No symbol in binary after "go build"

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I'm following this article to understand how eBPF tracing works, one of the first steps is to identify the symbol for the function, example code is picked up from here: https://github.com/pixie-labs/pixie-demos/blob/main/simple-gotracing/app/app.go

However, after doing the build, I'm unable to find the symbol. Why is that the case?

$ ls
go.mod  main.go
$ grep func main.go
func computeE(iterations int64) float64 {
func main() {
        http.HandleFunc("/e", func(w http.ResponseWriter, r *http.Request) {
$ go build
$ objdump --syms ./demowebservice | grep compute
0000000000840a40 g     O .bss   0000000000000008              crypto/elliptic.p256Precomputed
00000000008704c0 g     O .noptrbss      000000000000000c              crypto/elliptic.precomputeOnce
$

Go version:-

$ go version
go version go1.16.5 linux/amd64
go
1 Answers

Your computeE() function will be inlined and thus the function name will leave no "marks" in the executable binary. You can use go build -gcflags=-m to see what functions are being inlined in the build process.

$ go build -gcflags=-m |& grep inlining
./main.go:24:17: inlining call to http.HandleFunc
./main.go:24:17: inlining call to http.(*ServeMux).HandleFunc
./main.go:43:12: inlining call to fmt.Printf
./main.go:44:28: inlining call to http.ListenAndServe
./main.go:46:13: inlining call to fmt.Printf
./main.go:40:53: inlining call to computeE      <-- NOTE THIS

If you disable inlining:

//go:noinline
func computeE(iterations int64) float64 {
    // ...
}

And then build and check again:

$ go build -gcflags=-m |& grep inlining
./main.go:24:17: inlining call to http.HandleFunc
./main.go:24:17: inlining call to http.(*ServeMux).HandleFunc
./main.go:43:12: inlining call to fmt.Printf
./main.go:44:28: inlining call to http.ListenAndServe
./main.go:46:13: inlining call to fmt.Printf

$ objdump --syms ./demowebservice | grep compute

Then output will be something like this:

000000000062a940 g     F .text  000000000000004c              main.computeE
0000000000840a40 g     O .bss   0000000000000008              crypto/elliptic.p256Precomputed
00000000008704c0 g     O .noptrbss      000000000000000c              crypto/elliptic.precomputeOnce

See related: forbid inlining in golang

user_17055980
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