1 .\" Copyright (c) 2001 by John Levon <moz@compsoc.man.ac.uk>
2 .\" Based in part on GNU libc documentation.
4 .\" %%%LICENSE_START(VERBATIM)
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14 .\" Since the Linux kernel and libraries are constantly changing, this
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26 .\" 2001-10-11, 2003-08-22, aeb, added some details
27 .\" 2012-03-23, Michael Kerrisk <mtk.manpages@mail.com>
28 .\" Document pvalloc() and aligned_alloc()
29 .TH POSIX_MEMALIGN 3 2012-03-23 "GNU" "Linux Programmer's Manual"
31 posix_memalign, aligned_alloc, memalign, valloc, pvalloc \- allocate aligned memory
34 .B #include <stdlib.h>
36 .BI "int posix_memalign(void **" memptr ", size_t " alignment ", size_t " size );
37 .BI "void *aligned_alloc(size_t " alignment ", size_t " size );
38 .BI "void *valloc(size_t " size );
40 .B #include <malloc.h>
42 .BI "void *memalign(size_t " alignment ", size_t " size );
43 .BI "void *pvalloc(size_t " size );
47 Feature Test Macro Requirements for glibc (see
48 .BR feature_test_macros (7)):
52 .BR posix_memalign ():
53 _POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
66 (_XOPEN_SOURCE\ >=\ 500 ||
67 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED) &&
68 !(_POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600)
73 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
74 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
77 (The (nonstandard) header file
79 also exposes the declaration of
81 no feature test macros are required.)
89 bytes and places the address of the allocated memory in
91 The address of the allocated memory will be a multiple of
93 which must be a power of two and a multiple of
101 or a unique pointer value that can later be successfully passed to
104 The obsolete function
108 bytes and returns a pointer to the allocated memory.
109 The memory address will be a multiple of
111 which must be a power of two.
112 .\" The behavior of memalign() for size==0 is as for posix_memalign()
113 .\" but no standards govern this.
119 except for the added restriction that
121 should be a multiple of
124 The obsolete function
128 bytes and returns a pointer to the allocated memory.
129 The memory address will be a multiple of the page size.
131 .IR "memalign(sysconf(_SC_PAGESIZE),size)" .
133 The obsolete function
137 but rounds the size of the allocation up to
138 the next multiple of the system page size.
140 For all of these functions, the memory is not zeroed.
142 .BR aligned_alloc (),
147 return a pointer to the allocated memory, or NULL if the request fails.
149 .BR posix_memalign ()
150 returns zero on success, or one of the error values listed in the
151 next section on failure.
160 argument was not a power of two, or was not a multiple of
161 .IR "sizeof(void *)" .
164 There was insufficient memory to fulfill the allocation request.
171 have been available in all Linux libc libraries.
175 was added to glibc in version 2.16.
178 .BR posix_memalign ()
179 is available since glibc 2.1.91.
184 It is documented as being obsolete in 4.3BSD,
185 and as legacy in SUSv2.
186 It does not appear in POSIX.1-2001.
194 appears in SunOS 4.1.3 but not in 4.4BSD.
197 .BR posix_memalign ()
202 is specified in the C11 standard.
205 Everybody agrees that
206 .BR posix_memalign ()
207 is declared in \fI<stdlib.h>\fP.
211 is declared in \fI<stdlib.h>\fP instead of \fI<malloc.h>\fP.
215 is declared in \fI<stdlib.h>\fP.
216 Libc4,5 and glibc declare it in \fI<malloc.h>\fP, and also in
218 if suitable feature test macros are defined (see above).
220 On many systems there are alignment restrictions, for example, on buffers
221 used for direct block device I/O.
223 .I "pathconf(path,_PC_REC_XFER_ALIGN)"
224 call that tells what alignment is needed.
226 .BR posix_memalign ()
227 to satisfy this requirement.
229 .BR posix_memalign ()
232 matches the requirements detailed above.
234 may not check that the
238 POSIX requires that memory obtained from
239 .BR posix_memalign ()
242 Some systems provide no way to reclaim memory allocated with
246 (because one can only pass to
248 a pointer gotten from
254 and then align the obtained value).
255 .\" Other systems allow passing the result of
261 The glibc implementation
262 allows memory obtained from any of these functions to be
268 always returns 8-byte aligned memory addresses, so these functions are only
269 needed if you require larger alignment values.