need to debug embedded Go

[am21]

Hi,

I need to debug a Go application that has to reside in a DLL. In order to have the DLL loading work properly, I had to write a small C layer on top of Go.
How can I get dlv to attach to the Go code? Example code to reproduce my steps is at https://groups.google.com/d/msg/golang-nuts/ywzTYaalWLE/kn4GoobJAAAJ.

[aarzilli]

What @alexbrainman told you is 100% correct, what you want to debug is not a go program and delve does not work if the program isn't a go program. It is possible, in theory, to get delve there but it's a huge change.
Honestly I'm not even sure how your approach there is even working. What's initializing go's runtime? What happens if you try to start a goroutine?

[am21]

I added a simple goroutine call in sayhello(), and it seems it's running properly. I'm not sure about Go runtime initialization, but gdb shows a number of threads starting, I assumed it was related to Go's runtime.

Starting program: C:\Users\amellan\src\ngm\examples\sharedlib\dload.exe
[New Thread 17104.0x4350]
[New Thread 17104.0x4a50]
[New Thread 17104.0x23a4]
[New Thread 17104.0x2dc4]
[New Thread 17104.0x42f8]
[New Thread 17104.0x4d50]
[New Thread 17104.0x4c]
[New Thread 17104.0x2ad0]
Hello!
hello goroutine

Goodbye
[Thread 17104.0x42f8 exited with code 0]
[Thread 17104.0x4c exited with code 0]
[Thread 17104.0x4d50 exited with code 0]
[Thread 17104.0x2ad0 exited with code 0]
[Thread 17104.0x23a4 exited with code 0]
[Thread 17104.0x4a50 exited with code 0]
[Thread 17104.0x2dc4 exited with code 0]
[Inferior 1 (process 17104) exited normally]

I assume the issue is exactly the same with a .so on Linux? go build -buidmode=c-shared is supposed to work on Linux, not sure if it would really change the problem.

[aarzilli]

Probably not, I don't know.

[am21]

Based on the documentation from go build -buildmode=c-archive, I assume go takes care of the proper initialization:

  -buildmode=c-archive
	Build the listed main package, plus all packages it imports,
	into a C archive file. The only callable symbols will be those
	functions exported using a cgo //export comment. Requires
	exactly one main package to be listed.

[antJack]

still unable to debug embedded Go? or are there any solutions?

[Robert-M-Muench]

Looks like debugging embedded Go is still not possible.

Every Go main package can be built as a C shared library. The runtime initialization works and is done at DLL load time. Thereafter, things like goroutines can be used.

I think what's needed is some way to trigger Delve from the Go code. Something like a break into debugger function.

The other option that comes to mind is, to call a function that gets the DLL into a state that gops can detect it. But I don't have any idea how gops works.