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@node Internal Probes
@c @node Internal Probes, , POSIX Threads, Top
@c %MENU% Probes to monitor libc internal behavior
@chapter Internal probes

In order to aid in debugging and monitoring internal behavior,
@theglibc{} exposes nearly-zero-overhead SystemTap probes marked with
the @code{libc} provider.

These probes are not part of the @glibcadj{} stable ABI, and they are
subject to change or removal across releases.  Our only promise with
regard to them is that, if we find a need to remove or modify the
arguments of a probe, the modified probe will have a different name, so
that program monitors relying on the old probe will not get unexpected
arguments.

@menu
* Memory Allocation Probes::  Probes in the memory allocation subsystem
@end menu

@node Memory Allocation Probes
@section Memory Allocation Probes

These probes are designed to signal relatively unusual situations within
the virtual memory subsystem of @theglibc{}.

@deftp Probe memory_arena_new (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered when @code{malloc} allocates and initializes an
additional arena (not the main arena), but before the arena is assigned
to the running thread or inserted into the internal linked list of
arenas.  The arena's @code{malloc_state} internal data structure is
located at @var{$arg1}, within a newly-allocated heap big enough to hold
at least @var{$arg2} bytes.
@end deftp

@deftp Probe memory_mallopt (int @var{$arg1}, int @var{$arg2})
This probe is triggered when function @code{mallopt} is called to change
@code{malloc} internal configuration parameters, before any change to
the parameters is made.  The arguments @var{$arg1} and @var{$arg2} are
the ones passed to the @code{mallopt} function.
@end deftp