mirror of https://github.com/mkerrisk/man-pages
131 lines
3.2 KiB
Groff
131 lines
3.2 KiB
Groff
.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
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.\" Distributed under GPL
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.\" Heavily based on glibc documentation
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.\" Polished, added docs, removed glibc doc bug, 2002-07-20, aeb
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.TH MALLOC_HOOK 3 2002-07-20 "GNU" "Linux Programmer's Manual"
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.SH NAME
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__malloc_hook, __malloc_initialize_hook,
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__memalign_hook, __free_hook, __realloc_hook,
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__after_morecore_hook \- malloc debugging variables
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.SH SYNOPSIS
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.sp
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.BR "#include <malloc.h>"
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.sp
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.BI "void *(*__malloc_hook)(size_t " size ,
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.BI "const void *" caller );
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.sp
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.BI "void *(*__realloc_hook)(void *" ptr ,
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.BI "size_t " size ,
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.BI "const void *" caller );
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.sp
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.BI "void *(*__memalign_hook)(size_t " alignment ,
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.BI "size_t " size ,
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.BI "const void *" caller );
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.sp
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.BI "void (*__free_hook)(void *" ptr ,
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.BI "const void *" caller );
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.sp
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.BI "void (*__malloc_initialize_hook)(void);"
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.sp
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.BI "void (*__after_morecore_hook)(void);"
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.SH DESCRIPTION
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The GNU C library lets you modify the behavior of
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.BR malloc (),
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.BR realloc (),
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and
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.BR free ()
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by specifying appropriate hook functions. You can use these hooks
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to help you debug programs that use dynamic memory allocation,
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for example.
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.LP
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The variable
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.B __malloc_initialize_hook
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points at a function that is called once when the malloc implementation
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is initialized. This is a weak variable, so it can be overridden in
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the application with a definition like the following:
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.br
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.nf
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void (*__malloc_initialize_hook)(void) = my_init_hook;
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.fi
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.br
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Now the function
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.IR my_init_hook ()
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can do the initialization of all hooks.
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.LP
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The four functions pointed to by
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.BR __malloc_hook ,
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.BR __realloc_hook ,
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.BR __memalign_hook ,
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.BR __free_hook
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have a prototype like the functions
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.BR malloc (),
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.BR realloc (),
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.BR memalign (),
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.BR free (),
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respectively, except that they have a final argument
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.I caller
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that gives the address of the caller of
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.BR malloc (),
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etc.
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.LP
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The variable
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.B __after_morecore_hook
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points at a function that is called each time after
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.BR sbrk ()
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was asked for more memory.
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.SH "EXAMPLE"
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Here is a short example of how to use these variables.
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.sp
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.nf
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#include <stdio.h>
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#include <malloc.h>
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/* Prototypes for our hooks. */
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static void my_init_hook(void);
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static void *my_malloc_hook(size_t, const void *);
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/* Variables to save original hooks. */
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static void *(*old_malloc_hook)(size_t, const void *);
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/* Override initialising hook from the C library. */
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void (*__malloc_initialize_hook) (void) = my_init_hook;
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static void
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my_init_hook(void)
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{
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old_malloc_hook = __malloc_hook;
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__malloc_hook = my_malloc_hook;
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}
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static void *
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my_malloc_hook(size_t size, const void *caller)
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{
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void *result;
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/* Restore all old hooks */
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__malloc_hook = old_malloc_hook;
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/* Call recursively */
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result = malloc(size);
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/* Save underlying hooks */
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old_malloc_hook = __malloc_hook;
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/* `printf' might call `malloc', so protect it too. */
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printf("malloc(%u) called from %p returns %p\\n",
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(unsigned int) size, caller, result);
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/* Restore our own hooks */
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__malloc_hook = my_malloc_hook;
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return result;
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}
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.fi
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.SH "CONFORMING TO"
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These functions are GNU extensions.
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.SH "SEE ALSO"
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.BR mallinfo (3),
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.BR malloc (3),
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.BR mcheck (3),
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.BR mtrace (3)
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