Linux x64 Assembly Syscall ABI: Registers, File Descriptors & .bss Segment | open, read, write, exit
Every Linux syscall follows the x64 ABI register protocol: RAX holds the syscall number, RDI/RSI/RDX hold the first three arguments, return value lands in RAX. File descriptors 0/1/2 map to stdin/stdout/stderr — everything else (files, sockets, pipes) is a number above 2 returned by open(). .bss reserves zero-initialized RAM without increasing binary size on disk — ideal for runtime buffers. Complete implementation: sys_open → sys_read into .bss buffer → sys_write to stdout → sys_close → sys_exit.
