1# purego
2[![Go Reference](https://pkg.go.dev/badge/github.com/bnema/purego?GOOS=darwin.svg)](https://pkg.go.dev/github.com/bnema/purego?GOOS=darwin)
3
4A library for calling C functions from Go without Cgo.
5
6> Fork notice: this repository is a maintained fork of `github.com/ebitengine/purego` with additional ABI, callback, and generator-facing fixes needed by the PureGoTK stack.
7
8> This is beta software so expect bugs and potentially API breaking changes
9> but each release will be tagged to avoid breaking people's code.
10> Bug reports are encouraged.
11
12## Motivation
13
14The [Ebitengine](https://github.com/hajimehoshi/ebiten) game engine was ported to use only Go on Windows. This enabled
15cross-compiling to Windows from any other operating system simply by setting `GOOS=windows`. The purego project was
16born to bring that same vision to the other platforms supported by Ebitengine.
17
18## Benefits
19
20- **Simple Cross-Compilation**: No C means you can build for other platforms easily without a C compiler.
21- **Faster Compilation**: Efficiently cache your entirely Go builds.
22- **Smaller Binaries**: Using Cgo generates a C wrapper function for each C function called. Purego doesn't!
23- **Dynamic Linking**: Load symbols at runtime and use it as a plugin system.
24- **Foreign Function Interface**: Call into other languages that are compiled into shared objects.
25- **Cgo Fallback**: Works even with CGO_ENABLED=1 so incremental porting is possible. 
26This also means unsupported GOARCHs (freebsd/riscv64, linux/mips, etc.) will still work
27except for float arguments and return values.
28
29## Supported Platforms
30
31### Tier 1
32
33Tier 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.
34
35- **Android**: amd64<sup>1</sup>, arm64<sup>1</sup>
36- **iOS**: amd64<sup>1</sup>, arm64<sup>1</sup>
37- **Linux**: amd64, arm64
38- **macOS**: amd64, arm64
39- **Windows**: amd64, arm64
40
41### Tier 2
42
43Tier 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.
44
45- **Android**: 386<sup>1</sup>, arm<sup>1</sup>
46- **FreeBSD**: amd64<sup>2</sup>, arm64<sup>2</sup>
47- **Linux**: 386, arm, loong64, ppc64le, riscv64, s390x<sup>1</sup>
48- **NetBSD**: amd64<sup>2</sup>, arm64<sup>2</sup>
49- **Windows**: 386<sup>3</sup>, arm<sup>3,4</sup>
50
51#### Support Notes
52
531. These architectures require CGO_ENABLED=1 to compile
542. These architectures require the special flag `-gcflags="github.com/bnema/purego/internal/fakecgo=-std"` to compile with CGO_ENABLED=0
553. These architectures only support `SyscallN` and `NewCallback`
564. These architectures are no longer supported as of Go 1.26
57
58## Example
59
60The example below only showcases purego use for macOS and Linux. The other platforms require special handling which can
61be seen in the complete example at [examples/libc](https://github.com/bnema/purego/tree/main/examples/libc) which supports FreeBSD and Windows.
62
63```go
64package main
65
66import (
67	"fmt"
68	"runtime"
69
70	"github.com/bnema/purego"
71)
72
73func getSystemLibrary() string {
74	switch runtime.GOOS {
75	case "darwin":
76		return "/usr/lib/libSystem.B.dylib"
77	case "linux":
78		return "libc.so.6"
79	default:
80		panic(fmt.Errorf("GOOS=%s is not supported", runtime.GOOS))
81	}
82}
83
84func main() {
85	libc, err := purego.Dlopen(getSystemLibrary(), purego.RTLD_NOW|purego.RTLD_GLOBAL)
86	if err != nil {
87		panic(err)
88	}
89	var puts func(string)
90	purego.RegisterLibFunc(&puts, libc, "puts")
91	puts("Calling C from Go without Cgo!")
92}
93```
94
95Then to run: `CGO_ENABLED=0 go run main.go`
96
97## Questions
98
99If you have questions about how to incorporate purego in your project or want to discuss
100how it works join the [Discord](https://discord.gg/HzGZVD6BkY)!
101
102### External Code
103
104Purego uses code that originates from the Go runtime. These files are under the BSD-3
105License that can be found [in the Go Source](https://github.com/golang/go/blob/master/LICENSE).
106This is a list of the copied files:
107
108* `abi_*.h` from package `runtime/cgo`
109* `wincallback.go` from package `runtime`
110* `zcallback_darwin_*.s` from package `runtime`
111* `internal/fakecgo/abi_*.h` from package `runtime/cgo`
112* `internal/fakecgo/asm_GOARCH.s` from package `runtime/cgo`
113* `internal/fakecgo/callbacks.go` from package `runtime/cgo`
114* `internal/fakecgo/iscgo.go` from package `runtime/cgo`
115* `internal/fakecgo/setenv.go` from package `runtime/cgo`
116* `internal/fakecgo/freebsd.go` from package `runtime/cgo`
117* `internal/fakecgo/netbsd.go` from package `runtime/cgo`
118* `internal/fakecgo/linux.go` from package `runtime/cgo`
119
120The `internal/fakecgo/go_GOOS.go` files were modified from `runtime/cgo/gcc_GOOS_GOARCH.go`.
121The `internal/fakecgo/linux.go` file is a combination of `runtime/cgo/linux.go` and `runtime/cgo/linux_syscall.c`.
122
123The files `abi_*.h` and `internal/fakecgo/abi_*.h` are the same because Bazel does not support cross-package use of
124`#include` so we need each one once per package. (cf. [issue](https://github.com/bazelbuild/rules_go/issues/3636))