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Re: bndmov MPX instructions in dynamic linker breaks valgrind

From: Florian Weimer <fweimer at redhat dot com>
To: "H.J. Lu" <hjl dot tools at gmail dot com>
Cc: Roland McGrath <roland at hack dot frob dot com>, Markus Trippelsdorf <markus at trippelsdorf dot de>, GNU C Library <libc-alpha at sourceware dot org>, Igor Zamyatin <igor dot zamyatin at intel dot com>
Date: Mon, 18 Aug 2014 17:52:06 +0200
Subject: Re: bndmov MPX instructions in dynamic linker breaks valgrind
Authentication-results: sourceware.org; auth=none
References: <20140802175103 dot GC294 at x4> <20140806211851 dot D3F5A2C3983 at topped-with-meat dot com> <53E32B32 dot 7070309 at redhat dot com> <CAMe9rOq8CJ8W2-a6=caRnoLDhC0Hxr8=aVhwgmMjNGNJBi1UYw at mail dot gmail dot com>

On 08/07/2014 05:03 PM, H.J. Lu wrote:

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


Thanks, interesting.

I'm a bit worried about the performance on non-Intel implementations,but my test on an AMD Turion II Neo N40L showed a similar performanceimpact. I guess we'll have to make a release with these changes and seewhat happens.


--
Florian Weimer / Red Hat Product Security

References:
- bndmov MPX instructions in dynamic linker breaks valgrind
  - From: Markus Trippelsdorf
- Re: bndmov MPX instructions in dynamic linker breaks valgrind
  - From: Roland McGrath
- Re: bndmov MPX instructions in dynamic linker breaks valgrind
  - From: Florian Weimer
- Re: bndmov MPX instructions in dynamic linker breaks valgrind
  - From: H.J. Lu

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