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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9 .\" Permission is granted to copy and distribute modified versions of this
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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 2013-09-02 "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
94 .IR "sizeof(void\ *)" .
102 or a unique pointer value that can later be successfully passed to
105 The obsolete function
109 bytes and returns a pointer to the allocated memory.
110 The memory address will be a multiple of
112 which must be a power of two.
113 .\" The behavior of memalign() for size==0 is as for posix_memalign()
114 .\" but no standards govern this.
120 except for the added restriction that
122 should be a multiple of
125 The obsolete function
129 bytes and returns a pointer to the allocated memory.
130 The memory address will be a multiple of the page size.
132 .IR "memalign(sysconf(_SC_PAGESIZE),size)" .
134 The obsolete function
138 but rounds the size of the allocation up to
139 the next multiple of the system page size.
141 For all of these functions, the memory is not zeroed.
143 .BR aligned_alloc (),
148 return a pointer to the allocated memory, or NULL if the request fails.
150 .BR posix_memalign ()
151 returns zero on success, or one of the error values listed in the
152 next section on failure.
155 is indeterminate after a call to
156 .BR posix_memalign ().
162 argument was not a power of two, or was not a multiple of
163 .IR "sizeof(void\ *)" .
166 There was insufficient memory to fulfill the allocation request.
173 have been available in all Linux libc libraries.
177 was added to glibc in version 2.16.
180 .BR posix_memalign ()
181 is available since glibc 2.1.91.
186 It is documented as being obsolete in 4.3BSD,
187 and as legacy in SUSv2.
188 It does not appear in POSIX.1-2001.
196 appears in SunOS 4.1.3 but not in 4.4BSD.
199 .BR posix_memalign ()
204 is specified in the C11 standard.
207 Everybody agrees that
208 .BR posix_memalign ()
209 is declared in \fI<stdlib.h>\fP.
213 is declared in \fI<stdlib.h>\fP instead of \fI<malloc.h>\fP.
217 is declared in \fI<stdlib.h>\fP.
218 Libc4,5 and glibc declare it in \fI<malloc.h>\fP, and also in
220 if suitable feature test macros are defined (see above).
222 On many systems there are alignment restrictions, for example, on buffers
223 used for direct block device I/O.
225 .I "pathconf(path,_PC_REC_XFER_ALIGN)"
226 call that tells what alignment is needed.
228 .BR posix_memalign ()
229 to satisfy this requirement.
231 .BR posix_memalign ()
234 matches the requirements detailed above.
236 may not check that the
240 POSIX requires that memory obtained from
241 .BR posix_memalign ()
244 Some systems provide no way to reclaim memory allocated with
248 (because one can pass to
250 only a pointer obtained from
256 and then align the obtained value).
257 .\" Other systems allow passing the result of
263 The glibc implementation
264 allows memory obtained from any of these functions to be
270 always returns 8-byte aligned memory addresses, so these functions are
271 needed only if you require larger alignment values.