CODEWITHSUNDEEP
go
shadyabhi
shadyabhi

Reputation: 17234

No symbol in binary after "go build"

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

Upvotes: 2

Views: 454

Answers (1)

icza
icza

Reputation: 417592

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

Upvotes: 6

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