https://github.com/jmhodges/copyfighter

Statically analyzes Go code and reports functions that are passing large structs by value
https://github.com/jmhodges/copyfighter

Last synced: 3 months ago
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Statically analyzes Go code and reports functions that are passing large structs by value

• Host: GitHub
• URL: https://github.com/jmhodges/copyfighter
• Owner: jmhodges
• Created: 2015-11-12T21:51:13.000Z (about 9 years ago)
• Default Branch: master
• Last Pushed: 2021-04-25T06:13:34.000Z (over 3 years ago)
• Last Synced: 2024-06-18T20:09:00.209Z (5 months ago)
• Language: Go
• Homepage:
• Size: 16.6 KB
• Stars: 200
• Watchers: 4
• Forks: 8
• Open Issues: 6
• Metadata Files:
  • Readme: README.md

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README

        
copyfighter

===========

Copyfighter statically analyzes Go code and reports functions that are passing

large structs by value. It helps you help your code.

Every Go function call copies the values given to it, including structs. When

large structs are passed around without using a pointer to them, the copying of

new data in memory causes more allocations and more work for your garbage

collector.

Copyfighter's static analysis will identify where large structs, without

pointers, are being used as method receivers, function parameters and return

values.

Install with `go get` or similar.

Example output

---------------

    $ copyfighter /gopath/path/to/pkg

    # parameter 'f' at index 0 should be made into a pointer

    func CallsFoo(f Foo)

    

    # receiver, and parameter 'o' at index 0 should be made into pointers

    func (Foo).OnOtherToo(o other)

    

    # receiver should be made into a pointer

    func (other).OnStruct()

    

    # receiver should be made into a pointer

    func (other).OnStruct2()

    $ copyfighter -max 32 path/to/pkg

    # parameter 'f' at index 0 should be made into a pointer

    func CallsFoo(f Foo)

    # receiver should be made into a pointer

    func (Foo).OnOtherToo(o other)

Defaults And Flags

------------------

By default, copyfighter assumes structs wider than 16 bytes (two words on x86\_64) should

not be copied. This can be adjusted with the `-max` flag. `max` should typically

be set to some multiple of the word size. You can also adjust the word size and alignment offset for your preferred architecture with `-wordSize` and `-maxAlign`.

Flags like `-max` have to go before the package name.

FAQ

---

Why not just use Go's heap profiler to fix these problems when they show up?

Because copyfighter can find problems before you put your code in production. It's nice to prevent issues before they matter.