Re: Systemtap user space probing issue - Unknown symbol in module

[buddhika chamith <chamibuddhika at gmail dot com>]

Thanks. So I tried the following. The basic call that you've given
works (I was also able to get a similar one working before).

# stap -ve 'probe begin { printf("hello world\n"); exit() }'

Pass 1: parsed user script and 113 library scripts using
65884virt/29736res/4868shr/25512data kb, in 170usr/10sys/176real ms.
Pass 2: analyzed script: 1 probe, 1 function, 0 embeds, 0 globals
using 66676virt/31068res/5444shr/26304data kb, in 0usr/0sys/3real ms.
Pass 3: using cached
/u/budkahaw/.systemtap/cache/36/stap_3678792131e4a93931146ace8f2569d0_1020.c
Pass 4: using cached
/u/budkahaw/.systemtap/cache/36/stap_3678792131e4a93931146ace8f2569d0_1020.ko
Pass 5: starting run.
hello world
Pass 5: run completed in 0usr/40sys/367real ms.




But the next one fails. Missing kernel symbols?

# stap -ve 'probe nd_syscall.read { printf("hello world\n"); exit() }'

WARNING: Kernel function symbol table missing [man warning::symbols]
Pass 1: parsed user script and 113 library scripts using
65884virt/29804res/4936shr/25512data kb, in 130usr/0sys/132real ms.
semantic error: while resolving probe point: identifier 'kprobe' at
/opt/systemtap/3.0/share/systemtap/tapset/linux/nd_syscalls2.stp:1021:27
        source: probe __nd_syscall.read = kprobe.function("sys_read")
                                          ^

semantic error: no match

semantic error: while resolving probe point: identifier '__nd_syscall'
at :1011:2
        source: __nd_syscall.read
                ^

semantic error: no match

semantic error: while resolving probe point: identifier 'nd_syscall'
at <input>:1:7
        source: probe nd_syscall.read { printf("hello world\n"); exit() }
                      ^

semantic error: no match

Pass 2: analyzed script: 0 probes, 0 functions, 0 embeds, 0 globals
using 66676virt/31136res/5512shr/26304data kb, in 0usr/0sys/3real ms.
Pass 2: analysis failed.  [man error::pass2]




Interestingly the call # stap -vL 'process("./h264ref").function("*")'
seem to be working with it spitting out some information on probe
points. I am building this with debugging symbols.

Thanks



On Mon, Jul 18, 2016 at 2:11 PM, David Smith <dsmith@redhat.com> wrote:
> On 07/18/2016 05:58 AM, buddhika chamith wrote:
>> Hi All,
>>
>> Not sure if this has been addressed before. Checked the archive and
>> couldn't find a solution there. I tried user space probing with
>> Systemtap 3.0. But it gives me the following error.
>>
>> $ sudo stap -e 'probe process("./h264ref").function("*") { printf("hello\n"); }'
>> ERROR: Couldn't insert module
>> '/tmp/stapsPVPF2/stap_b964ab648506800b700ce82c4e1cf5cd_167937.ko':
>> Unknown symbol in module
>> WARNING: /usr/bin/staprun exited with status: 1
>> Pass 5: run failed.  [man error::pass5]
>> Tip: /usr/share/doc/systemtap/README.Debian should help you get started.
>
> ... stuff deleted ...
>
>> What do I need to do in order to fix this?
>
> The first thing to try would be to see if your systemtap installation
> can run simple systemtap scripts. The error you see of "Unknown symbol
> in module" makes me doubt that it can. Can you look in your kernel logs
> to see if the unknown symbol is actually listed?
>
> Let's try the most basic systemtap script possible:
>
> # stap -ve 'probe begin { printf("hello world\n"); exit() }'
>
> Let's try a bit more challenging script:
>
> # stap -ve 'probe nd_syscall.read { printf("hello world\n"); exit() }'
>
> If those 2 scripts work, then we'll look at your executable you are
> trying to probe. Was your 'h264ref' executable compiled with debugging
> info (-g)?
>
> Try the following:
>
> # stap -vL 'process("./h264ref").function("*")'
>
> --
> David Smith
> dsmith@redhat.com
> Red Hat
> http://www.redhat.com
> 256.217.0141 (direct)
> 256.837.0057 (fax)