This is a short post describing the procedure for discovering which version of Go was used to compile a Go binary.

This procedure relies on the fact that each Go program includes a copy of the version string reported by runtime.Version() . Linker magic ensures that this value will be present in the final binary irrespective of whether runtime.Version() is called by the resulting program. The value in question is stored in the runtime.buildVersion variable and can be recovered by a debugger.

The rest of this post describes the mechanisms for recovering the contents of runtime.buildVersion on various platforms.

Linux/FreeBSD/OpenBSD/NetBSD

If you’re on a Linux or *BSD platform, you can recover the binary build version with gdb.

% gdb $HOME/bin/godoc
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.04) 7.11.1
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
(gdb) p 'runtime.buildVersion'
$1 = 0xa9ceb8 "go1.8.3"

Darwin

The debugging situation on OS X isn’t great, but here are several options.

gdb

gdb was removed from the XCode toolchain following the switch from gcc to llvm. If you are running a version of XCode that has gdb, you should used the instructions from the previous section.

Delve

Delve can be used to print the value of runtime.buildVersion.

% dlv exec $HOME/bin/godoc
Type 'help' for list of commands.
(dlv) b main.main
Breakpoint 1 set at 0x15596eb for main.main() ./golang.org/x/tools/cmd/godoc/main.go:156
(dlv) c
> main.main() ./golang.org/x/tools/cmd/godoc/main.go:156 (hits goroutine(1):1 total:1) (PC: 0x15596eb)
   151:                 }
   152:         }
   153:         log.Fatalf("too many redirects")
   154: }
   155:
=> 156: func main() {
   157:         flag.Usage = usage
   158:         flag.Parse()
   159:
   160:         playEnabled = *showPlayground
   161:
(dlv) p runtime.buildVersion
"go1.8.1"

lldb

Christian Witts reports on Twitter that XCode 8.3.3 ships with a version of lldb, version 370.0.42, that can interpret the Go string syntax.

$ lldb $HOME/bin/godoc
(lldb) b main.main
(lldb) run
(lldb) p runtime.buildVersion

I’ve tested earlier versions of lldb and found they do not work. Instread, use delve

Windows

Good news, everyone. Brian Ketelsen of GopherCon and GoTime.fm fame, reports that delve works perfectly on Windows for recovering this binaries’ build version.

PS C:\Users\bkete\go\src\http://github.com \derekparker\delve\cmd\dlv> dlv exec C:\Users\bkete\go\bin\dlv.exe
Type 'help' for list of commands.
(dlv) b main.main
Breakpoint 1 set at 0x8ec666 for main.main() c:/Users/bkete/go/src/github.com/derekparker/delve/cmd/dlv/main.go:11
(dlv) c
> main.main() c:/Users/bkete/go/src/github.com/derekparker/delve/cmd/dlv/main.go:11 (hits goroutine(1):1 total:1) (PC: 0x8ec666)
     6: )
     7:
     8: // Build is the git sha of this binaries build.
     9: var Build string
    10:
=>  11: func main() {
    12:         http://version.DelveVersion.Build  = Build
    13:         http://cmds.New ().Execute()
    14: }
(dlv) p runtime.buildVersion
"go1.8.1"

If someone wants to figure out the correct WinDbg or Visual Studio Debugger incantation, please let me know and I’ll link to you from this post.