Re: [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.