GCC packed struct including unpacked struct is packed in 4.4.3

Asked May 01 '13 at 12:52

Active May 01 '13 at 12:52

Viewed 560 times

Consider the following code from ttyrpld 2.60 include/rpl_packet.h:

struct rpltime {
    uint64_t tv_sec;
    uint32_t tv_usec;
};

union rpldev_evmagic {
    uint32_t n;
    char m[4];
};

struct rpldsk_packet {
    union rpldev_evmagic evmagic;
    uint32_t size;
    struct rpltime time;
} __attribute__((packed));

That is, rpltime is not packed, rpldsk_packet that includes an rpltime member is packed.

If you take the sizeof struct rpldsk_packet using ppc_85xxDP-gcc (GCC) 4.2.2 from the ELDK distribution, you get 24. Using gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3 you get 20. That is, struct rpltime is also packed on the Ubuntu GCC. According to the GCC documentation, I would expect that the sizeof would be 24 with any GCC, incuding gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3.

Did the behavior of the packed attribute regarding unpacked members change between 4.2.2 and 4.4.3? and if so, when? Or is the documentation out-of-date? What did I miss?

asked May 01 '13 at 12:52

Jonathan Ben-Avraham

4,615
2
34
37

1

I get 24 with gcc-4.7.2. Seems to be a bug in 4.4.3. – Daniel Fischer May 01 '13 at 12:57
The answer is that it depends on word length. On 64 bit machines (PPC) the sizeof will be 24, on 32 bit machines it will be 20. No bug in GCC. If someone cares to write this up I will mark as answered. – Jonathan Ben-Avraham May 01 '13 at 16:37

GCC packed struct including unpacked struct is packed in 4.4.3

0 Answers0