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87 lines
1.7 KiB
Markdown
87 lines
1.7 KiB
Markdown
---
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title: "Debugging and Performance"
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date: 2019-06-15T10:59:30-04:00
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draft: false
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tags: [ "linux" ]
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---
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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.
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## GNU Debugger
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To attach gbd to an existing process do the following
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```bash
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gdb -p pid_of_process
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```
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Otherwise you can start a new application
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```bash
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gdb name_of_executable
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```
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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.
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```bash
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(gdb) break FunctionName
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```
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```bash
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(gdb) break code.cpp:81
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```
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If you just started a new application you can begin running the program with whatever arguments you wish
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```bash
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(gdb) run -arg1 -arg2
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```
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If you have attached to a process then you can continue its execution.
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```bash
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(gdb) continue
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```
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### Breakpoints
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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.
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**Print variables on stack:**
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```bash
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(gdb) info locals
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```
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**Print a specific variable:**
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```bash
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(gdb) print variable_name
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```
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**Show backtrace:**
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```bash
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(gdb) bt
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```
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**Continue on with program execution:**
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```bash
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(gdb) continue
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```
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## Perf
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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.
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To attach to a process and show samples:
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```bash
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perf top -p pid -K
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```
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