;Name: extxterm.asm
;
;Build: nasm -felf64 extxterm.asm -o extxterm.o
; ld -s -melf_x86_64 -o extxterm extxterm.o
;
;Description: redirect stderr to a separate terminal, xterm in this example.
bits 64
[list -]
%include "unistd.inc"
%include "sys/stat.inc"
%include "errors.inc"
[list +]
%define SCRIPT 'tty > /tmp/xterm_fifo;trap \"\" INT QUIT TSTP;exec<&-;exec>&-;while :;do sleep 3600;done'
%define COMMAND '/usr/bin/xterm'
%define FIFOBUFFER '/tmp/xterm_fifo'
%define DISPLAYNAME "TERMINAL"
section .bss
stderrchildpid: resq 1
stdoutchildpid: resq 1
fdfifo: resq 1
buffer: resb 1024
.len: equ $-buffer
nbytesread: resq 1
fdterm: resq 1
oldstdout: resq 1
oldstderr: resq 1
section .rodata
;error messages
mknoderror: db "mknod error",10
.len: equ $-mknoderror
forkerror: db "fork error",10
.len: equ $-forkerror
execveerror: db "execve error(not expected)",10
.len: equ $-execveerror
wait4error: db "wait4 error",10
.len: equ $-wait4error
;fifoname
fifobuffer: db FIFOBUFFER,0
;xterm
command: db COMMAND,0
;arguments to pass to xterm
arg:
.1: db "/usr/bin/xterm",0
.2: db "-fa",0
;to chose another font:
;http://www.futurile.net/2016/06/14/xterm-setup-and-truetype-font-configuration/
.3: db "DejaVu Sans Mono",0
.4: db "-fs",0
.5: db "11",0
.6: db "-hold",0
.7: db "-title",0
.8: db DISPLAYNAME,0
.9: db "-e",0
.10: db "sh",0
.11: db "-c",0
.12: db SCRIPT,0
argp: dq arg.1,arg.2,arg.3,arg.4,arg.5,arg.6,arg.7,arg.8,arg.9,arg.10,arg.11,arg.12
dq 0
;environment parameters to pass to xterm
env:
.1: db "DISPLAY=:0",0
.2: db "PATH=/bin:/usr/bin",0
envp: dq env.1,env.2
dq 0
stderrmsg: db "stderr: message received",0x0A
.len: equ $-stderrmsg
stdoutmsg: db "stdout: message received",0x0A
.len: equ $-stdoutmsg
section .text
global _start
_start:
;create a FIFO file to communicate with the terminal to get the tty of it.
;once we got it, we can delete it and communication continues over the
;tty device.
syscall mknod , fifobuffer , S_IFIFO | S_IRUSR | S_IWUSR , 0
and rax,rax ;if mknod doesn't return zero there is a problem
jz .startfork ;all ok here
cmp rax,EEXIST ;if fifo already exists on disk so we can continue
jne .mknoderror ;otherwise there is something else wrong
.startfork:
;fork to get a child process, this will terminate when the parent terminates.
syscall fork
mov [stderrchildpid],rax ;save pid from child
and rax,rax
js .forkerror
jnz .parent
.stderrchild:
;we are in the child process. The child starts xterm.
syscall execve,command,argp,envp
and rax,rax
js .execveerror
jmp .exit ;if success we will not get it to here
.stdoutchild:
.parent:
;we are in the parent process
;open a connection to the fifo to read from it
syscall open,fifobuffer, 666o ,O_RDONLY
and rax,rax
js .openerror ;if negative we got an error
mov [fdfifo],rax ;save filedescriptor to fifo
;read the message the shell script in xterm has send to us. This should contain the
;pseude terminal device of xterm
;wait until child is done
syscall read,[fdfifo],buffer,buffer.len
and rax,rax
js .readerror ;if return value is negative we have an error
jz .commerror ;if return value is zero we have a communication error
mov [nbytesread],rax ;save length of returned string
;close the fifo
syscall close,[fdfifo]
and rax,rax ;if negative there was an error
js .closeerror
;delete the FIFO file, we don't need it any more(?)
syscall unlink,fifobuffer ;if return value negative then error
js .unlinkerror
;the problem we got is that this string contains an end of line character in it
;we have to replace this with a zero
mov rax,buffer ;get address of buffer
add rax,[nbytesread] ;go to last character+1
dec rax ;go to location of 0x0A
mov byte[rax],0 ;overwrite with 0x00
;the buffer contains the path to xterm
;at this point we can check, when debugging that we can send messages to the terminal with
;for example: echo "message" > /dev/pts/6. Just replace /dev/pts/6 with the string in the buffer.
;open a connection to the new path, we just want to write
syscall open, buffer, 0666o ,O_WRONLY ;we just want to write
js .openerror ;if negative we got an error
mov [fdterm],rax ;save filedescriptor to terminal
syscall close,stderr
syscall dup,[fdterm]
syscall close,[fdterm]
syscall write,stderr,stderrmsg,stderrmsg.len
syscall write,stdout,stdoutmsg,stdoutmsg.len
;wait for the kid to end
syscall wait4,0,0,0,0
and rax,rax
js .waiterror
.exit:
;exit program
syscall exit,0
;this section can be used to deal with errors
.unlinkerror:
;
;jmp .errexit
.writeerror:
;
;jmp .errexit
.commerror:
;
;jmp .errexit
.closeerror:
;
;jmp .errexit
.readerror:
;
;jmp .errexit
.openerror:
;
;jmp .errexit
.waiterror:
;
;jmp .errexit
.execveerror:
;
;jmp .errexit
.forkerror:
;
;jmp .errexit
.mknoderror:
;
;jmp .errexit
.errexit:
syscall exit,1
