arch/x86/entry/entry_64_compat.S - kernel/msm-4.9 - Gitiles

 /*
  * Compatibility mode system call entry point for x86-64.
  *
  * Copyright 2000-2002 Andi Kleen, SuSE Labs.
  */
 #include "calling.h"
 #include <asm/asm-offsets.h>
 #include <asm/current.h>
 #include <asm/errno.h>
 #include <asm/ia32_unistd.h>
 #include <asm/thread_info.h>
 #include <asm/segment.h>
 #include <asm/irqflags.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
 #include <linux/linkage.h>
 #include <linux/err.h>

 	.section .entry.text, "ax"

 #ifdef CONFIG_PARAVIRT
 ENTRY(native_usergs_sysret32)
 	swapgs
 	sysretl
 ENDPROC(native_usergs_sysret32)
 #endif

 /*
  * 32-bit SYSENTER instruction entry.
  *
  * SYSENTER loads ss, rsp, cs, and rip from previously programmed MSRs.
  * IF and VM in rflags are cleared (IOW: interrupts are off).
  * SYSENTER does not save anything on the stack,
  * and does not save old rip (!!!) and rflags.
  *
  * Arguments:
  * eax  system call number
  * ebx  arg1
  * ecx  arg2
  * edx  arg3
  * esi  arg4
  * edi  arg5
  * ebp  user stack
  * 0(%ebp) arg6
  *
  * This is purely a fast path. For anything complicated we use the int 0x80
  * path below. We set up a complete hardware stack frame to share code
  * with the int 0x80 path.
  */
 ENTRY(entry_SYSENTER_compat)
 	/* Interrupts are off on entry. */
 	SWAPGS_UNSAFE_STACK
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp

 	/* Zero-extending 32-bit regs, do not remove */
 	movl	%ebp, %ebp
 	movl	%eax, %eax

 	movl	ASM_THREAD_INFO(TI_sysenter_return, %rsp, 0), %r10d

 	/* Construct struct pt_regs on stack */
 	pushq	$__USER32_DS		/* pt_regs->ss */
 	pushq	%rbp			/* pt_regs->sp */

 	/*
 	 * Push flags.  This is nasty.  First, interrupts are currently
 	 * off, but we need pt_regs->flags to have IF set.  Second, even
 	 * if TF was set when SYSENTER started, it's clear by now.  We fix
 	 * that later using TIF_SINGLESTEP.
 	 */
 	pushfq				/* pt_regs->flags (except IF = 0) */
 	orl	$X86_EFLAGS_IF, (%rsp)	/* Fix saved flags */

 	pushq	$__USER32_CS		/* pt_regs->cs */
 	pushq	%r10			/* pt_regs->ip = thread_info->sysenter_return */
 	pushq	%rax			/* pt_regs->orig_ax */
 	pushq	%rdi			/* pt_regs->di */
 	pushq	%rsi			/* pt_regs->si */
 	pushq	%rdx			/* pt_regs->dx */
 	pushq	%rcx			/* pt_regs->cx */
 	pushq	$-ENOSYS		/* pt_regs->ax */
 	cld
 	sub	$(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */

 	/*
 	 * Sysenter doesn't filter flags, so we need to clear NT
 	 * ourselves.  To save a few cycles, we can check whether
 	 * NT was set instead of doing an unconditional popfq.
 	 * This needs to happen before enabling interrupts so that
 	 * we don't get preempted with NT set.
 	 */
 	testl	$X86_EFLAGS_NT, EFLAGS(%rsp)
 	jnz	sysenter_fix_flags
 sysenter_flags_fixed:

 	/* Temporary: SYSENTER is disabled. */
 #ifdef CONFIG_CONTEXT_TRACKING
 	call enter_from_user_mode
 #endif
 	ENABLE_INTERRUPTS(CLBR_NONE)
 	movl $11, %edi
 	call do_exit

 	/*
 	 * Re-enable interrupts.  IRQ tracing already thinks that IRQs are
 	 * on (since we treat user mode as having IRQs on), and the
 	 * prologue above is too short for it to be worth adding a
 	 * tracing round trip.
 	 */
 	ENABLE_INTERRUPTS(CLBR_NONE)

 	/*
 	 * No need to do an access_ok() check here because RBP has been
 	 * 32-bit zero extended:
 	 */
 	ASM_STAC
 1:	movl	(%rbp), %ebp
 	_ASM_EXTABLE(1b, ia32_badarg)
 	ASM_CLAC

 	orl	$TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl	$_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz	sysenter_tracesys

 sysenter_do_call:
 	/* 32-bit syscall -> 64-bit C ABI argument conversion */
 	movl	%edi, %r8d		/* arg5 */
 	movl	%ebp, %r9d		/* arg6 */
 	xchg	%ecx, %esi		/* rsi:arg2, rcx:arg4 */
 	movl	%ebx, %edi		/* arg1 */
 	movl	%edx, %edx		/* arg3 (zero extension) */
 sysenter_dispatch:
 	cmpq	$(IA32_NR_syscalls-1), %rax
 	ja	1f
 	call	*ia32_sys_call_table(, %rax, 8)
 	movq	%rax, RAX(%rsp)
 1:
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
 	testl	$_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz	ia32_ret_from_sys_call_irqs_off
 sysexit_from_sys_call:
 	/*
 	 * NB: SYSEXIT is not obviously safe for 64-bit kernels -- an
 	 * NMI between STI and SYSEXIT has poorly specified behavior,
 	 * and and NMI followed by an IRQ with usergs is fatal.  So
 	 * we just pretend we're using SYSEXIT but we really use
 	 * SYSRETL instead.
 	 *
 	 * This code path is still called 'sysexit' because it pairs
 	 * with 'sysenter' and it uses the SYSENTER calling convention.
 	 */
 	andl	$~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	movl	RIP(%rsp), %ecx		/* User %eip */
 	movq    RAX(%rsp), %rax
 	movl	RSI(%rsp), %esi
 	movl	RDI(%rsp), %edi
 	xorl	%edx, %edx		/* Do not leak kernel information */
 	xorq	%r8, %r8
 	xorq	%r9, %r9
 	xorq	%r10, %r10
 	movl	EFLAGS(%rsp), %r11d	/* User eflags */
 	TRACE_IRQS_ON

 	/*
 	 * SYSRETL works even on Intel CPUs.  Use it in preference to SYSEXIT,
 	 * since it avoids a dicey window with interrupts enabled.
 	 */
 	movl	RSP(%rsp), %esp

 	/*
 	 * USERGS_SYSRET32 does:
 	 *  gsbase = user's gs base
 	 *  eip = ecx
 	 *  rflags = r11
 	 *  cs = __USER32_CS
 	 *  ss = __USER_DS
 	 *
 	 * The prologue set RIP(%rsp) to VDSO32_SYSENTER_RETURN, which does:
 	 *
 	 *  pop %ebp
 	 *  pop %edx
 	 *  pop %ecx
 	 *
 	 * Therefore, we invoke SYSRETL with EDX and R8-R10 zeroed to
 	 * avoid info leaks.  R11 ends up with VDSO32_SYSENTER_RETURN's
 	 * address (already known to user code), and R12-R15 are
 	 * callee-saved and therefore don't contain any interesting
 	 * kernel data.
 	 */
 	USERGS_SYSRET32

 sysenter_fix_flags:
 	pushq	$X86_EFLAGS_FIXED
 	popfq
 	jmp	sysenter_flags_fixed

 sysenter_tracesys:
 	SAVE_EXTRA_REGS
 	xorl	%eax, %eax		/* Do not leak kernel information */
 	movq	%rax, R11(%rsp)
 	movq	%rax, R10(%rsp)
 	movq	%rax, R9(%rsp)
 	movq	%rax, R8(%rsp)
 	movq	%rsp, %rdi		/* &pt_regs -> arg1 */
 	call	syscall_trace_enter

 	/* Reload arg registers from stack. (see sysenter_tracesys) */
 	movl	RCX(%rsp), %ecx
 	movl	RDX(%rsp), %edx
 	movl	RSI(%rsp), %esi
 	movl	RDI(%rsp), %edi
 	movl	%eax, %eax		/* zero extension */

 	RESTORE_EXTRA_REGS
 	jmp	sysenter_do_call
 ENDPROC(entry_SYSENTER_compat)

 /*
  * 32-bit SYSCALL instruction entry.
  *
  * 32-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11,
  * then loads new ss, cs, and rip from previously programmed MSRs.
  * rflags gets masked by a value from another MSR (so CLD and CLAC
  * are not needed). SYSCALL does not save anything on the stack
  * and does not change rsp.
  *
  * Note: rflags saving+masking-with-MSR happens only in Long mode
  * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
  * Don't get confused: rflags saving+masking depends on Long Mode Active bit
  * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
  * or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
  *
  * Arguments:
  * eax  system call number
  * ecx  return address
  * ebx  arg1
  * ebp  arg2	(note: not saved in the stack frame, should not be touched)
  * edx  arg3
  * esi  arg4
  * edi  arg5
  * esp  user stack
  * 0(%esp) arg6
  *
  * This is purely a fast path. For anything complicated we use the int 0x80
  * path below. We set up a complete hardware stack frame to share code
  * with the int 0x80 path.
  */
 ENTRY(entry_SYSCALL_compat)
 	/*
 	 * Interrupts are off on entry.
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
 	 * it is too small to ever cause noticeable irq latency.
 	 */
 	SWAPGS_UNSAFE_STACK

 	/* Temporary: SYSCALL32 is disabled. */
 	movl	$-ENOSYS, %eax
 	USERGS_SYSRET32

 	movl	%esp, %r8d
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 	ENABLE_INTERRUPTS(CLBR_NONE)

 	/* Zero-extending 32-bit regs, do not remove */
 	movl	%eax, %eax

 	/* Construct struct pt_regs on stack */
 	pushq	$__USER32_DS		/* pt_regs->ss */
 	pushq	%r8			/* pt_regs->sp */
 	pushq	%r11			/* pt_regs->flags */
 	pushq	$__USER32_CS		/* pt_regs->cs */
 	pushq	%rcx			/* pt_regs->ip */
 	pushq	%rax			/* pt_regs->orig_ax */
 	pushq	%rdi			/* pt_regs->di */
 	pushq	%rsi			/* pt_regs->si */
 	pushq	%rdx			/* pt_regs->dx */
 	pushq	%rbp			/* pt_regs->cx */
 	movl	%ebp, %ecx
 	pushq	$-ENOSYS		/* pt_regs->ax */
 	sub	$(10*8), %rsp		/* pt_regs->r8-11, bp, bx, r12-15 not saved */

 	/*
 	 * No need to do an access_ok check here because r8 has been
 	 * 32-bit zero extended:
 	 */
 	ASM_STAC
 1:	movl	(%r8), %r9d
 	_ASM_EXTABLE(1b, ia32_badarg)
 	ASM_CLAC
 	orl	$TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl	$_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz	cstar_tracesys

 cstar_do_call:
 	/* 32-bit syscall -> 64-bit C ABI argument conversion */
 	movl	%edi, %r8d		/* arg5 */
 	/* r9 already loaded */		/* arg6 */
 	xchg	%ecx, %esi		/* rsi:arg2, rcx:arg4 */
 	movl	%ebx, %edi		/* arg1 */
 	movl	%edx, %edx		/* arg3 (zero extension) */

 cstar_dispatch:
 	cmpq	$(IA32_NR_syscalls-1), %rax
 	ja	1f

 	call	*ia32_sys_call_table(, %rax, 8)
 	movq	%rax, RAX(%rsp)
 1:
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
 	testl	$_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz	ia32_ret_from_sys_call_irqs_off

 sysretl_from_sys_call:
 	andl	$~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	movl	RDX(%rsp), %edx
 	movl	RSI(%rsp), %esi
 	movl	RDI(%rsp), %edi
 	movl	RIP(%rsp), %ecx
 	movl	EFLAGS(%rsp), %r11d
 	movq    RAX(%rsp), %rax
 	xorq	%r10, %r10
 	xorq	%r9, %r9
 	xorq	%r8, %r8
 	TRACE_IRQS_ON
 	movl	RSP(%rsp), %esp
 	/*
 	 * 64-bit->32-bit SYSRET restores eip from ecx,
 	 * eflags from r11 (but RF and VM bits are forced to 0),
 	 * cs and ss are loaded from MSRs.
 	 * (Note: 32-bit->32-bit SYSRET is different: since r11
 	 * does not exist, it merely sets eflags.IF=1).
 	 *
 	 * NB: On AMD CPUs with the X86_BUG_SYSRET_SS_ATTRS bug, the ss
 	 * descriptor is not reinitialized.  This means that we must
 	 * avoid SYSRET with SS == NULL, which could happen if we schedule,
 	 * exit the kernel, and re-enter using an interrupt vector.  (All
 	 * interrupt entries on x86_64 set SS to NULL.)  We prevent that
 	 * from happening by reloading SS in __switch_to.
 	 */
 	USERGS_SYSRET32

 cstar_tracesys:
 	xchgl	%r9d, %ebp
 	SAVE_EXTRA_REGS
 	xorl	%eax, %eax		/* Do not leak kernel information */
 	movq	%rax, R11(%rsp)
 	movq	%rax, R10(%rsp)
 	movq	%r9, R9(%rsp)
 	movq	%rax, R8(%rsp)
 	movq	%rsp, %rdi		/* &pt_regs -> arg1 */
 	call	syscall_trace_enter
 	movl	R9(%rsp), %r9d

 	/* Reload arg registers from stack. (see sysenter_tracesys) */
 	movl	RCX(%rsp), %ecx
 	movl	RDX(%rsp), %edx
 	movl	RSI(%rsp), %esi
 	movl	RDI(%rsp), %edi
 	movl	%eax, %eax		/* zero extension */

 	RESTORE_EXTRA_REGS
 	xchgl	%ebp, %r9d
 	jmp	cstar_do_call
 END(entry_SYSCALL_compat)

 ia32_badarg:
 	/*
 	 * So far, we've entered kernel mode, set AC, turned on IRQs, and
 	 * saved C regs except r8-r11.  We haven't done any of the other
 	 * standard entry work, though.  We want to bail, but we shouldn't
 	 * treat this as a syscall entry since we don't even know what the
 	 * args are.  Instead, treat this as a non-syscall entry, finish
 	 * the entry work, and immediately exit after setting AX = -EFAULT.
 	 *
 	 * We're really just being polite here.  Killing the task outright
 	 * would be a reasonable action, too.  Given that the only valid
 	 * way to have gotten here is through the vDSO, and we already know
 	 * that the stack pointer is bad, the task isn't going to survive
 	 * for long no matter what we do.
 	 */

 	ASM_CLAC			/* undo STAC */
 	movq	$-EFAULT, RAX(%rsp)	/* return -EFAULT if possible */

 	/* Fill in the rest of pt_regs */
 	xorl	%eax, %eax
 	movq	%rax, R11(%rsp)
 	movq	%rax, R10(%rsp)
 	movq	%rax, R9(%rsp)
 	movq	%rax, R8(%rsp)
 	SAVE_EXTRA_REGS

 	/* Turn IRQs back off. */
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF

 	/* Now finish entering normal kernel mode. */
 #ifdef CONFIG_CONTEXT_TRACKING
 	call enter_from_user_mode
 #endif

 	/* And exit again. */
 	jmp retint_user

 ia32_ret_from_sys_call_irqs_off:
 	TRACE_IRQS_ON
 	ENABLE_INTERRUPTS(CLBR_NONE)

 ia32_ret_from_sys_call:
 	xorl	%eax, %eax		/* Do not leak kernel information */
 	movq	%rax, R11(%rsp)
 	movq	%rax, R10(%rsp)
 	movq	%rax, R9(%rsp)
 	movq	%rax, R8(%rsp)
 	jmp	int_ret_from_sys_call

 /*
  * Emulated IA32 system calls via int 0x80.
  *
  * Arguments:
  * eax  system call number
  * ebx  arg1
  * ecx  arg2
  * edx  arg3
  * esi  arg4
  * edi  arg5
  * ebp  arg6	(note: not saved in the stack frame, should not be touched)
  *
  * Notes:
  * Uses the same stack frame as the x86-64 version.
  * All registers except eax must be saved (but ptrace may violate that).
  * Arguments are zero extended. For system calls that want sign extension and
  * take long arguments a wrapper is needed. Most calls can just be called
  * directly.
  * Assumes it is only called from user space and entered with interrupts off.
  */

 ENTRY(entry_INT80_compat)
 	/*
 	 * Interrupts are off on entry.
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
 	 * it is too small to ever cause noticeable irq latency.
 	 */
 	PARAVIRT_ADJUST_EXCEPTION_FRAME
 	SWAPGS
 	ENABLE_INTERRUPTS(CLBR_NONE)

 	/* Zero-extending 32-bit regs, do not remove */
 	movl	%eax, %eax

 	/* Construct struct pt_regs on stack (iret frame is already on stack) */
 	pushq	%rax			/* pt_regs->orig_ax */
 	pushq	%rdi			/* pt_regs->di */
 	pushq	%rsi			/* pt_regs->si */
 	pushq	%rdx			/* pt_regs->dx */
 	pushq	%rcx			/* pt_regs->cx */
 	pushq	$-ENOSYS		/* pt_regs->ax */
 	pushq	$0			/* pt_regs->r8 */
 	pushq	$0			/* pt_regs->r9 */
 	pushq	$0			/* pt_regs->r10 */
 	pushq	$0			/* pt_regs->r11 */
 	cld
 	sub	$(6*8), %rsp /* pt_regs->bp, bx, r12-15 not saved */

 	orl	$TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl	$_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz	ia32_tracesys

 ia32_do_call:
 	/* 32-bit syscall -> 64-bit C ABI argument conversion */
 	movl	%edi, %r8d		/* arg5 */
 	movl	%ebp, %r9d		/* arg6 */
 	xchg	%ecx, %esi		/* rsi:arg2, rcx:arg4 */
 	movl	%ebx, %edi		/* arg1 */
 	movl	%edx, %edx		/* arg3 (zero extension) */
 	cmpq	$(IA32_NR_syscalls-1), %rax
 	ja	1f

 	call	*ia32_sys_call_table(, %rax, 8)
 	movq	%rax, RAX(%rsp)
 1:
 	jmp	int_ret_from_sys_call

 ia32_tracesys:
 	SAVE_EXTRA_REGS
 	movq	%rsp, %rdi			/* &pt_regs -> arg1 */
 	call	syscall_trace_enter
 	/*
 	 * Reload arg registers from stack in case ptrace changed them.
 	 * Don't reload %eax because syscall_trace_enter() returned
 	 * the %rax value we should see.  But do truncate it to 32 bits.
 	 * If it's -1 to make us punt the syscall, then (u32)-1 is still
 	 * an appropriately invalid value.
 	 */
 	movl	RCX(%rsp), %ecx
 	movl	RDX(%rsp), %edx
 	movl	RSI(%rsp), %esi
 	movl	RDI(%rsp), %edi
 	movl	%eax, %eax		/* zero extension */
 	RESTORE_EXTRA_REGS
 	jmp	ia32_do_call
 END(entry_INT80_compat)

 	.macro PTREGSCALL label, func
 	ALIGN
 GLOBAL(\label)
 	leaq	\func(%rip), %rax
 	jmp	ia32_ptregs_common
 	.endm

 	PTREGSCALL stub32_rt_sigreturn,	sys32_rt_sigreturn
 	PTREGSCALL stub32_sigreturn,	sys32_sigreturn
 	PTREGSCALL stub32_fork,		sys_fork
 	PTREGSCALL stub32_vfork,	sys_vfork

 	ALIGN
 GLOBAL(stub32_clone)
 	leaq	sys_clone(%rip), %rax
 	/*
 	 * The 32-bit clone ABI is: clone(..., int tls_val, int *child_tidptr).
 	 * The 64-bit clone ABI is: clone(..., int *child_tidptr, int tls_val).
 	 *
 	 * The native 64-bit kernel's sys_clone() implements the latter,
 	 * so we need to swap arguments here before calling it:
 	 */
 	xchg	%r8, %rcx
 	jmp	ia32_ptregs_common

 	ALIGN
 ia32_ptregs_common:
 	SAVE_EXTRA_REGS 8
 	call	*%rax
 	RESTORE_EXTRA_REGS 8
 	ret
 END(ia32_ptregs_common)
	/*
	* Compatibility mode system call entry point for x86-64.
	*
	* Copyright 2000-2002 Andi Kleen, SuSE Labs.
	*/
	#include "calling.h"
	#include <asm/asm-offsets.h>
	#include <asm/current.h>
	#include <asm/errno.h>
	#include <asm/ia32_unistd.h>
	#include <asm/thread_info.h>
	#include <asm/segment.h>
	#include <asm/irqflags.h>
	#include <asm/asm.h>
	#include <asm/smap.h>
	#include <linux/linkage.h>
	#include <linux/err.h>

	.section .entry.text, "ax"

	#ifdef CONFIG_PARAVIRT
	ENTRY(native_usergs_sysret32)
	swapgs
	sysretl
	ENDPROC(native_usergs_sysret32)
	#endif

	/*
	* 32-bit SYSENTER instruction entry.
	*
	* SYSENTER loads ss, rsp, cs, and rip from previously programmed MSRs.
	* IF and VM in rflags are cleared (IOW: interrupts are off).
	* SYSENTER does not save anything on the stack,
	* and does not save old rip (!!!) and rflags.
	*
	* Arguments:
	* eax system call number
	* ebx arg1
	* ecx arg2
	* edx arg3
	* esi arg4
	* edi arg5
	* ebp user stack
	* 0(%ebp) arg6
	*
	* This is purely a fast path. For anything complicated we use the int 0x80
	* path below. We set up a complete hardware stack frame to share code
	* with the int 0x80 path.
	*/
	ENTRY(entry_SYSENTER_compat)
	/* Interrupts are off on entry. */
	SWAPGS_UNSAFE_STACK
	movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp

	/* Zero-extending 32-bit regs, do not remove */
	movl %ebp, %ebp
	movl %eax, %eax

	movl ASM_THREAD_INFO(TI_sysenter_return, %rsp, 0), %r10d

	/* Construct struct pt_regs on stack */
	pushq $__USER32_DS /* pt_regs->ss */
	pushq %rbp /* pt_regs->sp */

	/*
	* Push flags. This is nasty. First, interrupts are currently
	* off, but we need pt_regs->flags to have IF set. Second, even
	* if TF was set when SYSENTER started, it's clear by now. We fix
	* that later using TIF_SINGLESTEP.
	*/
	pushfq /* pt_regs->flags (except IF = 0) */
	orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */

	pushq $__USER32_CS /* pt_regs->cs */
	pushq %r10 /* pt_regs->ip = thread_info->sysenter_return */
	pushq %rax /* pt_regs->orig_ax */
	pushq %rdi /* pt_regs->di */
	pushq %rsi /* pt_regs->si */
	pushq %rdx /* pt_regs->dx */
	pushq %rcx /* pt_regs->cx */
	pushq $-ENOSYS /* pt_regs->ax */
	cld
	sub $(108), %rsp / pt_regs->r8-11, bp, bx, r12-15 not saved */

	/*
	* Sysenter doesn't filter flags, so we need to clear NT
	* ourselves. To save a few cycles, we can check whether
	* NT was set instead of doing an unconditional popfq.
	* This needs to happen before enabling interrupts so that
	* we don't get preempted with NT set.
	*/
	testl $X86_EFLAGS_NT, EFLAGS(%rsp)
	jnz sysenter_fix_flags
	sysenter_flags_fixed:

	/* Temporary: SYSENTER is disabled. */
	#ifdef CONFIG_CONTEXT_TRACKING
	call enter_from_user_mode
	#endif
	ENABLE_INTERRUPTS(CLBR_NONE)
	movl $11, %edi
	call do_exit

	/*
	* Re-enable interrupts. IRQ tracing already thinks that IRQs are
	* on (since we treat user mode as having IRQs on), and the
	* prologue above is too short for it to be worth adding a
	* tracing round trip.
	*/
	ENABLE_INTERRUPTS(CLBR_NONE)

	/*
	* No need to do an access_ok() check here because RBP has been
	* 32-bit zero extended:
	*/
	ASM_STAC
	1: movl (%rbp), %ebp
	_ASM_EXTABLE(1b, ia32_badarg)
	ASM_CLAC

	orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
	testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
	jnz sysenter_tracesys

	sysenter_do_call:
	/* 32-bit syscall -> 64-bit C ABI argument conversion */
	movl %edi, %r8d /* arg5 */
	movl %ebp, %r9d /* arg6 */
	xchg %ecx, %esi /* rsi:arg2, rcx:arg4 */
	movl %ebx, %edi /* arg1 */
	movl %edx, %edx /* arg3 (zero extension) */
	sysenter_dispatch:
	cmpq $(IA32_NR_syscalls-1), %rax
	ja 1f
	call *ia32_sys_call_table(, %rax, 8)
	movq %rax, RAX(%rsp)
	1:
	DISABLE_INTERRUPTS(CLBR_NONE)
	TRACE_IRQS_OFF
	testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
	jnz ia32_ret_from_sys_call_irqs_off
	sysexit_from_sys_call:
	/*
	* NB: SYSEXIT is not obviously safe for 64-bit kernels -- an
	* NMI between STI and SYSEXIT has poorly specified behavior,
	* and and NMI followed by an IRQ with usergs is fatal. So
	* we just pretend we're using SYSEXIT but we really use
	* SYSRETL instead.
	*
	* This code path is still called 'sysexit' because it pairs
	* with 'sysenter' and it uses the SYSENTER calling convention.
	*/
	andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
	movl RIP(%rsp), %ecx /* User %eip */
	movq RAX(%rsp), %rax
	movl RSI(%rsp), %esi
	movl RDI(%rsp), %edi
	xorl %edx, %edx /* Do not leak kernel information */
	xorq %r8, %r8
	xorq %r9, %r9
	xorq %r10, %r10
	movl EFLAGS(%rsp), %r11d /* User eflags */
	TRACE_IRQS_ON

	/*
	* SYSRETL works even on Intel CPUs. Use it in preference to SYSEXIT,
	* since it avoids a dicey window with interrupts enabled.
	*/
	movl RSP(%rsp), %esp

	/*
	* USERGS_SYSRET32 does:
	* gsbase = user's gs base
	* eip = ecx
	* rflags = r11
	* cs = __USER32_CS
	* ss = __USER_DS
	*
	* The prologue set RIP(%rsp) to VDSO32_SYSENTER_RETURN, which does:
	*
	* pop %ebp
	* pop %edx
	* pop %ecx
	*
	* Therefore, we invoke SYSRETL with EDX and R8-R10 zeroed to
	* avoid info leaks. R11 ends up with VDSO32_SYSENTER_RETURN's
	* address (already known to user code), and R12-R15 are
	* callee-saved and therefore don't contain any interesting
	* kernel data.
	*/
	USERGS_SYSRET32

	sysenter_fix_flags:
	pushq $X86_EFLAGS_FIXED
	popfq
	jmp sysenter_flags_fixed

	sysenter_tracesys:
	SAVE_EXTRA_REGS
	xorl %eax, %eax /* Do not leak kernel information */
	movq %rax, R11(%rsp)
	movq %rax, R10(%rsp)
	movq %rax, R9(%rsp)
	movq %rax, R8(%rsp)
	movq %rsp, %rdi /* &pt_regs -> arg1 */
	call syscall_trace_enter

	/* Reload arg registers from stack. (see sysenter_tracesys) */
	movl RCX(%rsp), %ecx
	movl RDX(%rsp), %edx
	movl RSI(%rsp), %esi
	movl RDI(%rsp), %edi
	movl %eax, %eax /* zero extension */

	RESTORE_EXTRA_REGS
	jmp sysenter_do_call
	ENDPROC(entry_SYSENTER_compat)

	/*
	* 32-bit SYSCALL instruction entry.
	*
	* 32-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11,
	* then loads new ss, cs, and rip from previously programmed MSRs.
	* rflags gets masked by a value from another MSR (so CLD and CLAC
	* are not needed). SYSCALL does not save anything on the stack
	* and does not change rsp.
	*
	* Note: rflags saving+masking-with-MSR happens only in Long mode
	* (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
	* Don't get confused: rflags saving+masking depends on Long Mode Active bit
	* (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
	* or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
	*
	* Arguments:
	* eax system call number
	* ecx return address
	* ebx arg1
	* ebp arg2 (note: not saved in the stack frame, should not be touched)
	* edx arg3
	* esi arg4
	* edi arg5
	* esp user stack
	* 0(%esp) arg6
	*
	* This is purely a fast path. For anything complicated we use the int 0x80
	* path below. We set up a complete hardware stack frame to share code
	* with the int 0x80 path.
	*/
	ENTRY(entry_SYSCALL_compat)
	/*
	* Interrupts are off on entry.
	* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
	* it is too small to ever cause noticeable irq latency.
	*/
	SWAPGS_UNSAFE_STACK

	/* Temporary: SYSCALL32 is disabled. */
	movl $-ENOSYS, %eax
	USERGS_SYSRET32

	movl %esp, %r8d
	movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
	ENABLE_INTERRUPTS(CLBR_NONE)

	/* Zero-extending 32-bit regs, do not remove */
	movl %eax, %eax

	/* Construct struct pt_regs on stack */
	pushq $__USER32_DS /* pt_regs->ss */
	pushq %r8 /* pt_regs->sp */
	pushq %r11 /* pt_regs->flags */
	pushq $__USER32_CS /* pt_regs->cs */
	pushq %rcx /* pt_regs->ip */
	pushq %rax /* pt_regs->orig_ax */
	pushq %rdi /* pt_regs->di */
	pushq %rsi /* pt_regs->si */
	pushq %rdx /* pt_regs->dx */
	pushq %rbp /* pt_regs->cx */
	movl %ebp, %ecx
	pushq $-ENOSYS /* pt_regs->ax */
	sub $(108), %rsp / pt_regs->r8-11, bp, bx, r12-15 not saved */

	/*
	* No need to do an access_ok check here because r8 has been
	* 32-bit zero extended:
	*/
	ASM_STAC
	1: movl (%r8), %r9d
	_ASM_EXTABLE(1b, ia32_badarg)
	ASM_CLAC
	orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
	testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
	jnz cstar_tracesys

	cstar_do_call:
	/* 32-bit syscall -> 64-bit C ABI argument conversion */
	movl %edi, %r8d /* arg5 */
	/* r9 already loaded / / arg6 */
	xchg %ecx, %esi /* rsi:arg2, rcx:arg4 */
	movl %ebx, %edi /* arg1 */
	movl %edx, %edx /* arg3 (zero extension) */

	cstar_dispatch:
	cmpq $(IA32_NR_syscalls-1), %rax
	ja 1f

	call *ia32_sys_call_table(, %rax, 8)
	movq %rax, RAX(%rsp)
	1:
	DISABLE_INTERRUPTS(CLBR_NONE)
	TRACE_IRQS_OFF
	testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
	jnz ia32_ret_from_sys_call_irqs_off

	sysretl_from_sys_call:
	andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
	movl RDX(%rsp), %edx
	movl RSI(%rsp), %esi
	movl RDI(%rsp), %edi
	movl RIP(%rsp), %ecx
	movl EFLAGS(%rsp), %r11d
	movq RAX(%rsp), %rax
	xorq %r10, %r10
	xorq %r9, %r9
	xorq %r8, %r8
	TRACE_IRQS_ON
	movl RSP(%rsp), %esp
	/*
	* 64-bit->32-bit SYSRET restores eip from ecx,
	* eflags from r11 (but RF and VM bits are forced to 0),
	* cs and ss are loaded from MSRs.
	* (Note: 32-bit->32-bit SYSRET is different: since r11
	* does not exist, it merely sets eflags.IF=1).
	*
	* NB: On AMD CPUs with the X86_BUG_SYSRET_SS_ATTRS bug, the ss
	* descriptor is not reinitialized. This means that we must
	* avoid SYSRET with SS == NULL, which could happen if we schedule,
	* exit the kernel, and re-enter using an interrupt vector. (All
	* interrupt entries on x86_64 set SS to NULL.) We prevent that
	* from happening by reloading SS in __switch_to.
	*/
	USERGS_SYSRET32

	cstar_tracesys:
	xchgl %r9d, %ebp
	SAVE_EXTRA_REGS
	xorl %eax, %eax /* Do not leak kernel information */
	movq %rax, R11(%rsp)
	movq %rax, R10(%rsp)
	movq %r9, R9(%rsp)
	movq %rax, R8(%rsp)
	movq %rsp, %rdi /* &pt_regs -> arg1 */
	call syscall_trace_enter
	movl R9(%rsp), %r9d

	/* Reload arg registers from stack. (see sysenter_tracesys) */
	movl RCX(%rsp), %ecx
	movl RDX(%rsp), %edx
	movl RSI(%rsp), %esi
	movl RDI(%rsp), %edi
	movl %eax, %eax /* zero extension */

	RESTORE_EXTRA_REGS
	xchgl %ebp, %r9d
	jmp cstar_do_call
	END(entry_SYSCALL_compat)

	ia32_badarg:
	/*
	* So far, we've entered kernel mode, set AC, turned on IRQs, and
	* saved C regs except r8-r11. We haven't done any of the other
	* standard entry work, though. We want to bail, but we shouldn't
	* treat this as a syscall entry since we don't even know what the
	* args are. Instead, treat this as a non-syscall entry, finish
	* the entry work, and immediately exit after setting AX = -EFAULT.
	*
	* We're really just being polite here. Killing the task outright
	* would be a reasonable action, too. Given that the only valid
	* way to have gotten here is through the vDSO, and we already know
	* that the stack pointer is bad, the task isn't going to survive
	* for long no matter what we do.
	*/

	ASM_CLAC /* undo STAC */
	movq $-EFAULT, RAX(%rsp) /* return -EFAULT if possible */

	/* Fill in the rest of pt_regs */
	xorl %eax, %eax
	movq %rax, R11(%rsp)
	movq %rax, R10(%rsp)
	movq %rax, R9(%rsp)
	movq %rax, R8(%rsp)
	SAVE_EXTRA_REGS

	/* Turn IRQs back off. */
	DISABLE_INTERRUPTS(CLBR_NONE)
	TRACE_IRQS_OFF

	/* Now finish entering normal kernel mode. */
	#ifdef CONFIG_CONTEXT_TRACKING
	call enter_from_user_mode
	#endif

	/* And exit again. */
	jmp retint_user

	ia32_ret_from_sys_call_irqs_off:
	TRACE_IRQS_ON
	ENABLE_INTERRUPTS(CLBR_NONE)

	ia32_ret_from_sys_call:
	xorl %eax, %eax /* Do not leak kernel information */
	movq %rax, R11(%rsp)
	movq %rax, R10(%rsp)
	movq %rax, R9(%rsp)
	movq %rax, R8(%rsp)
	jmp int_ret_from_sys_call

	/*
	* Emulated IA32 system calls via int 0x80.
	*
	* Arguments:
	* eax system call number
	* ebx arg1
	* ecx arg2
	* edx arg3
	* esi arg4
	* edi arg5
	* ebp arg6 (note: not saved in the stack frame, should not be touched)
	*
	* Notes:
	* Uses the same stack frame as the x86-64 version.
	* All registers except eax must be saved (but ptrace may violate that).
	* Arguments are zero extended. For system calls that want sign extension and
	* take long arguments a wrapper is needed. Most calls can just be called
	* directly.
	* Assumes it is only called from user space and entered with interrupts off.
	*/

	ENTRY(entry_INT80_compat)
	/*
	* Interrupts are off on entry.
	* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
	* it is too small to ever cause noticeable irq latency.
	*/
	PARAVIRT_ADJUST_EXCEPTION_FRAME
	SWAPGS
	ENABLE_INTERRUPTS(CLBR_NONE)

	/* Zero-extending 32-bit regs, do not remove */
	movl %eax, %eax

	/* Construct struct pt_regs on stack (iret frame is already on stack) */
	pushq %rax /* pt_regs->orig_ax */
	pushq %rdi /* pt_regs->di */
	pushq %rsi /* pt_regs->si */
	pushq %rdx /* pt_regs->dx */
	pushq %rcx /* pt_regs->cx */
	pushq $-ENOSYS /* pt_regs->ax */
	pushq $0 /* pt_regs->r8 */
	pushq $0 /* pt_regs->r9 */
	pushq $0 /* pt_regs->r10 */
	pushq $0 /* pt_regs->r11 */
	cld
	sub $(68), %rsp / pt_regs->bp, bx, r12-15 not saved */

	orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
	testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
	jnz ia32_tracesys

	ia32_do_call:
	/* 32-bit syscall -> 64-bit C ABI argument conversion */
	movl %edi, %r8d /* arg5 */
	movl %ebp, %r9d /* arg6 */
	xchg %ecx, %esi /* rsi:arg2, rcx:arg4 */
	movl %ebx, %edi /* arg1 */
	movl %edx, %edx /* arg3 (zero extension) */
	cmpq $(IA32_NR_syscalls-1), %rax
	ja 1f

	call *ia32_sys_call_table(, %rax, 8)
	movq %rax, RAX(%rsp)
	1:
	jmp int_ret_from_sys_call

	ia32_tracesys:
	SAVE_EXTRA_REGS
	movq %rsp, %rdi /* &pt_regs -> arg1 */
	call syscall_trace_enter
	/*
	* Reload arg registers from stack in case ptrace changed them.
	* Don't reload %eax because syscall_trace_enter() returned
	* the %rax value we should see. But do truncate it to 32 bits.
	* If it's -1 to make us punt the syscall, then (u32)-1 is still
	* an appropriately invalid value.
	*/
	movl RCX(%rsp), %ecx
	movl RDX(%rsp), %edx
	movl RSI(%rsp), %esi
	movl RDI(%rsp), %edi
	movl %eax, %eax /* zero extension */
	RESTORE_EXTRA_REGS
	jmp ia32_do_call
	END(entry_INT80_compat)

	.macro PTREGSCALL label, func
	ALIGN
	GLOBAL(\label)
	leaq \func(%rip), %rax
	jmp ia32_ptregs_common
	.endm

	PTREGSCALL stub32_rt_sigreturn, sys32_rt_sigreturn
	PTREGSCALL stub32_sigreturn, sys32_sigreturn
	PTREGSCALL stub32_fork, sys_fork
	PTREGSCALL stub32_vfork, sys_vfork

	ALIGN
	GLOBAL(stub32_clone)
	leaq sys_clone(%rip), %rax
	/*
	* The 32-bit clone ABI is: clone(..., int tls_val, int *child_tidptr).
	* The 64-bit clone ABI is: clone(..., int *child_tidptr, int tls_val).
	*
	* The native 64-bit kernel's sys_clone() implements the latter,
	* so we need to swap arguments here before calling it:
	*/
	xchg %r8, %rcx
	jmp ia32_ptregs_common

	ALIGN
	ia32_ptregs_common:
	SAVE_EXTRA_REGS 8
	call *%rax
	RESTORE_EXTRA_REGS 8
	ret
	END(ia32_ptregs_common)