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      1 /*	$NetBSD: resumecontext.S,v 1.9 2025/05/03 19:55:32 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 
     32 #include <machine/asm.h>
     33 #include "SYS.h"
     34 
     35 #if defined(LIBC_SCCS) && !defined(lint)
     36 	RCSID("$NetBSD: resumecontext.S,v 1.9 2025/05/03 19:55:32 riastradh Exp $")
     37 #endif /* LIBC_SCCS && !lint */
     38 
     39 /*
     40  * This assembly-language implementation differs from the (obvious)
     41  * C-language implementation only in not clobbering the previous
     42  * function's return address (us), which is the point of the exercise.
     43  */
     44 
     45 NENTRY(_resumecontext)	/* profiling prologue would clobber TOS */
     46 	leal	-(4 + 776)(%esp),%ecx	/* retaddr + sizeof (ucontext_t) */
     47 	andl	$~(0xf),%ecx		/* align on _UC_UCONTEXT_ALIGN */
     48 	movl	%ecx,%esp
     49 	PIC_PROLOGUE
     50 	pushl	%ecx
     51 	call	PIC_PLT(_C_LABEL(_getcontext))
     52 	addl	$4,%esp
     53 	PIC_EPILOGUE
     54 	movl	4(%esp),%ecx		/* uc_link */
     55 	PIC_PROLOGUE
     56 	pushl	%ecx	/* argument for exit() or setcontext() */
     57 	testl	%ecx,%ecx		/* link end? */
     58 	jnz	9f	/* watch out for local label use in PIC_* */
     59 
     60 	/* normal exit */
     61 	call	PIC_PLT(_C_LABEL(exit))
     62 	/* NOTREACHED */
     63 
     64 9:
     65 	call	PIC_PLT(_C_LABEL(setcontext))
     66 	/* NOTREACHED */
     67 
     68 	/* something is wrong, pull the brake */
     69 	pushl	$-1
     70 	pushl	%eax	/* unused return address */
     71 	SYSTRAP(exit)
     72 END(_resumecontext)
     73