Comment 0 for bug 669641

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.