%
% (c) The AQUA Project, Glasgow University, 1995
%
%************************************************************************
%*                                                                      *
\section[mprotect.lc]{Memory Protection}
%*									*
%************************************************************************

Is @mprotect@ POSIX now?

\begin{code}
#if STACK_CHECK_BY_PAGE_FAULT

/* #define STK_CHK_DEBUG */

#include "rtsdefs.h"

# ifdef HAVE_SYS_TYPES_H
#  include <sys/types.h>
# endif

# ifdef HAVE_SYS_MMAN_H
#  include <sys/mman.h>
# endif

# if defined(_SC_PAGE_SIZE) && !defined(_SC_PAGESIZE)
    /* Death to HP-UX.  What are standards for, anyway??? */
#  define _SC_PAGESIZE _SC_PAGE_SIZE
# endif

# if defined(_SC_PAGESIZE)
#  define GETPAGESIZE()	sysconf(_SC_PAGESIZE)
# else
#  if defined(HAVE_GETPAGESIZE)
#   define GETPAGESIZE()    getpagesize()
#  else
#   if defined(linux_TARGET_OS) || defined(linuxaout_TARGET_OS)
#    /* it has it, but it is in BSD land; easier to just say so */
#    define GETPAGESIZE()   getpagesize()
#   else 
#    error getpagesize
#   endif
#  endif
# endif

#if defined(sunos4_TARGET_OS)
int getpagesize PROTO((void));
int mprotect PROTO((caddr_t, size_t, int));
#endif

/* Needed for FreeBSD (SDM, 96/03) */
#ifndef PROT_NONE
#define PROT_NONE 0
#endif

void 
unmapMiddleStackPage(addr_, size)
char * /*caddr_t*/ addr_;
int size;
{
    int pagesize = GETPAGESIZE();
    caddr_t addr = addr_;
    caddr_t middle = (caddr_t) (((W_) (addr + size / 2)) / pagesize * pagesize);

# ifdef STK_CHK_DEBUG
    fprintf(stderr, "pagesize: %x\nstack start: %08lx\nstack size: %08lx\nstack middle: %08lx\n",
      pagesize, addr, size, middle);
# endif

    if (middle < addr || middle + pagesize > addr + size) {
	fprintf(stderr, "Stack too small; stack overflow trap disabled.\n");
	return;
    }
    if (mprotect(middle, pagesize, PROT_NONE) == -1) {
	perror("mprotect");
	EXIT(EXIT_FAILURE);
    }
    if (install_segv_handler()) {
	fprintf(stderr, "Can't install SIGSEGV handler for stack overflow check.\n");
	EXIT(EXIT_FAILURE);
    }
}

#endif /* STACK_CHECK_BY_PAGE_FAULT */
\end{code}