GDB Tracepoint

Setup Trace
`trace demo.c:10`	Set tracepoint at demo.c line 10.
`actions`	Set actions for current tracepoint.
`actions 3`	Set actions for tracepoint 3.
`while-stepping 8`	Step 8 instructions, collect data each step
`collect exp`	Data to collect when trace hit: variables, registers, etc.
`passcount 5 3`	Stop after tracepoint 3 hit 5 times
`info tracepoints`	Show tracepoint list

Collect Trace
`tstart`	Start trace collection
`tstop`	Stop trace collection
`tstatus`	Status of collection

Manage Data
`tsave -r filename`	Save data to server
`tsave filename`	Save data to client
`target tfile filename`	Load trace data

Analyze data
`tfind start`	Frame 0
`tfind n`	Frame n
`tfind`	Next frame
`tfind -`	Previous frame
`tfind end`	Back to live debug
`tfind tracepoint`	Filter by tracepoint
`tfind line`	Filter by line
`tfind pc`
`tfind range`
`tfind outside`
`tdump`	Print collected data

Convenience variable
`(int) $trace_frame`
`(int) $tracepoint`
`(int) $trace_line`
`(char []) $trace_file`
`(char []) $trace_func`

#include <unistd.h>

int main()
{
  int s = 0;
  int i = 0;
  while (1)
  {
    s += i;
    i += 1;
    sleep(3);
  }
}

Trace only work in remote mode, so start program under gdbserver.

$ gdbserver --multi :12345

(gdb) target extended-remote :12345
(gdb) set remote exec-file demo
(gdb) file demo
(gdb) start

Setup tracepoint.

(gdb) trace demo.c:10
(gdb) actions
> collect i, s
> while-stepping 2
  > collect i
  > end
> end
(gdb) passcount 20 2


(gdb) info tracepoints

Collect trace.

(gdb) tstart
(gdb) continue
(gdb) tstop

(gdb) tstatus
Trace stopped by a tstop.
Collected 24 trace frames.

Scan through the trace frames.

(gdb) tfind start
(gdb) while $trace_frame != -1
> frame
> tdump
> tfind
> end

Found trace frame 0, tracepoint 2
#0  0x00000000004006cc in main () at demo.c:10
Data collected at tracepoint 2, trace frame 0:
i = 16
s = 136

Found trace frame 1, tracepoint 2
#0  0x00000000004006d0 in main () at demo.c:10
Data collected at tracepoint 2, trace frame 1:
i = 16

Found trace frame 2, tracepoint 2
#0  0x00000000004006d4 in main () at demo.c:10
Data collected at tracepoint 2, trace frame 2:
i = 16

Found trace frame 3, tracepoint 2
#0  0x00000000004006cc in main () at demo.c:10
Data collected at tracepoint 2, trace frame 3:
i = 17
s = 153

Save collected data.

(gdb) tsave demo.trace

Load trace data.

(gdb) file demo
(gdb) target tfile demo.trace

(gdb) tfind start
Found trace frame 0, tracepoint 1
#0  0x00000000004006cc in main () at demo.c:10

(gdb) tdump
Data collected at tracepoint 1, trace frame 0:
i = 16
s = 136

Sample