foo.go

// filename: cmd/foo/foo.go

package main

import simple "simple"

func main() {
	d := simple.GetData()
	simple.PutData(d)
}

output.txt

data=hello
data=hello

simple.c

#include <runtime.h>

void
simple·GetData(int8* data) {
    data = runtime·malloc(6);
    runtime·memmove(data, "hello", 6);
    runtime·printf("data=%s\n", data);
    FLUSH(&data);
}

void
simple·PutData(int8* data) {
    runtime·printf("data=%s\n", data);
    runtime·free(data);
}

simple.go

package simple

func GetData() *byte
func PutData(*byte)