Tribblix: manual page: libc

LIBC_DB(3LIB) Interface Libraries LIBC_DB(3LIB)

NAME

libc_db - threads debugging library

SYNOPSIS

cc [ flag... ] file... -lc_db [ library... ]
#include <proc_service.h>
#include <thread_db.h>

DESCRIPTION

The libc_db library provides support for monitoring and manipulating
threads-related aspects of a multithreaded program. There are at
least two processes involved, the controlling process and one or
more target processes. The controlling process is the libc_db
client, which links with libc_db and uses libc_db to inspect or
modify threads-related aspects of one or more target processes. The
target processes must be multithreaded processes that use libc. The
controlling process might or might not be multithreaded itself.

The most commonly anticipated use for libc_db is that the controlling
process will be a debugger for a multithreaded program, hence the
"db" in libc_db.

The libc_db library is dependent on the internal implementation
details of libc. It is a "friend" of libc in the C++ sense, which is
precisely the "value added" by libc_db. It encapsulates the knowledge
of libc internals that a debugger needs to manipulate the threads-
related state of a target process.

To be able to inspect and manipulate target processes, libc_db makes
use of certain process control primitives that must be provided by
the process using libc_db. The imported interfaces are defined in
proc_service(3PROC). In other words, the controlling process is
linked with libc_db and calls routines in libc_db. In turn, libc_db
calls certain routines that it expects the controlling process to
provide. These process control primitives allow libc_db to:

o Look up symbols in a target process.

o Stop and continue individual lightweight processes ( LWPs)
within a target process.

o Stop and continue an entire target process.

o Read and write memory and registers in a target process.

Initially, a controlling process obtains a handle for a target
process. Through that handle it can then obtain handles for the
component objects of the target process, its threads, its
synchronization objects, and its thread-specific-data keys.

When libc_db needs to return sets of handles to the controlling
process, for example, when returning handles for all the threads in a
target process, it uses an iterator function. An iterator function
calls back a client-specified function once for each handle to be
returned, passing one handle back on each call to the callback
function. The calling function also passes another parameter to the
iterator function, which the iterator function passes on to the
callback function. This makes it easy to build a linked list of
thread handles for a particular target process. The additional
parameter is the head of the linked list, and the callback function
simply inserts the current handle into the linked list.

Callback functions are expected to return an integer. Iteration
terminates early if a callback function returns a non-zero value.
Otherwise, iteration terminates when there are no more handles to
pass back.

INTERFACES

The shared object libc_db.so.1 provides the public interfaces defined
below. See Intro(3) for additional information on shared object
interfaces.

td_init td_log
td_sync_get_info td_sync_get_stats
td_sync_setstate td_sync_waiters
td_ta_clear_event td_ta_delete
td_ta_enable_stats td_ta_event_addr
td_ta_event_getmsg td_ta_get_nthreads
td_ta_get_ph td_ta_get_stats
td_ta_map_addr2sync td_ta_map_id2thr
td_ta_map_lwp2thr td_ta_new
td_ta_reset_stats td_ta_set_event
td_ta_setconcurrency td_ta_sync_iter
td_ta_sync_tracking_enable td_ta_thr_iter
td_ta_tsd_iter td_thr_clear_event
td_thr_dbresume td_thr_dbsuspend
td_thr_event_enable td_thr_event_getmsg
td_thr_get_info td_thr_getfpregs
td_thr_getgregs td_thr_getxregs
td_thr_getxregsize td_thr_lockowner
td_thr_set_event td_thr_setfpregs
td_thr_setgregs td_thr_setprio
td_thr_setsigpending td_thr_setxregs
td_thr_sigsetmask td_thr_sleepinfo
td_thr_tsd td_thr_validate

FILES

/lib/libc_db.so.1
shared object

/lib/64/libc_db.so.1
64-bit shared object