• Forgotten memories (2)

    So in the first part of this experiment we saw a simple strategy to spill general-purpose registers into floating-point registers implemented in the RISC-V backend of LLVM.

    In this chapter, let’s see the results and some other interesting facts learnt during the process.

    Read on →

  • Forgotten memories (1)

    Most compiler infrastructures that target register machines do it by using the concept of virtual registers. In their intermediate representations instructions use virtual registers to represent their operands.

    Because hardware is finite, these virtual registers must be mapped to physical registers at some point. The compiler does this in a process called register allocation.

    Being physical registers finite, it may happen that not all the virtual registers used by the program can be held in physical registers at the same time. When this happens, the compiler must emit spill code. Spill code stores a value in a memory (spill) and loads it later, often close to the point of use (reload).

    The memory used for spill code is commonly the function stack. However nothing prevents us from using other kinds of “memories” as long as we can guarantee that nobody is going to use them. This is exactly the kind of experiment we will do today: we’re going to spill general-purpose registers into floating-point registers.

    Read on →

  • Create your own local domain and DHCP with dnsmasq

    Back in 2007, Bernat explained how to set up our own domain name using ISC BIND and ISC DHCP. You can’t go wrong with those servers but maybe you prefer something more straightforward. I present here a simpler alternative built on top of dnsmasq which is an integrated DNS and DHCP.

    Read on →

  • Using SSH Certificates

    Password-based authentication has a number of drawbacks, so many services (such as github) use SSH keys to authenticate. However distributing the keys over several nodes (be virtual machines or single-board computers such as Raspberry Pi) doesn’t scale over the number of nodes and users.

    Luckily, OpenSSH implementation of SSH supports a certificate-based mechanism. This mechanism may help reducing the complexity of users trusting SSH hosts and hosts trusting SSH users.

    Read on →

  • Fortran and modules

    Recently the committee that is preparing the next standard of C++, known as C++20, approved the inclusion of modules. Modules are good™ but they pose some interesting challenges to implementors and users. In this post I will ruminate a bit about what challenges have impacted Fortran.

    Read on →