From: erik quanstrom <quanstro@quanstro.net>
To: 9fans@cse.psu.edu
Subject: [9fans] 8c padding problem
Date: Fri, 21 Dec 2007 18:10:10 -0500 [thread overview]
Message-ID: <1ccc8ef58858daba6badd7543df078f4@quanstro.net> (raw)
i've got a structure that looks like this
/* ethernet header */
typedef struct{
uchar d[6];
uchar s[6];
uchar type[2];
}Ehdr;
typedef struct{
Ehdr;
uchar op[2];
...
}Pkt;
the problem is that 8c adds two bytes of padding between
the end of pkt->type and pkt->op. since sizeof Ehdr%wordsize != 0
this isn't totally unexpected. suprisingly, adding the
appropriate packed pragmas doesn't eliminate the padding.
is this a bug?
of course, if my original definition had been
typedef struct{
uchar d[6];
uchar s[6];
uchar type[2];
uchar op[2];
...
}Pkt;
i would have been fine. but doesn't this defeat
the point of unnamed structures?
also, the fact that there is padding contradicts
my mental model of unnamed structures. i thought
that all the elements of unnamed structures were
laid down as if they were elements of the enclosing
structure. my reading /sys/doc/compilers.ps doesn't
say much. is there another reference on unnamed
structures?
- erik
next reply other threads:[~2007-12-21 23:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-21 23:10 erik quanstrom [this message]
2007-12-21 23:24 ` Martin Neubauer
2007-12-22 0:00 ` erik quanstrom
2007-12-21 23:48 ` Skip Tavakkolian
2007-12-21 23:52 ` erik quanstrom
2007-12-21 23:59 ` Skip Tavakkolian
2007-12-22 0:20 ` erik quanstrom
2007-12-22 4:25 ` Bruce Ellis
2007-12-22 4:34 ` erik quanstrom
2007-12-22 4:41 ` Bruce Ellis
2007-12-22 11:09 ` C H Forsyth
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