Add CGo-free interp backend on linux

README.md

@@ -27,6 +27,23 @@ http://www.tcl-lang.org
 
 	$ sudo yum install tk-devel
 
+### Experimental CGo-free backend
+
+* At present, it only works in Linux.
+* Use [modernc.org/tk](https://pkg.go.dev/modernc.org/tk) to get rid of cgo.
+	* Need not to install Tcl/Tk.
+* Usage
+
+	Build without cgo enabled
+	```
+	CGO_ENABLED=0 go build
+	```
+
+	If cgo is necessary, you can also build with `tclgo` tag
+	```
+	go build -tags tclgo
+	```
+
 ### Demo
 
 https://github.com/visualfc/atk_demo

go.mod

@@ -1,3 +1,10 @@
 module github.com/visualfc/atk
 
 go 1.14
+
+require (
+	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
+	modernc.org/libc v1.16.0
+	modernc.org/tcl v1.13.0
+	modernc.org/tk v1.0.23
+)

tk/interp/cbytes_unix.go

@@ -1,6 +1,6 @@
 // Copyright 2018 visualfc. All rights reserved.
 
-// +build go1.7,!windows
+// +build go1.7,!windows,!tclgo
 
 package interp
 

tk/interp/cbytes_unix_tclgo.go

@@ -0,0 +1,22 @@
+// Copyright 2018 visualfc. All rights reserved.
+
+// +build !windows,tclgo !windows,!cgo
+
+package interp
+
+import (
+	"unsafe"
+
+	"modernc.org/libc"
+	"modernc.org/libc/sys/types"
+)
+
+func toCBytes(tls *libc.TLS, b []byte) uintptr {
+	if len(b) == 0 {
+		return 0
+	}
+
+	p := libc.Xcalloc(tls, types.Size_t(len(b)), 1)
+	copy((*libc.RawMem)(unsafe.Pointer(p))[:len(b):len(b)], b)
+	return p
+}

tk/interp/interp_unix.go

@@ -1,6 +1,6 @@
 // Copyright 2018 visualfc. All rights reserved.
 
-// +build !windows
+// +build !windows,!tclgo
 
 package interp