headius

Algorithm

1. A secret byte you want to read is stored at inaccessible memory location priv_mem.
2. The sender triggers an access exception by attempting to read priv_mem.
3. Due to CPU optimization (out-of-order execution), the load of secret from priv_mem and the use of its value in (4) and (5) below may execute before the exception is triggered.
4. Calculate an offset into a known array probe by multiplying secret by the width of a cache line (or whatever block size the CPU typically fetches, like a 4096-byte page). This guarantees each of those 256 possible offsets will cache separately.
5. Load probe[offset], which causes the CPU to cache exactly one chunk of of our array, populating one cache line.
6. The exception finally triggers, clearing the modified registers...but cached data is not excised.
7. Iterate over all 256 offsets into probe to find out which one loads fast. You've determined the value of secret.

scott-maddox

// Paste in console
var getThings = function(){
    var divs = [...document.querySelectorAll("#manufacture__container > div")]
    var things = divs.map(function(e){
        var result = {e};
        var spans = [...e.getElementsByTagName("span")]
        spans.map(function(s){
            var str = s.innerText.replace(/[^/.0-9]/g, '');
            var a = str.split("/");
            var num = +a[0];

viktorklang

/*
Copyright 2015 Viktor Klang
 
   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at
 
       http://www.apache.org/licenses/LICENSE-2.0
 
   Unless required by applicable law or agreed to in writing, software

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

unclebob

Today I gave a keynote at ACCU in Oxford.  In the midst of it I made two (count them) two statements that I should have known better than to make.  I was describing the late '70s, and the way we felt about the C language at the time.  My slide said something like: "C was for real men."  Emily Bache, whom I know and hold in high regard, spoke up and said "What about women?".  And I said something like: "We didn't allow women in those days."  It was a dumb crack, and should either not have been said, or should have been followed up with a statement to the effect that that was wrong headed.  

The second mistake I made was while describing Cobol. I mentioned Adm. Grace Hopper.  I said something like "May she rest in peace."  I don't know that any of the words were actually demeaning, but the tone was not as respectful as it should have been to an Admiral in the United State Navy, and one who was so instrumental in our industry; despite what I feel about Cobol.  

I am a 59 year old programmer who was brought up