From: Jim Wilson <wilson@cygnus.com>
To: rth@cygnus.com
Cc: egcs@cygnus.com
Subject: Re: m68k structure packing
Date: Tue, 30 Sep 1997 21:42:00 -0000 [thread overview]
Message-ID: <199710010442.VAA02338@cygnus.com> (raw)
> Gcc knows that it needs to access bitfields differently when a structure
> is packed. It may be that gcc will generate correct code with your patch
> for cases that would ordinarily fail ...
Yes it will. I've used this on a number of occasions to get
machine independant unaligned loads. It works on all machines,
even if gcc has to resort to byte loads and shifts.
I know that bitfield references to packed structures work. This has never
been in doubt.
However, there remains a specific question here as to how this affects the
m68k port with respect to the known and documented problems with
PCC_BITFIELD_TYPE_MATTERS and STRUCTURE_SIZE_BOUNDARY. It is not obvious
what the interaction is. But as I mentioned in my previous mail, I am starting
to suspect that improvements to the unaligned/packed structure field support
over the years has accidentally solved this known problem, in which case this
may now be a `historical' problem. If you haven't done so already, and if
you really care about this problem, take a look at the
PCC_BITFIELD_TYPE_MATTERS documentation.
Jim
next reply other threads:[~1997-09-30 21:42 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-09-30 21:42 Jim Wilson [this message]
1997-10-01 5:44 ` Kamil Iskra
-- strict thread matches above, loose matches on Subject: below --
1997-10-01 15:08 Mike Stump
1997-10-01 15:56 ` Peter Barada
1997-10-01 16:16 ` Per Bothner
1997-10-02 20:14 ` Jim Wilson
1997-10-02 6:49 ` Paul Koning
1997-10-02 20:09 ` Jim Wilson
1997-10-02 20:01 ` Jim Wilson
1997-10-02 21:40 ` Richard Henderson
1997-10-01 12:16 Mike Stump
1997-10-01 12:39 ` Joel Sherrill
1997-10-02 18:37 ` Jim Wilson
1997-09-30 20:16 Mike Stump
1997-09-30 22:03 ` Jeffrey A Law
1997-09-30 16:58 Mike Stump
1997-09-30 18:20 ` Jim Wilson
1997-10-01 9:02 ` Peter Barada
1997-09-30 13:32 Mike Stump
1997-09-30 14:56 ` Jim Wilson
1997-09-30 12:08 Mike Stump
1997-09-30 12:57 ` Charles M. Hannum
1997-09-30 19:58 ` Jim Wilson
1997-09-30 21:13 ` Richard Henderson
1997-09-30 21:22 ` Jim Wilson
1997-10-01 15:14 ` Jim Wilson
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