From mint-bounce@lists.fishpool.fi Tue Jan 22 17:29:05 2008 X-Original-To: fnaumann@mail.boerde.de Delivered-To: fnaumann@mail.boerde.de From: "Roger Burrows" Organization: Anodyne Software To: mint@fishpool.com Date: Sat, 24 Nov 2007 17:05:34 -0500 MIME-Version: 1.0 Subject: Re: [MiNT] GCC 4.2.2 and binary compatibility Message-ID: <474859DE.29216.569B12@localhost> Priority: normal In-reply-to: <4747F03E.4050101@freesbee.fr> X-mailer: Pegasus Mail for Windows (v4.02a) Content-type: text/plain; charset=ISO-8859-1 Content-description: Mail message body X-Authenticated: anodyne@magma.ca - (MYCROFT) [142.46.8.6] X-ecartis-version: Ecartis v1.0.0 Sender: mint-bounce@lists.fishpool.fi Errors-To: mint-bounce@lists.fishpool.fi X-original-sender: anodyne@cyberus.ca Precedence: bulk List-help: List-unsubscribe: List-Id: X-List-ID: List-subscribe: List-owner: List-post: X-Virus-Scanned: by amavisd-new at relay.boerde.de X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on relay.boerde.de X-Spam-Status: No, hits=3.0 tagged_above=-50.5 required=7.0 tests=AWL, BAYES_00, RCVD_IN_BL_SPAMCOP_NET, RCVD_IN_SORBS X-Spam-Level: *** Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from Quoted-printable to 8bit by freemint id m0MGP1ap004618 Status: X-Status: X-Keywords: Hi Vincent, On 24 Nov 2007 at 10:34, Vincent Rivière wrote: > > The first problem was about functions returning pointers. Traditional > compilers used to return them into d0. GCC for Linux/m68k returns them > into a0. My current binaries behaves like Linux, but it breaks the > compatibility with older Atari functions written in assembly language. > Thus in my next build, I'll disable that a0/d0 stuff and use d0 in all > cases, just like older compilers. > > The second question is about alignment. > > Vincent Rivière wrote: > > I would like to speak about another "feature" : alignment. > > > > By default, GCC aligns structure members on 4-byte boundaries, > > producing useless 2-byte holes in a structure where longs and shorts > > are mixed. I patched it long ago to use a 2-byte default alignment, > > so no space is wasted. Some people said that the 68020+ CPU have > > faster memory access to longs aligned on 32-bit boundaries. Is it > > true on Atari computers ? > > > > I recently discovered another "feature" of GCC. When function > > arguments are pushed on the stack, they are aligned on an "int" > > boundary. When compiling with -mshort, there is no additional filler. > > But when -mshort is not used, pushing a short then a long causes the > > long to be aligned 2 bytes further. A short filler is inserted > > between the 2 values. Just like structure alignment, it seems to me > > that such alignment is useless on the Atari platform. I plan to > > remove this alignment in my next build. > > > > So what do you think about removing the alignments, for structure > > members and stack parameters ? Does it break some compatibility ? > > Petr Stehlik answered: > > yes, it does. > > > > If you want to help the Atari community with your GCC port then > > please don't mess with these settings (including the a0/d0 trials) > > and make sure that you use the very same settings the gcc 2.95 for > > MiNT had. > > Feel free to post any further comment. > The Lattice C compiler (in default mode) uses 32-bit integers and widens shorter integer type (i.e. shorts and chars) to 32 bits before placing them on the stack. However (also in default mode), non-character structure members are aligned on word boundaries rather than long boundaries. Both these behaviours may be changed by appropriate compiler arguments. Since I suspect GCC is used a lot more than Lattice for current development, it would probably be best to stick to the existing GCC implementation behaviour. Regards, Roger Burrows