Dissection: A New Paradigm for Solving Bicomposite Search Problems

Dissection: A New Paradigm for Solving Bicomposite Search Problems

http://cacm.acm.org/magazines/2014/10/178791-dissection/fulltext

bash vulnerability test

env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

Floating point numbers ...

Floating point numbers have some unexpected properties.

Try this in your favourite language (if it has real floats)

Python:

>>> print 0.1 + 0.2 == 0.3

False

 C:

#include <stdio.h>

int main() {  printf("%s\n", 0.1 + 0.2 == 0.3 ? "True" : "False");

} 

$ gcc float.c -o float && ./float 

False 

Installing a specific branch of a python package with pip

pip install --user 'git+git://github.com/llvmpy/llvmpy@llvm-3.4'

Parallela16 temperature

Reading the temperature for the Xilinx Zynq chip is done as described in http://forums.parallella.org/viewtopic.php?t=930

with

python -c "T=open('/sys/bus/iio/devices/iio:device0/in_temp0_raw').read(); T = (float(T) / 4096. * 503.975) - 273.15; print T"

ARM debugging with Qemu and gdb

To set up a pty to capture the serial port info, use socat

socat -d -d pty  pty

which prints out which pty to connect Qemu's virtual serial port to, for instance /dev/pts/1, and the other pty, for instance /dev/pty/6, to which one may for instance attach a GNU Screen

screen /dev/pty/6

Now run Qemu

QEMU_AUDIO_DRV=none qemu-system-arm \
-cpu cortex-a15 -machine vexpress-a15 \
-kernel /tmp/vmlinuz-3.10 -append "earlyprintk console=tty1 console=ttyAMA0" \
-nographic \
-gdb tcp:localhost:1234 -S -serial /dev/pts/1

which tells Qemu to start a gdb-server at port 1234 and wait (-S) until a gdb server attaches.

Make sure to have a gdb configured for arm targets, compiled with

./configure --target=arm-linux-gnueabi
make

and run it.  Connect to the qemu gdb-server with

target remote :1234 

To see the machine code, type

C-x a

to enable the terminal interface that shows code cursor, and enable asm with

layout asm