entry.s

//linux内核入口

 

 

/*
 *  linux/arch/x86_64/entry.S
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 2000, 2001, 2002  Andi Kleen SuSE Labs
 *  Copyright (C) 2000  Pavel Machek <[e-mail]>
 */

/*
 * entry.S contains the system-call and fault low-level handling routines.
 *
 * Some of this is documented in Documentation/x86/entry_64.txt
 *
 * NOTE: This code handles signal-recognition, which happens every time
 * after an interrupt and after each system call.
 *
 * Normal syscalls and interrupts don't save a full stack frame, this is
 * only done for syscall tracing, signals or fork/exec et.al.
 *
 * A note on terminology:
 * - top of stack: Architecture defined interrupt frame from SS to RIP
 * at the top of the kernel process stack.
 * - partial stack frame: partially saved registers up to R11.
 * - full stack frame: Like partial stack frame, but all register saved.
 *
 * Some macro usage:
 * - CFI macros are used to generate dwarf2 unwind information for better
 * backtraces. They don't change any code.
 * - SAVE_ALL/RESTORE_ALL - Save/restore all registers
 * - SAVE_ARGS/RESTORE_ARGS - Save/restore registers that C functions modify.
 * There are unfortunately lots of special cases where some registers
 * not touched. The macro is a big mess that should be cleaned up.
 * - SAVE_REST/RESTORE_REST - Handle the registers not saved by SAVE_ARGS.
 * Gives a full stack frame.
 * - ENTRY/END Define functions in the symbol table.
 * - FIXUP_TOP_OF_STACK/RESTORE_TOP_OF_STACK - Fix up the hardware stack
 * frame that is otherwise undefined after a SYSCALL
 * - TRACE_IRQ_* - Trace hard interrupt state for lock debugging.
 * - errorentry/paranoidentry/zeroentry - Define exception entry points.
 */

#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/cache.h>
#include <asm/errno.h>
#include <asm/dwarf2.h>
#include <asm/calling.h>
#include <asm/asm-offsets.h>
#include <asm/msr.h>
#include <asm/unistd.h>
#include <asm/thread_info.h>
#include <asm/hw_irq.h>
#include <asm/page_types.h>
#include <asm/irqflags.h>
#include <asm/paravirt.h>
#include <asm/ftrace.h>
#include <asm/percpu.h>
#include <asm/asm.h>
#include <asm/context_tracking.h>
#include <asm/smap.h>
#include <linux/err.h>

/* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */
#include <linux/elf-em.h>
#define AUDIT_ARCH_X86_64 (EM_X86_64|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
#define __AUDIT_ARCH_64BIT 0x80000000
#define __AUDIT_ARCH_LE    0x40000000

 .code64
 .section .entry.text, "ax"

#ifdef CONFIG_FUNCTION_TRACER

#ifdef CC_USING_FENTRY
# define function_hook __fentry__
#else
# define function_hook mcount
#endif

#ifdef CONFIG_DYNAMIC_FTRACE

ENTRY(function_hook)
 retq
END(function_hook)

/* skip is set if stack has been adjusted */
.macro ftrace_caller_setup skip=0
 MCOUNT_SAVE_FRAME \skip

 /* Load the ftrace_ops into the 3rd parameter */
 leaq function_trace_op, %rdx

 /* Load ip into the first parameter */
 movq RIP(%rsp), %rdi
 subq $MCOUNT_INSN_SIZE, %rdi
 /* Load the parent_ip into the second parameter */
#ifdef CC_USING_FENTRY
 movq SS+16(%rsp), %rsi
#else
 movq 8(%rbp), %rsi
#endif
.endm

ENTRY(ftrace_caller)
 /* Check if tracing was disabled (quick check) */
 cmpl $0, function_trace_stop
 jne  ftrace_stub

 ftrace_caller_setup
 /* regs go into 4th parameter (but make it NULL) */
 movq $0, %rcx

GLOBAL(ftrace_call)
 call ftrace_stub

 MCOUNT_RESTORE_FRAME
ftrace_return:

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
GLOBAL(ftrace_graph_call)
 jmp ftrace_stub
#endif

GLOBAL(ftrace_stub)
 retq
END(ftrace_caller)

ENTRY(ftrace_regs_caller)
 /* Save the current flags before compare (in SS location)*/
 pushfq

 /* Check if tracing was disabled (quick check) */
 cmpl $0, function_trace_stop
 jne  ftrace_restore_flags

 /* skip=8 to skip flags saved in SS */
 ftrace_caller_setup 8

 /* Save the rest of pt_regs */
 movq %r15, R15(%rsp)
 movq %r14, R14(%rsp)
 movq %r13, R13(%rsp)
 movq %r12, R12(%rsp)
 movq %r11, R11(%rsp)
 movq %r10, R10(%rsp)
 movq %rbp, RBP(%rsp)
 movq %rbx, RBX(%rsp)
 /* Copy saved flags */
 movq SS(%rsp), %rcx
 movq %rcx, EFLAGS(%rsp)
 /* Kernel segments */
 movq $__KERNEL_DS, %rcx
 movq %rcx, SS(%rsp)
 movq $__KERNEL_CS, %rcx
 movq %rcx, CS(%rsp)
 /* Stack - skipping return address */
 leaq SS+16(%rsp), %rcx
 movq %rcx, RSP(%rsp)

 /* regs go into 4th parameter */
 leaq (%rsp), %rcx

GLOBAL(ftrace_regs_call)
 call ftrace_stub

 /* Copy flags back to SS, to restore them */
 movq EFLAGS(%rsp), %rax
 movq %rax, SS(%rsp)

 /* Handlers can change the RIP */
 movq RIP(%rsp), %rax
 movq %rax, SS+8(%rsp)

 /* restore the rest of pt_regs */
 movq R15(%rsp), %r15
 movq R14(%rsp), %r14
 movq R13(%rsp), %r13
 movq R12(%rsp), %r12
 movq R10(%rsp), %r10
 movq RBP(%rsp), %rbp
 movq RBX(%rsp), %rbx

 /* skip=8 to skip flags saved in SS */
 MCOUNT_RESTORE_FRAME 8

 /* Restore flags */
 popfq

 jmp ftrace_return
ftrace_restore_flags:
 popfq
 jmp  ftrace_stub

END(ftrace_regs_caller)

#else /* ! CONFIG_DYNAMIC_FTRACE */

ENTRY(function_hook)
 cmpl $0, function_trace_stop
 jne  ftrace_stub

 cmpq $ftrace_stub, ftrace_trace_function
 jnz trace

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
 cmpq $ftrace_stub, ftrace_graph_return
 jnz ftrace_graph_caller

 cmpq $ftrace_graph_entry_stub, ftrace_graph_entry
 jnz ftrace_graph_caller
#endif

GLOBAL(ftrace_stub)
 retq

trace:
 MCOUNT_SAVE_FRAME

 movq RIP(%rsp), %rdi
#ifdef CC_USING_FENTRY
 movq SS+16(%rsp), %rsi
#else
 movq 8(%rbp), %rsi
#endif
 subq $MCOUNT_INSN_SIZE, %rdi

 call   *ftrace_trace_function

 MCOUNT_RESTORE_FRAME

 jmp ftrace_stub
END(function_hook)
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_TRACER */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller)
 MCOUNT_SAVE_FRAME

#ifdef CC_USING_FENTRY
 leaq SS+16(%rsp), %rdi
 movq $0, %rdx /* No framepointers needed */
#else
 leaq 8(%rbp), %rdi
 movq (%rbp), %rdx
#endif
 movq RIP(%rsp), %rsi
 subq $MCOUNT_INSN_SIZE, %rsi

 call prepare_ftrace_return

 MCOUNT_RESTORE_FRAME

 retq
END(ftrace_graph_caller)

GLOBAL(return_to_handler)
 subq  $24, %rsp

 /* Save the return values */
 movq %rax, (%rsp)
 movq %rdx, 8(%rsp)
 movq %rbp, %rdi

 call ftrace_return_to_handler

 movq %rax, %rdi
 movq 8(%rsp), %rdx
 movq (%rsp), %rax
 addq $24, %rsp
 jmp *%rdi
#endif

#ifndef CONFIG_PREEMPT
#define retint_kernel retint_restore_args
#endif

#ifdef CONFIG_PARAVIRT
ENTRY(native_usergs_sysret64)
 swapgs
 sysretq
ENDPROC(native_usergs_sysret64)
#endif /* CONFIG_PARAVIRT */

.macro TRACE_IRQS_IRETQ offset=ARGOFFSET
#ifdef CONFIG_TRACE_IRQFLAGS
 bt   $9,EFLAGS-\offset(%rsp) /* interrupts off? */
 jnc  1f
 TRACE_IRQS_ON
1:
#endif
.endm

/*
 * When dynamic function tracer is enabled it will add a breakpoint
 * to all locations that it is about to modify, sync CPUs, update
 * all the code, sync CPUs, then remove the breakpoints. In this time
 * if lockdep is enabled, it might jump back into the debug handler
 * outside the updating of the IST protection. (TRACE_IRQS_ON/OFF).
 *
 * We need to change the IDT table before calling TRACE_IRQS_ON/OFF to
 * make sure the stack pointer does not get reset back to the top
 * of the debug stack, and instead just reuses the current stack.
 */
#if defined(CONFIG_DYNAMIC_FTRACE) && defined(CONFIG_TRACE_IRQFLAGS)

.macro TRACE_IRQS_OFF_DEBUG
 call debug_stack_set_zero
 TRACE_IRQS_OFF
 call debug_stack_reset
.endm

.macro TRACE_IRQS_ON_DEBUG
 call debug_stack_set_zero
 TRACE_IRQS_ON
 call debug_stack_reset
.endm

.macro TRACE_IRQS_IRETQ_DEBUG offset=ARGOFFSET
 bt   $9,EFLAGS-\offset(%rsp) /* interrupts off? */
 jnc  1f
 TRACE_IRQS_ON_DEBUG
1:
.endm

#else
# define TRACE_IRQS_OFF_DEBUG  TRACE_IRQS_OFF
# define TRACE_IRQS_ON_DEBUG  TRACE_IRQS_ON
# define TRACE_IRQS_IRETQ_DEBUG  TRACE_IRQS_IRETQ
#endif

/*
 * C code is not supposed to know about undefined top of stack. Every time
 * a C function with an pt_regs argument is called from the SYSCALL based
 * fast path FIXUP_TOP_OF_STACK is needed.
 * RESTORE_TOP_OF_STACK syncs the syscall state after any possible ptregs
 * manipulation.
 */

 /* %rsp:at FRAMEEND */
 .macro FIXUP_TOP_OF_STACK tmp offset=0
 movq PER_CPU_VAR(old_rsp),\tmp
 movq \tmp,RSP+\offset(%rsp)
 movq $__USER_DS,SS+\offset(%rsp)
 movq $__USER_CS,CS+\offset(%rsp)
 movq $-1,RCX+\offset(%rsp)
 movq R11+\offset(%rsp),\tmp  /* get eflags */
 movq \tmp,EFLAGS+\offset(%rsp)
 .endm

 .macro RESTORE_TOP_OF_STACK tmp offset=0
 movq RSP+\offset(%rsp),\tmp
 movq \tmp,PER_CPU_VAR(old_rsp)
 movq EFLAGS+\offset(%rsp),\tmp
 movq \tmp,R11+\offset(%rsp)
 .endm

 .macro FAKE_STACK_FRAME child_rip
 /* push in order ss, rsp, eflags, cs, rip */
 xorl %eax, %eax
 pushq_cfi $__KERNEL_DS /* ss */
 /*CFI_REL_OFFSET ss,0*/
 pushq_cfi %rax /* rsp */
 CFI_REL_OFFSET rsp,0
 pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_BIT1) /* eflags - interrupts on */
 /*CFI_REL_OFFSET rflags,0*/
 pushq_cfi $__KERNEL_CS /* cs */
 /*CFI_REL_OFFSET cs,0*/
 pushq_cfi \child_rip /* rip */
 CFI_REL_OFFSET rip,0
 pushq_cfi %rax /* orig rax */
 .endm

 .macro UNFAKE_STACK_FRAME
 addq $8*6, %rsp
 CFI_ADJUST_CFA_OFFSET -(6*8)
 .endm

/*
 * initial frame state for interrupts (and exceptions without error code)
 */
 .macro EMPTY_FRAME start=1 offset=0
 .if \start
 CFI_STARTPROC simple
 CFI_SIGNAL_FRAME
 CFI_DEF_CFA rsp,8+\offset
 .else
 CFI_DEF_CFA_OFFSET 8+\offset
 .endif
 .endm

/*
 * initial frame state for interrupts (and exceptions without error code)
 */
 .macro INTR_FRAME start=1 offset=0
 EMPTY_FRAME \start, SS+8+\offset-RIP
 /*CFI_REL_OFFSET ss, SS+\offset-RIP*/
 CFI_REL_OFFSET rsp, RSP+\offset-RIP
 /*CFI_REL_OFFSET rflags, EFLAGS+\offset-RIP*/
 /*CFI_REL_OFFSET cs, CS+\offset-RIP*/
 CFI_REL_OFFSET rip, RIP+\offset-RIP
 .endm

/*
 * initial frame state for exceptions with error code (and interrupts
 * with vector already pushed)
 */
 .macro XCPT_FRAME start=1 offset=0
 INTR_FRAME \start, RIP+\offset-ORIG_RAX
 /*CFI_REL_OFFSET orig_rax, ORIG_RAX-ORIG_RAX*/
 .endm

/*
 * frame that enables calling into C.
 */
 .macro PARTIAL_FRAME start=1 offset=0
 XCPT_FRAME \start, ORIG_RAX+\offset-ARGOFFSET
 CFI_REL_OFFSET rdi, RDI+\offset-ARGOFFSET
 CFI_REL_OFFSET rsi, RSI+\offset-ARGOFFSET
 CFI_REL_OFFSET rdx, RDX+\offset-ARGOFFSET
 CFI_REL_OFFSET rcx, RCX+\offset-ARGOFFSET
 CFI_REL_OFFSET rax, RAX+\offset-ARGOFFSET
 CFI_REL_OFFSET r8, R8+\offset-ARGOFFSET
 CFI_REL_OFFSET r9, R9+\offset-ARGOFFSET
 CFI_REL_OFFSET r10, R10+\offset-ARGOFFSET
 CFI_REL_OFFSET r11, R11+\offset-ARGOFFSET
 .endm

/*
 * frame that enables passing a complete pt_regs to a C function.
 */
 .macro DEFAULT_FRAME start=1 offset=0
 PARTIAL_FRAME \start, R11+\offset-R15
 CFI_REL_OFFSET rbx, RBX+\offset
 CFI_REL_OFFSET rbp, RBP+\offset
 CFI_REL_OFFSET r12, R12+\offset
 CFI_REL_OFFSET r13, R13+\offset
 CFI_REL_OFFSET r14, R14+\offset
 CFI_REL_OFFSET r15, R15+\offset
 .endm

/* save partial stack frame */
 .macro SAVE_ARGS_IRQ
 cld
 /* start from rbp in pt_regs and jump over */
 movq_cfi rdi, (RDI-RBP)
 movq_cfi rsi, (RSI-RBP)
 movq_cfi rdx, (RDX-RBP)
 movq_cfi rcx, (RCX-RBP)
 movq_cfi rax, (RAX-RBP)
 movq_cfi  r8,  (R8-RBP)
 movq_cfi  r9,  (R9-RBP)
 movq_cfi r10, (R10-RBP)
 movq_cfi r11, (R11-RBP)

 /* Save rbp so that we can unwind from get_irq_regs() */
 movq_cfi rbp, 0

 /* Save previous stack value */
 movq %rsp, %rsi

 leaq -RBP(%rsp),%rdi /* arg1 for handler */
 testl $3, CS-RBP(%rsi)
 je 1f
 SWAPGS
 /*
  * irq_count is used to check if a CPU is already on an interrupt stack
  * or not. While this is essentially redundant with preempt_count it is
  * a little cheaper to use a separate counter in the PDA (short of
  * moving irq_enter into assembly, which would be too much work)
  */
1: incl PER_CPU_VAR(irq_count)
 cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
 CFI_DEF_CFA_REGISTER rsi

 /* Store previous stack value */
 pushq %rsi
 CFI_ESCAPE 0x0f /* DW_CFA_def_cfa_expression */, 6, \
   0x77 /* DW_OP_breg7 */, 0, \
   0x06 /* DW_OP_deref */, \
   0x08 /* DW_OP_const1u */, SS+8-RBP, \
   0x22 /* DW_OP_plus */
 /* We entered an interrupt context - irqs are off: */
 TRACE_IRQS_OFF
 .endm

ENTRY(save_rest)
 PARTIAL_FRAME 1 (REST_SKIP+8)
 movq 5*8+16(%rsp), %r11 /* save return address */
 movq_cfi rbx, RBX+16
 movq_cfi rbp, RBP+16
 movq_cfi r12, R12+16
 movq_cfi r13, R13+16
 movq_cfi r14, R14+16
 movq_cfi r15, R15+16
 movq %r11, 8(%rsp) /* return address */
 FIXUP_TOP_OF_STACK %r11, 16
 ret
 CFI_ENDPROC
END(save_rest)

/* save complete stack frame */
 .pushsection .kprobes.text, "ax"
ENTRY(save_paranoid)
 XCPT_FRAME 1 RDI+8
 cld
 movq_cfi rdi, RDI+8
 movq_cfi rsi, RSI+8
 movq_cfi rdx, RDX+8
 movq_cfi rcx, RCX+8
 movq_cfi rax, RAX+8
 movq_cfi r8, R8+8
 movq_cfi r9, R9+8
 movq_cfi r10, R10+8
 movq_cfi r11, R11+8
 movq_cfi rbx, RBX+8
 movq_cfi rbp, RBP+8
 movq_cfi r12, R12+8
 movq_cfi r13, R13+8
 movq_cfi r14, R14+8
 movq_cfi r15, R15+8
 movl $1,%ebx
 movl $MSR_GS_BASE,%ecx
 rdmsr
 testl %edx,%edx
 js 1f /* negative -> in kernel */
 SWAPGS
 xorl %ebx,%ebx
1: ret
 CFI_ENDPROC
END(save_paranoid)
 .popsection

/*
 * A newly forked process directly context switches into this address.
 *
 * rdi: prev task we switched from
 */
ENTRY(ret_from_fork)
 DEFAULT_FRAME

 LOCK ; btr $TIF_FORK,TI_flags(%r8)

 pushq_cfi $0x0002
 popfq_cfi    # reset kernel eflags

 call schedule_tail   # rdi: 'prev' task parameter

 GET_THREAD_INFO(%rcx)

 RESTORE_REST

 testl $3, CS-ARGOFFSET(%rsp)  # from kernel_thread?
 jz   1f

 testl $_TIF_IA32, TI_flags(%rcx) # 32-bit compat task needs IRET
 jnz  int_ret_from_sys_call

 RESTORE_TOP_OF_STACK %rdi, -ARGOFFSET
 jmp ret_from_sys_call   # go to the SYSRET fastpath

1:
 subq $REST_SKIP, %rsp # leave space for volatiles
 CFI_ADJUST_CFA_OFFSET REST_SKIP
 movq %rbp, %rdi
 call *%rbx
 movl $0, RAX(%rsp)
 RESTORE_REST
 jmp int_ret_from_sys_call
 CFI_ENDPROC
END(ret_from_fork)

/*
 * System call entry. Up to 6 arguments in registers are supported.
 *
 * SYSCALL does not save anything on the stack and does not change the
 * stack pointer.  However, it does mask the flags register for us, so
 * CLD and CLAC are not needed.
 */

/*
 * Register setup:
 * rax  system call number
 * rdi  arg0
 * rcx  return address for syscall/sysret, C arg3
 * rsi  arg1
 * rdx  arg2
 * r10  arg3  (--> moved to rcx for C)
 * r8   arg4
 * r9   arg5
 * r11  eflags for syscall/sysret, temporary for C
 * r12-r15,rbp,rbx saved by C code, not touched.
 *
 * Interrupts are off on entry.
 * Only called from user space.
 *
 * XXX if we had a free scratch register we could save the RSP into the stack frame
 *      and report it properly in ps. Unfortunately we haven't.
 *
 * When user can change the frames always force IRET. That is because
 * it deals with uncanonical addresses better. SYSRET has trouble
 * with them due to bugs in both AMD and Intel CPUs.
 */

ENTRY(system_call)
 CFI_STARTPROC simple
 CFI_SIGNAL_FRAME
 CFI_DEF_CFA rsp,KERNEL_STACK_OFFSET
 CFI_REGISTER rip,rcx
 /*CFI_REGISTER rflags,r11*/
 SWAPGS_UNSAFE_STACK
 /*
  * A hypervisor implementation might want to use a label
  * after the swapgs, so that it can do the swapgs
  * for the guest and jump here on syscall.
  */
GLOBAL(system_call_after_swapgs)

 movq %rsp,PER_CPU_VAR(old_rsp)
 movq PER_CPU_VAR(kernel_stack),%rsp
 /*
  * No need to follow this irqs off/on section - it's straight
  * and short:
  */
 ENABLE_INTERRUPTS(CLBR_NONE)
 SAVE_ARGS 8,0
 movq  %rax,ORIG_RAX-ARGOFFSET(%rsp)
 movq  %rcx,RIP-ARGOFFSET(%rsp)
 CFI_REL_OFFSET rip,RIP-ARGOFFSET
 testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
 jnz tracesys
system_call_fastpath:
#if __SYSCALL_MASK == ~0
 cmpq $__NR_syscall_max,%rax
#else
 andl $__SYSCALL_MASK,%eax
 cmpl $__NR_syscall_max,%eax
#endif
 ja badsys
 movq %r10,%rcx
 call *sys_call_table(,%rax,8)  # XXX:  rip relative
 movq %rax,RAX-ARGOFFSET(%rsp)
/*
 * Syscall return path ending with SYSRET (fast path)
 * Has incomplete stack frame and undefined top of stack.
 */
ret_from_sys_call:
 movl $_TIF_ALLWORK_MASK,%edi
 /* edi: flagmask */
sysret_check:
 LOCKDEP_SYS_EXIT
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 movl TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET),%edx
 andl %edi,%edx
 jnz  sysret_careful
 CFI_REMEMBER_STATE
 /*
  * sysretq will re-enable interrupts:
  */
 TRACE_IRQS_ON
 movq RIP-ARGOFFSET(%rsp),%rcx
 CFI_REGISTER rip,rcx
 RESTORE_ARGS 1,-ARG_SKIP,0
 /*CFI_REGISTER rflags,r11*/
 movq PER_CPU_VAR(old_rsp), %rsp
 USERGS_SYSRET64

 CFI_RESTORE_STATE
 /* Handle reschedules */
 /* edx: work, edi: workmask */
sysret_careful:
 bt $TIF_NEED_RESCHED,%edx
 jnc sysret_signal
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_NONE)
 pushq_cfi %rdi
 SCHEDULE_USER
 popq_cfi %rdi
 jmp sysret_check

 /* Handle a signal */
sysret_signal:
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_NONE)
#ifdef CONFIG_AUDITSYSCALL
 bt $TIF_SYSCALL_AUDIT,%edx
 jc sysret_audit
#endif
 /*
  * We have a signal, or exit tracing or single-step.
  * These all wind up with the iret return path anyway,
  * so just join that path right now.
  */
 FIXUP_TOP_OF_STACK %r11, -ARGOFFSET
 jmp int_check_syscall_exit_work

badsys:
 movq $-ENOSYS,RAX-ARGOFFSET(%rsp)
 jmp ret_from_sys_call

#ifdef CONFIG_AUDITSYSCALL
 /*
  * Fast path for syscall audit without full syscall trace.
  * We just call __audit_syscall_entry() directly, and then
  * jump back to the normal fast path.
  */
auditsys:
 movq %r10,%r9   /* 6th arg: 4th syscall arg */
 movq %rdx,%r8   /* 5th arg: 3rd syscall arg */
 movq %rsi,%rcx   /* 4th arg: 2nd syscall arg */
 movq %rdi,%rdx   /* 3rd arg: 1st syscall arg */
 movq %rax,%rsi   /* 2nd arg: syscall number */
 movl $AUDIT_ARCH_X86_64,%edi /* 1st arg: audit arch */
 call __audit_syscall_entry
 LOAD_ARGS 0  /* reload call-clobbered registers */
 jmp system_call_fastpath

 /*
  * Return fast path for syscall audit.  Call __audit_syscall_exit()
  * directly and then jump back to the fast path with TIF_SYSCALL_AUDIT
  * masked off.
  */
sysret_audit:
 movq RAX-ARGOFFSET(%rsp),%rsi /* second arg, syscall return value */
 cmpq $-MAX_ERRNO,%rsi /* is it < -MAX_ERRNO? */
 setbe %al  /* 1 if so, 0 if not */
 movzbl %al,%edi  /* zero-extend that into %edi */
 call __audit_syscall_exit
 movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),%edi
 jmp sysret_check
#endif /* CONFIG_AUDITSYSCALL */

 /* Do syscall tracing */
tracesys:
#ifdef CONFIG_AUDITSYSCALL
 testl $(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT),TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
 jz auditsys
#endif
 SAVE_REST
 movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
 FIXUP_TOP_OF_STACK %rdi
 movq %rsp,%rdi
 call syscall_trace_enter
 /*
  * Reload arg registers from stack in case ptrace changed them.
  * We don't reload %rax because syscall_trace_enter() returned
  * the value it wants us to use in the table lookup.
  */
 LOAD_ARGS ARGOFFSET, 1
 RESTORE_REST
#if __SYSCALL_MASK == ~0
 cmpq $__NR_syscall_max,%rax
#else
 andl $__SYSCALL_MASK,%eax
 cmpl $__NR_syscall_max,%eax
#endif
 ja   int_ret_from_sys_call /* RAX(%rsp) set to -ENOSYS above */
 movq %r10,%rcx /* fixup for C */
 call *sys_call_table(,%rax,8)
 movq %rax,RAX-ARGOFFSET(%rsp)
 /* Use IRET because user could have changed frame */

/*
 * Syscall return path ending with IRET.
 * Has correct top of stack, but partial stack frame.
 */
GLOBAL(int_ret_from_sys_call)
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 movl $_TIF_ALLWORK_MASK,%edi
 /* edi: mask to check */
GLOBAL(int_with_check)
 LOCKDEP_SYS_EXIT_IRQ
 GET_THREAD_INFO(%rcx)
 movl TI_flags(%rcx),%edx
 andl %edi,%edx
 jnz   int_careful
 andl    $~TS_COMPAT,TI_status(%rcx)
 jmp   retint_swapgs

 /* Either reschedule or signal or syscall exit tracking needed. */
 /* First do a reschedule test. */
 /* edx: work, edi: workmask */
int_careful:
 bt $TIF_NEED_RESCHED,%edx
 jnc  int_very_careful
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_NONE)
 pushq_cfi %rdi
 SCHEDULE_USER
 popq_cfi %rdi
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 jmp int_with_check

 /* handle signals and tracing -- both require a full stack frame */
int_very_careful:
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_NONE)
int_check_syscall_exit_work:
 SAVE_REST
 /* Check for syscall exit trace */
 testl $_TIF_WORK_SYSCALL_EXIT,%edx
 jz int_signal
 pushq_cfi %rdi
 leaq 8(%rsp),%rdi # &ptregs -> arg1
 call syscall_trace_leave
 popq_cfi %rdi
 andl $~(_TIF_WORK_SYSCALL_EXIT|_TIF_SYSCALL_EMU),%edi
 jmp int_restore_rest

int_signal:
 testl $_TIF_DO_NOTIFY_MASK,%edx
 jz 1f
 movq %rsp,%rdi  # &ptregs -> arg1
 xorl %esi,%esi  # oldset -> arg2
 call do_notify_resume
1: movl $_TIF_WORK_MASK,%edi
int_restore_rest:
 RESTORE_REST
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 jmp int_with_check
 CFI_ENDPROC
END(system_call)

/*
 * Certain special system calls that need to save a complete full stack frame.
 */
 .macro PTREGSCALL label,func,arg
ENTRY(\label)
 PARTIAL_FRAME 1 8  /* offset 8: return address */
 subq $REST_SKIP, %rsp
 CFI_ADJUST_CFA_OFFSET REST_SKIP
 call save_rest
 DEFAULT_FRAME 0 8  /* offset 8: return address */
 leaq 8(%rsp), \arg /* pt_regs pointer */
 call \func
 jmp ptregscall_common
 CFI_ENDPROC
END(\label)
 .endm

 .macro FORK_LIKE func
ENTRY(stub_\func)
 CFI_STARTPROC
 popq %r11   /* save return address */
 PARTIAL_FRAME 0
 SAVE_REST
 pushq %r11   /* put it back on stack */
 FIXUP_TOP_OF_STACK %r11, 8
 DEFAULT_FRAME 0 8  /* offset 8: return address */
 call sys_\func
 RESTORE_TOP_OF_STACK %r11, 8
 ret $REST_SKIP  /* pop extended registers */
 CFI_ENDPROC
END(stub_\func)
 .endm

 FORK_LIKE  clone
 FORK_LIKE  fork
 FORK_LIKE  vfork
 PTREGSCALL stub_iopl, sys_iopl, %rsi

ENTRY(ptregscall_common)
 DEFAULT_FRAME 1 8 /* offset 8: return address */
 RESTORE_TOP_OF_STACK %r11, 8
 movq_cfi_restore R15+8, r15
 movq_cfi_restore R14+8, r14
 movq_cfi_restore R13+8, r13
 movq_cfi_restore R12+8, r12
 movq_cfi_restore RBP+8, rbp
 movq_cfi_restore RBX+8, rbx
 ret $REST_SKIP  /* pop extended registers */
 CFI_ENDPROC
END(ptregscall_common)

ENTRY(stub_execve)
 CFI_STARTPROC
 addq $8, %rsp
 PARTIAL_FRAME 0
 SAVE_REST
 FIXUP_TOP_OF_STACK %r11
 call sys_execve
 RESTORE_TOP_OF_STACK %r11
 movq %rax,RAX(%rsp)
 RESTORE_REST
 jmp int_ret_from_sys_call
 CFI_ENDPROC
END(stub_execve)

/*
 * sigreturn is special because it needs to restore all registers on return.
 * This cannot be done with SYSRET, so use the IRET return path instead.
 */
ENTRY(stub_rt_sigreturn)
 CFI_STARTPROC
 addq $8, %rsp
 PARTIAL_FRAME 0
 SAVE_REST
 movq %rsp,%rdi
 FIXUP_TOP_OF_STACK %r11
 call sys_rt_sigreturn
 movq %rax,RAX(%rsp) # fixme, this could be done at the higher layer
 RESTORE_REST
 jmp int_ret_from_sys_call
 CFI_ENDPROC
END(stub_rt_sigreturn)

#ifdef CONFIG_X86_X32_ABI
ENTRY(stub_x32_rt_sigreturn)
 CFI_STARTPROC
 addq $8, %rsp
 PARTIAL_FRAME 0
 SAVE_REST
 movq %rsp,%rdi
 FIXUP_TOP_OF_STACK %r11
 call sys32_x32_rt_sigreturn
 movq %rax,RAX(%rsp) # fixme, this could be done at the higher layer
 RESTORE_REST
 jmp int_ret_from_sys_call
 CFI_ENDPROC
END(stub_x32_rt_sigreturn)

ENTRY(stub_x32_execve)
 CFI_STARTPROC
 addq $8, %rsp
 PARTIAL_FRAME 0
 SAVE_REST
 FIXUP_TOP_OF_STACK %r11
 call compat_sys_execve
 RESTORE_TOP_OF_STACK %r11
 movq %rax,RAX(%rsp)
 RESTORE_REST
 jmp int_ret_from_sys_call
 CFI_ENDPROC
END(stub_x32_execve)

#endif

/*
 * Build the entry stubs and pointer table with some assembler magic.
 * We pack 7 stubs into a single 32-byte chunk, which will fit in a
 * single cache line on all modern x86 implementations.
 */
 .section .init.rodata,"a"
ENTRY(interrupt)
 .section .entry.text
 .p2align 5
 .p2align CONFIG_X86_L1_CACHE_SHIFT
ENTRY(irq_entries_start)
 INTR_FRAME
vector=FIRST_EXTERNAL_VECTOR
.rept (NR_VECTORS-FIRST_EXTERNAL_VECTOR+6)/7
 .balign 32
  .rept 7
    .if vector < NR_VECTORS
      .if vector <> FIRST_EXTERNAL_VECTOR
 CFI_ADJUST_CFA_OFFSET -8
      .endif
1: pushq_cfi $(~vector+0x80) /* Note: always in signed byte range */
      .if ((vector-FIRST_EXTERNAL_VECTOR)%7) <> 6
 jmp 2f
      .endif
      .previous
 .quad 1b
      .section .entry.text
vector=vector+1
    .endif
  .endr
2: jmp common_interrupt
.endr
 CFI_ENDPROC
END(irq_entries_start)

.previous
END(interrupt)
.previous

/*
 * Interrupt entry/exit.
 *
 * Interrupt entry points save only callee clobbered registers in fast path.
 *
 * Entry runs with interrupts off.
 */

/* 0(%rsp): ~(interrupt number) */
 .macro interrupt func
 /* reserve pt_regs for scratch regs and rbp */
 subq $ORIG_RAX-RBP, %rsp
 CFI_ADJUST_CFA_OFFSET ORIG_RAX-RBP
 SAVE_ARGS_IRQ
 call \func
 .endm

/*
 * Interrupt entry/exit should be protected against kprobes
 */
 .pushsection .kprobes.text, "ax"
 /*
  * The interrupt stubs push (~vector+0x80) onto the stack and
  * then jump to common_interrupt.
  */
 .p2align CONFIG_X86_L1_CACHE_SHIFT
common_interrupt:
 XCPT_FRAME
 ASM_CLAC
 addq $-0x80,(%rsp)  /* Adjust vector to [-256,-1] range */
 interrupt do_IRQ
 /* 0(%rsp): old_rsp-ARGOFFSET */
ret_from_intr:
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 decl PER_CPU_VAR(irq_count)

 /* Restore saved previous stack */
 popq %rsi
 CFI_DEF_CFA rsi,SS+8-RBP /* reg/off reset after def_cfa_expr */
 leaq ARGOFFSET-RBP(%rsi), %rsp
 CFI_DEF_CFA_REGISTER rsp
 CFI_ADJUST_CFA_OFFSET RBP-ARGOFFSET

exit_intr:
 GET_THREAD_INFO(%rcx)
 testl $3,CS-ARGOFFSET(%rsp)
 je retint_kernel

 /* Interrupt came from user space */
 /*
  * Has a correct top of stack, but a partial stack frame
  * %rcx: thread info. Interrupts off.
  */
retint_with_reschedule:
 movl $_TIF_WORK_MASK,%edi
retint_check:
 LOCKDEP_SYS_EXIT_IRQ
 movl TI_flags(%rcx),%edx
 andl %edi,%edx
 CFI_REMEMBER_STATE
 jnz  retint_careful

retint_swapgs:  /* return to user-space */
 /*
  * The iretq could re-enable interrupts:
  */
 DISABLE_INTERRUPTS(CLBR_ANY)
 TRACE_IRQS_IRETQ
 SWAPGS
 jmp restore_args

retint_restore_args: /* return to kernel space */
 DISABLE_INTERRUPTS(CLBR_ANY)
 /*
  * The iretq could re-enable interrupts:
  */
 TRACE_IRQS_IRETQ
restore_args:
 RESTORE_ARGS 1,8,1

irq_return:
 INTERRUPT_RETURN
 _ASM_EXTABLE(irq_return, bad_iret)

#ifdef CONFIG_PARAVIRT
ENTRY(native_iret)
 iretq
 _ASM_EXTABLE(native_iret, bad_iret)
#endif

 .section .fixup,"ax"
bad_iret:
 /*
  * The iret traps when the %cs or %ss being restored is bogus.
  * We've lost the original trap vector and error code.
  * #GPF is the most likely one to get for an invalid selector.
  * So pretend we completed the iret and took the #GPF in user mode.
  *
  * We are now running with the kernel GS after exception recovery.
  * But error_entry expects us to have user GS to match the user %cs,
  * so swap back.
  */
 pushq $0

 SWAPGS
 jmp general_protection

 .previous

 /* edi: workmask, edx: work */
retint_careful:
 CFI_RESTORE_STATE
 bt    $TIF_NEED_RESCHED,%edx
 jnc   retint_signal
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_NONE)
 pushq_cfi %rdi
 SCHEDULE_USER
 popq_cfi %rdi
 GET_THREAD_INFO(%rcx)
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 jmp retint_check

retint_signal:
 testl $_TIF_DO_NOTIFY_MASK,%edx
 jz    retint_swapgs
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_NONE)
 SAVE_REST
 movq $-1,ORIG_RAX(%rsp)
 xorl %esi,%esi  # oldset
 movq %rsp,%rdi  # &pt_regs
 call do_notify_resume
 RESTORE_REST
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 GET_THREAD_INFO(%rcx)
 jmp retint_with_reschedule

#ifdef CONFIG_PREEMPT
 /* Returning to kernel space. Check if we need preemption */
 /* rcx:  threadinfo. interrupts off. */
ENTRY(retint_kernel)
 cmpl $0,TI_preempt_count(%rcx)
 jnz  retint_restore_args
 bt  $TIF_NEED_RESCHED,TI_flags(%rcx)
 jnc  retint_restore_args
 bt   $9,EFLAGS-ARGOFFSET(%rsp) /* interrupts off? */
 jnc  retint_restore_args
 call preempt_schedule_irq
 jmp exit_intr
#endif

 CFI_ENDPROC
END(common_interrupt)
/*
 * End of kprobes section
 */
       .popsection

/*
 * APIC interrupts.
 */
.macro apicinterrupt num sym do_sym
ENTRY(\sym)
 INTR_FRAME
 ASM_CLAC
 pushq_cfi $~(\num)
.Lcommon_\sym:
 interrupt \do_sym
 jmp ret_from_intr
 CFI_ENDPROC
END(\sym)
.endm

#ifdef CONFIG_SMP
apicinterrupt IRQ_MOVE_CLEANUP_VECTOR \
 irq_move_cleanup_interrupt smp_irq_move_cleanup_interrupt
apicinterrupt REBOOT_VECTOR \
 reboot_interrupt smp_reboot_interrupt
#endif

#ifdef CONFIG_X86_UV
apicinterrupt UV_BAU_MESSAGE \
 uv_bau_message_intr1 uv_bau_message_interrupt
#endif
apicinterrupt LOCAL_TIMER_VECTOR \
 apic_timer_interrupt smp_apic_timer_interrupt
apicinterrupt X86_PLATFORM_IPI_VECTOR \
 x86_platform_ipi smp_x86_platform_ipi

apicinterrupt THRESHOLD_APIC_VECTOR \
 threshold_interrupt smp_threshold_interrupt
apicinterrupt THERMAL_APIC_VECTOR \
 thermal_interrupt smp_thermal_interrupt

#ifdef CONFIG_SMP
apicinterrupt CALL_FUNCTION_SINGLE_VECTOR \
 call_function_single_interrupt smp_call_function_single_interrupt
apicinterrupt CALL_FUNCTION_VECTOR \
 call_function_interrupt smp_call_function_interrupt
apicinterrupt RESCHEDULE_VECTOR \
 reschedule_interrupt smp_reschedule_interrupt
#endif

apicinterrupt ERROR_APIC_VECTOR \
 error_interrupt smp_error_interrupt
apicinterrupt SPURIOUS_APIC_VECTOR \
 spurious_interrupt smp_spurious_interrupt

#ifdef CONFIG_IRQ_WORK
apicinterrupt IRQ_WORK_VECTOR \
 irq_work_interrupt smp_irq_work_interrupt
#endif

/*
 * Exception entry points.
 */
.macro zeroentry sym do_sym
ENTRY(\sym)
 INTR_FRAME
 ASM_CLAC
 PARAVIRT_ADJUST_EXCEPTION_FRAME
 pushq_cfi $-1  /* ORIG_RAX: no syscall to restart */
 subq $ORIG_RAX-R15, %rsp
 CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
 call error_entry
 DEFAULT_FRAME 0
 movq %rsp,%rdi  /* pt_regs pointer */
 xorl %esi,%esi  /* no error code */
 call \do_sym
 jmp error_exit  /* %ebx: no swapgs flag */
 CFI_ENDPROC
END(\sym)
.endm

.macro paranoidzeroentry sym do_sym
ENTRY(\sym)
 INTR_FRAME
 ASM_CLAC
 PARAVIRT_ADJUST_EXCEPTION_FRAME
 pushq_cfi $-1  /* ORIG_RAX: no syscall to restart */
 subq $ORIG_RAX-R15, %rsp
 CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
 call save_paranoid
 TRACE_IRQS_OFF
 movq %rsp,%rdi  /* pt_regs pointer */
 xorl %esi,%esi  /* no error code */
 call \do_sym
 jmp paranoid_exit /* %ebx: no swapgs flag */
 CFI_ENDPROC
END(\sym)
.endm

#define INIT_TSS_IST(x) PER_CPU_VAR(init_tss) + (TSS_ist + ((x) - 1) * 8)
.macro paranoidzeroentry_ist sym do_sym ist
ENTRY(\sym)
 INTR_FRAME
 ASM_CLAC
 PARAVIRT_ADJUST_EXCEPTION_FRAME
 pushq_cfi $-1  /* ORIG_RAX: no syscall to restart */
 subq $ORIG_RAX-R15, %rsp
 CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
 call save_paranoid
 TRACE_IRQS_OFF_DEBUG
 movq %rsp,%rdi  /* pt_regs pointer */
 xorl %esi,%esi  /* no error code */
 subq $EXCEPTION_STKSZ, INIT_TSS_IST(\ist)
 call \do_sym
 addq $EXCEPTION_STKSZ, INIT_TSS_IST(\ist)
 jmp paranoid_exit /* %ebx: no swapgs flag */
 CFI_ENDPROC
END(\sym)
.endm

.macro errorentry sym do_sym
ENTRY(\sym)
 XCPT_FRAME
 ASM_CLAC
 PARAVIRT_ADJUST_EXCEPTION_FRAME
 subq $ORIG_RAX-R15, %rsp
 CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
 call error_entry
 DEFAULT_FRAME 0
 movq %rsp,%rdi   /* pt_regs pointer */
 movq ORIG_RAX(%rsp),%rsi /* get error code */
 movq $-1,ORIG_RAX(%rsp)  /* no syscall to restart */
 call \do_sym
 jmp error_exit   /* %ebx: no swapgs flag */
 CFI_ENDPROC
END(\sym)
.endm

 /* error code is on the stack already */
.macro paranoiderrorentry sym do_sym
ENTRY(\sym)
 XCPT_FRAME
 ASM_CLAC
 PARAVIRT_ADJUST_EXCEPTION_FRAME
 subq $ORIG_RAX-R15, %rsp
 CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
 call save_paranoid
 DEFAULT_FRAME 0
 TRACE_IRQS_OFF
 movq %rsp,%rdi   /* pt_regs pointer */
 movq ORIG_RAX(%rsp),%rsi /* get error code */
 movq $-1,ORIG_RAX(%rsp)  /* no syscall to restart */
 call \do_sym
 jmp paranoid_exit  /* %ebx: no swapgs flag */
 CFI_ENDPROC
END(\sym)
.endm

zeroentry divide_error do_divide_error
zeroentry overflow do_overflow
zeroentry bounds do_bounds
zeroentry invalid_op do_invalid_op
zeroentry device_not_available do_device_not_available
paranoiderrorentry double_fault do_double_fault
zeroentry coprocessor_segment_overrun do_coprocessor_segment_overrun
errorentry invalid_TSS do_invalid_TSS
errorentry segment_not_present do_segment_not_present
zeroentry spurious_interrupt_bug do_spurious_interrupt_bug
zeroentry coprocessor_error do_coprocessor_error
errorentry alignment_check do_alignment_check
zeroentry simd_coprocessor_error do_simd_coprocessor_error

 /* Reload gs selector with exception handling */
 /* edi:  new selector */
ENTRY(native_load_gs_index)
 CFI_STARTPROC
 pushfq_cfi
 DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
 SWAPGS
gs_change:
 movl %edi,%gs
2: mfence  /* workaround */
 SWAPGS
 popfq_cfi
 ret
 CFI_ENDPROC
END(native_load_gs_index)

 _ASM_EXTABLE(gs_change,bad_gs)
 .section .fixup,"ax"
 /* running with kernelgs */
bad_gs:
 SWAPGS   /* switch back to user gs */
 xorl %eax,%eax
 movl %eax,%gs
 jmp  2b
 .previous

/* Call softirq on interrupt stack. Interrupts are off. */
ENTRY(call_softirq)
 CFI_STARTPROC
 pushq_cfi %rbp
 CFI_REL_OFFSET rbp,0
 mov  %rsp,%rbp
 CFI_DEF_CFA_REGISTER rbp
 incl PER_CPU_VAR(irq_count)
 cmove PER_CPU_VAR(irq_stack_ptr),%rsp
 push  %rbp   # backlink for old unwinder
 call __do_softirq
 leaveq
 CFI_RESTORE  rbp
 CFI_DEF_CFA_REGISTER rsp
 CFI_ADJUST_CFA_OFFSET   -8
 decl PER_CPU_VAR(irq_count)
 ret
 CFI_ENDPROC
END(call_softirq)

#ifdef CONFIG_XEN
zeroentry xen_hypervisor_callback xen_do_hypervisor_callback

/*
 * A note on the "critical region" in our callback handler.
 * We want to avoid stacking callback handlers due to events occurring
 * during handling of the last event. To do this, we keep events disabled
 * until we've done all processing. HOWEVER, we must enable events before
 * popping the stack frame (can't be done atomically) and so it would still
 * be possible to get enough handler activations to overflow the stack.
 * Although unlikely, bugs of that kind are hard to track down, so we'd
 * like to avoid the possibility.
 * So, on entry to the handler we detect whether we interrupted an
 * existing activation in its critical region -- if so, we pop the current
 * activation and restart the handler using the previous one.
 */
ENTRY(xen_do_hypervisor_callback)   # do_hypervisor_callback(struct *pt_regs)
 CFI_STARTPROC
/*
 * Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
 * see the correct pointer to the pt_regs
 */
 movq %rdi, %rsp            # we don't return, adjust the stack frame
 CFI_ENDPROC
 DEFAULT_FRAME
11: incl PER_CPU_VAR(irq_count)
 movq %rsp,%rbp
 CFI_DEF_CFA_REGISTER rbp
 cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
 pushq %rbp   # backlink for old unwinder
 call xen_evtchn_do_upcall
 popq %rsp
 CFI_DEF_CFA_REGISTER rsp
 decl PER_CPU_VAR(irq_count)
 jmp  error_exit
 CFI_ENDPROC
END(xen_do_hypervisor_callback)

/*
 * Hypervisor uses this for application faults while it executes.
 * We get here for two reasons:
 *  1. Fault while reloading DS, ES, FS or GS
 *  2. Fault while executing IRET
 * Category 1 we do not need to fix up as Xen has already reloaded all segment
 * registers that could be reloaded and zeroed the others.
 * Category 2 we fix up by killing the current process. We cannot use the
 * normal Linux return path in this case because if we use the IRET hypercall
 * to pop the stack frame we end up in an infinite loop of failsafe callbacks.
 * We distinguish between categories by comparing each saved segment register
 * with its current contents: any discrepancy means we in category 1.
 */
ENTRY(xen_failsafe_callback)
 INTR_FRAME 1 (6*8)
 /*CFI_REL_OFFSET gs,GS*/
 /*CFI_REL_OFFSET fs,FS*/
 /*CFI_REL_OFFSET es,ES*/
 /*CFI_REL_OFFSET ds,DS*/
 CFI_REL_OFFSET r11,8
 CFI_REL_OFFSET rcx,0
 movw %ds,%cx
 cmpw %cx,0x10(%rsp)
 CFI_REMEMBER_STATE
 jne 1f
 movw %es,%cx
 cmpw %cx,0x18(%rsp)
 jne 1f
 movw %fs,%cx
 cmpw %cx,0x20(%rsp)
 jne 1f
 movw %gs,%cx
 cmpw %cx,0x28(%rsp)
 jne 1f
 /* All segments match their saved values => Category 2 (Bad IRET). */
 movq (%rsp),%rcx
 CFI_RESTORE rcx
 movq 8(%rsp),%r11
 CFI_RESTORE r11
 addq $0x30,%rsp
 CFI_ADJUST_CFA_OFFSET -0x30
 pushq_cfi $0 /* RIP */
 pushq_cfi %r11
 pushq_cfi %rcx
 jmp general_protection
 CFI_RESTORE_STATE
1: /* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */
 movq (%rsp),%rcx
 CFI_RESTORE rcx
 movq 8(%rsp),%r11
 CFI_RESTORE r11
 addq $0x30,%rsp
 CFI_ADJUST_CFA_OFFSET -0x30
 pushq_cfi $-1 /* orig_ax = -1 => not a system call */
 SAVE_ALL
 jmp error_exit
 CFI_ENDPROC
END(xen_failsafe_callback)

apicinterrupt XEN_HVM_EVTCHN_CALLBACK \
 xen_hvm_callback_vector xen_evtchn_do_upcall

#endif /* CONFIG_XEN */

/*
 * Some functions should be protected against kprobes
 */
 .pushsection .kprobes.text, "ax"

paranoidzeroentry_ist debug do_debug DEBUG_STACK
paranoidzeroentry_ist int3 do_int3 DEBUG_STACK
paranoiderrorentry stack_segment do_stack_segment
#ifdef CONFIG_XEN
zeroentry xen_debug do_debug
zeroentry xen_int3 do_int3
errorentry xen_stack_segment do_stack_segment
#endif
errorentry general_protection do_general_protection
errorentry page_fault do_page_fault
#ifdef CONFIG_KVM_GUEST
errorentry async_page_fault do_async_page_fault
#endif
#ifdef CONFIG_X86_MCE
paranoidzeroentry machine_check *machine_check_vector(%rip)
#endif

 /*
  * "Paranoid" exit path from exception stack.
  * Paranoid because this is used by NMIs and cannot take
  * any kernel state for granted.
  * We don't do kernel preemption checks here, because only
  * NMI should be common and it does not enable IRQs and
  * cannot get reschedule ticks.
  *
  * "trace" is 0 for the NMI handler only, because irq-tracing
  * is fundamentally NMI-unsafe. (we cannot change the soft and
  * hard flags at once, atomically)
  */

 /* ebx: no swapgs flag */
ENTRY(paranoid_exit)
 DEFAULT_FRAME
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF_DEBUG
 testl %ebx,%ebx    /* swapgs needed? */
 jnz paranoid_restore
 testl $3,CS(%rsp)
 jnz   paranoid_userspace
paranoid_swapgs:
 TRACE_IRQS_IRETQ 0
 SWAPGS_UNSAFE_STACK
 RESTORE_ALL 8
 jmp irq_return
paranoid_restore:
 TRACE_IRQS_IRETQ_DEBUG 0
 RESTORE_ALL 8
 jmp irq_return
paranoid_userspace:
 GET_THREAD_INFO(%rcx)
 movl TI_flags(%rcx),%ebx
 andl $_TIF_WORK_MASK,%ebx
 jz paranoid_swapgs
 movq %rsp,%rdi   /* &pt_regs */
 call sync_regs
 movq %rax,%rsp   /* switch stack for scheduling */
 testl $_TIF_NEED_RESCHED,%ebx
 jnz paranoid_schedule
 movl %ebx,%edx   /* arg3: thread flags */
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_NONE)
 xorl %esi,%esi    /* arg2: oldset */
 movq %rsp,%rdi    /* arg1: &pt_regs */
 call do_notify_resume
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 jmp paranoid_userspace
paranoid_schedule:
 TRACE_IRQS_ON
 ENABLE_INTERRUPTS(CLBR_ANY)
 SCHEDULE_USER
 DISABLE_INTERRUPTS(CLBR_ANY)
 TRACE_IRQS_OFF
 jmp paranoid_userspace
 CFI_ENDPROC
END(paranoid_exit)

/*
 * Exception entry point. This expects an error code/orig_rax on the stack.
 * returns in "no swapgs flag" in %ebx.
 */
ENTRY(error_entry)
 XCPT_FRAME
 CFI_ADJUST_CFA_OFFSET 15*8
 /* oldrax contains error code */
 cld
 movq_cfi rdi, RDI+8
 movq_cfi rsi, RSI+8
 movq_cfi rdx, RDX+8
 movq_cfi rcx, RCX+8
 movq_cfi rax, RAX+8
 movq_cfi  r8,  R8+8
 movq_cfi  r9,  R9+8
 movq_cfi r10, R10+8
 movq_cfi r11, R11+8
 movq_cfi rbx, RBX+8
 movq_cfi rbp, RBP+8
 movq_cfi r12, R12+8
 movq_cfi r13, R13+8
 movq_cfi r14, R14+8
 movq_cfi r15, R15+8
 xorl %ebx,%ebx
 testl $3,CS+8(%rsp)
 je error_kernelspace
error_swapgs:
 SWAPGS
error_sti:
 TRACE_IRQS_OFF
 ret

/*
 * There are two places in the kernel that can potentially fault with
 * usergs. Handle them here. The exception handlers after iret run with
 * kernel gs again, so don't set the user space flag. B stepping K8s
 * sometimes report an truncated RIP for IRET exceptions returning to
 * compat mode. Check for these here too.
 */
error_kernelspace:
 incl %ebx
 leaq irq_return(%rip),%rcx
 cmpq %rcx,RIP+8(%rsp)
 je error_swapgs
 movl %ecx,%eax /* zero extend */
 cmpq %rax,RIP+8(%rsp)
 je bstep_iret
 cmpq $gs_change,RIP+8(%rsp)
 je error_swapgs
 jmp error_sti

bstep_iret:
 /* Fix truncated RIP */
 movq %rcx,RIP+8(%rsp)
 jmp error_swapgs
 CFI_ENDPROC
END(error_entry)

/* ebx: no swapgs flag (1: don't need swapgs, 0: need it) */
ENTRY(error_exit)
 DEFAULT_FRAME
 movl %ebx,%eax
 RESTORE_REST
 DISABLE_INTERRUPTS(CLBR_NONE)
 TRACE_IRQS_OFF
 GET_THREAD_INFO(%rcx)
 testl %eax,%eax
 jne retint_kernel
 LOCKDEP_SYS_EXIT_IRQ
 movl TI_flags(%rcx),%edx
 movl $_TIF_WORK_MASK,%edi
 andl %edi,%edx
 jnz retint_careful
 jmp retint_swapgs
 CFI_ENDPROC
END(error_exit)

/*
 * Test if a given stack is an NMI stack or not.
 */
 .macro test_in_nmi reg stack nmi_ret normal_ret
 cmpq %\reg, \stack
 ja \normal_ret
 subq $EXCEPTION_STKSZ, %\reg
 cmpq %\reg, \stack
 jb \normal_ret
 jmp \nmi_ret
 .endm

 /* runs on exception stack */
ENTRY(nmi)
 INTR_FRAME
 PARAVIRT_ADJUST_EXCEPTION_FRAME
 /*
  * We allow breakpoints in NMIs. If a breakpoint occurs, then
  * the iretq it performs will take us out of NMI context.
  * This means that we can have nested NMIs where the next
  * NMI is using the top of the stack of the previous NMI. We
  * can't let it execute because the nested NMI will corrupt the
  * stack of the previous NMI. NMI handlers are not re-entrant
  * anyway.
  *
  * To handle this case we do the following:
  *  Check the a special location on the stack that contains
  *  a variable that is set when NMIs are executing.
  *  The interrupted task's stack is also checked to see if it
  *  is an NMI stack.
  *  If the variable is not set and the stack is not the NMI
  *  stack then:
  *    o Set the special variable on the stack
  *    o Copy the interrupt frame into a "saved" location on the stack
  *    o Copy the interrupt frame into a "copy" location on the stack
  *    o Continue processing the NMI
  *  If the variable is set or the previous stack is the NMI stack:
  *    o Modify the "copy" location to jump to the repeate_nmi
  *    o return back to the first NMI
  *
  * Now on exit of the first NMI, we first clear the stack variable
  * The NMI stack will tell any nested NMIs at that point that it is
  * nested. Then we pop the stack normally with iret, and if there was
  * a nested NMI that updated the copy interrupt stack frame, a
  * jump will be made to the repeat_nmi code that will handle the second
  * NMI.
  */

 /* Use %rdx as out temp variable throughout */
 pushq_cfi %rdx
 CFI_REL_OFFSET rdx, 0

 /*
  * If %cs was not the kernel segment, then the NMI triggered in user
  * space, which means it is definitely not nested.
  */
 cmpl $__KERNEL_CS, 16(%rsp)
 jne first_nmi

 /*
  * Check the special variable on the stack to see if NMIs are
  * executing.
  */
 cmpl $1, -8(%rsp)
 je nested_nmi

 /*
  * Now test if the previous stack was an NMI stack.
  * We need the double check. We check the NMI stack to satisfy the
  * race when the first NMI clears the variable before returning.
  * We check the variable because the first NMI could be in a
  * breakpoint routine using a breakpoint stack.
  */
 lea 6*8(%rsp), %rdx
 test_in_nmi rdx, 4*8(%rsp), nested_nmi, first_nmi
 CFI_REMEMBER_STATE

nested_nmi:
 /*
  * Do nothing if we interrupted the fixup in repeat_nmi.
  * It's about to repeat the NMI handler, so we are fine
  * with ignoring this one.
  */
 movq $repeat_nmi, %rdx
 cmpq 8(%rsp), %rdx
 ja 1f
 movq $end_repeat_nmi, %rdx
 cmpq 8(%rsp), %rdx
 ja nested_nmi_out

1:
 /* Set up the interrupted NMIs stack to jump to repeat_nmi */
 leaq -1*8(%rsp), %rdx
 movq %rdx, %rsp
 CFI_ADJUST_CFA_OFFSET 1*8
 leaq -10*8(%rsp), %rdx
 pushq_cfi $__KERNEL_DS
 pushq_cfi %rdx
 pushfq_cfi
 pushq_cfi $__KERNEL_CS
 pushq_cfi $repeat_nmi

 /* Put stack back */
 addq $(6*8), %rsp
 CFI_ADJUST_CFA_OFFSET -6*8

nested_nmi_out:
 popq_cfi %rdx
 CFI_RESTORE rdx

 /* No need to check faults here */
 INTERRUPT_RETURN

 CFI_RESTORE_STATE
first_nmi:
 /*
  * Because nested NMIs will use the pushed location that we
  * stored in rdx, we must keep that space available.
  * Here's what our stack frame will look like:
  * +-------------------------+
  * | original SS             |
  * | original Return RSP     |
  * | original RFLAGS         |
  * | original CS             |
  * | original RIP            |
  * +-------------------------+
  * | temp storage for rdx    |
  * +-------------------------+
  * | NMI executing variable  |
  * +-------------------------+
  * | copied SS               |
  * | copied Return RSP       |
  * | copied RFLAGS           |
  * | copied CS               |
  * | copied RIP              |
  * +-------------------------+
  * | Saved SS                |
  * | Saved Return RSP        |
  * | Saved RFLAGS            |
  * | Saved CS                |
  * | Saved RIP               |
  * +-------------------------+
  * | pt_regs                 |
  * +-------------------------+
  *
  * The saved stack frame is used to fix up the copied stack frame
  * that a nested NMI may change to make the interrupted NMI iret jump
  * to the repeat_nmi. The original stack frame and the temp storage
  * is also used by nested NMIs and can not be trusted on exit.
  */
 /* Do not pop rdx, nested NMIs will corrupt that part of the stack */
 movq (%rsp), %rdx
 CFI_RESTORE rdx

 /* Set the NMI executing variable on the stack. */
 pushq_cfi $1

 /*
  * Leave room for the "copied" frame
  */
 subq $(5*8), %rsp
 CFI_ADJUST_CFA_OFFSET 5*8

 /* Copy the stack frame to the Saved frame */
 .rept 5
 pushq_cfi 11*8(%rsp)
 .endr
 CFI_DEF_CFA_OFFSET SS+8-RIP

 /* Everything up to here is safe from nested NMIs */

 /*
  * If there was a nested NMI, the first NMI's iret will return
  * here. But NMIs are still enabled and we can take another
  * nested NMI. The nested NMI checks the interrupted RIP to see
  * if it is between repeat_nmi and end_repeat_nmi, and if so
  * it will just return, as we are about to repeat an NMI anyway.
  * This makes it safe to copy to the stack frame that a nested
  * NMI will update.
  */
repeat_nmi:
 /*
  * Update the stack variable to say we are still in NMI (the update
  * is benign for the non-repeat case, where 1 was pushed just above
  * to this very stack slot).
  */
 movq $1, 10*8(%rsp)

 /* Make another copy, this one may be modified by nested NMIs */
 addq $(10*8), %rsp
 CFI_ADJUST_CFA_OFFSET -10*8
 .rept 5
 pushq_cfi -6*8(%rsp)
 .endr
 subq $(5*8), %rsp
 CFI_DEF_CFA_OFFSET SS+8-RIP
end_repeat_nmi:

 /*
  * Everything below this point can be preempted by a nested
  * NMI if the first NMI took an exception and reset our iret stack
  * so that we repeat another NMI.
  */
 pushq_cfi $-1  /* ORIG_RAX: no syscall to restart */
 subq $ORIG_RAX-R15, %rsp
 CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
 /*
  * Use save_paranoid to handle SWAPGS, but no need to use paranoid_exit
  * as we should not be calling schedule in NMI context.
  * Even with normal interrupts enabled. An NMI should not be
  * setting NEED_RESCHED or anything that normal interrupts and
  * exceptions might do.
  */
 call save_paranoid
 DEFAULT_FRAME 0

 /*
  * Save off the CR2 register. If we take a page fault in the NMI then
  * it could corrupt the CR2 value. If the NMI preempts a page fault
  * handler before it was able to read the CR2 register, and then the
  * NMI itself takes a page fault, the page fault that was preempted
  * will read the information from the NMI page fault and not the
  * origin fault. Save it off and restore it if it changes.
  * Use the r12 callee-saved register.
  */
 movq %cr2, %r12

 /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
 movq %rsp,%rdi
 movq $-1,%rsi
 call do_nmi

 /* Did the NMI take a page fault? Restore cr2 if it did */
 movq %cr2, %rcx
 cmpq %rcx, %r12
 je 1f
 movq %r12, %cr2
1:
 
 testl %ebx,%ebx    /* swapgs needed? */
 jnz nmi_restore
nmi_swapgs:
 SWAPGS_UNSAFE_STACK
nmi_restore:
 /* Pop the extra iret frame at once */
 RESTORE_ALL 6*8

 /* Clear the NMI executing stack variable */
 movq $0, 5*8(%rsp)
 jmp irq_return
 CFI_ENDPROC
END(nmi)

ENTRY(ignore_sysret)
 CFI_STARTPROC
 mov $-ENOSYS,%eax
 sysret
 CFI_ENDPROC
END(ignore_sysret)

/*
 * End of kprobes section
 */
 .popsection