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Date: Thu, 12 Jun 2014 07:26:39 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Gabriel Paubert <paubert@iram.es>
Subject: Re: power and percpu: Could we move the paca into the percpu area?
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 Christoph Lameter <cl@gentwo.org>
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> Actually, from gcc/config/rs6000.h:
> 
> /* 1 for registers that have pervasive standard uses
>    and are not available for the register allocator.

[snip]

> So cr5, which is number 73, is never used by gcc. 

Not available for RA is not the same thing at all as not used by GCC.
For example, GPR1 and XER[CA] are also fixed regs.

But, indeed, it does look like GCC doesn't use it.  It seems to me that
some ABI forbade userland (or non-libraries or whatever) from using it.
I'll see what I can find out.


Segher