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execsp.S revision 1.2 
      1 /*	$NetBSD: execsp.S,v 1.2 2025/04/20 22:31:25 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2025 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     17  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     20  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     21  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     22  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     23  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     24  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     25  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     26  * POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #define	_LOCORE
     30 
     31 #include <machine/asm.h>
     32 
     33 RCSID("$NetBSD: execsp.S,v 1.2 2025/04/20 22:31:25 riastradh Exp $")
     34 
     35 /*
     36  * void execsp_start(void (*cleanup@rbx)(void), void *obj_main@rcx,
     37  *     struct ps_strings *ps_strings@rbx)
     38  *
     39  *	ELF entry point.  Saves the stack pointer in startsp and defers
     40  *	to the usual csu __start routine.
     41  */
     42 ENTRY(execsp_start)
     43 	movq	%rsp,_C_LABEL(startsp)(%rip)
     44 	/*
     45 	 * No adjustment like in main because entry point is special
     46 	 * and the amd64 csu __start routine takes care of it.
     47 	 *
     48 	 * XXX Why don't we just arrange to align it in the kernel
     49 	 * anyway?
     50 	 */
     51 	jmp	_C_LABEL(__start)
     52 END(execsp_start)
     53 
     54 /*
     55  * void execsp_ctor(void)
     56  *
     57  *	ELF constructor.  Saves the stack pointer in ctorsp and
     58  *	returns.
     59  */
     60 ENTRY(execsp_ctor)
     61 	/*
     62 	 * `The end of the input argument area shall be aligned on a
     63 	 *  [16-byte] boundary.  In other words, the value of (%rsp + 8)
     64 	 *  is always a multiple of 16 when control is transferred to
     65 	 *  the function entry point.'
     66 	 *
     67 	 * To make it convenient for t_signal_and_sp.c, we subtract 8
     68 	 * from %rsp in order to get something congruent to zero modulo
     69 	 * the stack alignemnt.
     70 	 */
     71 	movq	%rsp,_C_LABEL(ctorsp)(%rip)
     72 	addq	$-8,_C_LABEL(ctorsp)(%rip)
     73 	ret
     74 END(execsp_ctor)
     75 
     76 	/* Make execsp_ctor a constructor. */
     77 	.section .ctors,"aw",@progbits
     78 	.p2align 3
     79 	.quad	_C_LABEL(execsp_ctor)
     80 
     81 /*
     82  * int main(int argc@rdi, char **argv@rsi, ...)
     83  *
     84  *	Main function.  Saves the stack pointer in mainsp and returns
     85  *	zero.  We will call execsp_main in execsp_dtor once dtorsp has
     86  *	been initialized.
     87  */
     88 ENTRY(main)
     89 	movq	%rsp,_C_LABEL(mainsp)(%rip)
     90 	addq	$-8,_C_LABEL(mainsp)(%rip)
     91 	xorl	%eax,%eax
     92 	ret
     93 END(main)
     94 
     95 /*
     96  * void execsp_dtor(void)
     97  *
     98  *	ELF destructor.  Saves the stack pointer in dtorsp and defers
     99  *	to the C execsp_main in h_execsp.c to report the stack pointers
    100  *	back to the t_signal_and_sp parent.
    101  */
    102 ENTRY(execsp_dtor)
    103 	movq	%rsp,_C_LABEL(dtorsp)(%rip)
    104 	addq	$-8,_C_LABEL(dtorsp)(%rip)
    105 	jmp	_C_LABEL(execsp_main)
    106 END(execsp_dtor)
    107 
    108 	/* Make execsp_ctor a destructor. */
    109 	.section .dtors,"aw",@progbits
    110 	.p2align 3
    111 	.quad	_C_LABEL(execsp_dtor)
    112