src/memattr.cpp

 /***************************************************************************
 *
 * memattr.cpp - source for C++ Standard Library helper functions
 *               to determine the attributes of regions of memory
 *
 * $Id$
 *
 ***************************************************************************
 *
 * Copyright (c) 1994-2005 Quovadx,  Inc., acting through its  Rogue Wave
 * Software division. Licensed under the Apache License, Version 2.0 (the
 * "License");  you may  not use this file except  in compliance with the
 * License.    You    may   obtain   a   copy   of    the   License    at
 * http://www.apache.org/licenses/LICENSE-2.0.    Unless   required    by
 * applicable law  or agreed to  in writing,  software  distributed under
 * the License is distributed on an "AS IS" BASIS,  WITHOUT WARRANTIES OR
 * CONDITIONS OF  ANY KIND, either  express or implied.  See  the License
 * for the specific language governing permissions  and limitations under
 * the License.
 * 
 **************************************************************************/

#define _RWSTD_LIB_SRC

#include <errno.h>    // for errno
#include <string.h>   // for memchr

#ifdef __CYGWIN__
   // use the Windows API on Cygwin
#  define _WIN32
#endif

#if !defined (_WIN32) && !defined (_WIN64)
#  ifdef __SUNPRO_CC
     // working around SunOS bug #568
#    include <time.h>
#  endif
#  include <unistd.h>     // for sysconf
#  include <sys/mman.h>   // for mincore
#  include <sys/types.h>

#  ifndef _SC_PAGE_SIZE
     // fall back on the alternative
#    define _SC_PAGE_SIZE _SC_PAGESIZE
#  endif

#else
#  include <windows.h>    // for everything (ugh)
#endif   // _WIN{32,64}

#include <rw/_defs.h>

// define ENOMEM if it's not #defined (e.g., when using pure libc headers)
#ifndef ENOMEM
#  define ENOMEM   12   /* HP-UX, Solaris, Tru64, ... */
#endif   // ENOMEM


// FIXME: implement PROT_READ and PROT_WRITE correctly
#ifndef _RWSTD_PROT_READ
#  define _RWSTD_PROT_READ -1
#endif

#ifndef _RWSTD_PROT_WRITE
#  define _RWSTD_PROT_WRITE 0
#endif


#define DIST(addr1, addr2)                         \
  (  _RWSTD_REINTERPRET_CAST (const char*, addr1)  \
   - _RWSTD_REINTERPRET_CAST (const char*, addr2))


_RWSTD_NAMESPACE (__rw) {

_RWSTD_EXPORT _RWSTD_SSIZE_T
__rw_memattr (const void *addr, _RWSTD_SIZE_T nbytes, int attr)
{
    // FIXME: allow attr to be set to the equivalent of PROT_READ,
    // PROT_WRITE, and (perhaps also) PROT_EXEC, or any combination
    // of the three, in addition to 0 (PROT_NONE)
    _RWSTD_UNUSED (attr);

#if !defined (_WIN32) && !defined (_WIN64)

    // determine the system page size in bytes
    static const _RWSTD_SIZE_T pgsz = size_t (sysconf (_SC_PAGE_SIZE));

    // compute the address of the beginning of the page
    // to which the address `addr' belongs
    caddr_t const page =
        _RWSTD_REINTERPRET_CAST (caddr_t,
            _RWSTD_REINTERPRET_CAST (_RWSTD_SIZE_T, addr) & ~(pgsz - 1));

    // compute the maximum number of pages occuppied by the memory
    // region pointed to by `addr' (nbytes may be -1 as a request
    // to compute, in a safe way, the length of the string pointed
    // to by `addr')
    _RWSTD_SIZE_T npages = nbytes ? nbytes / pgsz + 1 : 0;

    for (size_t i = 0; i < npages; ++i) {

        const caddr_t next = _RWSTD_REINTERPRET_CAST (char*, page) + i * pgsz;

#  ifdef _RWSTD_OS_SUNOS

        char dummy = '\0';

        // on Solaris use mincore() instead of madvise() since
        // the latter is unreliable
        if (-1 == mincore (next, 1, &dummy) && ENOMEM == errno)
            return next == page ? -1 : DIST (next, addr);

#  elif !defined (_RWSTD_NO_MADVISE)

        // on HP-UX, Linux, use madvise() as opposed to mincore()
        // since the latter fails for address ranges that aren't
        // backed by a file (such as stack variables)
        if (-1 == madvise (next, 1, MADV_WILLNEED) && ENOMEM == errno)
            return next == page ? -1 : DIST (next, addr);

#  endif

        if (_RWSTD_SIZE_MAX == nbytes) {

            // when the size of the region is unspecified look
            // for the first NUL byte and when found, return
            // the total size of the memory region between
            // `addr' and the NUL byte (i.e., the length of
            // the string pointed to by `addr')

            const _RWSTD_SIZE_T maxpage =
                next == page ? pgsz - DIST (addr, next) : pgsz;

            const void* const pnul =
                memchr (next == page ? addr : next, '\0', maxpage);

            if (pnul) {
                nbytes = DIST (pnul, addr);
                npages = nbytes / pgsz + 1;
                break;
            }
        }
    }

    return _RWSTD_STATIC_CAST (_RWSTD_SSIZE_T, nbytes);

#else   // if defined (_WIN{32,64})

    LPVOID const ptr = _RWSTD_CONST_CAST (LPVOID, addr);

    if (_RWSTD_SIZE_MAX == nbytes) {

        // treat the address as a pointer to a NUL-terminated string
        if (IsBadStringPtr (_RWSTD_STATIC_CAST (LPCSTR, ptr), nbytes))
            return -1;

        // compute the length of the string
        nbytes = strlen (_RWSTD_STATIC_CAST (const char*, addr));

        // disable read checking below (since it was done above)
        attr &= ~_RWSTD_PROT_READ;
    }

    if ((attr & _RWSTD_PROT_READ) && IsBadReadPtr (ptr, nbytes))
        return -1;

    if ((attr & _RWSTD_PROT_WRITE) && IsBadWritePtr (ptr, nbytes))
        return -1;

    return _RWSTD_STATIC_CAST (_RWSTD_SSIZE_T, nbytes);

#endif   // _RWSTD_NO_INCORE

}

}