/* Save current context and install the given one.

   Copyright (C) 2001-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   Contributed by Ulrich Drepper <drepper@redhat.com>, 2001.

   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"

ENTRY(__swapcontext)

	/* Load address of the context data structure we save in.  */

	movl	4(%esp), %eax

	/* Save the preserved register values and the return address.  */

	movl	%edi, oEDI(%eax)

	movl	%esi, oESI(%eax)

	movl	%ebp, oEBP(%eax)

	movl	(%esp), %ecx

	movl	%ecx, oEIP(%eax)

	leal	4(%esp), %ecx

	movl	%ecx, oESP(%eax)

	movl	%ebx, oEBX(%eax)

	/* Save the FS segment register.  */

	xorl	%edx, %edx

	movw	%fs, %dx

	movl	%edx, oFS(%eax)

	/* We have separate floating-point register content memory on the

	   stack.  We use the __fpregs_mem block in the context.  Set the

	   links up correctly.  */

	leal	oFPREGSMEM(%eax), %ecx

	movl	%ecx, oFPREGS(%eax)

	/* Save the floating-point context.  */

	fnstenv	(%ecx)

	/* Load address of the context data structure we have to load.  */

	movl	8(%esp), %ecx

	/* Save the current signal mask and install the new one.  */

	pushl	%ebx

	leal	oSIGMASK(%eax), %edx

	leal	oSIGMASK(%ecx), %ecx

	movl	$SIG_SETMASK, %ebx

	movl	$__NR_sigprocmask, %eax

	ENTER_KERNEL

	popl	%ebx

	cmpl	$-4095, %eax		/* Check %eax for error.  */

	jae	SYSCALL_ERROR_LABEL	/* Jump to error handler if error.  */

	/* EAX was modified, reload it.  */

	movl	8(%esp), %eax

	/* Restore the floating-point context.  Not the registers, only the

	   rest.  */

	movl	oFPREGS(%eax), %ecx

	fldenv	(%ecx)

	/* Restore the FS segment register.  We don't touch the GS register

	   since it is used for threads.  */

	movl	oFS(%eax), %edx

	movw	%dx, %fs

#if SHSTK_ENABLED

	/* Check if Shadow Stack is enabled.  */

	testl	$X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET

	jz	L(no_shstk)

	xorl	%eax, %eax

	cmpl	%gs:SSP_BASE_OFFSET, %eax

	jnz	L(shadow_stack_bound_recorded)

	/* Get the base address and size of the default shadow stack

	   which must be the current shadow stack since nothing has

	   been recorded yet.  */

	sub	$24, %esp

	mov	%esp, %ecx

	movl	$ARCH_CET_STATUS, %ebx

	movl	$__NR_arch_prctl, %eax

	ENTER_KERNEL

	testl	%eax, %eax

	jz	L(continue_no_err)

	/* This should never happen.  */

	hlt

L(continue_no_err):

	/* Record the base of the current shadow stack.  */

	movl	8(%esp), %eax

	movl	%eax, %gs:SSP_BASE_OFFSET

	add	$24, %esp

L(shadow_stack_bound_recorded):

	/* Load address of the context data structure we save in.  */

	movl	4(%esp), %eax

	/* Load address of the context data structure we swap in  */

	movl	8(%esp), %edx

       /* If we unwind the stack, we can't undo stack unwinding.  Just

	   save the target shadow stack pointer as the current shadow

	   stack pointer.   */

	movl	oSSP(%edx), %ecx

	movl	%ecx, oSSP(%eax)

	/* Save the current shadow stack base in ucontext.  */

	movl	%gs:SSP_BASE_OFFSET, %ecx

	movl	%ecx, (oSSP + 4)(%eax)

	/* 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.  */

	movl	oSSP(%edx), %esi

	movl	%esi, %edi

	/* Get the base of the target shadow stack.  */

	movl	(oSSP + 4)(%edx), %ecx

	cmpl	%gs:SSP_BASE_OFFSET, %ecx

	je	L(unwind_shadow_stack)

	/* Align the saved original shadow stack pointer to the next

	   8 byte aligned boundary.  */

	andl	$-8, %esi

L(find_restore_token_loop):

	/* Look for a restore token.  */

	movl	-8(%esi), %ebx

	andl	$-8, %ebx

	cmpl	%esi, %ebx

	je	L(restore_shadow_stack)

	/* Try the next slot.  */

	subl	$8, %esi

	jmp	L(find_restore_token_loop)

L(restore_shadow_stack):

	/* The target shadow stack will be restored.  Save the current

	   shadow stack pointer.  */

	rdsspd	%ecx

	movl	%ecx, oSSP(%eax)

	/* Use the restore stoken to restore the target shadow stack.  */

	rstorssp -8(%esi)

	/* 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.  */

	movl	(oSSP + 4)(%edx), %ebx

	movl	%ebx, %gs:SSP_BASE_OFFSET

L(unwind_shadow_stack):

	rdsspd	%ebx

	subl	%edi, %ebx

	je	L(skip_unwind_shadow_stack)

	negl	%ebx

	shrl	$2, %ebx

	movl	$255, %esi

L(loop):

	cmpl	%esi, %ebx

	cmovb	%ebx, %esi

	incsspd	%esi

	subl	%esi, %ebx

	ja	L(loop)

L(skip_unwind_shadow_stack):

	/* Load the new stack pointer.  */

	movl	oESP(%edx), %esp

	/* Load the values of all the preserved registers (except ESP).  */

	movl	oEDI(%edx), %edi

	movl	oESI(%edx), %esi

	movl	oEBP(%edx), %ebp

	movl	oEBX(%edx), %ebx

	/* Get the return address set with getcontext.  */

	movl	oEIP(%edx), %ecx

	/* Check if return address is valid for the case when setcontext

	   is invoked from L(exitcode) with linked context.  */

	rdsspd	%eax

	cmpl	(%eax), %ecx

	/* Clear EAX 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.  */

	pushl	%ecx

	ret

L(jmp):

	/* Jump to the new context directly.  */

	jmp	*%ecx

L(no_shstk):

#endif

	/* Fetch the address to return to.  */

	movl	oEIP(%eax), %ecx

	/* Load the new stack pointer.  */

	movl	oESP(%eax), %esp

	/* Push the return address on the new stack so we can return there.  */

	pushl	%ecx

	/* Load the values of all the preserved registers (except ESP).  */

	movl	oEDI(%eax), %edi

	movl	oESI(%eax), %esi

	movl	oEBP(%eax), %ebp

	movl	oEBX(%eax), %ebx

	/* All done, return 0 for success.  */

	xorl	%eax, %eax

	/* The following 'ret' will pop the address of the code and jump

	   to it.  */

	ret

PSEUDO_END(__swapcontext)

weak_alias (__swapcontext, swapcontext)