Syscalls

To get anything useful done, your program must interact with the outside world. There are two princpal ways of doing that, through syscalls, and through library calls. Library calls are described on another page. Here you’ll find the table of syscalls, and details on how to use syscalls generally.

how to syscall

• First load the RAX register with the call number
• Then load the arguments in left to right order into rdi, rsi, rdx, r10, r8, r9
• in the rare case you need more arguments push them on the stack left to right
• Get the argument list from the manpage in section 2 listing the system call, find it under it’s libc name.
• Remember that pointers are 64bits unsigned regardless of the ‘type’ of the pointer
• issue the syscall instruction
• return value will be in rax, if there is a second return value it will be in rdx

general notes

• Manually Aligning the stack doesn’t appear to be required when making syscalls on 64bit.
• My version of the table leaves out calls which are numbered differently in the x32 ABI, which is different from the i386 ABI

syscall table