Daniel Trebbien Daniel Trebbien - 1 year ago 220
C++ Question

gdb: Meaning of tstart error "You can't do that when your target is `exec'"

I would like to record the value of a local variable,

, each time that the program reaches a certain line. Accordingly, I tried:

(gdb) trace stoer_wagner_min_cut.hpp :197
Tracepoint 1 at 0x4123a0: file ./boost/graph/stoer_wagner_min_cut.hpp, line 197.
(gdb) actions
Enter actions for tracepoint 1, one per line.
End with a line saying just "end".
> collect t
> end
(gdb) tstart
You can't do that when your target is `exec'
(gdb) break main
Breakpoint 2 at 0x401448: file time_stoer_wagner.cpp, line 50.
(gdb) run
Starting program: C:\Users\Daniel\Documents\projects\stoer_wagner_min_cut/time_stoer_wagner.exe
[New Thread 3908.0x39c]

Breakpoint 2, main () at time_stoer_wagner.cpp:50
50 std::ifstream ifs("prgen_500_50_2.txt");
(gdb) tstart
You can't do that when your target is `child'

but the error messages "You can't do that when your target is `exec'" and "You can't do that when your target is `child'" are not helpful to me. What do these errors mean?

Answer Source

The tracepoint facility is currently available only for remote targets.

You should be able to perform the tracing experiment you desire by using gdbserver. Example:

$ gdbserver :0 ./a.out 
Process ./a.out created; pid = 21838
Listening on port 51596

In another window:

$ gdb -q ./a.out 
Reading symbols from /tmp/a.out...done.
(gdb) target remote :51596

0x00007fa76ec3fa60 in _start () from /lib64/ld-linux-x86-64.so.2
(gdb) list foo
1   int foo(int x)
2   {
3     return x;
4   }
6   int main()
7   {
8     for(int i = 0; i < 10; ++i)
9       foo(i);
10    return 0;
11  }
(gdb) trace 3
Tracepoint 1 at 0x40053f: file t.c, line 3.
(gdb) actions
> collect x
> end
(gdb) c

Tracing experiment now collects the data ...

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