1 /* Support for an sbrk-like function that uses mmap.
2 Copyright 1992, 2000 Free Software Foundation, Inc.
4 Contributed by Fred Fish at Cygnus Support. fnf@cygnus.com
6 This file is part of the GNU C Library.
8 The GNU C Library is free software; you can redistribute it and/or
9 modify it under the terms of the GNU Library General Public License as
10 published by the Free Software Foundation; either version 2 of the
11 License, or (at your option) any later version.
13 The GNU C Library is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 Library General Public License for more details.
18 You should have received a copy of the GNU Library General Public
19 License along with the GNU C Library; see the file COPYING.LIB. If
20 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
21 Boston, MA 02111-1307, USA. */
23 #if defined(HAVE_MMAP)
26 #include <unistd.h> /* Prototypes for lseek */
36 #include "mmprivate.h"
38 /* Cache the pagesize for the current host machine. Note that if the host
39 does not readily provide a getpagesize() function, we need to emulate it
40 elsewhere, not clutter up this file with lots of kluges to try to figure
43 static size_t pagesize;
44 #if NEED_DECLARATION_GETPAGESIZE
45 extern int getpagesize PARAMS ((void));
48 #define PAGE_ALIGN(addr) (PTR) (((long)(addr) + pagesize - 1) & \
51 /* Return MAP_PRIVATE if MDP represents /dev/zero. Otherwise, return
54 #define MAP_PRIVATE_OR_SHARED(MDP) ((MDP -> flags & MMALLOC_DEVZERO) \
58 /* Return MAP_ANONYMOUS if MDP uses anonymous mapping. Otherwise, return 0 */
60 #define MAP_IS_ANONYMOUS(MDP) (((MDP) -> flags & MMALLOC_ANONYMOUS) \
64 /* Return -1 if MDP uses anonymous mapping. Otherwise, return MDP->FD */
65 #define MAP_ANON_OR_FD(MDP) (((MDP) -> flags & MMALLOC_ANONYMOUS) \
69 /* Get core for the memory region specified by MDP, using SIZE as the
70 amount to either add to or subtract from the existing region. Works
71 like sbrk(), but using mmap(). */
74 __mmalloc_mmap_morecore (mdp, size)
79 off_t foffset; /* File offset at which new mapping will start */
80 size_t mapbytes; /* Number of bytes to map */
81 PTR moveto; /* Address where we wish to move "break value" to */
82 PTR mapto; /* Address we actually mapped to */
83 char buf = 0; /* Single byte to write to extend mapped file */
86 pagesize = getpagesize();
90 /* Just return the current "break" value. */
91 result = mdp -> breakval;
95 /* We are deallocating memory. If the amount requested would cause
96 us to try to deallocate back past the base of the mmap'd region
97 then do nothing, and return NULL. Otherwise, deallocate the
98 memory and return the old break value. */
99 if (mdp -> breakval + size >= mdp -> base)
101 result = (PTR) mdp -> breakval;
102 mdp -> breakval += size;
103 moveto = PAGE_ALIGN (mdp -> breakval);
104 munmap (moveto, (size_t) (mdp -> top - moveto) - 1);
110 /* We are allocating memory. Make sure we have an open file
111 descriptor if not working with anonymous memory. */
112 if ( !(mdp->flags & MMALLOC_ANONYMOUS) && mdp -> fd < 0)
116 else if (mdp -> breakval + size > mdp -> top)
118 /* The request would move us past the end of the currently
119 mapped memory, so map in enough more memory to satisfy
120 the request. This means we also have to grow the mapped-to
121 file by an appropriate amount, since mmap cannot be used
123 moveto = PAGE_ALIGN (mdp -> breakval + size);
124 mapbytes = moveto - mdp -> top;
125 foffset = mdp -> top - mdp -> base;
128 /* FIXME: Test results of lseek() and write() */
129 lseek (mdp -> fd, foffset + mapbytes - 1, SEEK_SET);
130 write (mdp -> fd, &buf, 1);
133 /* Let's call mmap. Note that it is possible that mdp->top
134 is 0. In this case mmap will choose the address for us */
135 mapto = mmap (mdp->top, mapbytes, PROT_READ | PROT_WRITE,
136 MAP_PRIVATE_OR_SHARED(mdp) | MAP_IS_ANONYMOUS(mdp) | MAP_FIXED,
137 MAP_ANON_OR_FD(mdp), foffset);
139 if (mapto != (PTR) -1){
142 mdp -> base = mdp -> breakval = mapto;
144 mdp -> top = PAGE_ALIGN (mdp -> breakval + size);
145 result = (PTR) mdp -> breakval;
146 mdp -> breakval += size;
151 result = (PTR) mdp -> breakval;
152 mdp -> breakval += size;
159 __mmalloc_remap_core (mdp)
164 /* FIXME: Quick hack, needs error checking and other attention. */
166 base = mmap (mdp -> base, mdp -> top - mdp -> base,
167 PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE_OR_SHARED (mdp) | MAP_FIXED,
173 mmalloc_findbase (size)
181 flags = MAP_PRIVATE | MAP_ANONYMOUS;
185 flags = MAP_PRIVATE | MAP_FILE;
189 fd = open ("/dev/zero", O_RDWR);
195 base = mmap (0, size, PROT_READ | PROT_WRITE, flags, fd, 0);
196 if (base != (PTR) -1)
198 munmap (base, (size_t) size);
206 /* Don't allow mapping at address zero. We use that value
207 to signal an error return, and besides, it is useful to
208 catch NULL pointers if it is unmapped. Instead start
209 at the next page boundary. */
210 base = (PTR) getpagesize ();
212 else if (base == (PTR) -1)
219 #else /* defined(HAVE_MMAP) */
220 /* Prevent "empty translation unit" warnings from the idiots at X3J11. */
221 //static char ansi_c_idiots = 69;
222 #endif /* defined(HAVE_MMAP) */