extern __errno_location section .text global ft_read ft_read: mov rax, 0 ; syscall read, other arguments should be good accord to calling convention syscall cmp eax, -1 ; linux syscalls errors are always in the range -4095 to -1 jg .done cmp eax, -4095 jl .done mov rbx, rax ; save return value of syscall call __errno_location ; put address of errno in rax neg rbx ; errno should be positive mov [rax], rbx ; set errno mov rax, -1 ; set return value of ft_read to -1 ret .done: ret