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execregs.c revision 1.1 
      1 /*	$NetBSD: execregs.c,v 1.1 2025/02/27 00:55:32 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 #include <sys/cdefs.h>
     30 __RCSID("$NetBSD: execregs.c,v 1.1 2025/02/27 00:55:32 riastradh Exp $");
     31 
     32 #include "execregs.h"
     33 
     34 #include <errno.h>
     35 #include <spawn.h>
     36 #include <stddef.h>
     37 #include <unistd.h>
     38 
     39 extern char **environ;
     40 
     41 static unsigned long
     42 nonnull(unsigned long x)
     43 {
     44 
     45 	x |= x << 8;
     46 	x |= x << 16;
     47 	x |= x << 32;
     48 	return x;
     49 }
     50 
     51 int
     52 execregschild(char *path)
     53 {
     54 	/* rdi: used to pass exec arg0, nonnull anyway (path) */
     55 	/* rsi: used to pass exec arg1, nonnull anyway (argv) */
     56 	/* rdx: used to pass exec arg2, nonnull anyway (environ) */
     57 	register long r10 __asm("r10") = nonnull(10);
     58 	register long r8 __asm("r8") = nonnull(8);
     59 	register long r9 __asm("r9") = nonnull(9);
     60 	register long rcx __asm("rcx") = nonnull('c');
     61 	register long r11 __asm("r11") = nonnull(11);
     62 	register long r12 __asm("r12") = nonnull(12);
     63 	register long r13 __asm("r13") = nonnull(13);
     64 	register long r14 __asm("r14") = nonnull(14);
     65 	register long r15 __asm("r15") = nonnull(15);
     66 	/* rbp: frame pointer, can't touch that here, but it'll be nonnull */
     67 	/* rbx: ps_strings, passed to child */
     68 	register long rax __asm("rax") = nonnull('a');
     69 
     70 	char *argv[] = {path, NULL};
     71 	char **envp = environ;
     72 
     73 	/*
     74 	 * Not perfect -- compiler might use some registers for
     75 	 * stack/argument transfers, but all the arguments are nonnull
     76 	 * so this is probably a good test anyway.
     77 	 */
     78 	__asm volatile("" :
     79 	    "+r"(r10),
     80 	    "+r"(r8),
     81 	    "+r"(r9),
     82 	    "+r"(rcx),
     83 	    "+r"(r11),
     84 	    "+r"(r12),
     85 	    "+r"(r13),
     86 	    "+r"(r14),
     87 	    "+r"(r15),
     88 	    "+r"(rax)
     89 	    :: "memory");
     90 
     91 	return execve(path, argv, envp);
     92 }
     93 
     94 pid_t
     95 spawnregschild(char *path, int fd)
     96 {
     97 	/* rdi: used to pass posix_spawn arg0, nonnull anyway (&pid) */
     98 	/* rsi: used to pass posix_spawn arg1, nonnull anyway (path) */
     99 	/* rdx: used to pass posix_spawn arg2, nonnull anyway (&fileacts) */
    100 	register long r10 __asm("r10") = nonnull(10);
    101 	/* r8: used to pass posix_spawn arg4, nonnull anyway (argv) */
    102 	/* r9: used to pass posix_spawn arg5, nonnull anyway (environ) */
    103 	/* rcx: used to pass posix_spawn arg3, nonnull anyway (&attr) */
    104 	register long r11 __asm("r11") = nonnull(11);
    105 	register long r12 __asm("r12") = nonnull(12);
    106 	register long r13 __asm("r13") = nonnull(13);
    107 	register long r14 __asm("r14") = nonnull(14);
    108 	register long r15 __asm("r15") = nonnull(15);
    109 	/* rbp: frame pointer, can't touch that here, but it'll be nonnull */
    110 	/* rbx: ps_strings, passed to child */
    111 	register long rax __asm("rax") = nonnull('a');
    112 
    113 	char *argv[] = {path, NULL};
    114 	char **envp = environ;
    115 	posix_spawn_file_actions_t fileacts;
    116 	posix_spawnattr_t attr;
    117 	pid_t pid;
    118 	int error;
    119 
    120 	error = posix_spawn_file_actions_init(&fileacts);
    121 	if (error)
    122 		goto out;
    123 	error = posix_spawn_file_actions_adddup2(&fileacts, fd, STDOUT_FILENO);
    124 	if (error)
    125 		goto out;
    126 	error = posix_spawnattr_init(&attr);
    127 	if (error)
    128 		goto out;
    129 
    130 	/*
    131 	 * Not perfect -- compiler might use some registers for
    132 	 * stack/argument transfers, but all the arguments are nonnull
    133 	 * so this is probably a good test anyway.
    134 	 */
    135 	__asm volatile("" :
    136 	    "+r"(r10),
    137 	    "+r"(r11),
    138 	    "+r"(r12),
    139 	    "+r"(r13),
    140 	    "+r"(r14),
    141 	    "+r"(r15),
    142 	    "+r"(rax)
    143 	    :: "memory");
    144 
    145 	error = posix_spawn(&pid, path, &fileacts, &attr, argv, envp);
    146 	if (error)
    147 		goto out;
    148 
    149 out:	posix_spawnattr_destroy(&attr);
    150 	posix_spawn_file_actions_destroy(&fileacts);
    151 	if (error) {
    152 		errno = error;
    153 		return -1;
    154 	}
    155 	return 0;
    156 }
    157