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Subject: Re: 32 bit userland on G5
From: David Woodhouse <dwmw2@infradead.org>
To: Paul Mackerras <paulus@samba.org>
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Date: Wed, 14 Jun 2006 00:31:49 +0100
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On Wed, 2006-06-14 at 08:52 +1000, Paul Mackerras wrote:
> Historically the PPC32 ELF ABI has used an executable PLT, containing
> instructions constructed at runtime, located next to the BSS, and
> without the corresponding program header entry indicating execute
> permission.  Alan Modra devised a new way of doing the PLT which
> doesn't require it to be executable, but of course it is only used in
> programs that have been built since the new method went into the
> toolchain (in fact all of the .o files being linked have to have been
> compiled with the new method in order for it to be used).

'Historical' being until about 4 years ago, around the time of
http://ecos.sourceware.org/ml/binutils/2002-05/msg00097.html ?

> So if you are absolutely sure that every program you will ever want to
> run on your kernel has been built with an up-to-date toolchain, you
> can turn on enforcement of execute permissions for 32-bit processes.
> It would be a "courageous" step (in the Yes Minister sense :) for a
> distro to do it, IMHO. 

We already did it in Fedora. We don't default to READ_IMPLIES_EXEC for
32-bit processes on the 64-bit kernel.

-- 
dwmw2