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/* Install given context.
Copyright (C) 2002-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <asm/prctl.h>
#include "ucontext_i.h"
/* int __setcontext (const ucontext_t *ucp)
Restores the machine context in UCP and thereby resumes execution
in that context.
This implementation is intended to be used for *synchronous* context
switches only. Therefore, it does not have to restore anything
other than the PRESERVED state. */
ENTRY(__setcontext)
/* Save argument since syscall will destroy it. */
pushq %rdi
cfi_adjust_cfa_offset(8)
/* Set the signal mask with
rt_sigprocmask (SIG_SETMASK, mask, NULL, _NSIG/8). */
leaq oSIGMASK(%rdi), %rsi
xorl %edx, %edx
movl $SIG_SETMASK, %edi
movl $_NSIG8,%r10d
movl $__NR_rt_sigprocmask, %eax
syscall
/* Pop the pointer into RDX. The choice is arbitrary, but
leaving RDI and RSI available for use later can avoid
shuffling values. */
popq %rdx
cfi_adjust_cfa_offset(-8)
cmpq $-4095, %rax /* Check %rax for error. */
jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
/* Restore the floating-point context. Not the registers, only the
rest. */
movq oFPREGS(%rdx), %rcx
fldenv (%rcx)
ldmxcsr oMXCSR(%rdx)
/* Load the new stack pointer, the preserved registers and
registers used for passing args. */
cfi_def_cfa(%rdx, 0)
cfi_offset(%rbx,oRBX)
cfi_offset(%rbp,oRBP)
cfi_offset(%r12,oR12)
cfi_offset(%r13,oR13)
cfi_offset(%r14,oR14)
cfi_offset(%r15,oR15)
cfi_offset(%rsp,oRSP)
cfi_offset(%rip,oRIP)
movq oRSP(%rdx), %rsp
movq oRBX(%rdx), %rbx
movq oRBP(%rdx), %rbp
movq oR12(%rdx), %r12
movq oR13(%rdx), %r13
movq oR14(%rdx), %r14
movq oR15(%rdx), %r15
#if SHSTK_ENABLED
/* Check if shadow stack is enabled. */
testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
jz L(no_shstk)
/* If the base of the target shadow stack is the same as the
base of the current shadow stack, we unwind the shadow
stack. Otherwise it is a stack switch and we look for a
restore token. */
movq oSSP(%rdx), %rsi
movq %rsi, %rdi
/* Get the base of the target shadow stack. */
movq (oSSP + 8)(%rdx), %rcx
cmpq %fs:SSP_BASE_OFFSET, %rcx
je L(unwind_shadow_stack)
L(find_restore_token_loop):
/* Look for a restore token. */
movq -8(%rsi), %rax
andq $-8, %rax
cmpq %rsi, %rax
je L(restore_shadow_stack)
/* Try the next slot. */
subq $8, %rsi
jmp L(find_restore_token_loop)
L(restore_shadow_stack):
/* Pop return address from the shadow stack since setcontext
will not return. */
movq $1, %rax
incsspq %rax
/* Use the restore stoken to restore the target shadow stack. */
rstorssp -8(%rsi)
/* Save the restore token on the old shadow stack. NB: This
restore token may be checked by setcontext or swapcontext
later. */
saveprevssp
/* Record the new shadow stack base that was switched to. */
movq (oSSP + 8)(%rdx), %rax
movq %rax, %fs:SSP_BASE_OFFSET
L(unwind_shadow_stack):
rdsspq %rcx
subq %rdi, %rcx
je L(skip_unwind_shadow_stack)
negq %rcx
shrq $3, %rcx
movl $255, %esi
L(loop):
cmpq %rsi, %rcx
cmovb %rcx, %rsi
incsspq %rsi
subq %rsi, %rcx
ja L(loop)
L(skip_unwind_shadow_stack):
movq oRSI(%rdx), %rsi
movq oRDI(%rdx), %rdi
movq oRCX(%rdx), %rcx
movq oR8(%rdx), %r8
movq oR9(%rdx), %r9
/* Get the return address set with getcontext. */
movq oRIP(%rdx), %r10
/* Setup finally %rdx. */
movq oRDX(%rdx), %rdx
/* Check if return address is valid for the case when setcontext
is invoked from __start_context with linked context. */
rdsspq %rax
cmpq (%rax), %r10
/* Clear RAX to indicate success. NB: Don't use xorl to keep
EFLAGS for jne. */
movl $0, %eax
jne L(jmp)
/* Return to the new context if return address valid. */
pushq %r10
ret
L(jmp):
/* Jump to the new context directly. */
jmp *%r10
L(no_shstk):
#endif
/* The following ret should return to the address set with
getcontext. Therefore push the address on the stack. */
movq oRIP(%rdx), %rcx
pushq %rcx
movq oRSI(%rdx), %rsi
movq oRDI(%rdx), %rdi
movq oRCX(%rdx), %rcx
movq oR8(%rdx), %r8
movq oR9(%rdx), %r9
/* Setup finally %rdx. */
movq oRDX(%rdx), %rdx
/* End FDE here, we fall into another context. */
cfi_endproc
cfi_startproc
/* Clear rax to indicate success. */
xorl %eax, %eax
ret
PSEUDO_END(__setcontext)
weak_alias (__setcontext, setcontext)
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