Assembly - Why I get the wrong character in my newly created file?

Question

I am learning assembly and write the following:

   Section .text
         global   _start

   _start:
         jmp short  GoToFilename

   open:
         pop            esi           ; esi gets address of the filename
         xor            eax, eax      ; clear eax
         mov            [esi+13], al  ; terminate file name(see # at the end of the first db)
         mov            dl, 0xa       ; dl gets code of newline(\n)
         mov byte       [esi+15], dl  ; place it between A and # (see 2nd db)
         mov            [esi+16], al  ; place NULL for # (at the 2nd db) gets 
         lea            edi, [esi+14] ; edi gets address of input text (here it should be only A as input)
         mov            [esi+17], edi ; place its address for XXXX
         mov            dx, 0x1b6     ; permissions
         mov            cl, 0x42      ; flags
         mov            ebx, esi      ; address of file name 
         mov            al, 0x5       ; syscall of open
         int            0x80          ; go, lets do it
         mov            edi, eax      ; put handle to file in edi
         xor            eax, eax      ; clear because we will need it 

  write: 
        xor             edx, edx
        xor             ecx, ecx      
        xor             ebx, ebx
        mov             dl, 0x1         ; number of bytes to write = 1
        lea             ecx, [esi+17]   ; ecx gets address of input text
        mov             ebx, edi        ; put handle to file in edi
        mov             al, 0x4         ; syscall of write 
        int             0x80            ; go, lets do it 

  close:
         mov            ebx, edi      ; handle to file 
         mov            al, 0x6       ; syscall of open
         int            0x80          ; go, lets do it

  exit:
         xor            ebx, ebx      ; clear ebx
         mov            al, 0x1       ; syscall of exit
         int            0x80          ; go, lets do it

  GoToFilename:
         call          open
         db            '/tmp/file.txt#'
         db            'A #XXXX'

[For that, I use the jmp-call-pop-technique. Those who know what shellcodes are will it know what I mean, but if not then its not so important here]

So, when I let it run, then the file is created but when I open the file then I get the sign # written in file, and not the character 'A'.

Do you know where I made the mistake ? I couldnt find it. I check the offsets, go through the code many times...but without success.

best regards,

Answer 1

You are wrongly reffering to the address stored at [esi+17]. Better use:

lea  ecx, [esi+14]   ; ecx gets address of input text

Alternatively

mov ecx, [esi+17]