SYSCALL_MODULE() macro and modfind() issues

[Selphie Keller]

hi fbsd-hackers,

Noticed a issue in 8.1-release, 8.1p1-release and 8.1-stable
amd64/i386, to where modfind() will no longer find pmap_helper for the
/usr/ports/sysutils/pmap port, or other syscall modules using
SYSCALL_MODULE() macro.
The issue is that modfind() function no longer finds any modules using
SYSCALL_MODULE() macro to register the kernel module. Making it
difficult for userland apps to call the syscall provided. modfind()
always returns -1 which prevents modstat() from getting the required
information to perform the syscall.

Also tested, the demo syscall module:

cat /usr/share/examples/kld/syscall/module/syscall.c
/*-
 * Copyright (c) 1999 Assar Westerlund
 * 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 AUTHOR 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 AUTHOR 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.
 *
 * $FreeBSD: src/share/examples/kld/syscall/module/syscall.c,v
1.6.2.1.4.1 2010/06/14 02:09:06 kensmith Exp $
 */

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/module.h>
#include <sys/sysproto.h>
#include <sys/sysent.h>
#include <sys/kernel.h>
#include <sys/systm.h>

/*
 * The function for implementing the syscall.
 */
static int
hello(struct thread *td, void *arg)
{

        printf("hello kernel\n");
        return (0);
}

/*
 * The `sysent' for the new syscall
 */
static struct sysent hello_sysent = {
        0,                      /* sy_narg */
        hello                   /* sy_call */
};

/*
 * The offset in sysent where the syscall is allocated.
 */
static int offset = NO_SYSCALL;

/*
 * The function called at load/unload.
 */
static int
load(struct module *module, int cmd, void *arg)
{
        int error = 0;

        switch (cmd) {
        case MOD_LOAD :
                printf("syscall loaded at %d\n", offset);
                break;
        case MOD_UNLOAD :
                printf("syscall unloaded from %d\n", offset);
                break;
        default :
                error = EOPNOTSUPP;
                break;
        }
        return (error);
}

SYSCALL_MODULE(syscall, &offset, &hello_sysent, load, NULL);

---------------------------------------------------------------------------------------------------------------------
/* userland app to call syscall */
#include <stdio.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/module.h>

int main(int argc, char **argv) {
  char *endptr;
  int syscall_num;
  struct module_stat stat;

  /*Helloworld syscall test*/
  stat.version = sizeof(stat);
  modstat(modfind("syscall"), &stat);
  syscall_num = stat.data.intval;
  syscall (syscall_num);
}
---------------------------------------------------------------------------------------------------------------------

-Estella Mystagic (Selphie)