Go: How to Take Advantage of the Symbols Table

Illustration created for “A Journey With Go”, made from the original Go Gopher, created by Renee French.

ℹ️ This article is based on Go 1.13.

A symbol table is created and maintained by the compiler and stores information relating to the program, such as functions or global variables. Understanding the symbols table will help us to interact with and take advantage of it.

Symbol table

Each binary compiled with Go embeds the symbols table by default. Let’s take an example and inspect its symbols table. Here is our code:

var AppVersion string

func main() {
   fmt.Println(`Version: `+AppVersion)
}

The symbols table can be displayed via the command nm; here is an extract of the result on OSX:

0000000001177220 b io.ErrUnexpectedEOF
[...]
0000000001177250 b main.AppVersion
00000000010994c0 t main.main
[...]
0000000001170b00 d runtime.buildVersion

The symbol marked with b (shortcode for bss) is uninitialized data. Since our previous variable AppVersion is not initialized, it is part of it. The other symbols stand for initialized data (d) and text symbols (t), which comprises functions.

Go also ships the nm command, accessible from the command go tool nm, and produces the same results:

1177220 B io.ErrUnexpectedEOF
[...]
1177250 B main.AppVersion
10994c0 T main.main…