Tag: C

CPUs used to perform better when memory accesses are aligned, that is when the pointer value is a multiple of the alignment value. This differentiation still exists in current CPUs, and still some have only instructions that perform aligned accesses. To take into account this issue, the C standard has alignment rules in place, and so the compilers exploit them to generate efficient code whenever possible. As we will see in this article, we need to be careful while casting pointers around to be sure not to break any of these rules. The goal of this article is to be educative by showcasing the problem and by giving some solutions to easily get over it.

CPUs used to perform better when memory accesses are aligned, that is when the pointer value is a multiple of the alignment value. This differentiation still exists in current CPUs, and still some have only instructions that perform aligned accesses. To take into account this issue, the C standard has alignment rules in place, and so the compilers exploit them to generate efficient code whenever possible. As we will see in this article, we need to be careful while casting pointers around to be sure not to break any of these rules. The goal of this article is to be educative by showcasing the problem and by giving some solutions to easily get over it.

Two engineers from QuarksLab had talks accepted at CppCon this year: two tools presentation, Easy::jit, and Frozen; and a general introduction to the ELF format. It's hard to cope with the 9 hours of jet-lag, but it is definitively worth the effort, so here is our conf report!

Quarkslab was present at CppCon 2016, presenting general thoughts on the C++ optimization process and how much the so-called zero-cost abstraction relied on the compiler implementation, and not on the standard. Now comes a humble report from this great event!

Why does some memset calls get optimized away by the compiler? Let's investigate!

C++ is well-known to be tedious to analyze, the use of both inheritance and polymorphism (i.e. virtual method) makes the compiler generate indirect calls. Usually, this kind of assembly code forces the reverse engineer to execute the code in order to figure out the destination of a call. In fact, we are looking for the VFT (Virtual Function Table). This table contains all virtual methods for a specific instance of a class. This article shows how to retrieve this information to make the analysis of a C++ software easier.