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Re: [RFC PATCH 0/5] arm64: Signal context expansion
On 09/12/2016 05:30 PM, Dave Martin wrote:
On Mon, Sep 12, 2016 at 04:01:17PM +0100, Szabolcs Nagy wrote:
i assume the kernel can avoid saving SVE regs when
they are not used by the process.
I can (and do), in my patches (not posted yet).
The real issue here is that a recently updated shared library might be
optimised to use SVE, where the program using it is an older, SVE-
(think of an optimised math library using some new fancy SVE-based
number crunching internally).
In my little world, binaries are expected to do run-time CPU feature
discovery and fall back to the baseline ABI if the system does not
support ABI extensions. This means that a personality flag can disable
the extension, the optimized math libraries run with the slower baseline
code instead, and the rest of the application sees the expected kernel
From this perspective, it is quite important that it is possible to get
legacy applications running on newer hardware, preferably with out
wrapping them in a dedicated VM.
I understand that there are other environments were this is less of a
concern, but I also believe that the age of an architecture factors less
into this than one might want.