Bug 597329

Summary:	Backport the uprobes singlestep bypass
Product:	Red Hat Enterprise Linux 6	Reporter:	Josh Stone <jistone>
Component:	systemtap	Assignee:	Frank Ch. Eigler <fche>
Status:	CLOSED CURRENTRELEASE	QA Contact:	Petr Muller <pmuller>
Severity:	medium	Docs Contact:
Priority:	low
Version:	6.0	CC:	mjw, ohudlick, pmuller
Target Milestone:	rc
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	systemtap-1.2-5.el6	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2010-11-10 21:44:43 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Josh Stone 2010-05-28 16:34:33 UTC

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 19:02:47 UTC

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 22:53:09 UTC

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 21:44:43 UTC

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.