starbind: fix Starlark slice unmarshaling

[andreimatei]

The unmarshaling code for slices wasn't actually setting the destination. This patch fixes it.

[aarzilli]

LGTM thank you

[aarzilli]

Are you using the scripting engine for something?

If your using it I'm curious what you think about this: I've been thinking about moving starlark evaluation server side for a while (#2887) this would make it faster and allow for it to be used for more things (pretty printing, breakpoint conditions), OTOH it wouldn't be possible to invoke command line commands (i.e. dlv_command).

[andreimatei]

Hi Alessandro!
I've been using the scripting engine for the past few weeks to prototype a debugging product. Delve is probably not what I'll ultimately use, but rather some dynamic instrumentation techniques like BPF (for the sake of speed of the instrumented binary). Still, prototyping with Delve is immensely useful.
I've hacked Delve to allow running scripts when breakpoints are hit, and I've also added my own RPC that stops the target and runs a custom script. For example, I have a script that walks all the stacks and recognizes certain frames. I could clean up and upstream this support for running scripts in more contexts, if you're interested. Depending on what exactly you mean by moving script evaluation "server side", I may have already hacked it.

#2887 talks specifically about pretty-printing, which is something that I've also been thinking a lot about. Besides Starlark, I'm wondering if you've considered ways to directly invoke String() methods on the respective type (for example through general the support Delve already has for invoking function from the target).

[derekparker]

Hi Alessandro! I've been using the scripting engine for the past few weeks to prototype a debugging product. Delve is probably not what I'll ultimately use, but rather some dynamic instrumentation techniques like BPF (for the sake of speed of the instrumented binary).

Delve does also have the ability to set eBPF probes, any help with regard to support there would be great if you're interested!

[derekparker]

LGTM