1 /* Support for an sbrk-like function that uses mmap.
2 Copyright 1992 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)
33 #include "mmprivate.h"
35 /* Cache the pagesize for the current host machine. Note that if the host
36 does not readily provide a getpagesize() function, we need to emulate it
37 elsewhere, not clutter up this file with lots of kluges to try to figure
40 static size_t pagesize
;
41 extern int getpagesize
PARAMS ((void));
43 #define PAGE_ALIGN(addr) (caddr_t) (((long)(addr) + pagesize - 1) & \
46 /* Get core for the memory region specified by MDP, using SIZE as the
47 amount to either add to or subtract from the existing region. Works
48 like sbrk(), but using mmap(). */
51 __mmalloc_mmap_morecore (mdp
, size
)
56 off_t foffset
; /* File offset at which new mapping will start */
57 size_t mapbytes
; /* Number of bytes to map */
58 caddr_t moveto
; /* Address where we wish to move "break value" to */
59 caddr_t mapto
; /* Address we actually mapped to */
60 char buf
= 0; /* Single byte to write to extend mapped file */
64 pagesize
= getpagesize ();
68 /* Just return the current "break" value. */
69 result
= mdp
-> breakval
;
73 /* We are deallocating memory. If the amount requested would cause
74 us to try to deallocate back past the base of the mmap'd region
75 then do nothing, and return NULL. Otherwise, deallocate the
76 memory and return the old break value. */
77 if (mdp
-> breakval
+ size
>= mdp
-> base
)
79 result
= (PTR
) mdp
-> breakval
;
80 mdp
-> breakval
+= size
;
81 moveto
= PAGE_ALIGN (mdp
-> breakval
);
82 munmap (moveto
, (size_t) (mdp
-> top
- moveto
));
88 /* We are allocating memory. Make sure we have an open file
89 descriptor and then go on to get the memory. */
94 else if (mdp
-> breakval
+ size
> mdp
-> top
)
96 /* The request would move us past the end of the currently
97 mapped memory, so map in enough more memory to satisfy
98 the request. This means we also have to grow the mapped-to
99 file by an appropriate amount, since mmap cannot be used
101 moveto
= PAGE_ALIGN (mdp
-> breakval
+ size
);
102 mapbytes
= moveto
- mdp
-> top
;
103 foffset
= mdp
-> top
- mdp
-> base
;
104 /* FIXME: Test results of lseek() and write() */
105 lseek (mdp
-> fd
, foffset
+ mapbytes
- 1, SEEK_SET
);
106 write (mdp
-> fd
, &buf
, 1);
107 if (mdp
-> base
== 0)
109 /* Let mmap pick the map start address */
110 mapto
= mmap (0, mapbytes
, PROT_READ
| PROT_WRITE
,
111 MAP_SHARED
, mdp
-> fd
, foffset
);
112 if (mapto
!= (caddr_t
) -1)
114 mdp
-> base
= mdp
-> breakval
= mapto
;
115 mdp
-> top
= mdp
-> base
+ mapbytes
;
116 result
= (PTR
) mdp
-> breakval
;
117 mdp
-> breakval
+= size
;
122 mapto
= mmap (mdp
-> top
, mapbytes
, PROT_READ
| PROT_WRITE
,
123 MAP_SHARED
| MAP_FIXED
, mdp
-> fd
, foffset
);
124 if (mapto
== mdp
-> top
)
127 result
= (PTR
) mdp
-> breakval
;
128 mdp
-> breakval
+= size
;
134 result
= (PTR
) mdp
-> breakval
;
135 mdp
-> breakval
+= size
;
142 __mmalloc_remap_core (mdp
)
147 /* FIXME: Quick hack, needs error checking and other attention. */
149 base
= mmap (mdp
-> base
, mdp
-> top
- mdp
-> base
,
150 PROT_READ
| PROT_WRITE
, MAP_SHARED
| MAP_FIXED
,
156 mmalloc_findbase (size
)
162 fd
= open ("/dev/zero", O_RDWR
);
165 base
= mmap (0, size
, PROT_READ
| PROT_WRITE
, MAP_SHARED
, fd
, 0);
166 if (base
!= (caddr_t
) -1)
168 munmap (base
, (size_t) size
);
173 /* Don't allow mapping at address zero. We use that value
174 to signal an error return, and besides, it is useful to
175 catch NULL pointers if it is unmapped. Instead start
176 at the next page boundary. */
177 base
= (caddr_t
) getpagesize ();
179 else if (base
== (caddr_t
) -1)
187 #else /* defined(HAVE_MMAP) */
188 /* Prevent "empty translation unit" warnings from the idiots at X3J11. */
189 static char ansi_c_idiots
= 69;
190 #endif /* defined(HAVE_MMAP) */
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