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Re: gdb vs. gdbserver with -mips3 / 32bitmode userspace

To: Michael Uhler <uhler@mips.com>
Subject: Re: gdb vs. gdbserver with -mips3 / 32bitmode userspace
From: Daniel Jacobowitz <dan@debian.org>
Date: Wed, 1 Feb 2006 14:24:04 -0500
Cc: "'Maciej W. Rozycki'" <macro@linux-mips.org>, 'Johannes Stezenbach' <js@linuxtv.org>, linux-mips@linux-mips.org
In-reply-to: <005901c62754$b414dc80$bb14a8c0@MIPS.COM>
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References: <20060201164423.GA4891@nevyn.them.org> <005901c62754$b414dc80$bb14a8c0@MIPS.COM>
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On Wed, Feb 01, 2006 at 09:26:57AM -0800, Michael Uhler wrote:
> Daniel,
> 
> The O/S maybe doing something different, but the architecture has 3 bits in
> Status: KX, SX, and UX that enable access to the address space above 32
> bits.  With these bits off, an attempt to access these addresses causes an
> exception.  So while 32-bit apps have the full 64-bit address space, most of
> it is inaccessible to the 32-bit app.

That's not actually what I was referring to: there's at least one MIPS
implementation where the results of 32-bit arithmetic operations are
not just architecturally unpredictable but actually wrong if the upper
bits are not properly sign extended (I might be misremembering, but I
think I'm talking about the SB-1).  That's the sort of thing that can
be basically impossible to track down if your debugger doesn't show
you the whole register.

-- 
Daniel Jacobowitz
CodeSourcery

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