; Name          : pipe3.asm
;
; Build         : nasm -felf64 pipe3.asm -l pipe3.lst -o pipe3.o
;                 ld -s -melf_x86_64 -o pipe3 pipe3.o
;
; Description   : converted program pipe3
;
; Source        : Beejs guide to IPC - http://beej.us/guide/bgipc/output/html/multipage/pipes.html
 
bits 64
 
[list -]
        %include "unistd.inc"
[list +]
 
section .bss
 
section .data

    pdfs:
    .read:          dd      0                       ; read end
    .write:         dd      0                       ; write end
    
    Child.Cmd:
    .filename       db      "/bin/ls",0                        ; full path! 
    .argvPtr        dq      Child.Cmd.filename
    ; to save space the end of argvPtr list is the same as the end of the envPtr list
    .envPtr         dq      0                                  ; terminate the list of pointers with NULL

    Parent.Cmd:
    .filename       db      "/usr/bin/wc",0                    ; again full path!
    .argv1          db      "-l", 0                            ; argument to pass
    .argvPtr        dq      Parent.Cmd.filename
                    dq      Parent.Cmd.argv1
    ; to save space the end of argvPtr list is the same as the end of the envPtr list
    .envPtr         dq      0                                  ; terminate the list of pointers with NULL
    
    errorexecve:    db      "execve error", 10
    .length:        equ     $-errorexecve
    errorfork:      db      "fork error", 10
    .length:        equ     $-errorpipe
    errorpipe:      db      "pipe error", 10
    .length:        equ     $-errorpipe
    
section .text
 
global _start
_start:

    ; create pipe
    syscall    pipe, pdfs
    and        rax, rax
    js         Error.PIPE
    ; fork child
    syscall    fork
    and        rax, rax
    js         Error.FORK
    jnz        ParentProcess
    
    ; close STDOUT
    syscall    close, stdout
    ; duplicate STDOUT to pdfs.stdout
    mov       edi, dword[pdfs.write]
    syscall    dup, rdi
    ; close read end of the pipe, not needed
    mov       edi, DWORD[pdfs.read]
    syscall    close, rdi
    ; execute ls command
    syscall    execve, Child.Cmd.filename, Child.Cmd.argvPtr, Child.Cmd.envPtr
    and        rax, rax
    js         Error.EXECVE
    jmp        Exit
    
ParentProcess:      
    ; close STDIN
    syscall    close, stdin
    ; duplicate STDIN to pdfs.stdin
    mov        edi, dword[pdfs.read]
    syscall    dup, rdi
    ; close write end of the pipe, not needed
    mov        edi, dword[pdfs.write]
    syscall    close, rdi
    ; execute wc -l command with input from pdfs.read, output to stdout
    syscall    execve, Parent.Cmd.filename, Parent.Cmd.argvPtr, Parent.Cmd.envPtr
    and        rax, rax
    js         Error.EXECVE
    jmp        Exit

Error:
.EXECVE:
    mov        rsi, errorexecve
    mov        rdx, errorexecve.length
    jmp        Write
.FORK:
    mov        rsi, errorfork
    mov        rdx, errorfork.length
    jmp        Write
.PIPE:
    mov        rsi, errorpipe
    mov        rdx, errorpipe.length
    jmp        Write
Write:
    syscall    write, stdout
Exit:      
    syscall    exit, 0