/* Install given context.

   Copyright (C) 2002-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   Contributed by Andreas Jaeger <aj@suse.de>, 2002.

   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

   <http://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)