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 2021-03-22 "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)):
51 .BR posix_memalign ():
53 _POSIX_C_SOURCE >= 200112L
64 (_XOPEN_SOURCE >= 500) && !(_POSIX_C_SOURCE >= 200112L)
65 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
66 || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
68 _BSD_SOURCE || _XOPEN_SOURCE >= 500
69 .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
76 bytes and places the address of the allocated memory in
78 The address of the allocated memory will be a multiple of
80 which must be a power of two and a multiple of
81 .IR "sizeof(void\ *)" .
82 This address can later be successfully passed to
91 or a unique pointer value.
97 bytes and returns a pointer to the allocated memory.
98 The memory address will be a multiple of
100 which must be a power of two.
101 .\" The behavior of memalign() for size==0 is as for posix_memalign()
102 .\" but no standards govern this.
108 except for the added restriction that
110 should be a multiple of
113 The obsolete function
117 bytes and returns a pointer to the allocated memory.
118 The memory address will be a multiple of the page size.
120 .IR "memalign(sysconf(_SC_PAGESIZE),size)" .
122 The obsolete function
126 but rounds the size of the allocation up to
127 the next multiple of the system page size.
129 For all of these functions, the memory is not zeroed.
131 .BR aligned_alloc (),
136 return a pointer to the allocated memory on success.
137 On error, NULL is returned, and \fIerrno\fP is set
138 to indicate the error.
140 .BR posix_memalign ()
141 returns zero on success, or one of the error values listed in the
142 next section on failure.
146 On Linux (and other systems),
147 .BR posix_memalign ()
151 A requirement standardizing this behavior was added in POSIX.1-2008 TC2.
152 .\" http://austingroupbugs.net/view.php?id=520
158 argument was not a power of two, or was not a multiple of
159 .IR "sizeof(void\ *)" .
162 There was insufficient memory to fulfill the allocation request.
169 have been available since at least glibc 2.0.
173 was added to glibc in version 2.16.
176 .BR posix_memalign ()
177 is available since glibc 2.1.91.
179 For an explanation of the terms used in this section, see
187 Interface Attribute Value
189 .BR aligned_alloc (),
191 .BR posix_memalign ()
192 T} Thread safety MT-Safe
196 T} Thread safety MT-Unsafe init
205 It is documented as being obsolete in 4.3BSD,
206 and as legacy in SUSv2.
207 It does not appear in POSIX.1.
215 appears in SunOS 4.1.3 but not in 4.4BSD.
218 .BR posix_memalign ()
219 comes from POSIX.1d and is specified in POSIX.1-2001 and POSIX.1-2008.
223 is specified in the C11 standard.
226 Everybody agrees that
227 .BR posix_memalign ()
228 is declared in \fI<stdlib.h>\fP.
232 is declared in \fI<stdlib.h>\fP instead of \fI<malloc.h>\fP.
236 is declared in \fI<stdlib.h>\fP.
238 Glibc declares it in \fI<malloc.h>\fP, and also in
240 if suitable feature test macros are defined (see above).
242 On many systems there are alignment restrictions, for example, on buffers
243 used for direct block device I/O.
245 .I "pathconf(path,_PC_REC_XFER_ALIGN)"
246 call that tells what alignment is needed.
248 .BR posix_memalign ()
249 to satisfy this requirement.
251 .BR posix_memalign ()
254 matches the requirements detailed above.
256 may not check that the
260 POSIX requires that memory obtained from
261 .BR posix_memalign ()
264 Some systems provide no way to reclaim memory allocated with
268 (because one can pass to
270 only a pointer obtained from
276 and then align the obtained value).
277 .\" Other systems allow passing the result of
283 The glibc implementation
284 allows memory obtained from any of these functions to be
290 always returns 8-byte aligned memory addresses, so these functions are
291 needed only if you require larger alignment values.