Joel Sherrill joel at
Sat Jul 1 14:06:52 UTC 2017

On Jul 1, 2017 9:01 AM, "Kirspel, Kevin" <Kevin-Kirspel at> wrote:

I get a crash when running the tcpdump command in LIBBSD.  It is due to the
following structure

struct stp_bpdu_ {

    u_int8_t protocol_id[2];

    u_int8_t protocol_version;

    u_int8_t bpdu_type;

    u_int8_t flags;

    u_int8_t root_id[8];

    u_int8_t root_path_cost[4];

   u_int8_t bridge_id[8];

    u_int8_t port_id[2];

    u_int8_t message_age[2];

    u_int8_t max_age[2];

    u_int8_t hello_time[2];

    u_int8_t forward_delay[2];

    u_int8_t v1_length;


In the code, there is an access to the port_id field as follows:
EXTRACT_16BITS(&stp_bpdu->port_id).  EXTRACT_16BITS calls ntohs() .  Since
the address of “&stp_bpdu->port_id” is at an odd word (16 bit) boundary, an
exception is generated.  What is the correct way to fix this?  I was going
to update EXTRACT_16BITS to check for an odd boundary and fix it up before
calling ntohs().

There should be a bit in cp15 which determines is unaligned accesses are
enabled. Should be examples in other BSPs


Kevin Kirspel

Electrical Engineer - Sr. Staff

Idexx Roswell

235 Hembree Park Drive

Roswell GA 30076

Tel: (770)-510-4444 ext. 81642 <(770)%20510-4444>

Direct: (770)-688-1642 <(770)%20688-1642>

Fax: (770)-510-4445 <(770)%20510-4445>

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