amd64/bareMetalOS-0.5.3/os/ipv4/icmp.asm

   1 ; =============================================================================
   2 ; BareMetal -- a 64-bit OS written in Assembly for x86-64 systems
   3 ; Copyright (C) 2008-2012 Return Infinity -- see LICENSE.TXT
   4 ;
   5 ; ICMP (Internet Control Message Protocol)
   6 ; =============================================================================
   7
   8 align 16
   9 db 'DEBUG: IPv4 ICMP'
  10 align 16
  11
  12
  13 ; -----------------------------------------------------------------------------
  14 ; os_icmp_handler -- Handle an incoming ICMP packet; Called by Network interrupt
  15 ;  IN:  RCX = packet length
  16 ;       RSI = location of received ICMP packet
  17 os_icmp_handler:
  18         push rsi
  19         push rax
  20
  21         ; Check if reply or request
  22
  23
  24 os_icmp_handler_request:
  25         ; Swap the MAC addresses
  26         mov rax, [rsi]                  ; Grab the Destination MAC as 8 bytes even though the MAC is 6 bytes
  27         mov ax, [rsi+0x0C]              ; Store the EtherType in the low 16-bits of RAX
  28         push rax                        ; Save the new Source MAC (with EtherType) to the stack
  29         mov rax, [rsi+0x06]             ; Grab the Source MAC as 8 bytes (the last two bytes will be overwritten)
  30         mov [rsi], rax                  ; Store the new Destination MAC in the packet
  31         pop rax                         ; Restore the new Source MAC + EtherType
  32         mov [rsi+0x06], rax             ; Write it to the packet
  33
  34         ; Swap the IP addresses
  35         mov eax, [rsi+0x1A]             ; Grab the Source IP
  36         push rax
  37         mov eax, [rsi+0x1E]             ; Grab the Destination IP
  38         mov dword [rsi+0x1A], eax       ; Overwrite the 'old' Source with the 'new' Source
  39         pop rax
  40         mov dword [rsi+0x1E], eax       ; Overwrite the 'old' Destination with the 'new' Destination
  41
  42         ; Set to Echo Reply
  43         mov byte [rsi+0x22], 0x00       ; Set to 0 for Echo Reply (Was originally 8 for Echo Request)
  44
  45         ; Adjust the checksum
  46         mov ax, [rsi+0x24]
  47         add ax, 8                       ; Add 8 since we removed 8 (by clearing the Echo Request)
  48         mov word [rsi+0x24], ax
  49
  50         call os_ethernet_tx_raw         ; Send the packet
  51
  52         pop rax
  53         pop rsi
  54         ret
  55 ; -----------------------------------------------------------------------------
  56
  57
  58 ; =============================================================================
  59 ; EOF