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Re: Can't build a CONFIG_CPU_NEVADA kernel

To: "Kevin D. Kissell" <kevink@mips.com>
Subject: Re: Can't build a CONFIG_CPU_NEVADA kernel
From: "Kevin D. Kissell" <kevink@mips.com>
Date: Wed, 14 Mar 2001 23:47:31 +0100
Cc: <linux-mips@oss.sgi.com>
References: <20010314084633.A25674@nevyn.them.org> <20010314195919.A1911@bacchus.dhis.org> <20010314140529.A29525@nevyn.them.org> <20010314202058.B1911@bacchus.dhis.org> <00fc01c0acd3$c881ca80$0deca8c0@Ulysses>
Sender: owner-linux-mips@oss.sgi.com
> "Correct" usage would be to enable those three instructions
> with a "-mcpu=nevada", or better still, "-mcpu=r5200" (for 
> consistency), and to enable the rest of the MIPS IV ISA 
> with "-mips4" instead of the archaic r8000 hack.

I should add "Correct", but not useful for 32-bit
kernels.  "-mips32", once that percolates through
the gcc food chain, would be *almost* perfect
for 32-bit Nevada kernels.  I say almost, because
while MIPS32 is 32-bit MIPS IV plus MADD, it also
has a handfull of instructions that are not supported 
by the R52xx, of which it is wildly improbable but 
theoretically possible that the multiply-subtracts
might somehow get emitted in compiled application
code. It should work just fine for kernel purposes, though.

Meanwhile, try piping objdump of a "-mmad" kernel
through "grep -i mad".  I'd be stunned if a single MADD
turned up.  If it gains nothing, but breaks builds, then
for heaven's sake banish -mmad from the kernel
makefiles!

            Regards,

            Kevin K.


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