Web-based gdb front-end application
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README.md

Introduction

Tired of using the plain gdb command-line interface to debug your Go/C/C++ applications? Godbg is a graphical web-based front end for gdb!

The web-based UI makes godbg multi-platform and easier for remotely accessing your debug sessions.

Features

  • Thread information
  • Execution control (step, next, interrupt)
  • Breakpoints (line and function, enable, disable)
  • Variables (inspect, custom expressions)
  • Console output
  • Source line highlighting

Video

Check out the youtube video for a walkthrough: https://www.youtube.com/watch?v=OyWaAJD6hr8

Installation Notes

Godbg uses the gdb MI (Machine Interface) to debug your application. The MI changes from time to time. This version of godbg should work with gdb versions 7.5 and 7.6. Newer versions of Linux will often come with these versions of gdb but Windows and Mac need a little extra setup.

Windows

Gdb is available on Windows in either MinGW or Cygwin. To install the MinGW version, visit http://www.mingw.org/ to download and install the tool suite (mingw-get-setup.exe). Once MingW is installed, run the "MinGW Installer" to add the mingw32-gdb package (under "All Packages"). Make sure to add the "C:\MinGW\bin" directory to your PATH so that godbg can pick it up.

Mac OS X

The version of gdb on Mac OS X as part of Xcode is very old and will not work with godbg. Instead, you can download and compile the latest version of gdb from https://www.gnu.org/software/gdb/download/. Note that there is a bug in all versions of gdb including the latest (7.6.1 at the time of writing this) that prevents the Go language support from being loaded. A patch is available here. After applying the patch you compile it with the Xcode compiler using "./configure --with-expat --with-python && make".

Mac Codesigning Problem

Mac OS X requires that the debugger binary is signed with a trusted certificate before it can take control of another process. If you see a message in the gdb console similar to "Unable to find Mach task port for process-id 12345: (os/kern) failure (0x5). (please check gdb is codesigned - see taskgated(8))" then you will need to follow these steps:

  • Start the Keychain Access application (you can use Spotlight to find it)
  • Select Keychain Access -> Certificate Assistant -> Create a Certificate...
    • Choose a name for the certificate
    • Set Identity Type to Self Signed Root
    • Set Certificate Type to Code Signing
    • Activate the "Let me override defaults" option
  • Continue on to the "Specify a Location For The Certificate" page
    • Set Keychain to System
  • Continue and create the certificate
  • Double click on the newly created certificate
    • Set When using this certificate to Always Trust
  • Restart the computer (yes, this is a required step)
  • Sign the gdb binary by executing the following command
    • codesign -f -s "gdb-cert-name" "location-of-gdb-binary"

Go Runtime Support

GDB versions 7.5+ come with increased safety precautions for auto-loading scripts, including the Go language helper script. This script not only helps gdb to pretty print variables but also helps gdb to avoid analyzing unitialized variables, which can cause gdb to become unresponsive.

If the Go language helper script initializes properly you will see the message "Loading Go Runtime support." Otherwise, you might encounter the following message.

warning: File "/usr/local/go/src/pkg/runtime/runtime-gdb.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load". To enable execution of this file add add-auto-load-safe-path /usr/local/go/src/pkg/runtime/runtime-gdb.py line to your configuration file "/home/cmcgee/.gdbinit". ...

If you follow these instructions then your debugging experience will be much better.

Remote Access

Godbg has remote access capabilities using your web browser and https. Access is controlled using a magic url known only to the person who launches the godbg session. First, some setup is required to specify the fully qualified domain name of your system and establish a secure connection.

Generating SSL/TLS keys

Godbg uses HTTP over SSL/TLS, otherwise known as https, to encrypt information sent from the remote system and your local web browser. In order to set up the encryption both a certificate and encryption key is needed to establish the encrypted connection. You can use a tool like openssl or use a Go script included in every Go install to generate it.

To run the Go script to generate your certificates you can run the following command (replace / with \ on Windows, myhost.example.com with your fully qualified domain name):

$ go run /path/to/go/install/src/pkg/crypto/tls/generate _ cert.go -ca=true -duration=8760h0m0s -host=myhost.example.com

It is important to secure the certificates and keys with filesystem permissions so that others canot use them to intercept your communications.

$ chmod go-rwx cert.pem key.pem

Setting Environment Variables

Your fully qualified domain name, certificate file and key file are provided to gdbg using the following environment variables:

$ export GOHOST=myhost.example.com
$ export GOCERTFILE=/path/to/my/cert.pem
$ export GOKEYFILE=/path/to/my/key.pem

These variables can be set in the same place you set your GOPATH and PATH variables so that they are set automatically every time you run the tool.

Debug session sometimes freezes and gdb process consumes alot of CPU

There is a problem with the string pretty-printer in the standard Go runtime library for gdb, which causes it to attempt to parse uninitialized strings. If there are alot of uninitialized strings then gdb attempts to transfer alot of target memory to satisfy the pretty printer. There is a small tweak you can make to your runtime-gdb.py script (located in your $GOROOT/src/pkg/runtime directory). Find the StringTypePrinter class in the file and change the to_string() method body to look like this (be mindful of the tabs):

def to_string(self):
	l = int(self.val['len'])
	if l < 1024 and l > -1:
		return self.val['str'].string("utf-8", "ignore", l)
	return self.val['len']

Note that this tweak will print out the length of really big strings instead of their value.