Subject: Re: a new KNF (and some comments)
To: None <firstname.lastname@example.org>
From: Atsushi Onoe <email@example.com>
Date: 01/22/2000 11:17:17
> > If my memory is correct, all types except "(signed) int" and "unsigned int"
> > for bitfield are prohibited by ANSI. And you should not expect the size or
> > alignment of whole bitfields. This is why bitfield should not used in
> > protool header.
> If this is the case, then there is a fair bit of code in NetBSD, especially
> older device drivers, which needs to be fixed to be strict about this.
> In any case, GCC clearly supports it, because my Buslogic card works :-)
Since it is the restriction of ANSI C, we can go with GCC extensions.
Actually it is used for declaration of ip header in "/sys/netinet/ip.h",
and very commonly used in various *BSD, except FreeBSD, for years.
FYI, my MIPS ANSI C compiler warns:
cfe: Warning 658: bitfield2.c, line 5: bit-field 'bar' type required to be int, unsigned int, or signed int. (220.127.116.11(30))
cfe: Warning 658: bitfield2.c, line 6: bit-field 'baz' type required to be int, unsigned int, or signed int. (18.104.22.168(30))
cfe: Warning 658: bitfield2.c, line 7: bit-field 'zap' type required to be int, unsigned int, or signed int. (22.214.171.124(30))
Anyway the alignment of whole bitfield depends on the implementation of
compiler. For example, GCC has some configuration parameters, such as:
/* Writing `int' for a bitfield forces int alignment for the structure. */
#define PCC_BITFIELD_TYPE_MATTERS 1
The parameter itself does not affect to bitfield with "u_int8_t", but it may
cause some compatibility problems.