From: Shaun Jackman <sjackman@pathwayconnect.com>
To: gcc-help@gcc.gnu.org
Subject: Re: packed and aligned structures
Date: Wed, 12 Sep 2001 13:18:00 -0000 [thread overview]
Message-ID: <E15hGSt-0002Vq-00@dazed> (raw)
On the matter of exact structure size. I forget to mention I've already tried
specifying -mstructure-size-boundary=8, which had the desired with 2.95.2.
This doesn't seem to work with 3.0.1 though. Is it still a supported option?
Thanks,
Shaun
On September 12, 2001 13:58, you wrote:
> I'm sure this is a common question, and I thought I had it solved in
> 2.95.2, but I've recent upgraded to 3.01 and the problem rears its ugly
> head again. Here's a basic rundown of what I'm looking for.
>
> All my protocol structures must be PACKED (no padding in the structure),
> EXACT SIZE (no padding at the end of the structure, if the structure is 13
> bytes long, sizeof( mystruct) should return 13, not 16), and ALIGNED to a 4
> byte boundary. What combination of attributes and command line switches can
> I use to accomplish this?
>
> --- ALIGNED ---
> In 2.95.2 all my structures always seemed to be on 4 byte
> boundaries regardless of content, however 3.01 put a structure of this form
> typedef struct {
> char pad[2];
> char data[ 1400];
> } mystruct;
> on a 2 byte boundary. Will
> } __attribute__((aligned(4))) mystruct;
> fix this? Is there a command line switch to force this for all structs?
>
> --- EXACT SIZE ---
> typedef struct {
> long src,
> long dst,
> char mbz,
> char prot,
> short len,
> short checksum
> } mystruct;
> sizeof( mystruct) returns 16, how do I make this return 14?
>
> --- PACKED ---
> typedef struct {
> ...
> } __attribute__((packed)) mystruct;
> Will this force all the members of the structure to be packed (ie no
> padding in the structure)?
> typedef struct {
> ...
> } __attribute__((packed, aligned(4))) mystruct;
> Does this construct make sense to force the structure to a 4 byte boundary,
> as well as packing the members?
>
> Many thanks,
> Please cc me as I'm not a member of the list,
> Shaun
next reply other threads:[~2001-09-12 13:18 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-09-12 13:18 Shaun Jackman [this message]
-- strict thread matches above, loose matches on Subject: below --
2001-09-12 12:58 Shaun Jackman
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