Delve: Next generation debugger for Golang

In my previous post I demonstrated how you can debug golang applications with LLDB. In this article I will illustrate the most recent debugger for Go: Delve

The debugger is a community effort to bring a debugger in the toolchain of every Go developer.

It’s written in Go to debug Go code. It’s still in active development, but we can still benefit from its basic features.

Installation

You should install Delve with the following command:

$ go get -u github.com/derekparker/delve/cmd/dlv 

Note that you need at least Go 1.4.

Installation: Linux

In Linux you should NOT do anything else further. You are ready.

Installation: MacOSX

If you are using MacOSX as me, you need a self-signed certificate to sign the delve binary.

You should create a new certificate by using application “Keychain Access”.

  1. Choose a certificate name, set “Identity Type” to “Self Signed Root”, set “Certificate Type” to Code Signing and select the Let me override defaults:

    Certificate Name

  2. Continue to a certificate information wizard step. If you email address is missing, please fill the required field:

    Certificate Info

  3. Click several times on “Continue” until you get to the “Specify a Location For The Certificate” screen, then set “Keychain to System”.

    Certificate Keychain

Then we need sign the binary by using the created certificate. In order to do that we should execute the following command:

# CERT=<your_ceriticate_name> make install 

If you need more detailed guidelines, you should follow the official documentation.

You can watch the following video that demonstrates the installation process:

Integration

Right now the debugger does not have integration with any IDE. Nevertheless, the contributors are working hard to release an API interface that will allow that. For now Delve can be started from a command line.

Getting started

Compile, run, and attach in one step:

$ dlv run

Run program with tracepoints set at functions matching [regexp]:

$ dlv trace [regexp]

Compile test binary, start and attach:

$ dlv test

Provide the application path you want to debug:

$ dlv path/to/program

Provide the running application process id:

$ sudo dlv attach 47478 

Delve will pass any arguments after dlv run|test|trace to the newly created process:

$ dlv run -- -http=:6060
$ dlv run arg1 -- -flag1 -flag2

Commands

In debug session, you can use the following commands:

  • help - Prints the help message.
  • restart - Restarts the process, killing the current one if it is running.
  • break (break <address> [-stack <n>|-goroutine|<variable name>]*) - Set a breakpoint. Example: break foo.go:13 or break main.main.
  • trace - Set a tracepoint. Syntax identical to breakpoints.
  • continue - Run until breakpoint or program termination.
  • step - Single step through program.
  • next - Step over to next source line.
  • threads - Print status of all traced threads.
  • thread $tid - Switch to another thread.
  • goroutines - Print status of all goroutines.
  • breakpoints - Print information on all active breakpoints.
  • print $var - Evaluate a variable.
  • info $type [regex] - Outputs information about the symbol table. An optional regex filters the list. Example info funcs unicode. Valid types are:
    • args - Prints the name and value of all arguments to the current function
    • funcs - Prints the name of all defined functions
    • locals - Prints the name and value of all local variables in the current context
    • sources - Prints the path of all source files
    • vars - Prints the name and value of all package variables in the app. Any variable that is not local or arg is considered a package variables
    • regs - Prints the contents of CPU registers.
  • stack [ <depth> [ <goroutine id> ] ] - Prints the stacktrace of the current goroutine, up to <depth>. <depth> defaults to 10, pass a second argument to print the stacktrace of a different goroutine.
  • exit - Exit the debugger.

Demo

In the demo video, I am using the same application that I debugged in the LLDB article.

Note that parts of this article are taken from the official Delve commands documentation and usage documentation.

Published by in programming languages and tutorial and tagged #debug and #go using 655 words.