Re: Turning off JIT Optimisation

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <>
Sun, 16 May 2010 16:19:50 -0400
On 16-05-2010 10:44, Mike Amling wrote:

rossum wrote:

In a secure program I want to be able to wipe the byte array
containing the key, mKey[], before releasing the memory back to the
system. To do that I wrote a simple dispose() method to do a
reasonably secure overwrite of the array:

public void dispose() {

uW4HarMMBuLTqJ3E(true, true, true, true, true, 5) {
void uW4HarMMBuLTqJ3E(boolean x55, boolean xFF,
boolean xAA, boolean x00, boolean nullify, int loops) {

if (mKey != null) {
for (int i = 0; i < mKey.length; ++i) {
//for (int j = 0; j < 5; ++j) {

for (int j = 0; j < loops; ++j) {
if (x55) {

mKey[i] = (byte)0x55;

if (xFF) {

mKey[i] = (byte)0xFF;

if (xAA) {

mKey[i] = (byte)0xAA;

if (x00) {

mKey[i] = (byte)0x00;


} // end for
} // end for

if (nullify) {

mKey = null;


} // end if
} // end dispose()

The compiler can't know there won't be any other callers of
uW4HarMMBuLTqJ3E. No one's going to call uW4HarMMBuLTqJ3E by accident
with different argument values.
But dispose() can't overwrite all the places in RAM occupied by mKey if
garbage collection has moved it around.

I can not follow your argument at all.

Does the JVM spec prohibit global optimization across

Ot what prevent the JIT compiler from doing onething for
this dispose call and something else for another call?


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