Trace command:
The trace command is very similar to the break command. Its argument can be a source line, a function name, or an address in the target program.
The trace command defines a tracepoint, which is a point in the target program where the debugger will briefly stop, collect some data, and then allow the program
to continue.
Setting a tracepoint or changing its commands doesn't take effect until the next tstart command.
(gdb) trace foo.c:121 // a source file and line number
(gdb) trace +2 // 2 lines forward
(gdb) trace my_function // first source line of function
(gdb) trace *my_function // EXACT start address of function
(gdb) trace *0x2117c4 // an address
(gdb) delete trace 1 2 3 // remove three tracepoints
(gdb) delete trace // remove all tracepoints
(gdb) info trace // trace points info
Starting and Stopping Trace Experiment:
tstart : It starts the trace experiment, and begins collecting data.
tstop : It ends the trace experiment, and stops collecting data.
tstatus : This command displays the status of the current trace data collection.
Enable and Disable Tracepoints:
disable tracepoint [num] : Disable tracepoint num, or all tracepoints if no argument num is given.
enable tracepoint [num] : Enable tracepoint num, or all tracepoints.
Tracepoint Passcounts:
passcount [n [num]] : Set the passcount of a tracepoint. The passcount is a way to automatically stop a trace experiment. If a tracepoint's passcount is n, then the trace experiment will be automatically stopped on the n'th time that tracepoint is hit. If the tracepoint number num is not specified, the passcount command sets the passcount of the most recently defined tracepoint. If no passcount is given, the trace experiment will run until stopped explicitly by the user.
Examples:
(gdb) passcount 5 2 // Stop on the 5th execution of tracepoint 2
(gdb) passcount 12 // Stop on the 12th execution of the most recently defined tracepoint.
(gdb) trace foo
(gdb) pass 3
(gdb) trace bar
(gdb) pass 2
(gdb) trace baz
(gdb) pass 1 // Stop tracing when foo has been
// executed 3 times OR when bar has
// been executed 2 times
// OR when baz has been executed 1 time.
Tracepoint Action Lists:
actions [num] : This command will prompt for a list of actions to be taken when the tracepoint is hit. If the tracepoint number num is not specified, this command sets the actions for the one that was most recently defined . You specify the actions themselves on the following lines, one action at a time,
and terminate the actions list with a line containing just end.
(gdb) collect data // collect some data
(gdb) while-stepping 5 // single-step 5 times, collect data
(gdb) end // signals the end of actions.
collect expr1, expr2, ...
Collect values of the given expressions when the tracepoint is hit. This command accepts a comma-separated list of any valid expressions.
In addition to global, static, or local variables, the following special arguments are supported:
$regs
collect all registers
$args
collect all function arguments
$locals
collect all local variables.
Example:
(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
Using the collected data:
tfind start
Find the first snapshot in the buffer. This is a synonym for tfind 0 (since 0 is the number of the first snapshot).
tfind none
Stop debugging trace snapshots, resume live debugging.
tfind end
Same as `tfind none'.
tfind
No argument means find the next trace snapshot.
The tracepoint facility is currently available only for remote targets.
Reference Link:
ftp://ftp.gnu.org/old-gnu/Manuals/gdb/html_chapter/gdb_10.html
http://stackoverflow.com/questions/3691394/gdb-meaning-of-tstart-error-you-cant-do-that-when-your-target-is-exec
http://stackoverflow.com/questions/38716790/gdb-meaning-of-tstop-error-you-cant-do-that-when-your-target-is-multi-thread
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