Red Hat ENTERPRISE 5.4 RELEASE NOTES, Manual

Page: 260 / 466

Chapter 1. Package Updates
242
1.219.2. RHBA-2009:1313: bug fix and enhancement update
Updated
systemtap
packages that fix various bugs, enhance user-space probing, improve support
for debuginfo-less operations and apply several other enhancements are now available.
SystemTap
provides an instrumentation infrastructure for systems running the Linux 2.6 kernel. It
allows users to write scripts that probe and trace system events for monitoring and profiling purposes.
SystemTap's framework allows users to investigate and monitor a wide variety of wide variety of kernel
functions, system calls, and other events that occur in both kernel-space and user-space.
With this update, SystemTap is now re-based on upstream version 0.9.7. This applies several
enhancements and bug fixes, namely:
• On-file flight recording is now supported. This allows
stap
to run in the background and record
huge trace log information on the disk, rather than just to memory. (
BZ#438737
1693
)
• Kernel tracepoints are now supported for probing predefined kernel events without any debuginfo
information. Tracepoints incur less overhead than kprobes, and context parameters are available
with full type information. For a list of available, supported tracepoints, run the command
stap -L
'kernel.trace("*")'
. (
BZ#475456
1694
and
BZ#498040
1695
)
• A SystemTap initscript is now included with this release, and is provided by the package
systemtap-initscript
. This initscript allows users to run SystemTap scripts as system services
(in flight recorder mode) and control those scripts individually. For more information, refer to
/usr/
share/doc/systemtap-initscript- <version> /README.initscript
. (
BZ#474906
1696
and
BZ#481705
1697
)
• This update resolves a ref-count problem that prevented uprobes from properly disposing the
uprobe_process struct on exec while there are outstanding uretprobe instances. In addition, a bug
that caused utrace to incorrectly report events-in-progress to a recently-created engine is now
fixed as well. These fixes address several uretprobe bugs that could cause the system to hang in
previous releases. (
BZ#478711
1698
)
• SystemTap log rotation is now supported. With this, a running SystemTap script can switch to a
different log file during on-file flight recording without stopping. Users can specify a time or log
file size that triggers a log rotation, helping ensure that a SystemTap script never stops recording
information. (
BZ#481704
1699
)
•
stapprep.sh
is a script documented in the
SystemTap Beginner's Guide
, used to determine and
download (when able) the kernel information packages needed to run SystemTap. This script is now
included by default in the systemtap package as the command
stap-prep
. (
BZ#485498
1700
)
• When
stap
passed a kill signal to its children, it was possible for that signal to be sent to all other
processes in the same process group. This could include processes other than its children. This was
because SystemTap used
system()
to manipulate process groups. With this update, SystemTap
now uses
stap_system()
instead of
system()
; this allows
stap
to save the process ID of all its
children, ensuring that
stap
only sends signals to its children. (
BZ#494462
1701
)
• Probes that used
insn
probe points failed. While the upstream version of SystemTap fully supports
the use of
insn
probe points, the kernel and utrace versions used by Red Hat Enterprise Linux 5
did not define the required macros
arch_has_single_step()
and
arch_has_block_step()
.
With this release, SystemTap defines these macros during compile time whenever
insn
probe
points are used. (
BZ#498018
1702
)