I've come to like the GNU Debugger (GDB) and the `perf` tool recently. This post will be a short summary of the various interesting commands you can use.
## GNU Debugger
To attach gbd to an existing process do the following
```bash
gdb -p pid_of_process
```
Otherwise you can start a new application
```bash
gdb name_of_executable
```
Once it loads it will bring you into it's own `REPL` environment. Usually once this comes up I find it useful to add breakpoints to the program. You can either do it by function name or by line number.
```bash
(gdb) break FunctionName
```
```bash
(gdb) break code.cpp:81
```
If you just started a new application you can begin running the program with whatever arguments you wish
```bash
(gdb) run -arg1 -arg2
```
If you have attached to a process then you can continue its execution.
```bash
(gdb) continue
```
### Breakpoints
If you have set a breakpoint, it will stop the processes' execution when it lands on the breakpoint. From here, we can take a look at what's on the stack, print variables, and do whatever other debugging we wish.
**Print variables on stack:**
```bash
(gdb) info locals
```
**Print a specific variable:**
```bash
(gdb) print variable_name
```
**Show backtrace:**
```bash
(gdb) bt
```
**Continue on with program execution:**
```bash
(gdb) continue
```
## Perf
I haven't played with `perf` as much but one thing I found that was cool was the `perf top` command. This command gives you samples of which function calls keeps the program the most busy.
