/*      $NetBSD: execregs.c,v 1.1 2025/02/27 00:55:32 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 00:55:32 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)
{
        /* rdi: used to pass exec arg0, nonnull anyway (path) */
        /* rsi: used to pass exec arg1, nonnull anyway (argv) */
        /* rdx: used to pass exec arg2, nonnull anyway (environ) */
        register long r10 __asm("r10") = nonnull(10);
        register long r8 __asm("r8") = nonnull(8);
        register long r9 __asm("r9") = nonnull(9);
        register long rcx __asm("rcx") = nonnull('c');
        register long r11 __asm("r11") = nonnull(11);
        register long r12 __asm("r12") = nonnull(12);
        register long r13 __asm("r13") = nonnull(13);
        register long r14 __asm("r14") = nonnull(14);
        register long r15 __asm("r15") = nonnull(15);
        /* rbp: frame pointer, can't touch that here, but it'll be nonnull */
        /* rbx: ps_strings, passed to child */
        register long rax __asm("rax") = nonnull('a');

        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"(r10),
            "+r"(r8),
            "+r"(r9),
            "+r"(rcx),
            "+r"(r11),
            "+r"(r12),
            "+r"(r13),
            "+r"(r14),
            "+r"(r15),
            "+r"(rax)
            :: "memory");

        return execve(path, argv, envp);
}

pid_t
spawnregschild(char *path, int fd)
{
        /* rdi: used to pass posix_spawn arg0, nonnull anyway (&pid) */
        /* rsi: used to pass posix_spawn arg1, nonnull anyway (path) */
        /* rdx: used to pass posix_spawn arg2, nonnull anyway (&fileacts) */
        register long r10 __asm("r10") = nonnull(10);
        /* r8: used to pass posix_spawn arg4, nonnull anyway (argv) */
        /* r9: used to pass posix_spawn arg5, nonnull anyway (environ) */
        /* rcx: used to pass posix_spawn arg3, nonnull anyway (&attr) */
        register long r11 __asm("r11") = nonnull(11);
        register long r12 __asm("r12") = nonnull(12);
        register long r13 __asm("r13") = nonnull(13);
        register long r14 __asm("r14") = nonnull(14);
        register long r15 __asm("r15") = nonnull(15);
        /* rbp: frame pointer, can't touch that here, but it'll be nonnull */
        /* rbx: ps_strings, passed to child */
        register long rax __asm("rax") = nonnull('a');

        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"(r10),
            "+r"(r11),
            "+r"(r12),
            "+r"(r13),
            "+r"(r14),
            "+r"(r15),
            "+r"(rax)
            :: "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;
}