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On Thu, Aug 7, 2014 at 12:30 AM, Florian Weimer <fweimer@redhat.com> wrote: > On 08/06/2014 11:18 PM, Roland McGrath wrote: >> >> Because of Intel's assurance that the new opcode values are harmless NOPs, >> we didn't put any provision in the source for building a libc without the >> MPX support. > > > How confident are we that existing silicon is able to decode these NOPs > efficiently? Executing them as NOPs is just one partâif there's a > significant performance hit, we have a problem as well. > Here is the test I used. Latency on Intel processors is from 1 to 6 cycles for bndmov %bnd0, 56(%rsp) bndmov %bnd1, 72(%rsp) bndmov %bnd2, 88(%rsp) bndmov %bnd3, 104(%rsp) and bndmov 104(%rsp), %bnd3 bndmov 88(%rsp), %bnd2 bndmov 72(%rsp), %bnd1 bndmov 56(%rsp), %bnd0 -- H.J.
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