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252 lines
6.7 KiB
ArmAsm
252 lines
6.7 KiB
ArmAsm
/* Save current context and install the given one.
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Copyright (C) 2002-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Andreas Jaeger <aj@suse.de>, 2002.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include <asm/prctl.h>
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#include "ucontext_i.h"
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/* int __swapcontext (ucontext_t *oucp, const ucontext_t *ucp);
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Saves the machine context in oucp such that when it is activated,
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it appears as if __swapcontextt() returned again, restores the
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machine context in ucp and thereby resumes execution in that
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context.
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This implementation is intended to be used for *synchronous* context
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switches only. Therefore, it does not have to save anything
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other than the PRESERVED state. */
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ENTRY(__swapcontext)
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/* Save the preserved registers, the registers used for passing args,
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and the return address. */
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movq %rbx, oRBX(%rdi)
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movq %rbp, oRBP(%rdi)
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movq %r12, oR12(%rdi)
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movq %r13, oR13(%rdi)
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movq %r14, oR14(%rdi)
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movq %r15, oR15(%rdi)
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movq %rdi, oRDI(%rdi)
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movq %rsi, oRSI(%rdi)
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movq %rdx, oRDX(%rdi)
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movq %rcx, oRCX(%rdi)
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movq %r8, oR8(%rdi)
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movq %r9, oR9(%rdi)
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movq (%rsp), %rcx
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movq %rcx, oRIP(%rdi)
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leaq 8(%rsp), %rcx /* Exclude the return address. */
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movq %rcx, oRSP(%rdi)
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/* We have separate floating-point register content memory on the
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stack. We use the __fpregs_mem block in the context. Set the
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links up correctly. */
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leaq oFPREGSMEM(%rdi), %rcx
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movq %rcx, oFPREGS(%rdi)
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/* Save the floating-point environment. */
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fnstenv (%rcx)
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stmxcsr oMXCSR(%rdi)
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/* The syscall destroys some registers, save them. */
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movq %rsi, %r12
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movq %rdi, %r9
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/* Save the current signal mask and install the new one with
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rt_sigprocmask (SIG_BLOCK, newset, oldset,_NSIG/8). */
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leaq oSIGMASK(%rdi), %rdx
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leaq oSIGMASK(%rsi), %rsi
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movl $SIG_SETMASK, %edi
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movl $_NSIG8,%r10d
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movl $__NR_rt_sigprocmask, %eax
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syscall
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cmpq $-4095, %rax /* Check %rax for error. */
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jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
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/* Restore destroyed register into RDX. The choice is arbitrary,
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but leaving RDI and RSI available for use later can avoid
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shuffling values. */
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movq %r12, %rdx
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/* Restore the floating-point context. Not the registers, only the
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rest. */
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movq oFPREGS(%rdx), %rcx
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fldenv (%rcx)
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ldmxcsr oMXCSR(%rdx)
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/* Load the new stack pointer and the preserved registers. */
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movq oRSP(%rdx), %rsp
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movq oRBX(%rdx), %rbx
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movq oRBP(%rdx), %rbp
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movq oR12(%rdx), %r12
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movq oR13(%rdx), %r13
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movq oR14(%rdx), %r14
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movq oR15(%rdx), %r15
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#if SHSTK_ENABLED
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/* Check if shadow stack is enabled. */
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testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
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jz L(no_shstk)
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xorl %eax, %eax
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cmpq %fs:SSP_BASE_OFFSET, %rax
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jnz L(shadow_stack_bound_recorded)
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/* Get the base address and size of the default shadow stack
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which must be the current shadow stack since nothing has
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been recorded yet. */
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sub $24, %RSP_LP
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mov %RSP_LP, %RSI_LP
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movl $ARCH_CET_STATUS, %edi
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movl $__NR_arch_prctl, %eax
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syscall
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testq %rax, %rax
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jz L(continue_no_err)
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/* This should never happen. */
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hlt
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L(continue_no_err):
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/* Record the base of the current shadow stack. */
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movq 8(%rsp), %rax
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movq %rax, %fs:SSP_BASE_OFFSET
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add $24, %RSP_LP
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L(shadow_stack_bound_recorded):
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/* If we unwind the stack, we can't undo stack unwinding. Just
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save the target shadow stack pointer as the current shadow
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stack pointer. */
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movq oSSP(%rdx), %rcx
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movq %rcx, oSSP(%r9)
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/* Save the base of the current shadow stack. */
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movq %fs:SSP_BASE_OFFSET, %rax
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movq %rax, (oSSP + 8)(%r9)
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/* If the base of the target shadow stack is the same as the
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base of the current shadow stack, we unwind the shadow
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stack. Otherwise it is a stack switch and we look for a
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restore token. */
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movq oSSP(%rdx), %rsi
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movq %rsi, %rdi
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/* Get the base of the target shadow stack. */
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movq (oSSP + 8)(%rdx), %rcx
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cmpq %fs:SSP_BASE_OFFSET, %rcx
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je L(unwind_shadow_stack)
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L(find_restore_token_loop):
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/* Look for a restore token. */
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movq -8(%rsi), %rax
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andq $-8, %rax
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cmpq %rsi, %rax
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je L(restore_shadow_stack)
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/* Try the next slot. */
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subq $8, %rsi
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jmp L(find_restore_token_loop)
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L(restore_shadow_stack):
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/* The target shadow stack will be restored. Save the current
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shadow stack pointer. */
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rdsspq %rcx
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movq %rcx, oSSP(%r9)
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/* Restore the target shadow stack. */
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rstorssp -8(%rsi)
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/* Save the restore token on the old shadow stack. NB: This
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restore token may be checked by setcontext or swapcontext
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later. */
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saveprevssp
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/* Record the new shadow stack base that was switched to. */
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movq (oSSP + 8)(%rdx), %rax
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movq %rax, %fs:SSP_BASE_OFFSET
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L(unwind_shadow_stack):
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rdsspq %rcx
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subq %rdi, %rcx
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je L(skip_unwind_shadow_stack)
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negq %rcx
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shrq $3, %rcx
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movl $255, %esi
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L(loop):
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cmpq %rsi, %rcx
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cmovb %rcx, %rsi
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incsspq %rsi
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subq %rsi, %rcx
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ja L(loop)
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L(skip_unwind_shadow_stack):
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/* Setup registers used for passing args. */
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movq oRDI(%rdx), %rdi
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movq oRSI(%rdx), %rsi
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movq oRCX(%rdx), %rcx
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movq oR8(%rdx), %r8
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movq oR9(%rdx), %r9
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/* Get the return address set with getcontext. */
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movq oRIP(%rdx), %r10
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/* Setup finally %rdx. */
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movq oRDX(%rdx), %rdx
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/* Check if return address is valid for the case when setcontext
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is invoked from __start_context with linked context. */
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rdsspq %rax
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cmpq (%rax), %r10
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/* Clear rax to indicate success. NB: Don't use xorl to keep
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EFLAGS for jne. */
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movl $0, %eax
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jne L(jmp)
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/* Return to the new context if return address valid. */
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pushq %r10
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ret
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L(jmp):
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/* Jump to the new context directly. */
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jmp *%r10
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L(no_shstk):
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#endif
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/* The following ret should return to the address set with
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getcontext. Therefore push the address on the stack. */
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movq oRIP(%rdx), %rcx
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pushq %rcx
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/* Setup registers used for passing args. */
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movq oRDI(%rdx), %rdi
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movq oRSI(%rdx), %rsi
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movq oRCX(%rdx), %rcx
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movq oR8(%rdx), %r8
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movq oR9(%rdx), %r9
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/* Setup finally %rdx. */
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movq oRDX(%rdx), %rdx
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/* Clear rax to indicate success. */
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xorl %eax, %eax
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ret
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PSEUDO_END(__swapcontext)
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weak_alias (__swapcontext, swapcontext)
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