replace.go

package monkey

import (
	"reflect"
	"syscall"
	"unsafe"
)

func rawMemoryAccess(p uintptr, length int) []byte {
	return *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
		Data: p,
		Len:  length,
		Cap:  length,
	}))
}

func pageStart(ptr uintptr) uintptr {
	return ptr & ^(uintptr(syscall.Getpagesize() - 1))
}

// from is a pointer to the actual function
// to is a pointer to a go funcvalue
func replaceFunction(from, to uintptr) (original []byte) {
	jumpData := jmpToFunctionValue(to)
	f := rawMemoryAccess(from, len(jumpData))
	original = make([]byte, len(f))
	copy(original, f)

	copyToLocation(from, jumpData)
	return
}