Note: a trace experiment and data collection may stop automatically if any tracepoint's passcount is reached (see Tracepoint Passcounts), or if the trace buffer becomes full.
Here is an example of the commands we described so far:
(gdb) trace gdb_c_test (gdb) actions Enter actions for tracepoint #1, one per line. > collect $regs,$locals,$args > while-stepping 11 > collect $regs > end > end (gdb) tstart [time passes ...] (gdb) tstop
You can choose to continue running the trace experiment even if
gdb disconnects from the target, voluntarily or
involuntarily. For commands such as
detach, the debugger will
ask what you want to do with the trace. But for unexpected
terminations (gdb crash, network outage), it would be
unfortunate to lose hard-won trace data, so the variable
disconnected-tracing lets you decide whether the trace should
continue running without gdb.
set disconnected-tracing on
set disconnected-tracing off
quitwill ask you directly what to do about a running trace no matter what this variable's setting, so the variable is mainly useful for handling unexpected situations, such as loss of the network.
When you reconnect to the target, the trace experiment may or may not still be running; it might have filled the trace buffer in the meantime, or stopped for one of the other reasons. If it is running, it will continue after reconnection.
Upon reconnection, the target will upload information about the tracepoints in effect. gdb will then compare that information to the set of tracepoints currently defined, and attempt to match them up, allowing for the possibility that the numbers may have changed due to creation and deletion in the meantime. If one of the target's tracepoints does not match any in gdb, the debugger will create a new tracepoint, so that you have a number with which to specify that tracepoint. This matching-up process is necessarily heuristic, and it may result in useless tracepoints being created; you may simply delete them if they are of no use.
If your target agent supports a circular trace buffer, then you can run a trace experiment indefinitely without filling the trace buffer; when space runs out, the agent deletes already-collected trace frames, oldest first, until there is enough room to continue collecting. This is especially useful if your tracepoints are being hit too often, and your trace gets terminated prematurely because the buffer is full. To ask for a circular trace buffer, simply set ‘circular-trace-buffer’ to on. You can set this at any time, including during tracing; if the agent can do it, it will change buffer handling on the fly, otherwise it will not take effect until the next run.
set circular-trace-buffer on
set circular-trace-buffer off
tstoparguments; the set command is convenient way to fix a stop note that is mistaken or incomplete.