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SubjectRe: [PATCH 1/2] elf loader support for auxvec base platform string
Mikael Pettersson wrote:
> 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?

My apologies, I did not explain the motivation well.

The idea is that while AT_PLATFORM indicates the instruction set
supported, AT_BASE_PLATFORM indicates the underlying
microarchitecture. It's not a matter of buggy software, or of one
value taking precedence over the other.

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