;name: cwd.asm
;
;build: nasm -felf64 cwd.asm -o cwd.o
; ld -s -melf_x86_64 -o cwd cwd.o
;
;description: Linux alternative for pwd.
; returns the current working directory.
bits 64
[list -]
%include "unistd.inc"
[list +]
section .data
string:
.noMemory: db "Error: out of memory"
.lf: db 10
.length: equ $-.noMemory
section .text
global _start
_start:
syscall brk,0 ;get start of heap
and rax, rax ;if result is negative then error
js error ;no more memory available
mov r8, rax ;save the current memory break
repeat:
add rax, 16 ;add 16 bytes to the current memory break
syscall brk, rax
xor rax, rdi ;rax = new memory pointer, test if different from start of heap
jz getcwd ;if zero then memory is allocated
; no memory could be allocated, free the memory already allocated
syscall brk, r8
jmp error
getcwd:
sub rdi, r8
syscall getcwd, r8, rdi
and rax, rax
jns printit ;if RAX < 0 then buffer not large enough
mov rax, rdi ;buffer not large enough rax = r8
add rax, rsi ;add size of already allocated memory -> new memory break
jmp repeat ;retry allocating more memory
printit:
syscall write,stdout,r8,rax ;write directory to stdout
syscall write,stdout,string.lf,1 ;write linefeed to stdout
jmp exit
error:
syscall write,stderr,string.noMemory,string.length ;write error string
exit:
syscall exit,0
