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) (caddr_t) (((long)(addr) + pagesize - 1) & \
51 /* Get core for the memory region specified by MDP, using SIZE as the
52 amount to either add to or subtract from the existing region. Works
53 like sbrk(), but using mmap(). */
56 __mmalloc_mmap_morecore (mdp
, size
)
61 off_t foffset
; /* File offset at which new mapping will start */
62 size_t mapbytes
; /* Number of bytes to map */
63 caddr_t moveto
; /* Address where we wish to move "break value" to */
64 caddr_t mapto
; /* Address we actually mapped to */
65 char buf
= 0; /* Single byte to write to extend mapped file */
69 pagesize
= getpagesize ();
73 /* Just return the current "break" value. */
74 result
= mdp
-> breakval
;
78 /* We are deallocating memory. If the amount requested would cause
79 us to try to deallocate back past the base of the mmap'd region
80 then do nothing, and return NULL. Otherwise, deallocate the
81 memory and return the old break value. */
82 if (mdp
-> breakval
+ size
>= mdp
-> base
)
84 result
= (PTR
) mdp
-> breakval
;
85 mdp
-> breakval
+= size
;
86 moveto
= PAGE_ALIGN (mdp
-> breakval
);
87 munmap (moveto
, (size_t) (mdp
-> top
- moveto
));
93 /* We are allocating memory. Make sure we have an open file
94 descriptor and then go on to get the memory. */
99 else if (mdp
-> breakval
+ size
> mdp
-> top
)
101 /* The request would move us past the end of the currently
102 mapped memory, so map in enough more memory to satisfy
103 the request. This means we also have to grow the mapped-to
104 file by an appropriate amount, since mmap cannot be used
106 moveto
= PAGE_ALIGN (mdp
-> breakval
+ size
);
107 mapbytes
= moveto
- mdp
-> top
;
108 foffset
= mdp
-> top
- mdp
-> base
;
109 /* FIXME: Test results of lseek() and write() */
110 lseek (mdp
-> fd
, foffset
+ mapbytes
- 1, SEEK_SET
);
111 write (mdp
-> fd
, &buf
, 1);
112 if (mdp
-> base
== 0)
114 /* Let mmap pick the map start address */
115 mapto
= mmap (0, mapbytes
, PROT_READ
| PROT_WRITE
,
116 MAP_SHARED
, mdp
-> fd
, foffset
);
117 if (mapto
!= (caddr_t
) -1)
119 mdp
-> base
= mdp
-> breakval
= mapto
;
120 mdp
-> top
= mdp
-> base
+ mapbytes
;
121 result
= (PTR
) mdp
-> breakval
;
122 mdp
-> breakval
+= size
;
127 mapto
= mmap (mdp
-> top
, mapbytes
, PROT_READ
| PROT_WRITE
,
128 MAP_SHARED
| MAP_FIXED
, mdp
-> fd
, foffset
);
129 if (mapto
== mdp
-> top
)
132 result
= (PTR
) mdp
-> breakval
;
133 mdp
-> breakval
+= size
;
139 result
= (PTR
) mdp
-> breakval
;
140 mdp
-> breakval
+= size
;
147 __mmalloc_remap_core (mdp
)
152 /* FIXME: Quick hack, needs error checking and other attention. */
154 base
= mmap (mdp
-> base
, mdp
-> top
- mdp
-> base
,
155 PROT_READ
| PROT_WRITE
, MAP_SHARED
| MAP_FIXED
,
161 mmalloc_findbase (size
)
169 flags
= MAP_SHARED
| MAP_ANONYMOUS
;
173 flags
= MAP_SHARED
| MAP_FILE
;
177 fd
= open ("/dev/zero", O_RDWR
);
183 base
= mmap (0, size
, PROT_READ
| PROT_WRITE
, flags
, fd
, 0);
184 if (base
!= (caddr_t
) -1)
186 munmap (base
, (size_t) size
);
194 /* Don't allow mapping at address zero. We use that value
195 to signal an error return, and besides, it is useful to
196 catch NULL pointers if it is unmapped. Instead start
197 at the next page boundary. */
198 base
= (caddr_t
) getpagesize ();
200 else if (base
== (caddr_t
) -1)
207 #else /* defined(HAVE_MMAP) */
208 /* Prevent "empty translation unit" warnings from the idiots at X3J11. */
209 static char ansi_c_idiots
= 69;
210 #endif /* defined(HAVE_MMAP) */
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