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# purego
[](https://pkg.go.dev/github.com/ebitengine/purego?GOOS=darwin)
A library for calling C functions from Go without Cgo.
> This is beta software so expect bugs and potentially API breaking changes
> but each release will be tagged to avoid breaking people's code.
> Bug reports are encouraged.
## Motivation
The [Ebitengine](https://github.com/hajimehoshi/ebiten) game engine was ported to use only Go on Windows. This enabled
cross-compiling to Windows from any other operating system simply by setting `GOOS=windows`. The purego project was
born to bring that same vision to the other platforms supported by Ebitengine.
## Benefits
- **Simple Cross-Compilation**: No C means you can build for other platforms easily without a C compiler.
- **Faster Compilation**: Efficiently cache your entirely Go builds.
- **Smaller Binaries**: Using Cgo generates a C wrapper function for each C function called. Purego doesn't!
- **Dynamic Linking**: Load symbols at runtime and use it as a plugin system.
- **Foreign Function Interface**: Call into other languages that are compiled into shared objects.
- **Cgo Fallback**: Works even with CGO_ENABLED=1 so incremental porting is possible.
This also means unsupported GOARCHs (freebsd/riscv64, linux/mips, etc.) will still work
except for float arguments and return values.
## Supported Platforms
### Tier 1
Tier 1 platforms are the primary targets officially supported by PureGo. When a new version of PureGo is released, any critical bugs found on Tier 1 platforms are treated as release blockers. The release will be postponed until such issues are resolved.
- **Android**: amd64, arm64
- **iOS**: amd64, arm64
- **Linux**: amd64, arm64
- **macOS**: amd64, arm64
- **Windows**: amd64, arm64
### Tier 2
Tier 2 platforms are supported by PureGo on a best-effort basis. Critical bugs on Tier 2 platforms do not block new PureGo releases. However, fixes contributed by external contributors are very welcome and encouraged.
- **Android**: 386, arm
- **FreeBSD**: amd64, arm64
- **Linux**: 386, arm, loong64
- **Windows**: 386*, arm*
`*` These architectures only support `SyscallN` and `NewCallback`
## Example
The example below only showcases purego use for macOS and Linux. The other platforms require special handling which can
be seen in the complete example at [examples/libc](https://github.com/ebitengine/purego/tree/main/examples/libc) which supports FreeBSD and Windows.
```go
package main
import (
"fmt"
"runtime"
"github.com/ebitengine/purego"
)
func getSystemLibrary() string {
switch runtime.GOOS {
case "darwin":
return "/usr/lib/libSystem.B.dylib"
case "linux":
return "libc.so.6"
default:
panic(fmt.Errorf("GOOS=%s is not supported", runtime.GOOS))
}
}
func main() {
libc, err := purego.Dlopen(getSystemLibrary(), purego.RTLD_NOW|purego.RTLD_GLOBAL)
if err != nil {
panic(err)
}
var puts func(string)
purego.RegisterLibFunc(&puts, libc, "puts")
puts("Calling C from Go without Cgo!")
}
```
Then to run: `CGO_ENABLED=0 go run main.go`
## Questions
If you have questions about how to incorporate purego in your project or want to discuss
how it works join the [Discord](https://discord.gg/HzGZVD6BkY)!
### External Code
Purego uses code that originates from the Go runtime. These files are under the BSD-3
License that can be found [in the Go Source](https://github.com/golang/go/blob/master/LICENSE).
This is a list of the copied files:
* `abi_*.h` from package `runtime/cgo`
* `wincallback.go` from package `runtime`
* `zcallback_darwin_*.s` from package `runtime`
* `internal/fakecgo/abi_*.h` from package `runtime/cgo`
* `internal/fakecgo/asm_GOARCH.s` from package `runtime/cgo`
* `internal/fakecgo/callbacks.go` from package `runtime/cgo`
* `internal/fakecgo/go_GOOS_GOARCH.go` from package `runtime/cgo`
* `internal/fakecgo/iscgo.go` from package `runtime/cgo`
* `internal/fakecgo/setenv.go` from package `runtime/cgo`
* `internal/fakecgo/freebsd.go` from package `runtime/cgo`
* `internal/fakecgo/netbsd.go` from package `runtime/cgo`
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))
|
