75 lines
2.7 KiB
Markdown
75 lines
2.7 KiB
Markdown
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# purego
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[](https://pkg.go.dev/github.com/ebitengine/purego?GOOS=darwin)
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A library for calling C functions from Go without Cgo.
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## Motivation
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The [Ebitengine](https://github.com/hajimehoshi/ebiten) game engine was ported to use only Go on Windows. This enabled
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cross-compiling to Windows from any other operating system simply by setting `GOOS=windows`. The purego project was
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born to bring that same vision to the other platforms supported by Ebitengine.
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## Benefits
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- **Simple Cross-Compilation**: No C means you can build for other platforms easily without a C compiler.
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- **Faster Compilation**: Efficiently cache your entirely Go builds.
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- **Smaller Binaries**: Using Cgo generates a C wrapper function for each C function called. Purego doesn't!
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- **Dynamic Linking**: Load symbols at runtime and use it as a plugin system.
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- **Foreign Function Interface**: Call into other languages that are compiled into shared objects.
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## Example
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This example only works on macOS and Linux. For a complete example look at [libc](https://github.com/ebitengine/purego/tree/main/examples/libc) which supports Windows and FreeBSD.
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```go
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package main
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import (
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"fmt"
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"runtime"
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"github.com/ebitengine/purego"
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)
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func getSystemLibrary() string {
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switch runtime.GOOS {
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case "darwin":
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return "/usr/lib/libSystem.B.dylib"
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case "linux":
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return "libc.so.6"
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default:
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panic(fmt.Errorf("GOOS=%s is not supported", runtime.GOOS))
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}
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}
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func main() {
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libc, err := purego.Dlopen(getSystemLibrary(), purego.RTLD_NOW|purego.RTLD_GLOBAL)
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if err != nil {
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panic(err)
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}
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var puts func(string)
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purego.RegisterLibFunc(&puts, libc, "puts")
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puts("Calling C from Go without Cgo!")
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}
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```
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Then to run: `CGO_ENABLED=0 go run main.go`
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### External Code
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Purego uses code that originates from the Go runtime. These files are under the BSD-3
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License that can be found [in the Go Source](https://github.com/golang/go/blob/master/LICENSE).
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This is a list of the copied files:
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* `abi_*.h` from package `runtime/cgo`
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* `zcallback_darwin_*.s` from package `runtime`
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* `internal/fakecgo/abi_*.h` from package `runtime/cgo`
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* `internal/fakecgo/asm_GOARCH.s` from package `runtime/cgo`
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* `internal/fakecgo/callbacks.go` from package `runtime/cgo`
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* `internal/fakecgo/go_GOOS_GOARCH.go` from package `runtime/cgo`
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* `internal/fakecgo/iscgo.go` from package `runtime/cgo`
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* `internal/fakecgo/setenv.go` from package `runtime/cgo`
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* `internal/fakecgo/freebsd.go` from package `runtime/cgo`
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The files `abi_*.h` and `internal/fakecgo/abi_*.h` are the same because Bazel does not support cross-package use of `#include` so we need each one once per package. (cf. [issue](https://github.com/bazelbuild/rules_go/issues/3636))
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