/*      $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 fvdl@wasabisystems.com
 */

#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)