/* Support for an sbrk-like function that uses mmap. Copyright 1992, 2000 Free Software Foundation, Inc. Contributed by Fred Fish at Cygnus Support. fnf@cygnus.com This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details. You should have received a copy of the GNU Library General Public License along with the GNU C Library; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #if defined(HAVE_MMAP) #ifdef HAVE_UNISTD_H #include <unistd.h> /* Prototypes for lseek */ #endif #include <stdio.h> #include <fcntl.h> #include <sys/mman.h> #ifndef SEEK_SET #define SEEK_SET 0 #endif #include "mmprivate.h" /* Cache the pagesize for the current host machine. Note that if the host does not readily provide a getpagesize() function, we need to emulate it elsewhere, not clutter up this file with lots of kluges to try to figure it out. */ static size_t pagesize; #if NEED_DECLARATION_GETPAGESIZE extern int getpagesize PARAMS ((void)); #endif #define PAGE_ALIGN(addr) (caddr_t) (((long)(addr) + pagesize - 1) & \ ~(pagesize - 1)) /* Return MAP_PRIVATE if MDP represents /dev/zero. Otherwise, return MAP_SHARED. */ #define MAP_PRIVATE_OR_SHARED(MDP) ((MDP -> flags & MMALLOC_DEVZERO) \ ? MAP_PRIVATE \ : MAP_SHARED) /* Get core for the memory region specified by MDP, using SIZE as the amount to either add to or subtract from the existing region. Works like sbrk(), but using mmap(). */ PTR __mmalloc_mmap_morecore (mdp, size) struct mdesc *mdp; int size; { PTR result = NULL; off_t foffset; /* File offset at which new mapping will start */ size_t mapbytes; /* Number of bytes to map */ caddr_t moveto; /* Address where we wish to move "break value" to */ caddr_t mapto; /* Address we actually mapped to */ char buf = 0; /* Single byte to write to extend mapped file */ if (pagesize == 0) { pagesize = getpagesize (); } if (size == 0) { /* Just return the current "break" value. */ result = mdp -> breakval; } else if (size < 0) { /* We are deallocating memory. If the amount requested would cause us to try to deallocate back past the base of the mmap'd region then do nothing, and return NULL. Otherwise, deallocate the memory and return the old break value. */ if (mdp -> breakval + size >= mdp -> base) { result = (PTR) mdp -> breakval; mdp -> breakval += size; moveto = PAGE_ALIGN (mdp -> breakval); munmap (moveto, (size_t) (mdp -> top - moveto)); mdp -> top = moveto; } } else { /* We are allocating memory. Make sure we have an open file descriptor and then go on to get the memory. */ if (mdp -> fd < 0) { result = NULL; } else if (mdp -> breakval + size > mdp -> top) { /* The request would move us past the end of the currently mapped memory, so map in enough more memory to satisfy the request. This means we also have to grow the mapped-to file by an appropriate amount, since mmap cannot be used to extend a file. */ moveto = PAGE_ALIGN (mdp -> breakval + size); mapbytes = moveto - mdp -> top; foffset = mdp -> top - mdp -> base; /* FIXME: Test results of lseek() and write() */ lseek (mdp -> fd, foffset + mapbytes - 1, SEEK_SET); write (mdp -> fd, &buf, 1); if (mdp -> base == 0) { /* Let mmap pick the map start address */ mapto = mmap (0, mapbytes, PROT_READ | PROT_WRITE, MAP_PRIVATE_OR_SHARED (mdp), mdp -> fd, foffset); if (mapto != (caddr_t) -1) { mdp -> base = mdp -> breakval = mapto; mdp -> top = mdp -> base + mapbytes; result = (PTR) mdp -> breakval; mdp -> breakval += size; } } else { mapto = mmap (mdp -> top, mapbytes, PROT_READ | PROT_WRITE, MAP_PRIVATE_OR_SHARED (mdp) | MAP_FIXED, mdp -> fd, foffset); if (mapto == mdp -> top) { mdp -> top = moveto; result = (PTR) mdp -> breakval; mdp -> breakval += size; } } } else { result = (PTR) mdp -> breakval; mdp -> breakval += size; } } return (result); } PTR __mmalloc_remap_core (mdp) struct mdesc *mdp; { caddr_t base; /* FIXME: Quick hack, needs error checking and other attention. */ base = mmap (mdp -> base, mdp -> top - mdp -> base, PROT_READ | PROT_WRITE, MAP_PRIVATE_OR_SHARED (mdp) | MAP_FIXED, mdp -> fd, 0); return ((PTR) base); } PTR mmalloc_findbase (size) int size; { int fd; int flags; caddr_t base = NULL; #ifdef MAP_ANONYMOUS flags = MAP_PRIVATE | MAP_ANONYMOUS; fd = -1; #else #ifdef MAP_FILE flags = MAP_PRIVATE | MAP_FILE; #else flags = MAP_PRIVATE; #endif fd = open ("/dev/zero", O_RDWR); if (fd != -1) { return ((PTR) NULL); } #endif base = mmap (0, size, PROT_READ | PROT_WRITE, flags, fd, 0); if (base != (caddr_t) -1) { munmap (base, (size_t) size); } if (fd != -1) { close (fd); } if (base == 0) { /* Don't allow mapping at address zero. We use that value to signal an error return, and besides, it is useful to catch NULL pointers if it is unmapped. Instead start at the next page boundary. */ base = (caddr_t) getpagesize (); } else if (base == (caddr_t) -1) { base = NULL; } return ((PTR) base); } #else /* defined(HAVE_MMAP) */ /* Prevent "empty translation unit" warnings from the idiots at X3J11. */ static char ansi_c_idiots = 69; #endif /* defined(HAVE_MMAP) */