选题[tech]: 20200619 How to dump the GOSSAFUNC graph for a method

sources/tech/20200619 How to dump the GOSSAFUNC graph for a method.md
2024-12-26 21:30:55 +08:00 · 2020-06-20 05:02:09 +08:00 · 2020-06-20 05:02:09 +08:00 · 9bebad5012
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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (How to dump the GOSSAFUNC graph for a method)
+[#]: via: (https://dave.cheney.net/2020/06/19/how-to-dump-the-gossafunc-graph-for-a-method)
+[#]: author: (Dave Cheney https://dave.cheney.net/author/davecheney)
+
+How to dump the GOSSAFUNC graph for a method
+======
+
+The Go compiler’s SSA backend contains a facility to produce HTML debugging output of the compilation phases. This post covers how to print the SSA output for function _and_ methods.
+
+Let’s start with a sample program which contains a function, a value method, and a pointer method:
+
+```
+package main
+
+import (
+    "fmt"
+)
+
+type Numbers struct {
+    vals []int
+}
+
+func (n *Numbers) Add(v int) {
+    n.vals = append(n.vals, v)
+}
+
+func (n Numbers) Average() float64 {
+    sum := 0.0
+    for _, num := range n.vals {
+        sum += float64(num)
+    }
+    return sum / float64(len(n.vals))
+}
+
+
+func main() {
+    var numbers Numbers
+    numbers.Add(200)
+    numbers.Add(43)
+    numbers.Add(-6)
+    fmt.Println(numbers.Average())
+}
+```
+
+Control of the SSA debugging output is via the `GOSSAFUNC` environment variable. This variable takes the name of the function to dump. This is _not_ the functions fully qualified name. For `func main` above the name of the function is `main` _not_ `main.main`.
+
+```
+% env GOSSAFUNC=main go build
+runtime
+dumped SSA to ../../go/src/runtime/ssa.html
+t
+dumped SSA to ./ssa.html
+```
+
+In this example `GOSSAFUNC=main` matched both `main.main` and a function called `runtime.main`.[1][1] This is a little unfortunate, but in practice probably not a big deal as, if you’re performance tuning your code, it won’t be in a giant spaghetti blob in `func main`.
+
+What is more likely is your code will be in a _method_, so you’ve probably landed on this post looking for the correct incantation to dump the SSA output for a method.
+
+To print the SSA debug for the pointer method `func (n *Numbers) Add`, the equivalent function name is`(*Numbers).Add`:[2][2]
+
+```
+% env "GOSSAFUNC=(*Numbers).Add" go build
+t
+dumped SSA to ./ssa.html
+```
+
+To print the SSA debug for a value method `func (n Numbers) Average`, the equivalent function name is `(*Numbers).Average` _even though this is a value method_:
+
+```
+% env "GOSSAFUNC=(*Numbers).Average" go build
+t
+dumped SSA to ./ssa.html
+```
+
+  1. If you didn’t build Go from source then the path to the `runtime` package may be read only and you might receive an error. Please don’t use the `sudo` hammer to fix this.[][3]
+  2. Please pay attention to the shell quoting.[][4]
+
+
+
+### Related posts:
+
+  1. [Accidental method value][5]
+  2. [Never edit a method, always rewrite it][6]
+  3. [How to find out which Go version built your binary][7]
+  4. [Declaration scopes in Go][8]
+
+
+
+--------------------------------------------------------------------------------
+
+via: https://dave.cheney.net/2020/06/19/how-to-dump-the-gossafunc-graph-for-a-method
+
+作者：[Dave Cheney][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://dave.cheney.net/author/davecheney
+[b]: https://github.com/lujun9972
+[1]: tmp.kLSHpQXzhr#easy-footnote-bottom-1-4188 (If you didn’t build Go from source then the path to the <code>runtime</code> package may be read only and you might receive an error. Please don’t use the <code>sudo</code> hammer to fix this.)
+[2]: tmp.kLSHpQXzhr#easy-footnote-bottom-2-4188 (Please pay attention to the shell quoting.)
+[3]: tmp.kLSHpQXzhr#easy-footnote-1-4188
+[4]: tmp.kLSHpQXzhr#easy-footnote-2-4188
+[5]: https://dave.cheney.net/2014/05/19/accidental-method-value (Accidental method value)
+[6]: https://dave.cheney.net/2017/11/30/never-edit-a-method-always-rewrite-it (Never edit a method, always rewrite it)
+[7]: https://dave.cheney.net/2017/06/20/how-to-find-out-which-go-version-built-your-binary (How to find out which Go version built your binary)
+[8]: https://dave.cheney.net/2016/12/15/declaration-scopes-in-go (Declaration scopes in Go)