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RE: $ta0 .. $ta3 registers in O32 on MIPS

To: <ralf@linux-mips.org>, <binutils@sourceware.org>, <linux-mips@linux-mips.org>, <dvdkhlng@gmx.de>
Subject: RE: $ta0 .. $ta3 registers in O32 on MIPS
From: <Paul_Koning@Dell.com>
Date: Wed, 28 Sep 2011 10:11:40 -0500
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In-reply-to: <20110928123305.GA1971@linux-mips.org>
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Sender: linux-mips-bounce@linux-mips.org
Thread-index: Acx92r3YAHvtZ3s7Rm6mvuiE4xFJcAAFfHpw
Thread-topic: $ta0 .. $ta3 registers in O32 on MIPS
>The register names $ta0 .. $ta3 were added by SGI for N32 / N64 code.
>Because these reference $8 .. $11 just like $t0 .. $t3 in the O32 ABI their 
>availability in O32 as well appears dangerous, if not a bug:
>
>$ cat s.s 
>       addu    $ta0, $ta0
>$ mips-linux-as -o s.o s.s
>$ file s.o
>s.o: ELF 32-bit MSB relocatable, MIPS, MIPS-I version 1 (SYSV), not stripped $
>
>I was expecting an error message and I'm wondering, was this intentional?

I would say so.  I call this a feature.  It makes it easier to write assembly 
code that assembles without change in both O32 and N32/N64.  Consider a 
function that has 4 or fewer arguments, but needs a pile of scratch registers.  
It can use ta0-ta3 as four scratch registers, which is correct in all the ABIs.

        paul

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