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    SubjectRe: [PATCH -tip 3/6 V4.1] x86: instruction decorder API
    Jim Keniston wrote:
    > For user-space probing, we've been concentrating on native-built
    > executables. Am I correct in thinking that we'll see 16-bit or V86 mode
    > only on legacy apps built elsewhere? In any case, it only makes sense
    > to build on the kvm folks' work in this regard.

    That's a fair assumption; you will of course need to test it and take
    appropriate action if it doesn't pan out.

    > As noted, the INAT tables follow the kvm model of one fat bitmap of
    > attributes per opcode, rather than the kprobes/uprobes model of one or
    > two 256-bit tables per attribute. (This latter approach was due to the
    > gradual accumulation of tables over the years.)
    > I like the bitmap-per-opcode approach because it's relatively easy to
    > see in one place everything you're saying about a particular opcode.
    > But with all the potential clients for this service, it's not clear that
    > we'll get by with a single bitmap for every opcode. (x86 kvm uses 32
    > bits per opcode, I think, and the INAT tables use 10. Seems like we
    > could overrun 64 bits pretty quickly.) So I guess that means we'll have
    > to get a little creative as to how we expose these attribute sets to the
    > client.

    This is another very good reason to use an instruction table which is
    preprocessed into a usable format: it means that if the internal data
    structures change -- and they almost certainly will have to at some
    point -- the raw data isn't lost.


    H. Peter Anvin, Intel Open Source Technology Center
    I work for Intel. I don't speak on their behalf.

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