439 lines
14 KiB
ArmAsm
439 lines
14 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Compatibility mode system call entry point for x86-64.
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*
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* Copyright 2000-2002 Andi Kleen, SuSE Labs.
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*/
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#include <asm/asm-offsets.h>
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#include <asm/current.h>
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#include <asm/errno.h>
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#include <asm/ia32_unistd.h>
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#include <asm/thread_info.h>
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#include <asm/segment.h>
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#include <asm/irqflags.h>
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#include <asm/asm.h>
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#include <asm/smap.h>
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#include <asm/nospec-branch.h>
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#include <linux/linkage.h>
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#include <linux/err.h>
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#include "calling.h"
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.section .entry.text, "ax"
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/*
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* 32-bit SYSENTER entry.
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*
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* 32-bit system calls through the vDSO's __kernel_vsyscall enter here
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* on 64-bit kernels running on Intel CPUs.
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*
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* The SYSENTER instruction, in principle, should *only* occur in the
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* vDSO. In practice, a small number of Android devices were shipped
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* with a copy of Bionic that inlined a SYSENTER instruction. This
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* never happened in any of Google's Bionic versions -- it only happened
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* in a narrow range of Intel-provided versions.
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*
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* SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
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* IF and VM in RFLAGS are cleared (IOW: interrupts are off).
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* SYSENTER does not save anything on the stack,
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* and does not save old RIP (!!!), RSP, or RFLAGS.
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*
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* Arguments:
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* eax system call number
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* ebx arg1
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* ecx arg2
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* edx arg3
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* esi arg4
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* edi arg5
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* ebp user stack
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* 0(%ebp) arg6
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*/
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SYM_FUNC_START(entry_SYSENTER_compat)
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/* Interrupts are off on entry. */
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SWAPGS
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/* We are about to clobber %rsp anyway, clobbering here is OK */
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
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/*
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* User tracing code (ptrace or signal handlers) might assume that
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* the saved RAX contains a 32-bit number when we're invoking a 32-bit
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* syscall. Just in case the high bits are nonzero, zero-extend
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* the syscall number. (This could almost certainly be deleted
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* with no ill effects.)
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*/
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movl %eax, %eax
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/* Construct struct pt_regs on stack */
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pushq $__USER32_DS /* pt_regs->ss */
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pushq %rbp /* pt_regs->sp (stashed in bp) */
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/*
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* Push flags. This is nasty. First, interrupts are currently
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* off, but we need pt_regs->flags to have IF set. Second, even
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* if TF was set when SYSENTER started, it's clear by now. We fix
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* that later using TIF_SINGLESTEP.
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*/
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pushfq /* pt_regs->flags (except IF = 0) */
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orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */
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pushq $__USER32_CS /* pt_regs->cs */
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pushq $0 /* pt_regs->ip = 0 (placeholder) */
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pushq %rax /* pt_regs->orig_ax */
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pushq %rdi /* pt_regs->di */
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pushq %rsi /* pt_regs->si */
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pushq %rdx /* pt_regs->dx */
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pushq %rcx /* pt_regs->cx */
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pushq $-ENOSYS /* pt_regs->ax */
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pushq $0 /* pt_regs->r8 = 0 */
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xorl %r8d, %r8d /* nospec r8 */
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pushq $0 /* pt_regs->r9 = 0 */
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xorl %r9d, %r9d /* nospec r9 */
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pushq $0 /* pt_regs->r10 = 0 */
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xorl %r10d, %r10d /* nospec r10 */
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pushq $0 /* pt_regs->r11 = 0 */
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xorl %r11d, %r11d /* nospec r11 */
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pushq %rbx /* pt_regs->rbx */
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xorl %ebx, %ebx /* nospec rbx */
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pushq %rbp /* pt_regs->rbp (will be overwritten) */
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xorl %ebp, %ebp /* nospec rbp */
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pushq $0 /* pt_regs->r12 = 0 */
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xorl %r12d, %r12d /* nospec r12 */
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pushq $0 /* pt_regs->r13 = 0 */
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xorl %r13d, %r13d /* nospec r13 */
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pushq $0 /* pt_regs->r14 = 0 */
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xorl %r14d, %r14d /* nospec r14 */
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pushq $0 /* pt_regs->r15 = 0 */
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xorl %r15d, %r15d /* nospec r15 */
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cld
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/*
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* SYSENTER doesn't filter flags, so we need to clear NT and AC
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* ourselves. To save a few cycles, we can check whether
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* either was set instead of doing an unconditional popfq.
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* This needs to happen before enabling interrupts so that
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* we don't get preempted with NT set.
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*
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* If TF is set, we will single-step all the way to here -- do_debug
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* will ignore all the traps. (Yes, this is slow, but so is
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* single-stepping in general. This allows us to avoid having
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* a more complicated code to handle the case where a user program
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* forces us to single-step through the SYSENTER entry code.)
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*
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* NB.: .Lsysenter_fix_flags is a label with the code under it moved
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* out-of-line as an optimization: NT is unlikely to be set in the
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* majority of the cases and instead of polluting the I$ unnecessarily,
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* we're keeping that code behind a branch which will predict as
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* not-taken and therefore its instructions won't be fetched.
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*/
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testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp)
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jnz .Lsysenter_fix_flags
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.Lsysenter_flags_fixed:
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/*
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* CPU bugs mitigations mechanisms can call other functions. They
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* should be invoked after making sure TF is cleared because
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* single-step is ignored only for instructions inside the
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* entry_SYSENTER_compat function.
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*/
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IBRS_ENTER
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UNTRAIN_RET
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CLEAR_BRANCH_HISTORY
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/*
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* User mode is traced as though IRQs are on, and SYSENTER
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* turned them off.
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*/
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TRACE_IRQS_OFF
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movq %rsp, %rdi
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call do_fast_syscall_32
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/* XEN PV guests always use IRET path */
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ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
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"jmp .Lsyscall_32_done", X86_FEATURE_XENPV
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jmp sysret32_from_system_call
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.Lsysenter_fix_flags:
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pushq $X86_EFLAGS_FIXED
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popfq
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jmp .Lsysenter_flags_fixed
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SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
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SYM_FUNC_END(entry_SYSENTER_compat)
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/*
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* 32-bit SYSCALL entry.
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*
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* 32-bit system calls through the vDSO's __kernel_vsyscall enter here
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* on 64-bit kernels running on AMD CPUs.
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*
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* The SYSCALL instruction, in principle, should *only* occur in the
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* vDSO. In practice, it appears that this really is the case.
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* As evidence:
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*
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* - The calling convention for SYSCALL has changed several times without
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* anyone noticing.
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*
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* - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
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* user task that did SYSCALL without immediately reloading SS
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* would randomly crash.
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*
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* - Most programmers do not directly target AMD CPUs, and the 32-bit
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* SYSCALL instruction does not exist on Intel CPUs. Even on AMD
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* CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
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* because the SYSCALL instruction in legacy/native 32-bit mode (as
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* opposed to compat mode) is sufficiently poorly designed as to be
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* essentially unusable.
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*
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* 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
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* RFLAGS to R11, then loads new SS, CS, and RIP from previously
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* programmed MSRs. RFLAGS gets masked by a value from another MSR
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* (so CLD and CLAC are not needed). SYSCALL does not save anything on
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* the stack and does not change RSP.
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*
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* Note: RFLAGS saving+masking-with-MSR happens only in Long mode
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* (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
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* Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
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* (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
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* or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
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*
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* Arguments:
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* eax system call number
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* ecx return address
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* ebx arg1
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* ebp arg2 (note: not saved in the stack frame, should not be touched)
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* edx arg3
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* esi arg4
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* edi arg5
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* esp user stack
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* 0(%esp) arg6
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*/
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SYM_CODE_START(entry_SYSCALL_compat)
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/* Interrupts are off on entry. */
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swapgs
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/* Stash user ESP */
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movl %esp, %r8d
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/* Use %rsp as scratch reg. User ESP is stashed in r8 */
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
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/* Switch to the kernel stack */
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
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SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
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/* Construct struct pt_regs on stack */
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pushq $__USER32_DS /* pt_regs->ss */
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pushq %r8 /* pt_regs->sp */
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pushq %r11 /* pt_regs->flags */
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pushq $__USER32_CS /* pt_regs->cs */
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pushq %rcx /* pt_regs->ip */
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SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
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movl %eax, %eax /* discard orig_ax high bits */
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pushq %rax /* pt_regs->orig_ax */
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pushq %rdi /* pt_regs->di */
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pushq %rsi /* pt_regs->si */
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xorl %esi, %esi /* nospec si */
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pushq %rdx /* pt_regs->dx */
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xorl %edx, %edx /* nospec dx */
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pushq %rbp /* pt_regs->cx (stashed in bp) */
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xorl %ecx, %ecx /* nospec cx */
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pushq $-ENOSYS /* pt_regs->ax */
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pushq $0 /* pt_regs->r8 = 0 */
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xorl %r8d, %r8d /* nospec r8 */
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pushq $0 /* pt_regs->r9 = 0 */
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xorl %r9d, %r9d /* nospec r9 */
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pushq $0 /* pt_regs->r10 = 0 */
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xorl %r10d, %r10d /* nospec r10 */
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pushq $0 /* pt_regs->r11 = 0 */
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xorl %r11d, %r11d /* nospec r11 */
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pushq %rbx /* pt_regs->rbx */
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xorl %ebx, %ebx /* nospec rbx */
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pushq %rbp /* pt_regs->rbp (will be overwritten) */
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xorl %ebp, %ebp /* nospec rbp */
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pushq $0 /* pt_regs->r12 = 0 */
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xorl %r12d, %r12d /* nospec r12 */
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pushq $0 /* pt_regs->r13 = 0 */
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xorl %r13d, %r13d /* nospec r13 */
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pushq $0 /* pt_regs->r14 = 0 */
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xorl %r14d, %r14d /* nospec r14 */
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pushq $0 /* pt_regs->r15 = 0 */
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xorl %r15d, %r15d /* nospec r15 */
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/*
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* User mode is traced as though IRQs are on, and SYSENTER
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* turned them off.
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*/
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TRACE_IRQS_OFF
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IBRS_ENTER
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UNTRAIN_RET
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CLEAR_BRANCH_HISTORY
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movq %rsp, %rdi
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call do_fast_syscall_32
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/* XEN PV guests always use IRET path */
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ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
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"jmp .Lsyscall_32_done", X86_FEATURE_XENPV
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/* Opportunistic SYSRET */
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sysret32_from_system_call:
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TRACE_IRQS_ON /* User mode traces as IRQs on. */
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IBRS_EXIT
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movq RBX(%rsp), %rbx /* pt_regs->rbx */
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movq RBP(%rsp), %rbp /* pt_regs->rbp */
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movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
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movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */
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addq $RAX, %rsp /* Skip r8-r15 */
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popq %rax /* pt_regs->rax */
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popq %rdx /* Skip pt_regs->cx */
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popq %rdx /* pt_regs->dx */
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popq %rsi /* pt_regs->si */
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popq %rdi /* pt_regs->di */
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/*
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* USERGS_SYSRET32 does:
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* GSBASE = user's GS base
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* EIP = ECX
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* RFLAGS = R11
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* CS = __USER32_CS
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* SS = __USER_DS
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*
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* ECX will not match pt_regs->cx, but we're returning to a vDSO
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* trampoline that will fix up RCX, so this is okay.
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*
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* R12-R15 are callee-saved, so they contain whatever was in them
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* when the system call started, which is already known to user
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* code. We zero R8-R10 to avoid info leaks.
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*/
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movq RSP-ORIG_RAX(%rsp), %rsp
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SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
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/*
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* The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
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* on the process stack which is not mapped to userspace and
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* not readable after we SWITCH_TO_USER_CR3. Delay the CR3
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* switch until after after the last reference to the process
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* stack.
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*
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* %r8/%r9 are zeroed before the sysret, thus safe to clobber.
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*/
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SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9
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xorl %r8d, %r8d
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xorl %r9d, %r9d
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xorl %r10d, %r10d
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swapgs
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CLEAR_CPU_BUFFERS
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sysretl
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SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
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SYM_CODE_END(entry_SYSCALL_compat)
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/*
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* 32-bit legacy system call entry.
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*
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* 32-bit x86 Linux system calls traditionally used the INT $0x80
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* instruction. INT $0x80 lands here.
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*
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* This entry point can be used by 32-bit and 64-bit programs to perform
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* 32-bit system calls. Instances of INT $0x80 can be found inline in
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* various programs and libraries. It is also used by the vDSO's
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* __kernel_vsyscall fallback for hardware that doesn't support a faster
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* entry method. Restarted 32-bit system calls also fall back to INT
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* $0x80 regardless of what instruction was originally used to do the
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* system call.
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*
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* This is considered a slow path. It is not used by most libc
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* implementations on modern hardware except during process startup.
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*
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* Arguments:
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* eax system call number
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* ebx arg1
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* ecx arg2
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* edx arg3
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* esi arg4
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* edi arg5
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* ebp arg6
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*/
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SYM_CODE_START(entry_INT80_compat)
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/*
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* Interrupts are off on entry.
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*/
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ASM_CLAC /* Do this early to minimize exposure */
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SWAPGS
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/*
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* User tracing code (ptrace or signal handlers) might assume that
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* the saved RAX contains a 32-bit number when we're invoking a 32-bit
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* syscall. Just in case the high bits are nonzero, zero-extend
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* the syscall number. (This could almost certainly be deleted
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* with no ill effects.)
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*/
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movl %eax, %eax
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/* switch to thread stack expects orig_ax and rdi to be pushed */
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pushq %rax /* pt_regs->orig_ax */
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pushq %rdi /* pt_regs->di */
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/* Need to switch before accessing the thread stack. */
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
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movq %rsp, %rdi
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
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pushq 6*8(%rdi) /* regs->ss */
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pushq 5*8(%rdi) /* regs->rsp */
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pushq 4*8(%rdi) /* regs->eflags */
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pushq 3*8(%rdi) /* regs->cs */
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pushq 2*8(%rdi) /* regs->ip */
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pushq 1*8(%rdi) /* regs->orig_ax */
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pushq (%rdi) /* pt_regs->di */
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pushq %rsi /* pt_regs->si */
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xorl %esi, %esi /* nospec si */
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pushq %rdx /* pt_regs->dx */
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xorl %edx, %edx /* nospec dx */
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pushq %rcx /* pt_regs->cx */
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xorl %ecx, %ecx /* nospec cx */
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pushq $-ENOSYS /* pt_regs->ax */
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pushq %r8 /* pt_regs->r8 */
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xorl %r8d, %r8d /* nospec r8 */
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pushq %r9 /* pt_regs->r9 */
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xorl %r9d, %r9d /* nospec r9 */
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pushq %r10 /* pt_regs->r10*/
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xorl %r10d, %r10d /* nospec r10 */
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pushq %r11 /* pt_regs->r11 */
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xorl %r11d, %r11d /* nospec r11 */
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pushq %rbx /* pt_regs->rbx */
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xorl %ebx, %ebx /* nospec rbx */
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pushq %rbp /* pt_regs->rbp */
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xorl %ebp, %ebp /* nospec rbp */
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pushq %r12 /* pt_regs->r12 */
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xorl %r12d, %r12d /* nospec r12 */
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pushq %r13 /* pt_regs->r13 */
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xorl %r13d, %r13d /* nospec r13 */
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pushq %r14 /* pt_regs->r14 */
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xorl %r14d, %r14d /* nospec r14 */
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pushq %r15 /* pt_regs->r15 */
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xorl %r15d, %r15d /* nospec r15 */
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cld
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IBRS_ENTER
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UNTRAIN_RET
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CLEAR_BRANCH_HISTORY
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/*
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* User mode is traced as though IRQs are on, and the interrupt
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* gate turned them off.
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*/
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TRACE_IRQS_OFF
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movq %rsp, %rdi
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call do_int80_syscall_32
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.Lsyscall_32_done:
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/* Go back to user mode. */
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TRACE_IRQS_ON
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jmp swapgs_restore_regs_and_return_to_usermode
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SYM_CODE_END(entry_INT80_compat)
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