What if your DVD recorder sets bogus permissions to your DVDs?

Today we will see what happens when we nest a function inside another. It seems a harmless thing to do but it happens to come with its own dose of interesting details.

Several times in previous chapters we have talked about ARM as an architecture that has several features aimed at embedding systems. In embedded systems memory is scarce and expensive, so designs that help reduce the memory footprint are very welcome. Today we will see another of these features: the Thumb instruction set.

We already know that ARM is a 32-bit architecture: general purpose registers are 32-bit wide and addresses in memory are 32-bit numbers. The natural integer size for an architecture is usually called a word and in ARM is obviously 32-bit integers. Sometimes, though, we need to deal with subword data: integers of size smaller than 32 bits.

Today we will see how to make indirect calls.