fa/doc/md/SYS.md

Sys keyword in fa

Sys keyword will call a syscall with arguments on the stack

Sys takes at least two arguments of the stack:

• Register usage
• Syscall number

The arguments:

• Argument Register usage means how many registers should the syscall use (how many arguments)
• Argument Syscall number means the syscall number

Example of the sys keyword:

1 60 sys 2  -- Exists the program with code 1
            -- Will use 2 registers: rax (60) and rdi (1)
pop      -- Drop the result

This will call SYS_exit (60) syscall with argument 1, the sys keyword has to take two arguments off the stack, the syscall number and the last one argument as SYS_exit only takes one argument, then as every syscall returns something we drop it off the stack