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115 lines
4.1 KiB
Markdown
115 lines
4.1 KiB
Markdown
[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (How to dump the GOSSAFUNC graph for a method)
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[#]: via: (https://dave.cheney.net/2020/06/19/how-to-dump-the-gossafunc-graph-for-a-method)
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[#]: author: (Dave Cheney https://dave.cheney.net/author/davecheney)
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How to dump the GOSSAFUNC graph for a method
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======
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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.
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Let’s start with a sample program which contains a function, a value method, and a pointer method:
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```
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package main
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import (
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"fmt"
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)
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type Numbers struct {
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vals []int
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}
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func (n *Numbers) Add(v int) {
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n.vals = append(n.vals, v)
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}
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func (n Numbers) Average() float64 {
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sum := 0.0
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for _, num := range n.vals {
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sum += float64(num)
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}
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return sum / float64(len(n.vals))
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}
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func main() {
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var numbers Numbers
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numbers.Add(200)
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numbers.Add(43)
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numbers.Add(-6)
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fmt.Println(numbers.Average())
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}
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```
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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`.
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```
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% env GOSSAFUNC=main go build
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runtime
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dumped SSA to ../../go/src/runtime/ssa.html
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t
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dumped SSA to ./ssa.html
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```
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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`.
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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.
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To print the SSA debug for the pointer method `func (n *Numbers) Add`, the equivalent function name is`(*Numbers).Add`:[2][2]
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```
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% env "GOSSAFUNC=(*Numbers).Add" go build
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t
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dumped SSA to ./ssa.html
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```
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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_:
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```
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% env "GOSSAFUNC=(*Numbers).Average" go build
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t
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dumped SSA to ./ssa.html
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```
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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]
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2. Please pay attention to the shell quoting.[][4]
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### Related posts:
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1. [Accidental method value][5]
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2. [Never edit a method, always rewrite it][6]
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3. [How to find out which Go version built your binary][7]
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4. [Declaration scopes in Go][8]
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--------------------------------------------------------------------------------
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via: https://dave.cheney.net/2020/06/19/how-to-dump-the-gossafunc-graph-for-a-method
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作者：[Dave Cheney][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://dave.cheney.net/author/davecheney
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[b]: https://github.com/lujun9972
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[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.)
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[2]: tmp.kLSHpQXzhr#easy-footnote-bottom-2-4188 (Please pay attention to the shell quoting.)
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[3]: tmp.kLSHpQXzhr#easy-footnote-1-4188
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[4]: tmp.kLSHpQXzhr#easy-footnote-2-4188
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[5]: https://dave.cheney.net/2014/05/19/accidental-method-value (Accidental method value)
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[6]: https://dave.cheney.net/2017/11/30/never-edit-a-method-always-rewrite-it (Never edit a method, always rewrite it)
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[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)
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[8]: https://dave.cheney.net/2016/12/15/declaration-scopes-in-go (Declaration scopes in Go)
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