38cc378c61
This is a greatly pared down version of the full gdb-4.12, all the config stuff has been removed and the supporting libraries have been stripped to a minimum. This is a 1.1.5 only port, I'll do a more complete port for 2.0 which will have all the config stuff and will install the gnu support libraries as system libraries like we do for readline. There wasn't much point for 1.1.5 since only gdb would use them so I went for saving space instead. For 2.0 I'll config all the other gnu tools to use them as well.
259 lines
9.5 KiB
Plaintext
259 lines
9.5 KiB
Plaintext
\input texinfo @c -*- Texinfo -*-
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@setfilename mmalloc.info
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@ifinfo
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@format
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START-INFO-DIR-ENTRY
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* Mmalloc: (mmalloc). The GNU mapped-malloc package.
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END-INFO-DIR-ENTRY
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@end format
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This file documents the GNU mmalloc (mapped-malloc) package, written by
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fnf@@cygnus.com, based on GNU malloc written by mike@@ai.mit.edu.
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Copyright (C) 1992 Free Software Foundation, Inc.
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Permission is granted to make and distribute verbatim copies of
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this manual provided the copyright notice and this permission notice
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are preserved on all copies.
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@ignore
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Permission is granted to process this file through Tex and print the
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results, provided the printed document carries copying permission
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notice identical to this one except for the removal of this paragraph
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(this paragraph not being relevant to the printed manual).
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@end ignore
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided also that the
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entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions.
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@end ifinfo
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@iftex
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@c @finalout
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@setchapternewpage odd
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@settitle MMALLOC, the GNU memory-mapped malloc package
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@titlepage
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@title mmalloc
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@subtitle The GNU memory-mapped malloc package
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@author Fred Fish
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@author Cygnus Support
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@author Mike Haertel
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@author Free Software Foundation
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@page
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@tex
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\def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
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\xdef\manvers{\$Revision: 1.1.1.1 $} % For use in headers, footers too
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{\parskip=0pt
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\hfill Cygnus Support\par
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\hfill fnf\@cygnus.com\par
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\hfill {\it MMALLOC, the GNU memory-mapped malloc package}, \manvers\par
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\hfill \TeX{}info \texinfoversion\par
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}
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@end tex
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@vskip 0pt plus 1filll
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Copyright @copyright{} 1992 Free Software Foundation, Inc.
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Permission is granted to make and distribute verbatim copies of
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this manual provided the copyright notice and this permission notice
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are preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided also that
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the entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions.
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@end titlepage
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@end iftex
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@ifinfo
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@node Top, Overview, (dir), (dir)
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@top mmalloc
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This file documents the GNU memory-mapped malloc package mmalloc.
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@menu
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* Overview:: Overall Description
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* Implementation:: Implementation
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--- The Detailed Node Listing ---
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Implementation
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* Compatibility:: Backwards Compatibility
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* Functions:: Function Descriptions
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@end menu
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@end ifinfo
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@node Overview, Implementation, Top, Top
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@chapter Overall Description
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This is a heavily modified version of GNU @code{malloc}. It uses
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@code{mmap} as the basic mechanism for for obtaining memory from the
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system, rather than @code{sbrk}. This gives it several advantages over the
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more traditional malloc:
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@itemize @bullet
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@item
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Several different heaps can be used, each of them growing
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or shinking under control of @code{mmap}, with the @code{mmalloc} functions
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using a specific heap on a call by call basis.
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@item
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By using @code{mmap}, it is easy to create heaps which are intended to
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be persistent and exist as a filesystem object after the creating
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process has gone away.
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@item
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Because multiple heaps can be managed, data used for a
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specific purpose can be allocated into its own heap, making
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it easier to allow applications to ``dump'' and ``restore'' initialized
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malloc-managed memory regions. For example, the ``unexec'' hack popularized
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by GNU Emacs could potentially go away.
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@end itemize
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@node Implementation, , Overview, Top
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@chapter Implementation
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The @code{mmalloc} functions contain no internal static state. All
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@code{mmalloc} internal data is allocated in the mapped in region, along
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with the user data that it manages. This allows it to manage multiple
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such regions and to ``pick up where it left off'' when such regions are
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later dynamically mapped back in.
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In some sense, malloc has been ``purified'' to contain no internal state
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information and generalized to use multiple memory regions rather than a
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single region managed by @code{sbrk}. However the new routines now need an
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extra parameter which informs @code{mmalloc} which memory region it is dealing
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with (along with other information). This parameter is called the
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@dfn{malloc descriptor}.
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The functions initially provided by @code{mmalloc} are:
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@example
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void *mmalloc_attach (int fd, void *baseaddr);
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void *mmalloc_detach (void *md);
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int mmalloc_errno (void *md);
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int mmalloc_setkey (void *md, int keynum, void *key);
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void *mmalloc_getkey (void *md, int keynum);
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void *mmalloc (void *md, size_t size);
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void *mrealloc (void *md, void *ptr, size_t size);
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void *mvalloc (void *md, size_t size);
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void mfree (void *md, void *ptr);
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@end example
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@menu
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* Compatibility:: Backwards Compatibility
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* Functions:: Function Descriptions
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@end menu
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@node Compatibility, Functions, Implementation, Implementation
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@section Backwards Compatibility
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To allow a single malloc package to be used in a given application,
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provision is made for the traditional @code{malloc}, @code{realloc}, and
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@code{free} functions to be implemented as special cases of the
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@code{mmalloc} functions. In particular, if any of the functions that
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expect malloc descriptors are called with a @code{NULL} pointer rather than a
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valid malloc descriptor, then they default to using an @code{sbrk} managed
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region.
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The @code{mmalloc} package provides compatible @code{malloc}, @code{realloc},
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and @code{free} functions using this mechanism internally.
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Applications can avoid this extra interface layer by simply including the
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following defines:
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@example
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#define malloc(size) mmalloc ((void *)0, (size))
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#define realloc(ptr,size) mrealloc ((void *)0, (ptr), (size));
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#define free(ptr) mfree ((void *)0, (ptr))
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@end example
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@noindent
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or replace the existing @code{malloc}, @code{realloc}, and @code{free}
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calls with the above patterns if using @code{#define} causes problems.
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@node Functions, , Compatibility, Implementation
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@section Function Descriptions
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These are the details on the functions that make up the @code{mmalloc}
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package.
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@table @code
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@item void *mmalloc_attach (int @var{fd}, void *@var{baseaddr});
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Initialize access to a @code{mmalloc} managed region.
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If @var{fd} is a valid file descriptor for an open file, then data for the
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@code{mmalloc} managed region is mapped to that file. Otherwise
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@file{/dev/zero} is used and the data will not exist in any filesystem object.
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If the open file corresponding to @var{fd} is from a previous use of
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@code{mmalloc} and passes some basic sanity checks to ensure that it is
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compatible with the current @code{mmalloc} package, then its data is
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mapped in and is immediately accessible at the same addresses in
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the current process as the process that created the file.
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If @var{baseaddr} is not @code{NULL}, the mapping is established
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starting at the specified address in the process address space. If
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@var{baseaddr} is @code{NULL}, the @code{mmalloc} package chooses a
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suitable address at which to start the mapped region, which will be the
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value of the previous mapping if opening an existing file which was
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previously built by @code{mmalloc}, or for new files will be a value
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chosen by @code{mmap}.
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Specifying @var{baseaddr} provides more control over where the regions
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start and how big they can be before bumping into existing mapped
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regions or future mapped regions.
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On success, returns a malloc descriptor which is used in subsequent
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calls to other @code{mmalloc} package functions. It is explicitly
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@samp{void *} (@samp{char *} for systems that don't fully support
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@code{void}) so that users of the package don't have to worry about the
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actual implementation details.
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On failure returns @code{NULL}.
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@item void *mmalloc_detach (void *@var{md});
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Terminate access to a @code{mmalloc} managed region identified by the
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descriptor @var{md}, by closing the base file and unmapping all memory
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pages associated with the region.
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Returns @code{NULL} on success.
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Returns the malloc descriptor on failure, which can subsequently
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be used for further action (such as obtaining more information about
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the nature of the failure).
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@item void *mmalloc (void *@var{md}, size_t @var{size});
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Given an @code{mmalloc} descriptor @var{md}, allocate additional memory of
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@var{size} bytes in the associated mapped region.
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@item *mrealloc (void *@var{md}, void *@var{ptr}, size_t @var{size});
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Given an @code{mmalloc} descriptor @var{md} and a pointer to memory
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previously allocated by @code{mmalloc} in @var{ptr}, reallocate the
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memory to be @var{size} bytes long, possibly moving the existing
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contents of memory if necessary.
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@item void *mvalloc (void *@var{md}, size_t @var{size});
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Like @code{mmalloc} but the resulting memory is aligned on a page boundary.
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@item void mfree (void *@var{md}, void *@var{ptr});
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Given an @code{mmalloc} descriptor @var{md} and a pointer to memory previously
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allocated by @code{mmalloc} in @var{ptr}, free the previously allocated memory.
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@item int mmalloc_errno (void *@var{md});
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Given a @code{mmalloc} descriptor, if the last @code{mmalloc} operation
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failed for some reason due to a system call failure, then
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returns the associated @code{errno}. Returns 0 otherwise.
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(This function is not yet implemented).
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@end table
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@bye
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