295 lines
14 KiB
Plaintext
295 lines
14 KiB
Plaintext
@node Internal Probes
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@c @node Internal Probes, Tunables, Dynamic Linker, Top
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@c %MENU% Probes to monitor libc internal behavior
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@chapter Internal probes
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In order to aid in debugging and monitoring internal behavior,
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@theglibc{} exposes nearly-zero-overhead SystemTap probes marked with
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the @code{libc} provider.
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These probes are not part of the @glibcadj{} stable ABI, and they are
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subject to change or removal across releases. Our only promise with
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regard to them is that, if we find a need to remove or modify the
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arguments of a probe, the modified probe will have a different name, so
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that program monitors relying on the old probe will not get unexpected
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arguments.
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@menu
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* Memory Allocation Probes:: Probes in the memory allocation subsystem
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* Non-local Goto Probes:: Probes in setjmp and longjmp
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@end menu
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@node Memory Allocation Probes
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@section Memory Allocation Probes
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These probes are designed to signal relatively unusual situations within
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the virtual memory subsystem of @theglibc{}.
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@deftp Probe memory_sbrk_more (void *@var{$arg1}, size_t @var{$arg2})
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This probe is triggered after the main arena is extended by calling
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@code{sbrk}. Argument @var{$arg1} is the additional size requested to
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@code{sbrk}, and @var{$arg2} is the pointer that marks the end of the
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@code{sbrk} area, returned in response to the request.
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@end deftp
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@deftp Probe memory_sbrk_less (void *@var{$arg1}, size_t @var{$arg2})
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This probe is triggered after the size of the main arena is decreased by
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calling @code{sbrk}. Argument @var{$arg1} is the size released by
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@code{sbrk} (the positive value, rather than the negative value passed
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to @code{sbrk}), and @var{$arg2} is the pointer that marks the end of
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the @code{sbrk} area, returned in response to the request.
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@end deftp
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@deftp Probe memory_heap_new (void *@var{$arg1}, size_t @var{$arg2})
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This probe is triggered after a new heap is @code{mmap}ed. Argument
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@var{$arg1} is a pointer to the base of the memory area, where the
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@code{heap_info} data structure is held, and @var{$arg2} is the size of
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the heap.
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@end deftp
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@deftp Probe memory_heap_free (void *@var{$arg1}, size_t @var{$arg2})
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This probe is triggered @emph{before} (unlike the other sbrk and heap
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probes) a heap is completely removed via @code{munmap}. Argument
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@var{$arg1} is a pointer to the heap, and @var{$arg2} is the size of the
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heap.
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@end deftp
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@deftp Probe memory_heap_more (void *@var{$arg1}, size_t @var{$arg2})
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This probe is triggered after a trailing portion of an @code{mmap}ed
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heap is extended. Argument @var{$arg1} is a pointer to the heap, and
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@var{$arg2} is the new size of the heap.
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@end deftp
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@deftp Probe memory_heap_less (void *@var{$arg1}, size_t @var{$arg2})
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This probe is triggered after a trailing portion of an @code{mmap}ed
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heap is released. Argument @var{$arg1} is a pointer to the heap, and
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@var{$arg2} is the new size of the heap.
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@end deftp
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@deftp Probe memory_malloc_retry (size_t @var{$arg1})
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@deftpx Probe memory_realloc_retry (size_t @var{$arg1}, void *@var{$arg2})
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@deftpx Probe memory_memalign_retry (size_t @var{$arg1}, size_t @var{$arg2})
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@deftpx Probe memory_calloc_retry (size_t @var{$arg1})
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These probes are triggered when the corresponding functions fail to
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obtain the requested amount of memory from the arena in use, before they
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call @code{arena_get_retry} to select an alternate arena in which to
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retry the allocation. Argument @var{$arg1} is the amount of memory
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requested by the user; in the @code{calloc} case, that is the total size
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computed from both function arguments. In the @code{realloc} case,
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@var{$arg2} is the pointer to the memory area being resized. In the
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@code{memalign} case, @var{$arg2} is the alignment to be used for the
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request, which may be stricter than the value passed to the
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@code{memalign} function. A @code{memalign} probe is also used by functions
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@code{posix_memalign, valloc} and @code{pvalloc}.
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Note that the argument order does @emph{not} match that of the
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corresponding two-argument functions, so that in all of these probes the
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user-requested allocation size is in @var{$arg1}.
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@end deftp
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@deftp Probe memory_arena_retry (size_t @var{$arg1}, void *@var{$arg2})
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This probe is triggered within @code{arena_get_retry} (the function
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called to select the alternate arena in which to retry an allocation
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that failed on the first attempt), before the selection of an alternate
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arena. This probe is redundant, but much easier to use when it's not
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important to determine which of the various memory allocation functions
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is failing to allocate on the first try. Argument @var{$arg1} is the
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same as in the function-specific probes, except for extra room for
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padding introduced by functions that have to ensure stricter alignment.
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Argument @var{$arg2} is the arena in which allocation failed.
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@end deftp
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@deftp Probe memory_arena_new (void *@var{$arg1}, size_t @var{$arg2})
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This probe is triggered when @code{malloc} allocates and initializes an
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additional arena (not the main arena), but before the arena is assigned
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to the running thread or inserted into the internal linked list of
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arenas. The arena's @code{malloc_state} internal data structure is
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located at @var{$arg1}, within a newly-allocated heap big enough to hold
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at least @var{$arg2} bytes.
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@end deftp
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@deftp Probe memory_arena_reuse (void *@var{$arg1}, void *@var{$arg2})
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This probe is triggered when @code{malloc} has just selected an existing
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arena to reuse, and (temporarily) reserved it for exclusive use.
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Argument @var{$arg1} is a pointer to the newly-selected arena, and
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@var{$arg2} is a pointer to the arena previously used by that thread.
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This occurs within
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@code{reused_arena}, right after the mutex mentioned in probe
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@code{memory_arena_reuse_wait} is acquired; argument @var{$arg1} will
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point to the same arena. In this configuration, this will usually only
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occur once per thread. The exception is when a thread first selected
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the main arena, but a subsequent allocation from it fails: then, and
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only then, may we switch to another arena to retry that allocation, and
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for further allocations within that thread.
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@end deftp
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@deftp Probe memory_arena_reuse_wait (void *@var{$arg1}, void *@var{$arg2}, void *@var{$arg3})
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This probe is triggered when @code{malloc} is about to wait for an arena
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to become available for reuse. Argument @var{$arg1} holds a pointer to
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the mutex the thread is going to wait on, @var{$arg2} is a pointer to a
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newly-chosen arena to be reused, and @var{$arg3} is a pointer to the
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arena previously used by that thread.
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This occurs within
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@code{reused_arena}, when a thread first tries to allocate memory or
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needs a retry after a failure to allocate from the main arena, there
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isn't any free arena, the maximum number of arenas has been reached, and
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an existing arena was chosen for reuse, but its mutex could not be
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immediately acquired. The mutex in @var{$arg1} is the mutex of the
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selected arena.
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@end deftp
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@deftp Probe memory_arena_reuse_free_list (void *@var{$arg1})
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This probe is triggered when @code{malloc} has chosen an arena that is
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in the free list for use by a thread, within the @code{get_free_list}
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function. The argument @var{$arg1} holds a pointer to the selected arena.
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@end deftp
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@deftp Probe memory_mallopt (int @var{$arg1}, int @var{$arg2})
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This probe is triggered when function @code{mallopt} is called to change
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@code{malloc} internal configuration parameters, before any change to
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the parameters is made. The arguments @var{$arg1} and @var{$arg2} are
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the ones passed to the @code{mallopt} function.
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@end deftp
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@deftp Probe memory_mallopt_mxfast (int @var{$arg1}, int @var{$arg2})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_MXFAST}, and the requested
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value is in an acceptable range. Argument @var{$arg1} is the requested
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value, and @var{$arg2} is the previous value of this @code{malloc}
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parameter.
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@end deftp
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@deftp Probe memory_mallopt_trim_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_TRIM_THRESHOLD}. Argument
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@var{$arg1} is the requested value, @var{$arg2} is the previous value of
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this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
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threshold adjustment was already disabled.
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@end deftp
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@deftp Probe memory_mallopt_top_pad (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_TOP_PAD}. Argument
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@var{$arg1} is the requested value, @var{$arg2} is the previous value of
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this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
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threshold adjustment was already disabled.
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@end deftp
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@deftp Probe memory_mallopt_mmap_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_MMAP_THRESHOLD}, and the
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requested value is in an acceptable range. Argument @var{$arg1} is the
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requested value, @var{$arg2} is the previous value of this @code{malloc}
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parameter, and @var{$arg3} is nonzero if dynamic threshold adjustment
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was already disabled.
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@end deftp
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@deftp Probe memory_mallopt_mmap_max (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_MMAP_MAX}. Argument
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@var{$arg1} is the requested value, @var{$arg2} is the previous value of
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this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
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threshold adjustment was already disabled.
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@end deftp
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@deftp Probe memory_mallopt_perturb (int @var{$arg1}, int @var{$arg2})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_PERTURB}. Argument
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@var{$arg1} is the requested value, and @var{$arg2} is the previous
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value of this @code{malloc} parameter.
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@end deftp
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@deftp Probe memory_mallopt_arena_test (int @var{$arg1}, int @var{$arg2})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_ARENA_TEST}, and the
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requested value is in an acceptable range. Argument @var{$arg1} is the
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requested value, and @var{$arg2} is the previous value of this
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@code{malloc} parameter.
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@end deftp
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@deftp Probe memory_mallopt_arena_max (int @var{$arg1}, int @var{$arg2})
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This probe is triggered shortly after the @code{memory_mallopt} probe,
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when the parameter to be changed is @code{M_ARENA_MAX}, and the
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requested value is in an acceptable range. Argument @var{$arg1} is the
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requested value, and @var{$arg2} is the previous value of this
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@code{malloc} parameter.
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@end deftp
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@deftp Probe memory_mallopt_free_dyn_thresholds (int @var{$arg1}, int @var{$arg2})
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This probe is triggered when function @code{free} decides to adjust the
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dynamic brk/mmap thresholds. Argument @var{$arg1} and @var{$arg2} are
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the adjusted mmap and trim thresholds, respectively.
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@end deftp
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@deftp Probe memory_tunable_tcache_max_bytes (int @var{$arg1}, int @var{$arg2})
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This probe is triggered when the @code{glibc.malloc.tcache_max}
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tunable is set. Argument @var{$arg1} is the requested value, and
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@var{$arg2} is the previous value of this tunable.
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@end deftp
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@deftp Probe memory_tunable_tcache_count (int @var{$arg1}, int @var{$arg2})
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This probe is triggered when the @code{glibc.malloc.tcache_count}
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tunable is set. Argument @var{$arg1} is the requested value, and
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@var{$arg2} is the previous value of this tunable.
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@end deftp
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@deftp Probe memory_tunable_tcache_unsorted_limit (int @var{$arg1}, int @var{$arg2})
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This probe is triggered when the
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@code{glibc.malloc.tcache_unsorted_limit} tunable is set. Argument
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@var{$arg1} is the requested value, and @var{$arg2} is the previous
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value of this tunable.
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@end deftp
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@deftp Probe memory_tcache_double_free (void *@var{$arg1}, int @var{$arg2})
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This probe is triggered when @code{free} determines that the memory
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being freed has probably already been freed, and resides in the
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per-thread cache. Note that there is an extremely unlikely chance
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that this probe will trigger due to random payload data remaining in
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the allocated memory matching the key used to detect double frees.
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This probe actually indicates that an expensive linear search of the
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tcache, looking for a double free, has happened. Argument @var{$arg1}
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is the memory location as passed to @code{free}, Argument @var{$arg2}
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is the tcache bin it resides in.
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@end deftp
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@node Non-local Goto Probes
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@section Non-local Goto Probes
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These probes are used to signal calls to @code{setjmp}, @code{sigsetjmp},
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@code{longjmp} or @code{siglongjmp}.
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@deftp Probe setjmp (void *@var{$arg1}, int @var{$arg2}, void *@var{$arg3})
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This probe is triggered whenever @code{setjmp} or @code{sigsetjmp} is
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called. Argument @var{$arg1} is a pointer to the @code{jmp_buf}
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passed as the first argument of @code{setjmp} or @code{sigsetjmp},
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@var{$arg2} is the second argument of @code{sigsetjmp} or zero if this
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is a call to @code{setjmp} and @var{$arg3} is a pointer to the return
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address that will be stored in the @code{jmp_buf}.
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@end deftp
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@deftp Probe longjmp (void *@var{$arg1}, int @var{$arg2}, void *@var{$arg3})
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This probe is triggered whenever @code{longjmp} or @code{siglongjmp}
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is called. Argument @var{$arg1} is a pointer to the @code{jmp_buf}
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passed as the first argument of @code{longjmp} or @code{siglongjmp},
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@var{$arg2} is the return value passed as the second argument of
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@code{longjmp} or @code{siglongjmp} and @var{$arg3} is a pointer to
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the return address @code{longjmp} or @code{siglongjmp} will return to.
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The @code{longjmp} probe is triggered at a point where the registers
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have not yet been restored to the values in the @code{jmp_buf} and
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unwinding will show a call stack including the caller of
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@code{longjmp} or @code{siglongjmp}.
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@end deftp
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@deftp Probe longjmp_target (void *@var{$arg1}, int @var{$arg2}, void *@var{$arg3})
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This probe is triggered under the same conditions and with the same
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arguments as the @code{longjmp} probe.
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The @code{longjmp_target} probe is triggered at a point where the
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registers have been restored to the values in the @code{jmp_buf} and
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unwinding will show a call stack including the caller of @code{setjmp}
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or @code{sigsetjmp}.
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@end deftp
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