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authorWill Newton <will.newton@linaro.org>2013-11-06 09:48:10 +0000
committerWill Newton <will.newton@linaro.org>2013-12-16 14:51:29 +0000
commit0a096e4487541671336aa61b0fac10322a9bbbfe (patch)
tree782c1eea26d9740ed4cb4006e0e8813408f02da5 /manual/memory.texi
parent8d561986c0b44c1f9b489b30b661354cf456eac5 (diff)
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manual/memory.texi: Bring aligned allocation docs up to date.
The current documentation suggests using memalign and valloc which are now considered obsolete, so suggest using posix_memalign instead. Also document the possible error return and errno values for memalign and posix_memalign and improve documentation of __memalign_hook. ChangeLog: 2013-12-16 Will Newton <will.newton@linaro.org> * manual/memory.texi (Malloc Examples): Clarify default alignment documentation. Suggest posix_memalign rather than memalign or valloc. (Aligned Memory Blocks): Remove suggestion to use memalign or valloc. Remove obsolete comment about BSD. Document memalign errno values and mark the function obsolete. Document posix_memalign returned error codes. Mark valloc as obsolete. (Hooks for Malloc): __memalign_hook is also called for posix_memalign and valloc. (Summary of Malloc): Add posix_memalign to function summary. __memalign_hook is also called for posix_memalign and valloc.
Diffstat (limited to 'manual/memory.texi')
-rw-r--r--manual/memory.texi61
1 files changed, 44 insertions, 17 deletions
diff --git a/manual/memory.texi b/manual/memory.texi
index a80f87cbf3f..3d96f353bee 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -380,10 +380,10 @@ savestring (const char *ptr, size_t len)
The block that @code{malloc} gives you is guaranteed to be aligned so
that it can hold any type of data. On @gnusystems{}, the address is
-always a multiple of eight on most systems, and a multiple of 16 on
+always a multiple of eight on 32-bit systems, and a multiple of 16 on
64-bit systems. Only rarely is any higher boundary (such as a page
-boundary) necessary; for those cases, use @code{memalign},
-@code{posix_memalign} or @code{valloc} (@pxref{Aligned Memory Blocks}).
+boundary) necessary; for those cases, use @code{posix_memalign}
+(@pxref{Aligned Memory Blocks}).
Note that the memory located after the end of the block is likely to be
in use for something else; perhaps a block already allocated by another
@@ -616,14 +616,8 @@ after calling @code{free} wastes memory. The size threshold for
The address of a block returned by @code{malloc} or @code{realloc} in
@gnusystems{} is always a multiple of eight (or sixteen on 64-bit
systems). If you need a block whose address is a multiple of a higher
-power of two than that, use @code{memalign}, @code{posix_memalign}, or
-@code{valloc}. @code{memalign} is declared in @file{malloc.h} and
-@code{posix_memalign} is declared in @file{stdlib.h}.
-
-With @theglibc{}, you can use @code{free} to free the blocks that
-@code{memalign}, @code{posix_memalign}, and @code{valloc} return. That
-does not work in BSD, however---BSD does not provide any way to free
-such blocks.
+power of two than that, use @code{posix_memalign}. @code{posix_memalign}
+is declared in @file{stdlib.h}.
@comment malloc.h
@comment BSD
@@ -633,6 +627,21 @@ address is a multiple of @var{boundary}. The @var{boundary} must be a
power of two! The function @code{memalign} works by allocating a
somewhat larger block, and then returning an address within the block
that is on the specified boundary.
+
+The @code{memalign} function returns a null pointer on error and sets
+@code{errno} to one of the following values:
+
+@table @code
+@item ENOMEM
+There was insufficient memory available to satisfy the request.
+
+@item EINVAL
+@var{alignment} is not a power of two.
+
+@end table
+
+The @code{memalign} function is obsolete and @code{posix_memalign} should
+be used instead.
@end deftypefun
@comment stdlib.h
@@ -647,6 +656,16 @@ parameter @var{alignment}: the value must be a power of two multiple of
If the function succeeds in allocation memory a pointer to the allocated
memory is returned in @code{*@var{memptr}} and the return value is zero.
Otherwise the function returns an error value indicating the problem.
+The possible error values returned are:
+
+@table @code
+@item ENOMEM
+There was insufficient memory available to satisfy the request.
+
+@item EINVAL
+@var{alignment} is not a power of two multiple of @code{sizeof (void *)}.
+
+@end table
This function was introduced in POSIX 1003.1d.
@end deftypefun
@@ -667,6 +686,9 @@ valloc (size_t size)
@ref{Query Memory Parameters} for more information about the memory
subsystem.
+
+The @code{valloc} function is obsolete and @code{posix_memalign} should
+be used instead.
@end deftypefun
@node Malloc Tunable Parameters
@@ -902,17 +924,17 @@ memory consumption of the program.
@comment malloc.h
@comment GNU
@defvar __memalign_hook
-The value of this variable is a pointer to function that @code{memalign}
-uses whenever it is called. You should define this function to look
-like @code{memalign}; that is, like:
+The value of this variable is a pointer to function that @code{memalign},
+@code{posix_memalign} and @code{valloc} use whenever they are called.
+You should define this function to look like @code{memalign}; that is, like:
@smallexample
void *@var{function} (size_t @var{alignment}, size_t @var{size}, const void *@var{caller})
@end smallexample
The value of @var{caller} is the return address found on the stack when
-the @code{memalign} function was called. This value allows you to trace the
-memory consumption of the program.
+the @code{memalign}, @code{posix_memalign} or @code{valloc} functions are
+called. This value allows you to trace the memory consumption of the program.
@end defvar
You must make sure that the function you install as a hook for one of
@@ -1118,6 +1140,10 @@ Space}.
Allocate a block of @var{size} bytes, starting on a page boundary.
@xref{Aligned Memory Blocks}.
+@item int posix_memalign (void **@var{memptr}, size_t @var{alignment}, size_t @var{size})
+Allocate a block of @var{size} bytes, starting on an address that is a
+multiple of @var{alignment}. @xref{Aligned Memory Blocks}.
+
@item void *memalign (size_t @var{size}, size_t @var{boundary})
Allocate a block of @var{size} bytes, starting on an address that is a
multiple of @var{boundary}. @xref{Aligned Memory Blocks}.
@@ -1140,7 +1166,8 @@ A pointer to a function that @code{realloc} uses whenever it is called.
A pointer to a function that @code{free} uses whenever it is called.
@item void (*__memalign_hook) (size_t @var{size}, size_t @var{alignment}, const void *@var{caller})
-A pointer to a function that @code{memalign} uses whenever it is called.
+A pointer to a function that @code{memalign}, @code{posix_memalign} and
+@code{valloc} use whenever they are called.
@item struct mallinfo mallinfo (void)
Return information about the current dynamic memory usage.