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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 	return x;
     48 }
     49 
     50 int
     51 execregschild(char *path)
     52 {
     53 	register long edi __asm("edi") = nonnull('d');
     54 	register long esi __asm("esi") = nonnull('s');
     55 	/* ebp: frame pointer, can't touch that here, but it'll be nonnull */
     56 	/* ebx: ps_strings, passed to child */
     57 	register long edx __asm("edx") = nonnull('x');
     58 	register long ecx __asm("ecx") = nonnull('c');
     59 	register long eax __asm("eax") = nonnull('a');
     60 
     61 	char *argv[] = {path, NULL};
     62 	char **envp = environ;
     63 
     64 	/*
     65 	 * Not perfect -- compiler might use some registers for
     66 	 * stack/argument transfers, but all the arguments are nonnull
     67 	 * so this is probably a good test anyway.
     68 	 */
     69 	__asm volatile("" :
     70 	    "+r"(edi),
     71 	    "+r"(esi),
     72 	    "+r"(edx),
     73 	    "+r"(ecx),
     74 	    "+r"(eax)
     75 	    :: "memory");
     76 
     77 	return execve(path, argv, envp);
     78 }
     79 
     80 pid_t
     81 spawnregschild(char *path, int fd)
     82 {
     83 	register long edi __asm("edi") = nonnull('d');
     84 	register long esi __asm("esi") = nonnull('s');
     85 	/* ebp: frame pointer, can't touch that here, but it'll be nonnull */
     86 	/* ebx: ps_strings, passed to child */
     87 	register long edx __asm("edx") = nonnull('x');
     88 	register long ecx __asm("ecx") = nonnull('c');
     89 	register long eax __asm("eax") = nonnull('a');
     90 
     91 	char *argv[] = {path, NULL};
     92 	char **envp = environ;
     93 	posix_spawn_file_actions_t fileacts;
     94 	posix_spawnattr_t attr;
     95 	pid_t pid;
     96 	int error;
     97 
     98 	error = posix_spawn_file_actions_init(&fileacts);
     99 	if (error)
    100 		goto out;
    101 	error = posix_spawn_file_actions_adddup2(&fileacts, fd, STDOUT_FILENO);
    102 	if (error)
    103 		goto out;
    104 	error = posix_spawnattr_init(&attr);
    105 	if (error)
    106 		goto out;
    107 
    108 	/*
    109 	 * Not perfect -- compiler might use some registers for
    110 	 * stack/argument transfers, but all the arguments are nonnull
    111 	 * so this is probably a good test anyway.
    112 	 */
    113 	__asm volatile("" :
    114 	    "+r"(edi),
    115 	    "+r"(esi),
    116 	    "+r"(edx),
    117 	    "+r"(ecx),
    118 	    "+r"(eax)
    119 	    :: "memory");
    120 
    121 	error = posix_spawn(&pid, path, &fileacts, &attr, argv, envp);
    122 	if (error)
    123 		goto out;
    124 
    125 out:	posix_spawnattr_destroy(&attr);
    126 	posix_spawn_file_actions_destroy(&fileacts);
    127 	if (error) {
    128 		errno = error;
    129 		return -1;
    130 	}
    131 	return 0;
    132 }
    133