> It's the OS zeroing everything - learn something very day No, the operating system (kernel, actually) does not zero out anything. The runtime linker would be

> It's the OS zeroing everything - learn something very day No, the operating system (kernel, actually) does not zero out anything. The runtime linker would be the one initializing static memory declared in the ELF BSS sections at execution time. The rest (including the stack and heap) is setup by the prologue (crti.o, depending on the OS crt1.o, and crts.o).