Re: [MiNT] [Emutos-devel] Emutos and gcc-4.2.2

["Thomas Huth" <th.huth@googlemail.com>]

 Hi!

On Nov 24, 2007 12:34 AM, Vincent Rivière
<vriviere@users.sourceforge.net> wrote:
> I'm very happy you used my compiler ! So you recompiled it ? On which
> system ? It's always interesting to hear success stories !

I had to recompile it since I am running Linux on my PowerMac (Silver
G4), so that I can not use the pre-compiled binaries. Thanks to your
"build script howtos" the recompilation was very easy! Kudos to you
for that!

> In my next build, I'll disable the a0/d0 stuff, in order to make a more
> standard compiler. It's really easy, just some defines to remove.

Great :-)

> 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've heard that, too, but I am not an expert here ... that's maybe a
better question to the MiNT developers since they are more likely
working on 68030 machines than the folks here on the EmuTOS mailing
list.

> 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.

Well, I think the default size of items that are pushed on the stack
should be sizeof(int).
For example when you have declared following function in one file:

int myfunc(int a, int b)
{
    return a + b;
}

And in another file you call myfunc(3, 5), but there is no prototype
for myfunc before...
... this is perfectly valid C (despite it's ugly due to the missing
prototype), but it will fail as soon as you disable this "filler"
values on the stack. I think it's better not to disable these
"fillers".

 Thomas