(gdb.info.gz) Tracepoints

 
 Tracepoints
 ***********
 
    In some applications, it is not feasible for the debugger to
 interrupt the program's execution long enough for the developer to learn
 anything helpful about its behavior.  If the program's correctness
 depends on its real-time behavior, delays introduced by a debugger
 might cause the program to change its behavior drastically, or perhaps
 fail, even when the code itself is correct.  It is useful to be able to
 observe the program's behavior without interrupting it.
 
    Using GDB's `trace' and `collect' commands, you can specify
 locations in the program, called "tracepoints", and arbitrary
 expressions to evaluate when those tracepoints are reached.  Later,
 using the `tfind' command, you can examine the values those expressions
 had when the program hit the tracepoints.  The expressions may also
 denote objects in memory--structures or arrays, for example--whose
 values GDB should record; while visiting a particular tracepoint, you
 may inspect those objects as if they were in memory at that moment.
 However, because GDB records these values without interacting with you,
 it can do so quickly and unobtrusively, hopefully not disturbing the
 program's behavior.
 
    The tracepoint facility is currently available only for remote
 targets.   Targets.  In addition, your remote target must know
 how to collect trace data.  This functionality is implemented in the
 remote stub; however, none of the stubs distributed with GDB support
 tracepoints as of this writing.
 
    This chapter describes the tracepoint commands and features.
(gdb.info.gz) Tracepoints

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