linux-kernel - Re: [PATCH 1/2] elf loader support for auxvec base platform string

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Message-ID: <18541.35978.437115.957054@harpo.it.uu.se>
Date:	Fri, 4 Jul 2008 04:35:54 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	Nathan Lynch <ntl@...ox.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Paul Mackerras <paulus@...ba.org>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [PATCH 1/2] elf loader support for auxvec base platform string

Nathan Lynch writes:
 > Some IBM POWER-based platforms have the ability to run in a
 > mode which mostly appears to the OS as a different processor from the
 > actual hardware.  For example, a Power6 system may appear to be a
 > Power5+, which makes the AT_PLATFORM value "power5+".
 > 
 > However, some applications (virtual machines, optimized libraries) can
 > benefit from knowledge of the underlying CPU model.  A new aux vector
 > entry, AT_BASE_PLATFORM, will denote the actual hardware.  For
 > example, on a Power6 system in Power5+ compatibility mode, AT_PLATFORM
 > will be "power5+" and AT_BASE_PLATFORM will be "power6".

Why on earth would you ever want AT_PLATFORM to differ from AT_BASE_PLATFORM?
In cases that matter you admit that AT_BASE_PLATFORM takes precedence,
so why involve a fake lame not-quite-the-platform in the first place?

Workaround for buggy software?
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