os: implement and smoketest os.Setenv

src/runtime/env_linux.go

@@ -0,0 +1,27 @@
+// +build linux
+
+package runtime
+
+// Update the C environment if cgo is loaded.
+// Called from syscall.Setenv.
+//go:linkname syscall_setenv_c syscall.setenv_c
+func syscall_setenv_c(key string, val string) {
+	keydata := cstring(key)
+	valdata := cstring(val)
+	// ignore any errors
+	libc_setenv(&keydata[0], &valdata[0], 1)
+	return
+}
+
+// cstring converts a Go string to a C string.
+// borrowed from syscall
+func cstring(s string) []byte {
+	data := make([]byte, len(s)+1)
+	copy(data, s)
+	// final byte should be zero from the initial allocation
+	return data
+}
+
+// int setenv(const char *name, const char *val, int replace);
+//export setenv
+func libc_setenv(name *byte, val *byte, replace int32) int32