/* $NetBSD: resumecontext.S,v 1.7 2025/05/03 19:56:21 riastradh Exp $ */

/* $NetBSD: resumecontext.S,v 1.7 2025/05/03 19:56:21 riastradh Exp $ */

/*-
* Copyright (c) 1999 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Klaus Klein.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* Modified for x86-64 by [email protected]
*/

#include <machine/asm.h>
#include "SYS.h"

#if defined(LIBC_SCCS) && !defined(lint)
RCSID("$NetBSD: resumecontext.S,v 1.7 2025/05/03 19:56:21 riastradh Exp $")
#endif /* LIBC_SCCS && !lint */

/*
* This assembly-language implementation differs from the (obvious)
* C-language implementation only in not clobbering the previous
* function's return address (us), which is the point of the exercise.
*/

NENTRY(_resumecontext) /* profiling prologue would clobber TOS */
leaq -(8 + 784)(%rsp),%rdi /* retaddr + sizeof (ucontext_t) */
andq $~15,%rdi /* align on _UC_UCONTEXT_ALIGN */
movq %rdi,%rsp
call PIC_PLT(_C_LABEL(_getcontext))
movq 8(%rsp),%rdi /* uc_link */
testq %rdi,%rdi /* link end? */
jnz 9f

/* normal exit */
call PIC_PLT(_C_LABEL(exit))

9:
call PIC_PLT(_C_LABEL(setcontext))
/* NOTREACHED */

/* something is wrong, pull the brake */
movq $-1,%rdi
movq $SYS_exit,%rax
syscall
/* NOTREACHED */
END(_resumecontext)