[lwip-users] [lwip] netif alignment

[Wurmsdobler, Peter]

Hello,

When compiling and linking the lwIP stack to our application, the compiler
(gcc) apparently did not align the stucture netif correctly as I had
assumed. At runtime, the netif structure was allocated in an aligned manner,
24 bytes, the first few entries could be dereferenced, but not the input and
output functions. This could be solved by a slightly different struct
definition:

struct netif {
  struct netif *next;
  struct ip_addr ip_addr;
  struct ip_addr netmask;  /* netmask in network byte order */
  struct ip_addr gw;
  unsigned char hwaddr[6];
  char name[2];

  /* This function is called by the network device driver
     when it wants to pass a packet to the TCP/IP stack. */
  err_t (* input)(struct pbuf *p, struct netif *inp);

  /* The following two fields should be filled in by the
     initialization function for the device driver. */

  /* This function is called by the IP module when it wants
     to send a packet on the interface. */
  err_t (* output)(struct netif *netif, struct pbuf *p,
                   struct ip_addr *ipaddr);
  err_t (* linkoutput)(struct netif *netif, struct pbuf *p);

  /* This field can be set bu the device driver and could point
     to state information for the device. */
  void *state;
  u8_t num;
  u8_t dummy[MEM_ALIGNMENT-1];
};

peter


Peter Wurmsdober
Eurotherm Drives Ltd.
Littlehampton, BN17 7RZ, UK
TEL: +44 19 03 73 73 58
FAX: +44 19 03 73 71 07
[This message was sent through the lwip discussion list.]