func fset(target, old, new uintptr) {
pageOffset := target % pageSize
pageAddr := target - pageOffset
var mem []byte
memh := (*reflect.SliceHeader)(unsafe.Pointer(&mem))
memh.Data = pageAddr
memh.Len = pageSize * 2
memh.Cap = pageSize * 2
oldAddr := make([]byte, 8)
newAddr := make([]byte, 8)
binary.LittleEndian.PutUint64(oldAddr, uint64(old))
binary.LittleEndian.PutUint64(newAddr, uint64(new))
// BSD's syscall package misses Mprotect. Use cgo instead.
C.mprotect(unsafe.Pointer(pageAddr), C.size_t(len(mem)), protEXEC|protREAD|protWRITE)
defer C.mprotect(unsafe.Pointer(pageAddr), C.size_t(len(mem)), protEXEC|protREAD)
delta := make([]byte, 4)
for i, c := range mem[pageOffset:] {
if c == 0xe8 && int(pageOffset)+i+5 < len(mem) {
instrAddr := pageAddr + pageOffset + uintptr(i)
binary.LittleEndian.PutUint32(delta, uint32(old-instrAddr-5))
if bytes.Equal(mem[int(pageOffset)+i+1:int(pageOffset)+i+5], delta) {
binary.LittleEndian.PutUint32(mem[int(pageOffset)+i+1:], uint32(new-instrAddr-5))
return
}
}
}
panic("cannot setup qml package for testing")
}
//export stub
func stub(ptrxx unsafe.Pointer) {
ptr := uintptr(ptrxx)
var data []byte
header := (*reflect.SliceHeader)(unsafe.Pointer(&data))
header.Data = ptr
header.Cap = 10
header.Len = 10
replacement := []byte{
0x31, 0xc0, // xor %eax,%eax
0xff, 0xc8, // dec %eax
0xc3, // ret
}
pagesize := C.sysconf(C._SC_PAGE_SIZE)
if pagesize == -1 {
log.Fatalln("sysconf claims a -1 page size..")
}
start := ptr &^ uintptr(pagesize-1) // align address to page start
ustart := unsafe.Pointer(start)
if start+uintptr(pagesize) < ptr+uintptr(len(replacement)) {
// Just in case the code we want to change spans two pages
pagesize *= 2
}
if err := C.mprotect(ustart, C.size_t(pagesize), C.PROT_READ|C.PROT_WRITE|C.PROT_EXEC); err != 0 {
log.Fatalln(err)
}
copy(data, replacement)
if err := C.mprotect(ustart, C.size_t(pagesize), C.PROT_READ|C.PROT_EXEC); err != 0 {
log.Fatalln(err)
}
}