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415 lines
14 KiB
415 lines
14 KiB
/* 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 "calling.h" |
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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 <linux/linkage.h> |
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#include <linux/err.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_CODE_START(entry_SYSENTER_compat) |
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UNWIND_HINT_EMPTY |
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/* Interrupts are off on entry. */ |
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SWAPGS |
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pushq %rax |
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rax |
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popq %rax |
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp |
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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 $0 /* pt_regs->sp = 0 (placeholder) */ |
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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, if TS |
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* was set in usermode, it's still set, and we're singlestepping |
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* through this code. do_SYSENTER_32() will fix up IF. |
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*/ |
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pushfq /* pt_regs->flags (except IF = 0) */ |
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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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SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL) |
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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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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 $0 /* pt_regs->r15 = 0 */ |
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xorl %r15d, %r15d /* nospec r15 */ |
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UNWIND_HINT_REGS |
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cld |
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/* |
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* SYSENTER doesn't filter flags, so we need to clear NT and AC |
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* ourselves. To save a few cycles, we can check whether |
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* either was set instead of doing an unconditional popfq. |
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* This needs to happen before enabling interrupts so that |
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* we don't get preempted with NT set. |
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* |
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* If TF is set, we will single-step all the way to here -- do_debug |
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* will ignore all the traps. (Yes, this is slow, but so is |
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* single-stepping in general. This allows us to avoid having |
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* a more complicated code to handle the case where a user program |
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* forces us to single-step through the SYSENTER entry code.) |
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* |
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* NB.: .Lsysenter_fix_flags is a label with the code under it moved |
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* out-of-line as an optimization: NT is unlikely to be set in the |
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* majority of the cases and instead of polluting the I$ 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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movq %rsp, %rdi |
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call do_SYSENTER_32 |
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/* XEN PV guests always use IRET path */ |
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ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ |
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"jmp swapgs_restore_regs_and_return_to_usermode", 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_CODE_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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UNWIND_HINT_EMPTY |
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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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UNWIND_HINT_REGS |
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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 swapgs_restore_regs_and_return_to_usermode", \ |
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"jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV |
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/* Opportunistic SYSRET */ |
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sysret32_from_system_call: |
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/* |
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* We are not going to return to userspace from the trampoline |
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* stack. So let's erase the thread stack right now. |
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*/ |
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STACKLEAK_ERASE |
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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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/* |
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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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sysretl |
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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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UNWIND_HINT_EMPTY |
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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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/* In the Xen PV case we already run on the thread stack. */ |
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ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV |
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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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.Lint80_keep_stack: |
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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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UNWIND_HINT_REGS |
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cld |
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movq %rsp, %rdi |
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call do_int80_syscall_32 |
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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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