emacs/mps/code/protso.c

/*  impl.c.protso: PROTECTION FOR SOLARIS
 *
 *  $Id$
 *  $HopeName: MMsrc!protso.c(trunk.6) $
 *  Copyright (c) 2001 Ravenbrook Limited.
 *
 */

#include "mpm.h"

#ifndef MPS_OS_SO
#error "protso.c is Solaris specific, but MPS_OS_SO is not set"
#endif
#ifndef PROTECTION
#error "protso.c implements protection, but PROTECTION is not set"
#endif

/* open sesame magic */
#define _POSIX_SOURCE
#define _POSIX_C_SOURCE 199309L

#include <limits.h>
#include <stddef.h>
#include <stdlib.h>
#include <signal.h>
#include <siginfo.h>
#include <sys/mman.h>

#ifndef MPS_OS_SO
#error "protso.c is Solaris specific, but MPS_OS_SO is not set"
#endif

SRCID(protso, "$Id$");


/* Fix up unprototyped system calls.  */
/* Note that these are not fixed up by std.h because that only fixes */
/* up discrepancies with ANSI. */

extern int getpagesize(void);
extern pid_t getpid(void);
extern int kill(pid_t, int);

/* Crap that can't be included via "open sesame" */
/* definitions for the sa_flags field */
/* Where is the source for this?  (which header files / man pages) @@ */
#define SA_SIGINFO      0x00000008
/*
 * SIGSEGV signal codes
 */

#define SEGV_MAPERR     1       /* address not mapped to object */
#define SEGV_ACCERR     2       /* invalid permissions */
#define NSIGSEGV        2


/* 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.addr: We assume that the OS decodes the address to something
 *  sensible
 *  .sigh.limit: We throw away the limit information.
 */
 
static void sigHandle(int sig, siginfo_t *info, void *context)
{
  AVER(sig == SIGSEGV);
  AVER(info != NULL);

  if(info->si_code == SEGV_ACCERR) {
    AccessSet mode;
    Addr base, limit;

    /* We can't determine the access mode (read, write, etc.) */
    /* under Solaris without decoding the faulting instruction. */
    /* Don't bother, yet.  We can do this if necessary. */

    mode = AccessREAD | AccessWRITE;

    /* We assume that the access is for one word at the address. */
    /* (Nb. ldd has to be dword aligned,
     * hence cannot cross a page boundary) */

    base = (Addr)info->si_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. */

    /* MutatorFaultContext parameter is a dummy parameter for this */
    /* implementation */
    if(ArenaAccess(base, mode, NULL))
      return;
  }

  /* The exception was not handled by any known protection structure, */
  /* so throw it to the previously installed handler. */

  /* @@ This is really weak.
   * Need to implement rest of the contract of sigaction */
  (*sigNext.sa_handler)(sig, info, context);
}


/*  ProtSetup -- global protection setup
 *
 *  Under Solaris, the global setup involves installing a signal handler
 *  on SIGSEGV to catch and handle protection 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 wishes of the sigvec(2) entry 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_handler = sigHandle;
  sa.sa_flags = SA_SIGINFO;

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


/* ProtSet -- set protection
 *
 * This is just a thin veneer on top of mprotect(2).
 */

void ProtSet(Addr base, Addr limit, AccessSet mode)
{
  int flags;

  AVER(sizeof(int) == sizeof(Addr));
  AVER(base < limit);
  AVER(base != 0);
  AVER(AddrOffset(base, limit) <= INT_MAX);     /* should be redundant */

  flags = PROT_READ | PROT_WRITE | PROT_EXEC;
  if((mode & AccessREAD) != 0)
    flags &= ~PROT_READ;
  if((mode & AccessWRITE) != 0)
    flags &= ~PROT_WRITE;

  if(mprotect((caddr_t)base, (int)AddrOffset(base, limit), flags) != 0)
    NOTREACHED;
}


/* ProtSync -- synchronize protection settings with hardware
 *
 * This does nothing under Solaris.
 */

void ProtSync(Arena arena)
{
  NOOP;
}



/* ProtTramp -- protection trampoline
 *
 * The protection trampoline is trivial under Solaris, as there is nothing
 * that needs to be done in the dynamic context of the mutator in order
 * to catch faults.  (Contrast this with Win32 Structured Exception
 * Handling.)
 */

void ProtTramp(void **resultReturn, void *(*f)(void *, size_t),
               void *p, size_t s)
{
  AVER(resultReturn != NULL);
  AVER(FUNCHECK(f));
  /* Can't check p and s as they are interpreted by the client */

  *resultReturn = (*f)(p, s);
}