Sender: rich AT phekda DOT freeserve DOT co DOT uk
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Date: Sun, 27 Apr 2003 10:40:58 +0100
From: Richard Dawe <rich AT phekda DOT freeserve DOT co DOT uk>
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To: Ben Peddell <killer DOT lightspeed AT bigpond DOT com>, rudd AT cyberoptics DOT com
CC: DJGPP workers <djgpp-workers AT delorie DOT com>
Subject: gcc 3.x breaks ABI compatibility? [Was: Re: Bug 00314 -- div() still 
 broken]
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Reply-To: djgpp-workers AT delorie DOT com

Hello.

Ben Peddell wrote:
[snip]
> OK. GCC 3.2.1 has -fpcc-struct-return by default in DJGPP, whilst GCC
> 3.2.2 has -freg-struct-return by default in DJGPP.
> GCC 3.2.2 may need to be configured to make -fpcc-struct-return the
> default, to maintain compatibility with the DJGPP 2.03 libraries. Or,
> the libraries may need to be re-compiled for GCC 3.2.2, and marked as such.
> 
> These options are in `info gcc "Invoking GCC" "Code Gen Options"'

After rummaging around a bit more:

It's possible that 3.2.1 was broken. There were some ABI regressions in 3.2.1
that were fixed in 3.2.2:

http://gcc.gnu.org/gcc-3.2/changes.html#3.2.2

PR/9506 is the one:

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=9506

gcc defaults to using -fpcc-struct-return, but what does it actually use for
2.95.2 and 3.2.2?

I've just looked at the gcc 2.95.2 sources and it looks like
-fpcc-struct-return (i.e.: use memory) is the default there.

The gcc 3.2.2 source seems to default to using registers. See the end
gcc/config/i386/djgpp.h:

/* Don't default to pcc-struct-return, because gcc is the only compiler,
   and we want to retain compatibility with older gcc versions.  */
#define DEFAULT_PCC_STRUCT_RETURN 0

Why is this defined? I couldn't see a ChangeLog entry for djgpp.h. AFAICT this
breaks backwards compatibility, i.e.: the opposite of what the comment says.
Is there something I'm missing?

Thanks, bye, Rich =]

-- 
Richard Dawe [ http://www.phekda.freeserve.co.uk/richdawe/ ]