jm + via:bos   4

_Could a Neuroscientist Understand a Microprocessor?_
'There is a popular belief in neuroscience that we are primarily data limited, that producing large, multimodal, and complex datasets will, enabled by data analysis algorithms, lead to fundamental insights into the way the brain processes information. Microprocessors are among those artificial information processing systems that are both complex and that we understand at all levels, from the overall logical flow, via logical gates, to the dynamics of transistors. Here we take a simulated classical microprocessor as a model organism, and use our ability to perform arbitrary experiments on it to see if popular data analysis methods from neuroscience can elucidate the way it processes information. We show that the approaches reveal interesting structure in the data but do not meaningfully describe the hierarchy of information processing in the processor. This suggests that current approaches in neuroscience may fall short of producing meaningful models of the brain.'

via Bryan O'Sullivan.
via:bos  neuroscience  microprocessors  6502  computers  hardware  wetware  brain  biology  neural-systems 
june 2016 by jm
Facebook Infer
New static analysis goodnews, freshly open-sourced by Facebook:
Facebook Infer uses logic to do reasoning about a program's execution, but reasoning at this scale — for large applications built from millions of lines of source code — is hard. Theoretically, the number of possibilities that need to be checked is more than the number of estimated atoms in the observable universe. Furthermore, at Facebook our code is not a fixed artifact but an evolving system, updated frequently and concurrently by many developers. It is not unusual to see more than a thousand modifications to our mobile code submitted for review in a given day. The requirements on the program analyzer then become even more challenging because we expect a tool to report quickly on these code modifications — in the region of 10 minutes — to fit in with developers' workflow. Coping with this scale and velocity requires advanced mathematical techniques. Facebook Infer uses two such techniques: separation logic and bi-abduction.

Separation logic is a theory that allows Facebook Infer's analysis to reason about small, independent parts of the application storage, rather than having to consider the entirety of the memory potentially at every step. That would be a daunting task on modern processors with their large addressable virtual memories.

Bi-abduction is a logical inference technique that allows Facebook Infer to discover properties about the behavior of independent parts of the application code. By storing these properties between runs, Facebook Infer needs to analyze only the parts of the software that have changed, reusing the results of its previous analysis where it can.

By combining these approaches, our analyzer is able to find complex problems in modifications to an application built from millions of lines of code, in minutes.


(via Bryan O'Sullivan)
via:bos  infer  facebook  static-analysis  lint  code  java  ios  android  coding  bugs 
june 2015 by jm
rr
A cool-looking new debugging tool for C/C++ from Mozilla.
Many, many people have noticed that if we had a way to reliably record program execution and replay it later, with the ability to debug the replay, we could largely tame the nondeterminism problem. This would also allow us to deliberately introduce nondeterminism so tests can explore more of the possible execution space, without impacting debuggability. Many record and replay systems have been built in pursuit of this vision. (I built one myself.) For various reasons these systems have not seen wide adoption. So, a few years ago we at Mozilla started a project to create a new record-and-replay tool that would overcome the obstacles blocking adoption. We call this tool rr.


Low runtime overhead; easy deployability; targeted at 32-bit (?!) Linux; OSS. (via Bryan O'Sullivan)
via:bos  mozilla  debugging  coding  firefox  rr  record  replay  gdb  c++  linux 
march 2014 by jm
Exclusive: a behind-the-scenes look at Facebook release engineering
'Facebook gave me an exclusive behind-the-scenes look at the process it uses to deploy new functionality. I watched first-hand as the company's release engineers rolled out the new "timeline" feature for brand pages'. Hiphop, BitTorrent, 1.5GB binaries, and IRC!
facebook  deployment  engineering  releases  via:bos 
april 2012 by jm

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