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RE: $ta0 .. $ta3 registers in O32 on MIPS
- From: <Paul_Koning at Dell dot com>
- To: <ralf at linux-mips dot org>, <binutils at sourceware dot org>, <linux-mips at linux-mips dot org>, <dvdkhlng at gmx dot de>
- Date: Wed, 28 Sep 2011 10:11:40 -0500
- Subject: RE: $ta0 .. $ta3 registers in O32 on MIPS
- References: <20110928123305.GA1971@linux-mips.org>
>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.