Why do I need a Cross Compiler?: Difference between revisions

A cross compiler is useful for completely unambiguously targeting a specific machine. When you begin developing for a machine separate from your native distribution's stock compiler, you'll need a cross compiler. Actually, you already *do* target a machine that's different from your native machine frmofrom the very first time you begin trying to produce completely standalone executables (that is, when you're doing OSDev).

Later on, when you have a userspace and a set of system libraries for your programs to link to, you'll then build a compiler that targets: yourOsTargetArch-yourChosenFormat-yourOs while keeping the compiler that targets yourOsTargetArch-yourChosenFormat-none. The difference between the two is that the "none" OS targeting compiler does not have any libraries in its /lib directory, and has no system libraries to link in. It is therefore impossible for any software you compile using this "bare metal" targeting compiler to have unknown dependencies. The "yourOS" targeting cross compiler is where you would place your own system libraries, (in its /lib directory), such that when it builds software, it will link them against those system libraries, thus linking them against your kernel API. You would continue to use the "bare bones" targeting compiler to build the kernel, and whenever you build programs on your development machine which are expected to run on your kernel's target machine, you would use the yourOsTargetArch-yourChosenFormat-yourOs compiler, which has a /include and /lib directories full of your own OS's native system includes and libraries.

Later still, when you're confident that you can both develop and use your kernel, from within your kernel, you'll want to stop building all your programs on a separate "development" machine. More specifically, at this point, you want to have your "build" machine be the same as your test machine such that you build programs that run on your OS, from within your OS. At this point, it's time to take the final step, and, from your separate "development" machine, build a compiler that will run on your OS (host = yourOsTargetArch-yourChosenFormat-yourOs), and target your OS (target = yourOsTargetArch-yourChosenFormat-yourOs). This cross compiler, the canadian cross, will allow you to natively compile other programs while running on your own OS's userspace. It is essentially a "distribution native compiler", like the one that comes with your distro. From that point on, having a compiler that runs on and targets your OS, you can essentially more freely port programs, and allow people to do the same while running your OS, assuming you package that native compiler with your OS.