code */
        pushq   $(HNDL_SYSENTER)
        pushq   $(T_SYSENTER)
        orl     $(EFL_IF), ISF64_RFLAGS(%rsp)
        jmp L_dispatch

/*
 * Common dispatch point.
 * Determine what mode has been interrupted and save state accordingly.
 * Here with:
 *      rsp     from user-space:   interrupt state in PCB, or
 *              from kernel-space: interrupt state in kernel or interrupt stack
 *      GSBASE  from user-space:   pthread area, or
 *              from kernel-space: cpu_data
 */

L_dispatch:
        pushq   %rax
        testb   $3, 8+ISF64_CS(%rsp)
        jz      1f
        swapgs
        leaq    EXT(idt64_hndl_table0)(%rip), %rax
        mov     16(%rax), %rax

        mov     %gs:CPU_TASK_CR3(%rax), %rax 
        mov     %rax, %cr3
#if     DEBUG
        mov     %rax, %gs:CPU_ENTRY_CR3
#endif
1:
        /* The text/data relationship here must be preserved in the doublemap, and the contents must be remapped */
        leaq    EXT(idt64_hndl_table0)(%rip), %rax
        /* Indirect branch to non-doublemapped trampolines */
        jmp *(%rax)
/* User return: register restoration and address space switch sequence */
Entry(ks_64bit_return)
        mov     R64_R14(%r15), %r14
        mov     R64_R13(%r15), %r13
        mov     R64_R12(%r15), %r12
        mov     R64_R11(%r15), %r11
        mov     R64_R10(%r15), %r10
        mov     R64_R9(%r15),  %r9
        mov     R64_R8(%r15),  %r8
        mov     R64_RSI(%r15), %rsi
        mov     R64_RDI(%r15), %rdi
        mov     R64_RBP(%r15), %rbp
        mov     R64_RDX(%r15), %rdx
        mov     R64_RCX(%r15), %rcx
        mov     R64_RBX(%r15), %rbx
        mov     R64_RAX(%r15), %rax
        /* Switch to per-CPU exception stack */
        mov     %gs:CPU_ESTACK, %rsp

        /* Synthesize interrupt stack frame from PCB savearea to exception stack */
        push    R64_SS(%r15)
        push    R64_RSP(%r15)
        push    R64_RFLAGS(%r15)
        push    R64_CS(%r15)
        push    R64_RIP(%r15)

        mov     R64_R15(%r15), %r15
        cmpq    $(KERNEL64_CS), 8(%rsp)
        jz      1f
        /* Discover user cr3/ASID */
        push    %rax
        mov     %gs:CPU_UCR3, %rax
#if     DEBUG
        mov     %rax, %gs:CPU_EXIT_CR3
#endif
        mov     %rax, %cr3
        /* Continue execution on the shared/doublemapped trampoline */
        pop     %rax
        swapgs
1:
        cmpl    $(SYSCALL_CS), 8(%rsp) /* test for exit via SYSRET */
        je      L_sysret
EXT(ret64_iret):
        iretq                           /* return from interrupt */
L_sysret:
        /*
         * Here to restore rcx/r11/rsp and perform the sysret back to user-space.
         *      rcx     user rip
         *      r11     user rflags
         *      rsp     user stack pointer
         */
        pop     %rcx
        add     $8, %rsp
        pop     %r11
        pop     %rsp
        sysretq                         /* return from system call */
/* End of double-mapped TEXT */
.text

Entry(ks_dispatch)
        popq    %rax
        cmpl    $(KERNEL64_CS), ISF64_CS(%rsp)
        je      EXT(ks_dispatch_kernel)

        mov     %rax, %gs:CPU_UBER_TMP
        mov     %gs:CPU_UBER_ISF, %rax
        add     $(ISF64_SIZE), %rax

        xchg    %rsp, %rax
/* Memory to memory moves (aint x86 wonderful):
 * Transfer the exception frame from the per-CPU exception stack to the
 * 'PCB' stack programmed at cswitch.
 */
        push    ISF64_SS(%rax)
        push    ISF64_RSP(%rax)
        push    ISF64_RFLAGS(%rax)
        push    ISF64_CS(%rax)
        push    ISF64_RIP(%rax)
        push    ISF64_ERR(%rax)
        push    ISF64_TRAPFN(%rax)
        push    ISF64_TRAPNO(%rax)
        mov     %gs:CPU_UBER_TMP, %rax
        jmp     EXT(ks_dispatch_user)

Entry (ks_return)
     jmp .

Entry(ks_dispatch_user)
        cmpl    $(TASK_MAP_32BIT), %gs:CPU_TASK_MAP
        je      L_dispatch_U32          /* 32-bit user task */

L_dispatch_U64:
        subq    $(ISS64_OFFSET), %rsp
        mov     %r15, R64_R15(%rsp)
        mov     %rsp, %r15
        mov     %gs:CPU_KERNEL_STACK, %rsp
        jmp     L_dispatch_64bit

Entry(ks_dispatch_kernel)
        subq    $(ISS64_OFFSET), %rsp
        mov     %r15, R64_R15(%rsp)
        mov     %rsp, %r15

/*
 * Here for 64-bit user task or kernel
 */
L_dispatch_64bit:
        movl    $(SS_64), SS_FLAVOR(%r15)

        /*
         * Save segment regs - for completeness since theyre not used.
         */
        movl    %fs, R64_FS(%r15)
        movl    %gs, R64_GS(%r15)

        /* Save general-purpose registers */
        mov     %rax, R64_RAX(%r15)
        mov     %rbx, R64_RBX(%r15)
        mov     %rcx, R64_RCX(%r15)
        mov     %rdx, R64_RDX(%r15)
        mov     %rbp, R64_RBP(%r15)
        mov     %rdi, R64_RDI(%r15)
        mov     %rsi, R64_RSI(%r15)
        mov     %r8,  R64_R8(%r15)
        mov     %r9,  R64_R9(%r15)
        mov     %r10, R64_R10(%r15)
        mov     %r11, R64_R11(%r15)
        mov     %r12, R64_R12(%r15)
        mov     %r13, R64_R13(%r15)
        mov     %r14, R64_R14(%r15)

        /* cr2 is significant only for page-faults */
        mov     %cr2, %rax
        mov     %rax, R64_CR2(%r15)

        mov     R64_TRAPNO(%r15), %ebx  /* %ebx := trapno for later */
        mov     R64_TRAPFN(%r15), %rdx  /* %rdx := trapfn for later */
        mov     R64_CS(%r15), %esi      /* %esi := cs for later */

        jmp     L_common_dispatch

L_64bit_entry_reject:
        /*
         * Here for a 64-bit user attempting an invalid kernel entry.
         */
        movq    $(HNDL_ALLTRAPS), ISF64_TRAPFN(%rsp)
        movq    $(T_INVALID_OPCODE), ISF64_TRAPNO(%rsp)
        jmp     L_dispatch_U64
        
Entry(ks_32bit_entry_check)
        /*
         * Check we're not a confused 64-bit user.
         */
        cmpl    $(TASK_MAP_32BIT), %gs:CPU_TASK_MAP
        jne     L_64bit_entry_reject
        /* fall through to 32-bit handler: */

L_dispatch_U32: /* 32-bit user task */
        subq    $(ISS64_OFFSET), %rsp
        mov     %rsp, %r15
        mov     %gs:CPU_KERNEL_STACK, %rsp
        movl    $(SS_32), SS_FLAVOR(%r15)

        /*
         * Save segment regs
         */
        movl    %ds, R32_DS(%r15)
        movl    %es, R32_ES(%r15)
        movl    %fs, R32_FS(%r15)
        movl    %gs, R32_GS(%r15)

        /*
         * Save general 32-bit registers
         */
        mov     %eax, R32_EAX(%r15)
        mov     %ebx, R32_EBX(%r15)
        mov     %ecx, R32_ECX(%r15)
        mov     %edx, R32_EDX(%r15)
        mov     %ebp, R32_EBP(%r15)
        mov     %esi, R32_ESI(%r15)
        mov     %edi, R32_EDI(%r15)

        /* Unconditionally save cr2; only meaningful on page faults */
        mov     %cr2, %rax
        mov     %eax, R32_CR2(%r15)

        /*
         * Copy registers already saved in the machine state 
         * (in the interrupt stack frame) into the compat save area.
         */
        mov     R64_RIP(%r15), %eax
        mov     %eax, R32_EIP(%r15)
        mov     R64_RFLAGS(%r15), %eax
        mov     %eax, R32_EFLAGS(%r15)
        mov     R64_RSP(%r15), %eax
        mov     %eax, R32_UESP(%r15)
        mov     R64_SS(%r15), %eax
        mov     %eax, R32_SS(%r15)
L_dispatch_U32_after_fault:
        mov     R64_CS(%r15), %esi              /* %esi := %cs for later */
        mov     %esi, R32_CS(%r15)
        mov     R64_TRAPNO(%r15), %ebx          /* %ebx := trapno for later */
        mov     %ebx, R32_TRAPNO(%r15)
        mov     R64_ERR(%r15), %eax
        mov     %eax, R32_ERR(%r15)
        mov     R64_TRAPFN(%r15), %rdx          /* %rdx := trapfn for later */

L_common_dispatch:
        cld             /* Ensure the direction flag is clear in the kernel */
        cmpl    $0, EXT(pmap_smap_enabled)(%rip)
        je      1f
        clac            /* Clear EFLAGS.AC if SMAP is present/enabled */
1:
        /*
         * On entering the kernel, we typically don't switch CR3
         * because the kernel shares the user's address space.
         * But we mark the kernel's cr3 as "active" for TLB coherency evaluation
         * If, however, the CPU's invalid TLB flag is set, we have to invalidate the TLB
         * since the kernel pagetables were changed while we were in userspace.
         *
         * For threads with a mapped pagezero (some WINE games) on non-SMAP platforms,
         * we switch to the kernel's address space on entry. Also, 
         * if the global no_shared_cr3 is TRUE we do switch to the kernel's cr3
         * so that illicit accesses to userspace can be trapped.
         */
        mov     %gs:CPU_KERNEL_CR3, %rcx
        mov     %rcx, %gs:CPU_ACTIVE_CR3
        test    $3, %esi                        /* user/kernel? */
        jz      2f                              /* skip cr3 reload from kernel */
        xor     %rbp, %rbp
        cmpl    $0, %gs:CPU_PAGEZERO_MAPPED
        jnz     11f
        cmpl    $0, EXT(no_shared_cr3)(%rip)
        je      2f
11:
        xor     %eax, %eax
        movw    %gs:CPU_KERNEL_PCID, %ax
        or      %rax, %rcx
        mov     %rcx, %cr3                      /* load kernel cr3 */
        jmp     4f                              /* and skip tlb flush test */
2:
        mov     %gs:CPU_ACTIVE_CR3+4, %rcx
        shr     $32, %rcx
        testl   %ecx, %ecx
        jz      4f
        movl    $0, %gs:CPU_TLB_INVALID
        mov     %cr4, %rcx      /* RMWW CR4, for lack of an alternative*/
        and     $(~CR4_PGE), %rcx
        mov     %rcx, %cr4
        or      $(CR4_PGE), %rcx
        mov     %rcx, %cr4
4:
        mov     %gs:CPU_ACTIVE_THREAD, %rcx     /* Get the active thread */
        testq   %rcx, %rcx
        je      5f
        movl    $-1, TH_IOTIER_OVERRIDE(%rcx)   /* Reset IO tier override to -1 before handling trap */
        cmpq    $0, TH_PCB_IDS(%rcx)    /* Is there a debug register state? */
        je      5f
        xor     %ecx, %ecx              /* If so, reset DR7 (the control) */
        mov     %rcx, %dr7
5:
        incl    %gs:hwIntCnt(,%ebx,4)           // Bump the trap/intr count
        /* Dispatch the designated handler */
        leaq    EXT(idt64_hndl_table1)(%rip), %rax
        jmp     *(%rax, %rdx, 8)

/*
 * Control is passed here to return to user.
 */ 
Entry(return_to_user)
        TIME_TRAP_UEXIT

Entry(ret_to_user)
// XXX 'Be nice to tidy up this debug register restore sequence...
        mov     %gs:CPU_ACTIVE_THREAD, %rdx
        movq    TH_PCB_IDS(%rdx),%rax   /* Obtain this thread's debug state */
        
        test    %rax, %rax              /* Is there a debug register context? */
        je      2f                      /* branch if not */
        cmpl    $(TASK_MAP_32BIT), %gs:CPU_TASK_MAP /* Are we a 32-bit task? */
        jne     1f
        movl    DS_DR0(%rax), %ecx      /* If so, load the 32 bit DRs */
        movq    %rcx, %dr0
        movl    DS_DR1(%rax), %ecx
        movq    %rcx, %dr1
        movl    DS_DR2(%rax), %ecx
        movq    %rcx, %dr2
        movl    DS_DR3(%rax), %ecx
        movq    %rcx, %dr3
        movl    DS_DR7(%rax), %ecx
        movq    %rcx, %gs:CPU_DR7
        jmp     2f
1:
        mov     DS64_DR0(%rax), %rcx    /* Load the full width DRs*/
        mov     %rcx, %dr0
        mov     DS64_DR1(%rax), %rcx
        mov     %rcx, %dr1
        mov     DS64_DR2(%rax), %rcx
        mov     %rcx, %dr2
        mov     DS64_DR3(%rax), %rcx
        mov     %rcx, %dr3
        mov     DS64_DR7(%rax), %rcx
        mov     %rcx, %gs:CPU_DR7
2:
        /*
         * On exiting the kernel there's typically no need to switch cr3 since we're
         * already running in the user's address space which includes the
         * kernel. We now mark the task's cr3 as active, for TLB coherency.
         * If the target address space has a pagezero mapping present, or
         * if no_shared_cr3 is set, we do need to switch cr3 at this point.
         */
        mov     %gs:CPU_TASK_CR3, %rcx
        mov     %rcx, %gs:CPU_ACTIVE_CR3
        cmpl    $0, %gs:CPU_PAGEZERO_MAPPED
        jnz     L_cr3_switch_island
        movl    EXT(no_shared_cr3)(%rip), %eax
        test    %eax, %eax              /* -no_shared_cr3 */
        jnz     L_cr3_switch_island

L_cr3_switch_return:
        mov     %gs:CPU_DR7, %rax       /* Is there a debug control register?*/
        cmp     $0, %rax
        je      4f
        mov     %rax, %dr7              /* Set DR7 */
        movq    $0, %gs:CPU_DR7
4:
        cmpl    $(SS_64), SS_FLAVOR(%r15)       /* 64-bit state? */
        je      L_64bit_return

L_32bit_return:
#if DEBUG_IDT64
        cmpl    $(SS_32), SS_FLAVOR(%r15)       /* 32-bit state? */
        je      1f
        cli
        POSTCODE2(0x6432)
        CCALL1(panic_idt64, %r15)
1:
#endif /* DEBUG_IDT64 */

        /*
         * Restore registers into the machine state for iret.
         * Here on fault stack and PCB address in R11.
         */
        movl    R32_EIP(%r15), %eax
        movl    %eax, R64_RIP(%r15)
        movl    R32_EFLAGS(%r15), %eax
        movl    %eax, R64_RFLAGS(%r15)
        movl    R32_CS(%r15), %eax
        movl    %eax, R64_CS(%r15)
        movl    R32_UESP(%r15), %eax
        movl    %eax, R64_RSP(%r15)
        movl    R32_SS(%r15), %eax
        movl    %eax, R64_SS(%r15)

        /* Validate DS/ES/FS/GS segment selectors with the Load Access Rights instruction prior to restoration */
        /* Exempt "known good" statically configured selectors, e.g. USER_DS and 0 */
        cmpl    $(USER_DS), R32_DS(%r15)
        jz      22f
        cmpl    $0, R32_DS(%r15)
        jz      22f
        larw    R32_DS(%r15), %ax
        jz      22f
        movl    $(USER_DS), R32_DS(%r15)
22:
        cmpl    $(USER_DS), R32_ES(%r15)
        jz      33f
        cmpl    $0, R32_ES(%r15)
        jz      33f
        larw    R32_ES(%r15), %ax
        jz      33f
        movl    $(USER_DS), R32_ES(%r15)
33:
        cmpl    $(USER_DS), R32_FS(%r15)
        jz      44f
        cmpl    $0, R32_FS(%r15)
        jz      44f
        larw    R32_FS(%r15), %ax
        jz      44f
        movl    $(USER_DS), R32_FS(%r15)
44:
        cmpl    $(USER_CTHREAD), R32_GS(%r15)
        jz      55f
        cmpl    $0, R32_GS(%r15)
        jz      55f
        larw    R32_GS(%r15), %ax
        jz      55f
        movl    $(USER_CTHREAD), R32_GS(%r15)
55:
        /*
         * Restore general 32-bit registers
         */
        movl    R32_EAX(%r15), %eax
        movl    R32_EBX(%r15), %ebx
        movl    R32_ECX(%r15), %ecx
        movl    R32_EDX(%r15), %edx
        movl    R32_EBP(%r15), %ebp
        movl    R32_ESI(%r15), %esi
        movl    R32_EDI(%r15), %edi

        /*
         * Restore segment registers. A segment exception taken here will
         * push state on the IST1 stack and will not affect the "PCB stack".
         */
        mov     %r15, %rsp              /* Set the PCB as the stack */
        swapgs

        xor     %r8, %r8
        xor     %r9, %r9
        xor     %r10, %r10
        xor     %r11, %r11
        xor     %r12, %r12
        xor     %r13, %r13
        xor     %r14, %r14
        xor     %r15, %r15

EXT(ret32_set_ds):      
        movw    R32_DS(%rsp), %ds
EXT(ret32_set_es):
        movw    R32_ES(%rsp), %es
EXT(ret32_set_fs):
        movw    R32_FS(%rsp), %fs
EXT(ret32_set_gs):
        movw    R32_GS(%rsp), %gs

        /* pop compat frame + trapno, trapfn and error */       
        add     $(ISS64_OFFSET)+8+8+8, %rsp
        cmpl    $(SYSENTER_CS),ISF64_CS-8-8-8(%rsp)
                                        /* test for fast entry/exit */
        je      L_fast_exit
EXT(ret32_iret):
        iretq                           /* return from interrupt */

L_fast_exit:
        pop     %rdx                    /* user return eip */
        pop     %rcx                    /* pop and toss cs */
        andl    $(~EFL_IF), (%rsp)      /* clear interrupts enable, sti below */
        popf                            /* flags - carry denotes failure */
        pop     %rcx                    /* user return esp */
        sti                             /* interrupts enabled after sysexit */
        sysexitl                        /* 32-bit sysexit */

L_cr3_switch_island:
        xor     %eax, %eax
        movw    %gs:CPU_ACTIVE_PCID, %ax
        or      %rax, %rcx
        mov     %rcx, %cr3
        jmp     L_cr3_switch_return

ret_to_kernel:
#if DEBUG_IDT64
        cmpl    $(SS_64), SS_FLAVOR(%r15)       /* 64-bit state? */
        je      1f
        cli
        POSTCODE2(0x6464)
        CCALL1(panic_idt64, %r15)
        hlt
1:
        cmpl    $(KERNEL64_CS), R64_CS(%r15)
        je      2f
        CCALL1(panic_idt64, %r15)
        hlt
2:
#endif

L_64bit_return:
        /*
         * Restore general 64-bit registers.
         * Here on fault stack and PCB address in R15.
         */
        leaq    EXT(idt64_hndl_table0)(%rip), %rax
        jmp *8(%rax)

Entry(ks_idt64_debug_kernel)
        /*
         * trap came from kernel mode
         */

        push    %rax                    /* save %rax temporarily */
        lea     EXT(idt64_sysenter)(%rip), %rax
        cmp     %rax, ISF64_RIP+8(%rsp)
        pop     %rax
        jne     EXT(ks_dispatch_kernel)
        /*
         * Interrupt stack frame has been pushed on the temporary stack.
         * We have to switch to pcb stack and patch up the saved state.
         */ 
        mov     %rcx, ISF64_ERR(%rsp)   /* save %rcx in error slot */
        mov     ISF64_SS+8(%rsp), %rcx  /* top of temp stack -> pcb stack */
        xchg    %rcx,%rsp               /* switch to pcb stack */
        push    $(USER_DS)              /* ss */
        push    ISF64_ERR(%rcx)         /* saved %rcx into rsp slot */
        push    ISF64_RFLAGS(%rcx)      /* rflags */
        push    $(SYSENTER_TF_CS)       /* cs - not SYSENTER_CS for iret path */
        mov     ISF64_ERR(%rcx),%rcx    /* restore %rcx */
        jmp     L_sysenter_continue     /* continue sysenter entry */
        
Entry(ks_trap_check_kernel_exit)
        testb   $3,ISF64_CS(%rsp)
        jz      L_kernel_gpf

        /* Here for fault from user-space. Copy interrupt state to PCB. */
        swapgs
        push    %rax
        mov     %rcx, %gs:CPU_UBER_TMP          /* save user RCX  */
        mov     %gs:CPU_UBER_ISF, %rcx          /* PCB stack addr */
        mov     ISF64_SS+8(%rsp), %rax
        mov     %rax, ISF64_SS(%rcx)
        mov     ISF64_RSP+8(%rsp), %rax
        mov     %rax, ISF64_RSP(%rcx)
        mov     ISF64_RFLAGS+8(%rsp), %rax
        mov     %rax, ISF64_RFLAGS(%rcx)
        mov     ISF64_CS+8(%rsp), %rax
        mov     %rax, ISF64_CS(%rcx)
        mov     ISF64_RIP+8(%rsp), %rax
        mov     %rax, ISF64_RIP(%rcx)
        mov     ISF64_ERR+8(%rsp), %rax
        mov     %rax, ISF64_ERR(%rcx)
        mov     ISF64_TRAPFN+8(%rsp), %rax
        mov     %rax, ISF64_TRAPFN(%rcx)
        mov     ISF64_TRAPNO+8(%rsp), %rax
        mov     %rax, ISF64_TRAPNO(%rcx)
        pop     %rax
        mov     %gs:CPU_UBER_TMP, %rsp          /* user RCX into RSP */
        xchg    %rcx, %rsp                      /* to PCB stack with user RCX */
        jmp     EXT(ks_dispatch_user)

L_kernel_gpf:
        /* Here for GPF from kernel_space. Check for recoverable cases. */
        push    %rax
        leaq    EXT(ret32_iret)(%rip), %rax
        cmp     %rax, 8+ISF64_RIP(%rsp)
        je      L_fault_iret
        leaq    EXT(ret64_iret)(%rip), %rax
        cmp     %rax, 8+ISF64_RIP(%rsp)
        je      L_fault_iret
        leaq    EXT(ret32_set_ds)(%rip), %rax
        cmp     %rax, 8+ISF64_RIP(%rsp)
        je      L_32bit_fault_set_seg
        leaq    EXT(ret32_set_es)(%rip), %rax
        cmp     %rax, 8+ISF64_RIP(%rsp)
        je      L_32bit_fault_set_seg
        leaq    EXT(ret32_set_fs)(%rip), %rax
        cmp     %rax, 8+ISF64_RIP(%rsp)
        je      L_32bit_fault_set_seg
        leaq    EXT(ret32_set_gs)(%rip), %rax
        cmp     %rax, 8+ISF64_RIP(%rsp)
        je      L_32bit_fault_set_seg
        jmp     EXT(ks_kernel_trap)
        /* Fall through */

Entry(ks_kernel_trap)
        /*
         * Here after taking an unexpected trap from kernel mode - perhaps
         * while running in the trampolines hereabouts.
         * Note: %rax has been pushed on stack.
         * Make sure we're not on the PCB stack, if so move to the kernel stack.
         * This is likely a fatal condition.
         * But first, ensure we have the kernel gs base active...
         */
        push    %rcx
        push    %rdx
        mov     $(MSR_IA32_GS_BASE), %ecx
        rdmsr                                   /* read kernel gsbase */
        test    $0x80000000, %edx               /* test MSB of address */
        jne     1f
        swapgs                                  /* so swap */
1:
        pop     %rdx
        pop     %rcx

        movq    %gs:CPU_UBER_ISF, %rax          /* PCB stack addr */
        subq    %rsp, %rax
        cmpq    $(PAGE_SIZE), %rax              /* current stack in PCB? */
        jb      2f                              /*  - yes, deal with it */
        pop     %rax                            /*  - no, restore %rax */
        jmp     EXT(ks_dispatch_kernel)
2:
        /*
         *  Here if %rsp is in the PCB
         *  Copy the interrupt stack frame from PCB stack to kernel stack
         */
        movq    %gs:CPU_KERNEL_STACK, %rax
        xchgq   %rax, %rsp
        pushq   8+ISF64_SS(%rax)
        pushq   8+ISF64_RSP(%rax)
        pushq   8+ISF64_RFLAGS(%rax)
        pushq   8+ISF64_CS(%rax)
        pushq   8+ISF64_RIP(%rax)
        pushq   8+ISF64_ERR(%rax)
        pushq   8+ISF64_TRAPFN(%rax)
        pushq   8+ISF64_TRAPNO(%rax)
        movq    (%rax), %rax
        jmp     EXT(ks_dispatch_kernel)


/*
 * GP/NP fault on IRET: CS or SS is in error.
 * User GSBASE is active.
 * On IST1 stack containing:
 *  (rax saved above, which is immediately popped)
 *  0  ISF64_TRAPNO:    trap code (NP or GP)
 *  8  ISF64_TRAPFN:    trap function
 *  16 ISF64_ERR:       segment number in error (error code)
 *  24 ISF64_RIP:       kernel RIP
 *  32 ISF64_CS:        kernel CS
 *  40 ISF64_RFLAGS:    kernel RFLAGS 
 *  48 ISF64_RSP:       kernel RSP
 *  56 ISF64_SS:        kernel SS
 * On the PCB stack, pointed to by the kernel's RSP is:
 *   0                  user RIP
 *   8                  user CS
 *  16                  user RFLAGS
 *  24                  user RSP
 *  32                  user SS
 *
 * We need to move the kernel's TRAPNO, TRAPFN and ERR to the PCB and handle
 * as a user fault with:
 *  0  ISF64_TRAPNO:    trap code (NP or GP)
 *  8  ISF64_TRAPFN:    trap function
 *  16 ISF64_ERR:       segment number in error (error code)
 *  24                  user RIP
 *  32                  user CS
 *  40                  user RFLAGS
 *  48                  user RSP
 *  56                  user SS
 */
L_fault_iret:
        pop     %rax                    /* recover saved %rax */
        mov     %rax, ISF64_RIP(%rsp)   /* save rax (we don`t need saved rip) */
        mov     ISF64_RSP(%rsp), %rax
        xchg    %rax, %rsp              /* switch to PCB stack */
        push    ISF64_ERR(%rax)
        push    ISF64_TRAPFN(%rax)
        push    ISF64_TRAPNO(%rax)
        mov     ISF64_RIP(%rax), %rax   /* restore rax */
                                        /* now treat as fault from user */
        jmp     L_dispatch

/*
 * Fault restoring a segment register.  All of the saved state is still
 * on the stack untouched since we haven't yet moved the stack pointer.
 * On IST1 stack containing:
 *  (rax saved above, which is immediately popped)
 *  0  ISF64_TRAPNO:    trap code (NP or GP)
 *  8  ISF64_TRAPFN:    trap function
 *  16 ISF64_ERR:       segment number in error (error code)
 *  24 ISF64_RIP:       kernel RIP
 *  32 ISF64_CS:        kernel CS
 *  40 ISF64_RFLAGS:    kernel RFLAGS 
 *  48 ISF64_RSP:       kernel RSP
 *  56 ISF64_SS:        kernel SS
 * On the PCB stack, pointed to by the kernel's RSP is:
 *  0                   user trap code
 *  8                   user trap function
 *  16                  user err 
 *  24                  user RIP
 *  32                  user CS
 *  40                  user RFLAGS
 *  48                  user RSP
 *  56                  user SS
 */
L_32bit_fault_set_seg:
        swapgs
        pop     %rax                    /* toss saved %rax from stack */
        mov     ISF64_TRAPNO(%rsp), %rax
        mov     ISF64_TRAPFN(%rsp), %rcx
        mov     ISF64_ERR(%rsp), %rdx
        mov     ISF64_RSP(%rsp), %rsp   /* reset stack to saved state */
        mov     %rax,R64_TRAPNO(%rsp)
        mov     %rcx,R64_TRAPFN(%rsp)
        mov     %rdx,R64_ERR(%rsp)
                                        /* now treat as fault from user */
                                        /* except that all the state is */
                                        /* already saved - we just have to */
                                        /* move the trapno and error into */
                                        /* the compatibility frame */
        jmp     L_dispatch_U32_after_fault


Entry(ks_idt64_nmi_kernel)
        /* From user-space: copy interrupt state to user PCB */
        swapgs
        mov     %gs:CPU_UBER_ISF, %rcx          /* PCB stack addr */
        add     $(ISF64_SIZE), %rcx             /* adjust to base of ISF */     
        swapgs                                  /* swap back for L_dispatch */
        jmp     4f                              /* Copy state to PCB */

1:
        /*
        * From kernel-space:
         * Determine whether the kernel or user GS is set.
         * Set the kernel and ensure that we'll swap back correctly at IRET.
         */
        mov     $(MSR_IA32_GS_BASE), %ecx
        rdmsr                                   /* read kernel gsbase */
        test    $0x80000000, %edx               /* test MSB of address */
        jne     2f
        swapgs                                  /* so swap */
        movl    $1, ISF64_CS+4(%rsp)            /* and set flag in CS slot */
2:
        /*
         * Determine whether we're on the kernel or interrupt stack
         * when the NMI hit.
         */
        mov     ISF64_RSP(%rsp), %rcx
        mov     %gs:CPU_KERNEL_STACK, %rax
        xor     %rcx, %rax
        and     EXT(kernel_stack_mask)(%rip), %rax
        test    %rax, %rax              /* are we on the kernel stack? */
        je      3f                      /* yes */

        mov     %gs:CPU_INT_STACK_TOP, %rax
        dec     %rax                    /* intr stack top is byte above max */
        xor     %rcx, %rax
        and     EXT(kernel_stack_mask)(%rip), %rax
        test    %rax, %rax              /* are we on the interrupt stack? */
        je      3f                      /* yes */

        mov    %gs:CPU_KERNEL_STACK, %rcx
3:
        /* 16-byte-align kernel/interrupt stack for state push */
        and     $0xFFFFFFFFFFFFFFF0, %rcx

4:
        /*
         * Copy state from NMI stack (RSP) to the save area (RCX) which is
         * the PCB for user or kernel/interrupt stack from kernel.
         * ISF64_ERR(RSP)    saved RAX
         * ISF64_TRAPFN(RSP) saved RCX
         * ISF64_TRAPNO(RSP) saved RDX
         */
        xchg    %rsp, %rcx                      /* set for pushes */
        push    ISF64_SS(%rcx)
        push    ISF64_RSP(%rcx)
        push    ISF64_RFLAGS(%rcx)
        push    ISF64_CS(%rcx)
        push    ISF64_RIP(%rcx)
        push    $(0)                            /* error code 0 */
        push    $(HNDL_ALLINTRS)                /* trapfn allintrs */
        push    $(T_NMI)                        /* trapno T_NMI */
        mov     ISF64_ERR(%rcx), %rax
        mov     ISF64_TRAPNO(%rcx), %rdx
        mov     ISF64_TRAPFN(%rcx), %rcx
        jmp     L_dispatch


/* All 'exceptions' enter hndl_alltraps, with:
 *      r15     x86_saved_state_t address
 *      rsp     kernel stack if user-space, otherwise interrupt or kernel stack
 *      esi     cs at trap
 * 
 * The rest of the state is set up as:  
 *      both rsp and r15 are 16-byte aligned
 *      interrupts disabled
 *      direction flag cleared
 */
Entry(hndl_alltraps)
        mov     %esi, %eax
        testb   $3, %al
        jz      trap_from_kernel

        TIME_TRAP_UENTRY

        /* Check for active vtimers in the current task */
        mov     %gs:CPU_ACTIVE_THREAD, %rcx
        movl    $-1, TH_IOTIER_OVERRIDE(%rcx)   /* Reset IO tier override to -1 before handling trap/exception */
        mov     TH_TASK(%rcx), %rbx
        TASK_VTIMER_CHECK(%rbx, %rcx)

        CCALL1(user_trap, %r15)                 /* call user trap routine */
        /* user_trap() unmasks interrupts */
        cli                                     /* hold off intrs - critical section */
        xorl    %ecx, %ecx                      /* don't check if we're in the PFZ */


Entry(return_from_trap)
        movq    %gs:CPU_ACTIVE_THREAD,%r15      /* Get current thread */
        movl    $-1, TH_IOTIER_OVERRIDE(%r15)   /* Reset IO tier override to -1 before returning to userspace */
        cmpl    $0, TH_RWLOCK_COUNT(%r15)       /* Check if current thread has pending RW locks held */
        jz      1f
        xorq    %rbp, %rbp              /* clear framepointer */
        mov     %r15, %rdi              /* Set RDI to current thread */
        CCALL(lck_rw_clear_promotions_x86)      /* Clear promotions if needed */
1:      
        movq    TH_PCB_ISS(%r15), %r15          /* PCB stack */
        movl    %gs:CPU_PENDING_AST,%eax
        testl   %eax,%eax
        je      EXT(return_to_user)             /* branch if no AST */

L_return_from_trap_with_ast:
        testl   %ecx, %ecx              /* see if we need to check for an EIP in the PFZ */
        je      2f                      /* no, go handle the AST */
        cmpl    $(SS_64), SS_FLAVOR(%r15)       /* are we a 64-bit task? */
        je      1f
                                        /* no... 32-bit user mode */
        movl    R32_EIP(%r15), %edi
        xorq    %rbp, %rbp              /* clear framepointer */
        CCALL(commpage_is_in_pfz32)
        testl   %eax, %eax
        je      2f                      /* not in the PFZ... go service AST */
        movl    %eax, R32_EBX(%r15)     /* let the PFZ know we've pended an AST */
        jmp     EXT(return_to_user)
1:
        movq    R64_RIP(%r15), %rdi
        xorq    %rbp, %rbp              /* clear framepointer */
        CCALL(commpage_is_in_pfz64)
        testl   %eax, %eax
        je      2f                      /* not in the PFZ... go service AST */
        movl    %eax, R64_RBX(%r15)     /* let the PFZ know we've pended an AST */
        jmp     EXT(return_to_user)
2:

        xorq    %rbp, %rbp              /* clear framepointer */
        CCALL(ast_taken_user)           /* handle all ASTs (enables interrupts, may return via continuation) */

        cli
        mov     %rsp, %r15              /* AST changes stack, saved state */
        xorl    %ecx, %ecx              /* don't check if we're in the PFZ */
        jmp     EXT(return_from_trap)   /* and check again (rare) */

/*
 * Trap from kernel mode.  No need to switch stacks.
 * Interrupts must be off here - we will set them to state at time of trap
 * as soon as it's safe for us to do so and not recurse doing preemption
 * 
 */
trap_from_kernel:
        movq    %r15, %rdi              /* saved state addr */
        pushq   R64_RIP(%r15)           /* Simulate a CALL from fault point */
        pushq   %rbp                    /* Extend framepointer chain */
        movq    %rsp, %rbp
        CCALLWITHSP(kernel_trap)        /* to kernel trap routine */
        popq    %rbp
        addq    $8, %rsp
        mov     %rsp, %r15              /* DTrace slides stack/saved-state */
        cli

        movl    %gs:CPU_PENDING_AST,%eax        /* get pending asts */
        testl   $(AST_URGENT),%eax              /* any urgent preemption? */
        je      ret_to_kernel                   /* no, nothing to do */
        cmpl    $(T_PREEMPT),R64_TRAPNO(%r15)
        je      ret_to_kernel                   /* T_PREEMPT handled in kernel_trap() */
        testl   $(EFL_IF),R64_RFLAGS(%r15)      /* interrupts disabled? */
        je      ret_to_kernel
        cmpl    $0,%gs:CPU_PREEMPTION_LEVEL     /* preemption disabled? */
        jne     ret_to_kernel
        movq    %gs:CPU_KERNEL_STACK,%rax
        movq    %rsp,%rcx
        xorq    %rax,%rcx
        andq    EXT(kernel_stack_mask)(%rip),%rcx
        testq   %rcx,%rcx               /* are we on the kernel stack? */
        jne     ret_to_kernel           /* no, skip it */

        CCALL(ast_taken_kernel)         /* take the AST */

        mov     %rsp, %r15              /* AST changes stack, saved state */
        jmp     ret_to_kernel


/*
 * All interrupts on all tasks enter here with:
 *      r15      x86_saved_state_t
 *      rsp      kernel or interrupt stack
 *      esi      cs at trap
 *
 *      both rsp and r15 are 16-byte aligned
 *      interrupts disabled
 *      direction flag cleared
 */
Entry(hndl_allintrs)
        /*
         * test whether already on interrupt stack
         */
        movq    %gs:CPU_INT_STACK_TOP,%rcx
        cmpq    %rsp,%rcx
        jb      1f
        leaq    -INTSTACK_SIZE(%rcx),%rdx
        cmpq    %rsp,%rdx
        jb      int_from_intstack
1:
        xchgq   %rcx,%rsp               /* switch to interrupt stack */

        mov     %cr0,%rax               /* get cr0 */
        orl     $(CR0_TS),%eax          /* or in TS bit */
        mov     %rax,%cr0               /* set cr0 */

        pushq   %rcx                    /* save pointer to old stack */
        pushq   %gs:CPU_INT_STATE       /* save previous intr state */
        movq    %r15,%gs:CPU_INT_STATE  /* set intr state */
        
        TIME_INT_ENTRY                  /* do timing */

        /* Check for active vtimers in the current task */
        mov     %gs:CPU_ACTIVE_THREAD, %rcx
        mov     TH_TASK(%rcx), %rbx
        TASK_VTIMER_CHECK(%rbx, %rcx)

        incl    %gs:CPU_PREEMPTION_LEVEL
        incl    %gs:CPU_INTERRUPT_LEVEL

        CCALL1(interrupt, %r15)         /* call generic interrupt routine */

.globl  EXT(return_to_iret)
LEXT(return_to_iret)                    /* (label for kdb_kintr and hardclock) */

        decl    %gs:CPU_INTERRUPT_LEVEL
        decl    %gs:CPU_PREEMPTION_LEVEL

        TIME_INT_EXIT                   /* do timing */

        popq    %gs:CPU_INT_STATE       /* reset/clear intr state pointer */
        popq    %rsp                    /* switch back to old stack */

        movq    %gs:CPU_ACTIVE_THREAD,%rax
        movq    TH_PCB_FPS(%rax),%rax   /* get pcb's ifps */
        cmpq    $0,%rax                 /* Is there a context */
        je      1f                      /* Branch if not */
        movl    FP_VALID(%rax),%eax     /* Load fp_valid */
        cmpl    $0,%eax                 /* Check if valid */
        jne     1f                      /* Branch if valid */
        clts                            /* Clear TS */
        jmp     2f
1:
        mov     %cr0,%rax               /* get cr0 */
        orl     $(CR0_TS),%eax          /* or in TS bit */
        mov     %rax,%cr0               /* set cr0 */
2:
        /* Load interrupted code segment into %eax */
        movl    R32_CS(%r15),%eax       /* assume 32-bit state */
        cmpl    $(SS_64),SS_FLAVOR(%r15)/* 64-bit? */   
#if DEBUG_IDT64
        jne     4f
        movl    R64_CS(%r15),%eax       /* 64-bit user mode */
        jmp     3f
4:
        cmpl    $(SS_32),SS_FLAVOR(%r15)
        je      3f
        POSTCODE2(0x6431)
        CCALL1(panic_idt64, %r15)
        hlt
#else
        jne     3f
        movl    R64_CS(%r15),%eax       /* 64-bit user mode */
#endif
3:
        testb   $3,%al                  /* user mode, */
        jnz     ast_from_interrupt_user /* go handle potential ASTs */
        /*
         * we only want to handle preemption requests if
         * the interrupt fell in the kernel context
         * and preemption isn't disabled
         */
        movl    %gs:CPU_PENDING_AST,%eax        
        testl   $(AST_URGENT),%eax              /* any urgent requests? */
        je      ret_to_kernel                   /* no, nothing to do */

        cmpl    $0,%gs:CPU_PREEMPTION_LEVEL     /* preemption disabled? */
        jne     ret_to_kernel                   /* yes, skip it */

        /*
         * Take an AST from kernel space.  We don't need (and don't want)
         * to do as much as the case where the interrupt came from user
         * space.
         */
        CCALL(ast_taken_kernel)

        mov     %rsp, %r15              /* AST changes stack, saved state */
        jmp     ret_to_kernel


/*
 * nested int - simple path, can't preempt etc on way out
 */
int_from_intstack:
        incl    %gs:CPU_PREEMPTION_LEVEL
        incl    %gs:CPU_INTERRUPT_LEVEL
        incl    %gs:CPU_NESTED_ISTACK

        push    %gs:CPU_INT_STATE
        mov     %r15, %gs:CPU_INT_STATE

        CCALL1(interrupt, %r15)

        pop     %gs:CPU_INT_STATE

        decl    %gs:CPU_INTERRUPT_LEVEL
        decl    %gs:CPU_PREEMPTION_LEVEL
        decl    %gs:CPU_NESTED_ISTACK

        jmp     ret_to_kernel

/*
 *      Take an AST from an interrupted user
 */
ast_from_interrupt_user:
        movl    %gs:CPU_PENDING_AST,%eax
        testl   %eax,%eax               /* pending ASTs? */
        je      EXT(ret_to_user)        /* no, nothing to do */

        TIME_TRAP_UENTRY

        movl    $1, %ecx                /* check if we're in the PFZ */
        jmp     L_return_from_trap_with_ast     /* return */


/* Syscall dispatch routines! */

/*
 *
 * 32bit Tasks
 * System call entries via INTR_GATE or sysenter:
 *
 *      r15      x86_saved_state32_t
 *      rsp      kernel stack
 *
 *      both rsp and r15 are 16-byte aligned
 *      interrupts disabled
 *      direction flag cleared
 */

Entry(hndl_sysenter)
        /*
         * We can be here either for a mach syscall or a unix syscall,
         * as indicated by the sign of the code:
         */
        movl    R32_EAX(%r15),%eax
        testl   %eax,%eax
        js      EXT(hndl_mach_scall)            /* < 0 => mach */
                                                /* > 0 => unix */
        
Entry(hndl_unix_scall)

        TIME_TRAP_UENTRY

        movq    %gs:CPU_ACTIVE_THREAD,%rcx      /* get current thread     */
        movq    TH_TASK(%rcx),%rbx              /* point to current task  */
        incl    TH_SYSCALLS_UNIX(%rcx)          /* increment call count   */

        /* Check for active vtimers in the current task */
        TASK_VTIMER_CHECK(%rbx,%rcx)

        sti

        CCALL1(unix_syscall, %r15)
        /*
         * always returns through thread_exception_return
         */


Entry(hndl_mach_scall)
        TIME_TRAP_UENTRY

        movq    %gs:CPU_ACTIVE_THREAD,%rcx      /* get current thread     */
        movq    TH_TASK(%rcx),%rbx              /* point to current task  */
        incl    TH_SYSCALLS_MACH(%rcx)          /* increment call count   */

        /* Check for active vtimers in the current task */
        TASK_VTIMER_CHECK(%rbx,%rcx)

        sti

        CCALL1(mach_call_munger, %r15)
        /*
         * always returns through thread_exception_return
         */


Entry(hndl_mdep_scall)
        TIME_TRAP_UENTRY

        /* Check for active vtimers in the current task */
        movq    %gs:CPU_ACTIVE_THREAD,%rcx      /* get current thread     */
        movq    TH_TASK(%rcx),%rbx              /* point to current task  */
        TASK_VTIMER_CHECK(%rbx,%rcx)

        sti

        CCALL1(machdep_syscall, %r15)
        /*
         * always returns through thread_exception_return
         */

/*
 * 64bit Tasks
 * System call entries via syscall only:
 *
 *      r15      x86_saved_state64_t
 *      rsp      kernel stack
 *
 *      both rsp and r15 are 16-byte aligned
 *      interrupts disabled
 *      direction flag cleared
 */

Entry(hndl_syscall)
        TIME_TRAP_UENTRY

        movq    %gs:CPU_ACTIVE_THREAD,%rcx      /* get current thread     */
        movl    $-1, TH_IOTIER_OVERRIDE(%rcx)   /* Reset IO tier override to -1 before handling syscall */
        movq    TH_TASK(%rcx),%rbx              /* point to current task  */

        /* Check for active vtimers in the current task */
        TASK_VTIMER_CHECK(%rbx,%rcx)

        /*
         * We can be here either for a mach, unix machdep or diag syscall,
         * as indicated by the syscall class:
         */
        movl    R64_RAX(%r15), %eax             /* syscall number/class */
        movl    %eax, %edx
        andl    $(SYSCALL_CLASS_MASK), %edx     /* syscall class */
        cmpl    $(SYSCALL_CLASS_MACH<<SYSCALL_CLASS_SHIFT), %edx
        je      EXT(hndl_mach_scall64)
        cmpl    $(SYSCALL_CLASS_UNIX<<SYSCALL_CLASS_SHIFT), %edx
        je      EXT(hndl_unix_scall64)
        cmpl    $(SYSCALL_CLASS_MDEP<<SYSCALL_CLASS_SHIFT), %edx
        je      EXT(hndl_mdep_scall64)
        cmpl    $(SYSCALL_CLASS_DIAG<<SYSCALL_CLASS_SHIFT), %edx
        je      EXT(hndl_diag_scall64)

        /* Syscall class unknown */
        sti
        CCALL3(i386_exception, $(EXC_SYSCALL), %rax, $1)
        /* no return */


Entry(hndl_unix_scall64)
        incl    TH_SYSCALLS_UNIX(%rcx)          /* increment call count   */
        sti

        CCALL1(unix_syscall64, %r15)
        /*
         * always returns through thread_exception_return
         */


Entry(hndl_mach_scall64)
        incl    TH_SYSCALLS_MACH(%rcx)          /* increment call count   */
        sti

        CCALL1(mach_call_munger64, %r15)
        /*
         * always returns through thread_exception_return
         */



Entry(hndl_mdep_scall64)
        sti

        CCALL1(machdep_syscall64, %r15)
        /*
         * always returns through thread_exception_return
         */

Entry(hndl_diag_scall64)
        CCALL1(diagCall64, %r15)        // Call diagnostics
        test    %eax, %eax              // What kind of return is this?
        je      1f                      // - branch if bad (zero)
        jmp     EXT(return_to_user)     // Normal return, do not check asts...
1:
        sti
        CCALL3(i386_exception, $EXC_SYSCALL, $0x6000, $1)
        /* no return */
/* TODO assert at all 'C' entry points that we're never operating on the fault stack's alias mapping */
Entry(hndl_machine_check)
        /* Adjust SP and savearea to their canonical, non-aliased addresses */
        subq    EXT(dblmap_dist)(%rip), %rsp
        subq    EXT(dblmap_dist)(%rip), %r15
        CCALL1(panic_machine_check64, %r15)
        hlt

Entry(hndl_double_fault)
        subq    EXT(dblmap_dist)(%rip), %rsp
        subq    EXT(dblmap_dist)(%rip), %r15
        CCALL1(panic_double_fault64, %r15)
        hlt