LIBBSD TCPDUMP

[Kirspel, Kevin]

This is how I fixed it.  I did similar things for EXTRACT_32BITS and EXTRACT_64BITS.

static inline u_int16_t
EXTRACT_16BITS(const void *p)
{
#if defined(__arm__) && defined(__rtems__)
                if(((uint32_t)p % 2) != 0) {
                                u_int16_t value;
                                u_int8_t *ptr = (u_int8_t *)&value;
                                ptr[0] = ((const u_int8_t *)p)[0];
                                ptr[1] = ((const u_int8_t *)p)[1];
                                p = &value;
                }
#endif /* __rtems__ */
                return ((u_int16_t)ntohs(*(const u_int16_t *)(p)));
}

Kevin Kirspel
Electrical Engineer - Sr. Staff
Idexx Roswell
235 Hembree Park Drive
Roswell GA 30076
Tel: (770)-510-4444 ext. 81642
Direct: (770)-688-1642
Fax: (770)-510-4445

From: Joel Sherrill [mailto:joel at rtems.org]
Sent: Saturday, July 01, 2017 11:39 AM
To: Gedare Bloom <gedare at rtems.org>
Cc: rtems-devel at rtems.org <devel at rtems.org>; Kirspel, Kevin <Kevin-Kirspel at idexx.com>
Subject: Re: LIBBSD TCPDUMP



On Jul 1, 2017 10:34 AM, "Gedare Bloom" <gedare at rtems.org<mailto:gedare at rtems.org>> wrote:
On Sat, Jul 1, 2017 at 10:01 AM, Kirspel, Kevin <Kevin-Kirspel at idexx.com<mailto:Kevin-Kirspel at idexx.com>> 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().
>
That would probably be a more portable fix than allowing unaligned
accesses. I think the alignment should be made to the CPU_ALIGNMENT
macro.

Can't you also just pull it out a byte at a time, form the net version and then ntohs()?

That's what I coded recently in some marahalling code.



>
>
> Kevin Kirspel
>
> Electrical Engineer - Sr. Staff
>
> Idexx Roswell
>
> 235 Hembree Park Drive
>
> Roswell GA 30076
>
> Tel: (770)-510-4444 ext. 81642<tel:%28770%29-510-4444%20ext.%2081642>
>
> Direct: (770)-688-1642<tel:%28770%29-688-1642>
>
> Fax: (770)-510-4445<tel:%28770%29-510-4445>
>
>
>
>
> _______________________________________________
> devel mailing list
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