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    SubjectAT_BASE_PLATFORM (v2)
    Some IBM POWER-based systems have the ability to run in a
    "compatibility" mode which mostly appears to the OS as a different
    processor from the actual hardware. This feature of the platform is
    useful for live partition migration and for backwards compatibility
    with old kernels on new hardware. For example, a Power6 system may
    appear to be a Power5+, which makes the AT_PLATFORM value "power5+".

    Booting a system in a compatibility mode means that may load
    libraries that are inappropriately tuned for the real
    microarchitecture, and apps that use JIT techniques do not have the
    right information for generating tuned code. While the AT_PLATFORM
    auxiliary vector entry correctly indicates the ISA supported, it does
    not accurately reflect the underlying microarchitecture in this case,
    and there is no good way for userspace to get this information.

    Proposed solution:
    Add an AT_BASE_PLATFORM auxiliary vector entry which indicates the
    microarchitecture. This entry uses the same string format as
    AT_PLATFORM, and is readily usable by and other applications.

    Other solutions that have been suggested but found wanting:

    - Use a bit in AT_HWCAP to indicate compat mode -- this is not
    expressive enough. It's not possible to derive the microarchitecture
    from the combination of AT_PLATFORM's value and a single bit.

    - Use dsocaps -- this seems to be a interface and not
    easily usable by other programs. is not the only program
    that can use knowledge of the microarchitecture.

    The following two patches:
    - add the base support to binfmt_elf.c for AT_BASE_PLATFORM
    - implement AT_BASE_PLATFORM for powerpc

    Changes since v1:
    - increment AT_VECTOR_SIZE_BASE
    - define AT_BASE_PLATFORM in generic code instead of powerpc

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      Last update: 2008-07-16 02:01    [W:0.018 / U:14.776 seconds]
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