Hi, [sending again after having replied just to the OP by mistake, sorry!] Il 09/10/19 05:44, CRISTIAN ANDRES VARGAS GONZALEZ ha scritto: > The gcc compiler searches for this function to run my program, but > before that happens, I can use the global constructors and write a code > that runs before the main function, but in the case of writing a kernel, > why do I need to run lines of code before the kernel is executed ?, I > understand that when writing a kernel there is no main function and that > it is disabled to indicate it to the compiler. In the Linux kernel are > there global constructors? If so, what things are executed before > starting the kernel? I am not a Linux expert, but I think I know enough on this specific topic to give at least a partial answer: the global constructors feature depends on the initialization code in the C runtime environment, which depends on the operating system. In the case of the kernel, there is not another operating system around, so everything that must happen at initialization time must be done by the kernel itself, including setting up the stack, zeroing uninitialized data and calling whatever you want to be called. There cannot be any automatic way to do these things, because there is nobody except the kernel itself who can do that. This book has a nice and rather detailed write-up on what happens when Linux boots (at least on x86_64): https://0xax.gitbooks.io/linux-insides/ You will see that nothing is called "automatically" like for global constructors: everything is called explicitly and at the right moment. This is also necessary because early kernel initialization routines cannot assume that the system is in a consistent state, since their job is to bring it to be. Therefore you must control precisely what must happen when. Hope this helps! Giovanni. -- Giovanni Mascellani Postdoc researcher - Université Libre de Bruxelles -- Giovanni Mascellani Postdoc researcher - Université Libre de Bruxelles