** No longer affects: linux (Ubuntu Lucid)
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https://bugs.launchpad.net/bugs/669641
Title:
systemtap fails to discover installed debug modules
Status in Linaro Ubuntu Engineering Builds:
Fix Released
Status in “linux” package in Ubuntu:
Fix Released
Status in “linux” source package in Precise:
Fix Released
Status in “linux” source package in Quantal:
Fix Released
Status in “linux-2.6” package in Debian:
Fix Released
Bug description:
== Precise SRU Justification ==
Impact: When using systemtap with Ubuntu kernels, the proper debug
modules cannot be automatically discovered.
== Fix ==
This fix allows for the build system to insert the .gnu_debuglink
sections in the .ko files pointing to the full unstripped .ko in
/usr/lib/debug/.. in the dbgsym ddebs. In addition there are checks to
ensure the debug symbol actually exists before creating the
.gnu_debuglink section.
== Testcase ==
1) Install systemtap.
2) Run "stap -l 'module("serio_raw").function("*")'"
3) This should show list all the probe points for that module.
--
Binary package hint: systemtap
Even if the proper debug symbols are installed:
# stap -l 'kernel.function("acpi_*")' | sort
will succeed
and this will fail.
# stap -l 'module("ohci1394").function("*")' | sort
Now there's no shortage of blogs and wikis on how to work
around this but no one has seemingly ever investigated the root
cause. If one were to run this through strace you would find
the following.
open("/usr/lib/debug/.build-id/3b/6eb5a0f22ba2bc92c3c3f1fcb14fe7f31f3807.debug",
O_RDONLY) = -1 ENOENT (No such file or directory)
open("/lib/modules/2.6.32-25-generic/kernel/drivers/ieee1394/ohci1394.ko.debug",
O_RDONLY) = -1 ENOENT (No such file or directory)
open("/lib/modules/2.6.32-25-generic/kernel/drivers/ieee1394/.debug/ohci1394.ko.debug",
O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/lib/debug/lib/modules/2.6.32-25-generic/kernel/drivers/ieee1394/ohci1394.ko.debug",
O_RDONLY) = -1 ENOENT (No such file or directory)
open("/lib/modules/2.6.32-25-generic/kernel/drivers/ieee1394/build/ohci1394.ko.debug",
O_RDONLY) = -1 ENOENT (No such file or directory)
Note that the path is correct, it's the name of the KO that stap is expecting
that is wrong,
Kernel debug symbols provided by Ubuntu are unstripped yet maintain the .ko
extension,
systemtap (actually libelf/elfutils) is expecting the filename to be
module.ko.debug.
After discussing this on #systemtap on Freenode, the following script was
proposed to
generate a symlink tree, by build id, in /usr/lib/debug, with the proper
extension. This
completely solves the issue, and is also of benefit to things like gdb and
oprofile.
#!/bin/sh
for file in `find /usr/lib/debug -name '*.ko' -print`
do
buildid=`eu-readelf -n $file| grep Build.ID: | awk '{print $3}'`
dir=`echo $buildid | cut -c1-2`
fn=`echo $buildid | cut -c3-`
mkdir -p /usr/lib/debug/.build-id/$dir
ln -s $file /usr/lib/debug/.build-id/$dir/$fn
ln -s $file /usr/lib/debug/.build-id/$dir/${fn}.debug
done
If we could integrate this into the ddeb postinstall script, the problem would
be solved.
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