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malloc_get_state.3: New page documenting malloc_get_state(3) and malloc_set_state(3)
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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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 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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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH MALLOC_GET_STATE 3 2012-03-26 "GNU" "Linux Programmer's Manual"
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.SH NAME
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get_malloc_state, set_malloc_state \- record and restore state of malloc implementation
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.sp
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.BI "void* malloc_get_state(void);"
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.BI "int malloc_set_state(void *" state );
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.fi
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.SH DESCRIPTION
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The
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.BR malloc_get_state ()
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function records the current state of all
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.BR malloc (3)
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internal bookkeeping variables
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(but not the actual contents of the heap
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or the state of
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.BR malloc_hook (3)
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functions pointers).
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The state is recorded in a system-dependent opaque data structure
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dynamically allocated via
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.BR malloc (3),
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and a pointer to that data structure is returned as the function result.
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(It is the caller's responsibility to
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.BR free (3)
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this memory.)
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The
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.BR malloc_set_state ()
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function restores the state of all
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.BR malloc (3)
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internal bookkeeping variables to the values recorded in
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the opaque data structure pointed to by
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.IR state .
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.SH RETURN VALUE
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On success,
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.BR malloc_get_state ()
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returns a pointer to a newly allocated opaque data structure.
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On error (for example, memory could not be allocated for the data structure),
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.BR malloc_get_state ()
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returns NULL.
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On success,
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.BR malloc_set_state ()
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returns 0.
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If the implementation detects that
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.I state
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does not point to a correctly formed data structure,
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.\" if(ms->magic != MALLOC_STATE_MAGIC) return -1;
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.BR malloc_set_state ()
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returns \-1.
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If the implementation detects that
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the version of the data structure referred to by
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.I state
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is a more recent version than this implementation knows about,
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.\" /* Must fail if the major version is too high. */
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.\" if((ms->version & ~0xffl) > (MALLOC_STATE_VERSION & ~0xffl)) return -2;
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.BR malloc_set_state ()
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returns \-2.
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.SH CONFORMING TO
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These functions are GNU extensions.
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.SH NOTES
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These functions are especially useful when using this
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.BR malloc (3)
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implementation as part of a shared library,
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and the heap contents are saved/restored via some other method.
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This technique is used by the GNU Emacs to implement its "dumping" function.
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Hook function pointers are never saved or restored by these
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functions, with two exceptions:
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if malloc checking (see
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.BR mallopt (3))
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was in use when
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.BR malloc_get_state ()
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was called, then
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.BR malloc_set_state ()
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resets malloc checking hooks
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.\" i.e., calls __malloc_check_init()
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if possible;
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.\" i.e., malloc checking is not already in use
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.\" and the caller requested malloc checking
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if malloc checking was not in use in the recorded state,
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but the caller has requested malloc checking,
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then the hooks are reset to 0.
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.SH SEE ALSO
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.BR malloc (3),
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.BR mallopt (3)
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