go - "go build"后没有二进制符号

Question

我正在关注 this article要了解 eBPF 跟踪的工作原理，第一步是识别函数的符号，示例代码可从此处获取:https://github.com/pixie-labs/pixie-demos/blob/main/simple-gotracing/app/app.go

但是，在构建之后，我无法找到该符号。 为什么会这样？

$ 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 版本:-

$ go version
go version go1.16.5 linux/amd64

Answer 1

您的 computeE() 函数将被内联，因此函数名称将不会在可执行二进制文件中留下任何“标记”。您可以使用 go build -gcflags=-m 查看构建过程中正在内联的函数。

$ 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

如果禁用内联:

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

然后再次构建并检查:

$ 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

然后输出将是这样的:

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

参见相关:forbid inlining in golang