Bug 597329 - Backport the uprobes singlestep bypass
Backport the uprobes singlestep bypass
Status: CLOSED CURRENTRELEASE
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: systemtap (Show other bugs)
6.0
All Linux
low Severity medium
: rc
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Assigned To: Frank Ch. Eigler
Petr Muller
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Depends On:
Blocks:
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Reported: 2010-05-28 12:34 EDT by Josh Stone
Modified: 2016-09-19 22:06 EDT (History)
3 users (show)

See Also:
Fixed In Version: systemtap-1.2-5.el6
Doc Type: Bug Fix
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Last Closed: 2010-11-10 16:44:43 EST
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RHEL 7.3 requirements from Atomic Host:
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Description Josh Stone 2010-05-28 12:34:33 EDT
A recent change in systemtap's uprobes kernel module lets it skip singlestepping after a breakpoint on easily emulated instructions, especially NOPs.

http://sourceware.org/git/gitweb.cgi?p=systemtap.git;a=commit;h=f2c6cb7149b317baa7e1cb66312febc4b1ae5f9f

This is significant for SDT, our userspace static probes, because those probes always insert a NOP for systemtap to put a breakpoint on.  Using our benchmark scripts/probe_perf/bench.sh, which measures the overhead of nearly 4 million probe hits, I get these elapsed times:

   not instrumented:  0.86s
   uprobes w/ sstep: 16.46s
  uprobes w/o sstep:  7.81s

I believe this is a very worthwhile and easy change to backport into RHEL's systemtap package.
Comment 1 Josh Stone 2010-06-09 15:02:47 EDT
This commit is needed to fix powerpc:

http://sourceware.org/git/gitweb.cgi?p=systemtap.git;a=commit;h=8ea20756d7e3236da8aaee3f7db8cd76e5bbc3e6

We are also waiting on IBM folks to see if we need additions in powerpc's arch_validate_probed_insn().
Comment 2 Josh Stone 2010-06-14 18:53:09 EDT
uprobes_ppc: Don't emulate privileged MSR opcodes
http://sourceware.org/git/gitweb.cgi?p=systemtap.git;a=commit;h=51b7256

(FLW) I believe it's good to go...
Comment 5 releng-rhel@redhat.com 2010-11-10 16:44:43 EST
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.

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