/* protli.c: PROTECTION FOR LINUX
 *
 *  $Id$
 *  Copyright (c) 2001-2014 Ravenbrook Limited.  See end of file for license.
 *
 * SOURCES
 *
 * .source.linux.kernel: Linux kernel source files.
 */

#include "prmcix.h"

#ifndef MPS_OS_LI
#error "protli.c is Linux-specific, but MPS_OS_LI is not set"
#endif

#include <limits.h>
#include <stddef.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>

SRCID(protli, "$Id$");

#if !defined(MPS_OS_LI)
#error "protli.c is specific to MPS_OS_LI"
#endif


/* The previously-installed signal action, as returned by */
/* sigaction(3).  See ProtSetup. */

static struct sigaction sigNext;


/* sigHandle -- protection signal handler
 *
 *  This is the signal handler installed by ProtSetup to deal with
 *  protection faults.  It is installed on the SIGSEGV signal.
 *  It decodes the protection fault details from the signal context
 *  and passes them to ArenaAccess, which attempts to handle the
 *  fault and remove its cause.  If the fault is handled, then
 *  the handler returns and execution resumes.  If it isn't handled,
 *  then sigHandle does its best to pass the signal on to the
 *  previously installed signal handler (sigNext).
 *
 *  .sigh.context: We check si_code for being a memory access
 *  si_addr gives the fault address.  See 
 *  .source.linux.kernel (linux/arch/i386/mm/fault.c and
 *  linux/arch/x86/mm/fault.c).
 *
 *  .sigh.addr: We assume that the OS decodes the address to something
 *  sensible
 */

/* This is defined here to keep the sources closer to those in protsgix.c
 * They can't be merged yet because protsgix doesn't pass the context to
 * ArenaAccess */

#define PROT_SIGNAL SIGSEGV

static void sigHandle(int sig, siginfo_t *info, void *context)  /* .sigh.args */
{
  int e;
  /* sigset renamed to asigset due to clash with global on Darwin. */
  sigset_t asigset, oldset;
  struct sigaction sa;

  AVER(sig == PROT_SIGNAL);

  if(info->si_code == SEGV_ACCERR) {  /* .sigh.context */
    AccessSet mode;
    Addr base;
    ucontext_t *ucontext;
    MutatorFaultContextStruct mfContext;

    ucontext = (ucontext_t *)context;
    mfContext.ucontext = ucontext;
    mfContext.info = info;

    /* on linux we used to be able to tell whether this was a read or a write */
    mode = AccessREAD | AccessWRITE;

    /* We assume that the access is for one word at the address. */
    base = (Addr)info->si_addr;   /* .sigh.addr */
    /* limit = AddrAdd(base, (Size)sizeof(Addr)); */

    /* Offer each protection structure the opportunity to handle the */
    /* exception.  If it succeeds, then allow the mutator to continue. */

    if(ArenaAccess(base, mode, &mfContext))
      return;
  }

  /* The exception was not handled by any known protection structure, */
  /* so throw it to the previously installed handler.  That handler won't */
  /* get an accurate context (the MPS would fail if it were the second in */
  /* line) but it's the best we can do. */

  e = sigaction(PROT_SIGNAL, &sigNext, &sa);
  AVER(e == 0);
  sigemptyset(&asigset);
  sigaddset(&asigset, PROT_SIGNAL);
  e = sigprocmask(SIG_UNBLOCK, &asigset, &oldset);
  AVER(e == 0);
  kill(getpid(), PROT_SIGNAL);
  e = sigprocmask(SIG_SETMASK, &oldset, NULL);
  AVER(e == 0);
  e = sigaction(PROT_SIGNAL, &sa, NULL);
  AVER(e == 0);
}


/*  ProtSetup -- global protection setup
 *
 *  Under Linux, the global setup involves installing a signal handler
 *  on SIGSEGV to catch and handle page faults (see sigHandle).
 *  The previous handler is recorded so that it can be reached from
 *  sigHandle if it fails to handle the fault.
 *
 *  NOTE: There are problems with this approach:
 *    1. we can't honor the sa_flags for the previous handler,
 *    2. what if this thread is suspended just after calling signal(3)?
 *       The sigNext variable will never be initialized!
 */

void ProtSetup(void)
{
  struct sigaction sa;
  int result;

  sa.sa_sigaction = sigHandle;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = SA_SIGINFO;

  result = sigaction(PROT_SIGNAL, &sa, &sigNext);
  AVER(result == 0);
}


/* C. COPYRIGHT AND LICENSE
 *
 * Copyright (C) 2001-2014 Ravenbrook Limited <http://www.ravenbrook.com/>.
 * All rights reserved.  This is an open source license.  Contact
 * Ravenbrook for commercial licensing options.
 * 
 * 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.
 * 
 * 3. Redistributions in any form must be accompanied by information on how
 * to obtain complete source code for this software and any accompanying
 * software that uses this software.  The source code must either be
 * included in the distribution or be available for no more than the cost
 * of distribution plus a nominal fee, and must be freely redistributable
 * under reasonable conditions.  For an executable file, complete source
 * code means the source code for all modules it contains. It does not
 * include source code for modules or files that typically accompany the
 * major components of the operating system on which the executable file
 * runs.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT, ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS AND 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.
 */