-.\" (c) 2001 by John Levon <moz@compsoc.man.ac.uk>
+.\" Copyright (c) 2001 by John Levon <moz@compsoc.man.ac.uk>
.\" Based in part on GNU libc documentation.
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
-.\"
+.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
-.\"
+.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
-.\" License.
+.\" %%%LICENSE_END
.\"
.\" 2001-10-11, 2003-08-22, aeb, added some details
-.TH POSIX_MEMALIGN 3 2003-08-22 "GNU" "Linux Programmer's Manual"
+.\" 2012-03-23, Michael Kerrisk <mtk.manpages@mail.com>
+.\" Document pvalloc() and aligned_alloc()
+.TH POSIX_MEMALIGN 3 2019-05-09 "GNU" "Linux Programmer's Manual"
.SH NAME
-posix_memalign, memalign, valloc \- Allocate aligned memory
+posix_memalign, aligned_alloc, memalign, valloc, pvalloc \- allocate aligned memory
.SH SYNOPSIS
.nf
-.B #define _XOPEN_SOURCE 600
.B #include <stdlib.h>
-.sp
+.PP
.BI "int posix_memalign(void **" memptr ", size_t " alignment ", size_t " size );
-.sp
-.B #include <malloc.h>
-.sp
+.BI "void *aligned_alloc(size_t " alignment ", size_t " size );
.BI "void *valloc(size_t " size );
-.BI "void *memalign(size_t " boundary ", size_t " size );
-.nl
+
+.B #include <malloc.h>
+.PP
+.BI "void *memalign(size_t " alignment ", size_t " size );
+.BI "void *pvalloc(size_t " size );
.fi
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.PP
+.ad l
+.BR posix_memalign ():
+_POSIX_C_SOURCE\ >=\ 200112L
+.PP
+.BR aligned_alloc ():
+_ISOC11_SOURCE
+.PP
+.BR valloc ():
+.br
+.PD 0
+.RS 4
+.TP 4
+Since glibc 2.12:
+.nf
+(_XOPEN_SOURCE\ >=\ 500) && !(_POSIX_C_SOURCE\ >=\ 200112L)
+ || /* Glibc since 2.19: */ _DEFAULT_SOURCE
+ || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
+.br
+.fi
+.TP
+Before glibc 2.12:
+_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
+.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+.ad b
+.br
+(The (nonstandard) header file
+.I <malloc.h>
+also exposes the declaration of
+.BR valloc ();
+no feature test macros are required.)
+.RE
+.PD
.SH DESCRIPTION
The function
-.B posix_memalign()
+.BR posix_memalign ()
allocates
.I size
bytes and places the address of the allocated memory in
The address of the allocated memory will be a multiple of
.IR "alignment" ,
which must be a power of two and a multiple of
-.IR "sizeof(void *)".
-
+.IR "sizeof(void\ *)" .
+If
+.I size
+is 0, then
+the value placed in
+.IR "*memptr"
+is either NULL,
+.\" glibc does this:
+or a unique pointer value that can later be successfully passed to
+.BR free (3).
+.PP
The obsolete function
-.B memalign()
+.BR memalign ()
allocates
.I size
bytes and returns a pointer to the allocated memory.
The memory address will be a multiple of
-.IR "boundary" ,
+.IR alignment ,
which must be a power of two.
-
+.\" The behavior of memalign() for size==0 is as for posix_memalign()
+.\" but no standards govern this.
+.PP
+The function
+.BR aligned_alloc ()
+is the same as
+.BR memalign (),
+except for the added restriction that
+.I size
+should be a multiple of
+.IR alignment .
+.PP
The obsolete function
-.B valloc()
+.BR valloc ()
allocates
.I size
bytes and returns a pointer to the allocated memory.
The memory address will be a multiple of the page size.
It is equivalent to
.IR "memalign(sysconf(_SC_PAGESIZE),size)" .
-
-For all three routines, the memory is not zeroed.
-
-.SH "RETURN VALUE"
-.BR memalign()
+.PP
+The obsolete function
+.BR pvalloc ()
+is similar to
+.BR valloc (),
+but rounds the size of the allocation up to
+the next multiple of the system page size.
+.PP
+For all of these functions, the memory is not zeroed.
+.SH RETURN VALUE
+.BR aligned_alloc (),
+.BR memalign (),
+.BR valloc (),
and
-.BR valloc()
-return the pointer to the allocated memory, or
-.B NULL
-if the request fails.
-
-.BR posix_memalign()
+.BR pvalloc ()
+return a pointer to the allocated memory on success.
+On error, NULL is returned, and \fIerrno\fP is set
+to indicate the cause of the error.
+.PP
+.BR posix_memalign ()
returns zero on success, or one of the error values listed in the
-next section on failure. Note that
-.IR errno
+next section on failure.
+The value of
+.I errno
is not set.
-
-.SH "ERRORS"
+On Linux (and other systems),
+.BR posix_memalign ()
+does not modify
+.I memptr
+on failure.
+A requirement standardizing this behavior was added in POSIX.1-2016.
+.\" http://austingroupbugs.net/view.php?id=520
+.SH ERRORS
.TP
.B EINVAL
The
-.IR alignment
-parameter was not a power of two, or was not a multiple of
-.IR "sizeof(void *)" .
+.I alignment
+argument was not a power of two, or was not a multiple of
+.IR "sizeof(void\ *)" .
.TP
.B ENOMEM
There was insufficient memory to fulfill the allocation request.
-
+.SH VERSIONS
+The functions
+.BR memalign (),
+.BR valloc (),
+and
+.BR pvalloc ()
+have been available in all Linux libc libraries.
+.PP
+The function
+.BR aligned_alloc ()
+was added to glibc in version 2.16.
+.PP
+The function
+.BR posix_memalign ()
+is available since glibc 2.1.91.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lb lb lb
+l l l.
+Interface Attribute Value
+T{
+.BR aligned_alloc (),
+.br
+.BR memalign (),
+.br
+.BR posix_memalign ()
+T} Thread safety MT-Safe
+T{
+.BR valloc (),
+.br
+.BR pvalloc ()
+T} Thread safety MT-Unsafe init
+.TE
+.sp 1
+.SH CONFORMING TO
+The function
+.BR valloc ()
+appeared in 3.0BSD.
+It is documented as being obsolete in 4.3BSD,
+and as legacy in SUSv2.
+It does not appear in POSIX.1.
+.PP
+The function
+.BR pvalloc ()
+is a GNU extension.
+.PP
+The function
+.BR memalign ()
+appears in SunOS 4.1.3 but not in 4.4BSD.
+.PP
+The function
+.BR posix_memalign ()
+comes from POSIX.1d and is specified in POSIX.1-2001 and POSIX.1-2008.
+.PP
+The function
+.BR aligned_alloc ()
+is specified in the C11 standard.
+.\"
+.SS Headers
+Everybody agrees that
+.BR posix_memalign ()
+is declared in \fI<stdlib.h>\fP.
+.PP
+On some systems
+.BR memalign ()
+is declared in \fI<stdlib.h>\fP instead of \fI<malloc.h>\fP.
+.PP
+According to SUSv2,
+.BR valloc ()
+is declared in \fI<stdlib.h>\fP.
+Libc4,5 and glibc declare it in \fI<malloc.h>\fP, and also in
+\fI<stdlib.h>\fP
+if suitable feature test macros are defined (see above).
.SH NOTES
-On many systems there are alignment restrictions, e.g. on buffers
-used for direct block device I/O. POSIX specifies the
+On many systems there are alignment restrictions, for example, on buffers
+used for direct block device I/O.
+POSIX specifies the
.I "pathconf(path,_PC_REC_XFER_ALIGN)"
-call that tells what alignment is needed. Now one can use
+call that tells what alignment is needed.
+Now one can use
.BR posix_memalign ()
to satisfy this requirement.
-
+.PP
.BR posix_memalign ()
verifies that
-.IR alignment
+.I alignment
matches the requirements detailed above.
-.BR memalign()
+.BR memalign ()
may not check that the
-.IR boundary
-parameter is correct.
-
+.I alignment
+argument is correct.
+.PP
POSIX requires that memory obtained from
-.BR posix_memalign()
+.BR posix_memalign ()
can be freed using
-.IR free ().
+.BR free (3).
Some systems provide no way to reclaim memory allocated with
-.IR memalign ()
+.BR memalign ()
or
-.IR valloc ()
-(because one can only pass to
-.IR free ()
-a pointer gotten from
-.IR malloc (),
-while e.g.
-.IR memalign ()
+.BR valloc ()
+(because one can pass to
+.BR free (3)
+only a pointer obtained from
+.BR malloc (3),
+while, for example,
+.BR memalign ()
would call
-.IR malloc ()
+.BR malloc (3)
and then align the obtained value).
.\" Other systems allow passing the result of
.\" .IR valloc ()
.\" to
-.\" .IR free (),
+.\" .IR free (3),
.\" but not to
-.\" .IR realloc ().
-GNU libc allows memory obtained from any of these three routines to be
+.\" .IR realloc (3).
+The glibc implementation
+allows memory obtained from any of these functions to be
reclaimed with
-.IR free ().
-
-GNU libc
-.BR "malloc()"
-always returns 8-byte aligned memory addresses, so these routines are only
-needed if you require larger alignment values.
-
-.SH AVAILABILITY
-The functions
-.IR memalign ()
-and
-.IR valloc ()
-have been available in all Linux libc libraries.
-The function
-.IR posix_memalign ()
-is available since glibc 2.1.91.
-
-.SH "CONFORMING TO"
-The function
-.IR valloc ()
-appeared in 3.0 BSD. It is documented as being obsolete in 4.3BSD,
-and as legacy in SUSv2. It no longer occurs in SUSv3.
-The function
-.IR memalign ()
-appears in SunOS 4.1.3 but not in 4.4BSD.
-The function
-.IR posix_memalign ()
-comes from POSIX 1003.1d.
-
-.SH HEADERS
-Everybody agrees that
-.IR posix_memalign ()
-is declared in <stdlib.h>. In order to declare it, glibc needs
-_GNU_SOURCE defined, or _XOPEN_SOURCE defined to a value not less than 600.
-
-Everybody agrees that
-.IR memalign ()
-is declared in <malloc.h>.
-
-According to SUSv2,
-.IR valloc ()
-is declared in <stdlib.h>.
-Libc4,5 and glibc declare it in <malloc.h> and perhaps also in <stdlib.h>
-(namely, if _GNU_SOURCE is defined, or _BSD_SOURCE is defined, or,
-for glibc, if _XOPEN_SOURCE_EXTENDED is defined, or, equivalently,
-_XOPEN_SOURCE is defined to a value not less than 500).
-
-.SH "SEE ALSO"
+.BR free (3).
+.PP
+The glibc
+.BR malloc (3)
+always returns 8-byte aligned memory addresses, so these functions are
+needed only if you require larger alignment values.
+.SH SEE ALSO
.BR brk (2),
.BR getpagesize (2),
.BR free (3),
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