/*      $NetBSD: execregs.c,v 1.1 2025/02/27 00:55:31 riastradh Exp $   */

/*-
 * Copyright (c) 2025 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: execregs.c,v 1.1 2025/02/27 00:55:31 riastradh Exp $");

#include "execregs.h"

#include <errno.h>
#include <spawn.h>
#include <stddef.h>
#include <unistd.h>

extern char **environ;

static unsigned long
nonnull(unsigned long x)
{

        x |= x << 8;
        x |= x << 16;
        x |= x << 32;
        return x;
}

int
execregschild(char *path)
{
        /* x0: used to pass exec arg0, nonnull anyway (path) */
        /* x1: used to pass exec arg1, nonnull anyway (argv) */
        /* x2: used to pass exec arg2, nonnull anyway (environ) */
        register long x3 __asm("x3") = nonnull(3);
        register long x4 __asm("x4") = nonnull(4);
        register long x5 __asm("x5") = nonnull(5);
        register long x6 __asm("x6") = nonnull(6);
        register long x7 __asm("x7") = nonnull(7);
        register long x8 __asm("x8") = nonnull(8);
        register long x9 __asm("x9") = nonnull(9);
        register long x10 __asm("x10") = nonnull(10);
        register long x11 __asm("x11") = nonnull(11);
        register long x12 __asm("x12") = nonnull(12);
        register long x13 __asm("x13") = nonnull(13);
        register long x14 __asm("x14") = nonnull(14);
        register long x15 __asm("x15") = nonnull(15);
        register long x16 __asm("x16") = nonnull(16);
        register long x17 __asm("x17") = nonnull(17);
        register long x18 __asm("x18") = nonnull(18);
        register long x19 __asm("x19") = nonnull(19);
        register long x20 __asm("x20") = nonnull(20);
        register long x21 __asm("x21") = nonnull(21);
        register long x22 __asm("x22") = nonnull(22);
        register long x23 __asm("x23") = nonnull(23);
        register long x24 __asm("x24") = nonnull(24);
        register long x25 __asm("x25") = nonnull(25);
        register long x26 __asm("x26") = nonnull(26);
        register long x27 __asm("x27") = nonnull(27);
        register long x28 __asm("x28") = nonnull(28);
        /* x29: frame pointer, nonnull anyway */
        /* x30: link register, nonnull anyway */

        char *argv[] = {path, NULL};
        char **envp = environ;

        /*
         * Not perfect -- compiler might use some registers for
         * stack/argument transfers, but all the arguments are nonnull
         * so this is probably a good test anyway.
         */
        __asm volatile("" :
            "+r"(x3),
            "+r"(x4),
            "+r"(x5),
            "+r"(x6),
            "+r"(x7),
            "+r"(x8),
            "+r"(x9),
            "+r"(x10),
            "+r"(x11),
            "+r"(x12),
            "+r"(x13),
            "+r"(x14),
            "+r"(x15),
            "+r"(x16),
            "+r"(x17)
            :: "memory");
        /* pacify gcc error: more than 30 operands in 'asm' */
        __asm volatile("" :
            "+r"(x18),
            "+r"(x19),
            "+r"(x20),
            "+r"(x21),
            "+r"(x22),
            "+r"(x23),
            "+r"(x24),
            "+r"(x25),
            "+r"(x26),
            "+r"(x27),
            "+r"(x28)
            :: "memory");

        return execve(path, argv, envp);
}

pid_t
spawnregschild(char *path, int fd)
{
        /* x0: used to pass posix_spawn arg0, nonnull anyway (&pid) */
        /* x1: used to pass posix_spawn arg1, nonnull anyway (path) */
        /* x2: used to pass posix_spawn arg2, nonnull anyway (&fileacts) */
        /* x3: used to pass posix_spawn arg3, nonnull anyway (&attr) */
        /* x4: used to pass posix_spawn arg3, nonnull anyway (argv) */
        /* x5: used to pass posix_spawn arg3, nonnull anyway (environ) */
        register long x6 __asm("x6") = nonnull(6);
        register long x7 __asm("x7") = nonnull(7);
        register long x8 __asm("x8") = nonnull(8);
        register long x9 __asm("x9") = nonnull(9);
        register long x10 __asm("x10") = nonnull(10);
        register long x11 __asm("x11") = nonnull(11);
        register long x12 __asm("x12") = nonnull(12);
        register long x13 __asm("x13") = nonnull(13);
        register long x14 __asm("x14") = nonnull(14);
        register long x15 __asm("x15") = nonnull(15);
        register long x16 __asm("x16") = nonnull(16);
        register long x17 __asm("x17") = nonnull(17);
        register long x18 __asm("x18") = nonnull(18);
        register long x19 __asm("x19") = nonnull(19);
        register long x20 __asm("x20") = nonnull(20);
        register long x21 __asm("x21") = nonnull(21);
        register long x22 __asm("x22") = nonnull(22);
        register long x23 __asm("x23") = nonnull(23);
        register long x24 __asm("x24") = nonnull(24);
        register long x25 __asm("x25") = nonnull(25);
        register long x26 __asm("x26") = nonnull(26);
        register long x27 __asm("x27") = nonnull(27);
        register long x28 __asm("x28") = nonnull(28);
        /* x29: frame pointer, nonnull anyway */
        /* x30: link register, nonnull anyway */

        char *argv[] = {path, NULL};
        char **envp = environ;
        posix_spawn_file_actions_t fileacts;
        posix_spawnattr_t attr;
        pid_t pid;
        int error;

        error = posix_spawn_file_actions_init(&fileacts);
        if (error)
                goto out;
        error = posix_spawn_file_actions_adddup2(&fileacts, fd, STDOUT_FILENO);
        if (error)
                goto out;
        error = posix_spawnattr_init(&attr);
        if (error)
                goto out;

        /*
         * Not perfect -- compiler might use some registers for
         * stack/argument transfers, but all the arguments are nonnull
         * so this is probably a good test anyway.
         */
        __asm volatile("" :
            "+r"(x6),
            "+r"(x7),
            "+r"(x8),
            "+r"(x9),
            "+r"(x10),
            "+r"(x11),
            "+r"(x12),
            "+r"(x13),
            "+r"(x14),
            "+r"(x15),
            "+r"(x16),
            "+r"(x17),
            "+r"(x18),
            "+r"(x19),
            "+r"(x20)
            :: "memory");
        /* pacify gcc error: more than 30 operands in 'asm' */
        __asm volatile("" :
            "+r"(x21),
            "+r"(x22),
            "+r"(x23),
            "+r"(x24),
            "+r"(x25),
            "+r"(x26),
            "+r"(x27),
            "+r"(x28)
            :: "memory");

        error = posix_spawn(&pid, path, &fileacts, &attr, argv, envp);
        if (error)
                goto out;

out:    posix_spawnattr_destroy(&attr);
        posix_spawn_file_actions_destroy(&fileacts);
        if (error) {
                errno = error;
                return -1;
        }
        return 0;
}