Re: [linuxsh-dev] Re: FPU in kernel (SH-4)

[NIIBE Y. <gn...@m1...>]

Greg Banks wrote:
 >   Firstly, the gcc I have here (rather old) doesn't define __sh3__
 > when you give it -m4-nofpu.  This might be because we have one of
 > Kaz' patches.

Yes, this is because of our patch, perhaps I did that.  Original
implementaiton defines __sh3__ for -m4-nofpu (not __SH4__).  I thought
that it was mistake, but it seems it is intentional.

 > sh-linux-gnu-gcc --verbose -m3 -o foo-m3.o -c foo.c
 > [...]  -D__SH3__ -D__sh3__ -ml -m3
 > 
 > sh-linux-gnu-gcc --verbose -m4 -o foo-m4.o -c foo.c
 > [...]  -D__SH4__ -ml -m4
 > 
 > sh-linux-gnu-gcc --verbose -m4-nofpu -o foo-m4-nofpu.o -c foo.c
 > [...] -D__SH4__ -D__SH4_NOFPU__ -ml -m4-nofpu 
 > 
 >   Which looks pretty sensible to me.

Yes, we do that.  But the definition seems not that.  So, I'd like to
ask Hitachi what was the order/request (specification) to RedHat/Cygnus
about -m4-nofpu.

 > The -m4-nofpu option uses the same integer division millicode as
 > -m3, which is correct.

Yes, that's _our_ intention. 

 >   Secondly, defining __sh3__ is the *wrong* thing to do for the kernel.

Yes.  Because we distingush with it.  It's not just a kernel for all
program, because we share header files of kernel or C library among SH3 and
SH4.

 >   What the kernel needs is an option that generates SH4 code with __SH4__
 > defined, but no FPU code used from libgcc.a.  With the gcc I'm using here,
 > -m4-nofpu is that option.

Yes.

 >   So I'm very confused.  Niibe-san, does your gcc behave differently to mine?

Mine works exactly as yours.  But the original GCC does not.  And it
seems that it is my misunderstanding that -m4-nofpu is the one for our
demands (SH-4 with no FPU division).  At that time -m4-nofpu was
introduced, because we really wanted such a option, we're just hurry
to adopt this option (assuming this *is* for us), changing CPP macro.

Now, I think that it's not.  I think what we should use is -m4 and
say, -fno-fpudiv or -fidiv.  The option -m4-nofpu would be the option
for some custom model, variant of SH, perhaps.

BTW, thanks for the logos.  It looks pretty good.
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