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      1 /*	$NetBSD: resumecontext.S,v 1.7 2025/05/03 19:56:21 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1999 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Klaus Klein.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  *
     31  * Modified for x86-64 by fvdl (at) wasabisystems.com
     32  */
     33 
     34 #include <machine/asm.h>
     35 #include "SYS.h"
     36 
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 	RCSID("$NetBSD: resumecontext.S,v 1.7 2025/05/03 19:56:21 riastradh Exp $")
     39 #endif /* LIBC_SCCS && !lint */
     40 
     41 /*
     42  * This assembly-language implementation differs from the (obvious)
     43  * C-language implementation only in not clobbering the previous
     44  * function's return address (us), which is the point of the exercise.
     45  */
     46 
     47 NENTRY(_resumecontext)	/* profiling prologue would clobber TOS */
     48 	leaq	-(8 + 784)(%rsp),%rdi	/* retaddr + sizeof (ucontext_t) */
     49 	andq	$~15,%rdi		/* align on _UC_UCONTEXT_ALIGN */
     50 	movq	%rdi,%rsp
     51 	call	PIC_PLT(_C_LABEL(_getcontext))
     52 	movq	8(%rsp),%rdi	/* uc_link */
     53 	testq	%rdi,%rdi	/* link end? */
     54 	jnz	9f
     55 
     56 	/* normal exit */
     57 	call	PIC_PLT(_C_LABEL(exit))
     58 
     59 9:
     60 	call	PIC_PLT(_C_LABEL(setcontext))
     61 	/* NOTREACHED */
     62 
     63 	/* something is wrong, pull the brake */
     64 	movq	$-1,%rdi
     65 	movq	$SYS_exit,%rax
     66 	syscall
     67 	/* NOTREACHED */
     68 END(_resumecontext)
     69