sizeof(linkaddr_t) gives wrong size on 32bit platform

[beshrns]

I am porting Contiki to a new 32bit platform, and I am using gcc. I noticed that when using Rime, sizeof(linkaddr_t) gives 4 instead of 2. I suggest testing LINKADDR_SIZE directly.

Affected file: core/net/mac/framer-802154.c (which causes the framer to assume using long addresses when it should use short addresses).

[g-oikonomou]

And you're sure there's no definition of LINKADDR_CONF_SIZE changing the size to 4?

[beshrns]

Yes, I am sure, because when I test LINKADDR_SIZE directly it just gives 2. I think the problem comes from default alignment of union type to word-size of the CPU which is 32bit.

[vsaw]

What compiler are you using? Btw one could try to use a compiler independent packing of structs like the __attribute__((__packed__)) of GCC

[beshrns]

I am using ba-elf-gcc (GCC) 4.1.2 on jn5168 Thanks for the tip, I will try it.

On Mon, Feb 3, 2014 at 3:40 PM, Valentin notifications@github.com wrote:

What compiler are you using? Btw one could try to use a compiler independent packing of structs like the attribute((packed)) of GCChttp://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html

— Reply to this email directly or view it on GitHubhttps://github.com/contiki-os/contiki/issues/555#issuecomment-33959664 .

[beshrns]

Actually using __attribute__((__packed__)) solves the problem.

typedef union __attribute__((__packed__)) {
  unsigned char u8[LINKADDR_SIZE];
} linkaddr_t;

Now sizeof(linkaddr_t) gives LINKADDR_SIZE (i.e. 2). So maybe the definition of linkaddr_t should be modified?

[g-oikonomou]

@beshrns did you make any progress with that one? I am fairly certain we won't see __attribute__((__packed__)) or any other toolchain-specific extensions in Contiki's upstream core any time soon, but if you are happy with this workaround for your own work we can close this?

[beshrns]

Well, not really. Although it solves my problem in the mean time, I believe there are platform-specific pieces of code in core\net; i.e., testing for sizeof(linkaddr_t)==2 is platform-specific. Therefore, I suggest to test LINKADDR_SIZE directly (in core/net/mac/framer-802154.c)

[nvt]

@beshrns Sure, would you like to submit a pull request with this change?