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Date: Wed, 30 Oct 2013 08:18:04 -0400
From: Yaniv Sapir <yaniv@...pteva.com>
To: john-dev <john-dev@...ts.openwall.com>
Subject: Re: bcrypt-parallella on 64-core (was: Katja's weekly
 report #13)

IIRC, I named those registers based on Katja's printout for core states.
Some register values seemed odd so I specifically asked about them.
However, the limitation is certainly relevant to all registers.

I will consult Andreas and make up an errata list.



On Wed, Oct 30, 2013 at 8:05 AM, Solar Designer <solar@...nwall.com> wrote:

> Yaniv, Katja -
>
> On Wed, Oct 30, 2013 at 07:51:38AM -0400, Yaniv Sapir wrote:
> > The problem is not with certain registers, but with certain cores. Cores
> on
> > the 2nd row should not *load *or *fetch *from external memory. DMA reads
> > are OK.
>
> Oh.  I was referring to:
>
> http://www.openwall.com/lists/john-dev/2013/09/18/3
>
> "(A very long shot:) In the stuck cores, do you have external loads into
> registers R53, R0, R2, R38, respectively?"
>
> so it sounded like the problem had something to do with certain
> registers (as well as certain cores).
>
> Further in that thread, Katja confirmed that "there exists external load
> intto r38 in compiler generated code":
>
> http://www.openwall.com/lists/john-dev/2013/09/19/6
>
> and asked "Is it possible to force e-gcc not to use r38 and r53?":
>
> http://www.openwall.com/lists/john-dev/2013/10/01/8
>
> Maybe this can in fact be done by placing some local variables into
> those problematic registers (using the syntax I just posted about),
> and either only using those variables for other than external loads or
> keeping them unused.  Like I said, I am unsure if this syntax prevents
> gcc from making other use of the same registers, though.
>
> Yaniv, it'd be helpful if you post a full set of relevant Epiphany-IV
> errata (specifically for E64G401?) in one message.
>
> For example, I am confused whether the problem with certain registers
> occurs only on certain cores (that is, when both the core and the
> register number are problematic) or whether it's independent (that is,
> a problem occurs when either register or core number is problematic).
>
> Thanks,
>
> Alexander
>



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Yaniv Sapir
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Email: yaniv@...pteva.com
Web: www.adapteva.com
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