GDB - Attach to and break a running Go application - gdb

Question

I compiled a simple go application with debug flags:
go build -gcflags "-N -l" -o main main.go
main.go
package main
import (
"fmt"
"time"
)
func main() {
for i := 0; true; i++ {
fmt.Println("number:", i)
time.Sleep(time.Second)
}
}
In gdb, I attached to its pid and executed break and break 11.
gdb --pid=<pid>
Gdb reports that the breakpoints are successfully set, but they don't ever get hit. Is there a way to get this working?

Answer 1

Note: that same setup (even when adding your runtime-gdb.py to your .gdbrc) risks to not work with Ubuntu 13.10, where you would get a "SyntaxError" message, as illustrated in:
blog post "Debugging Go 1.2 on Ubuntu 13.10 with GDB" from Michael Susens-Schurter (schmichael)
issue 6698 (gdb: upgrade to be python 3 compatible)
The problem is that Ubuntu 13.10 links GDB against Python 3.3 while the script golang ships is for Python 2. Someone has already filed an issue, and it appears to be fixed upstream (so expect Go 1.3 to Just Work).
Luckily backporting the fix is easy. Simply move your exist runtime-gdb.py out of the way and download the upstream version in its place.
If your $GOROOT is /usr/local/go the following should Just Work:
sudo mv /usr/local/go/src/pkg/runtime/runtime-gdb.py /usr/local/go/src/pkg/runtime/runtime-gdb.py.orig
cd /usr/local/go/src/pkg/runtime/
sudo wget https://go.googlecode.com/hg/src/pkg/runtime/runtime-gdb.py

Answer 2

the go/src/pkg/runtime/runtime-gdb.py script needs to be loaded inside gdb to effectively be able to debug go programs.
You can add it to the .gdbrc file.