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Re: How to track the functions in self-written module using SystemTap?


Hi David,

> (1)
> I see I didn't explain well here. Once you copied your module to the
> kernel's module directory, systemtap no longer would need a full path to
> the module name - just "kex" should have worked.

Yeah, it worked!

> (2)
> Hmm, it could mean that we just need to make sure that the debuginfo is
> loaded. Try adding the '-d  /root/kernel/105.ops/kex.ko' option to the
> stap command line. (The '-d' option asks stap to load the symbol/unwind
> information for a module even if stap doesn't think it needs it.)

The output stills have error:

# stap -d /root/kernel/105.ops/kex.ko -v -e 'probe
module("/root/kernel/105.ops/kex.ko").function("*") { printf("%s\n",
print_backtrace()) }'
Pass 1: parsed user script and 110 library script(s) using
220072virt/37580res/3088shr/34880data kb, in 150usr/10sys/162real ms.
Pass 2: analyzed script: 6 probe(s), 1 function(s), 0 embed(s), 0
global(s) using 221348virt/39612res/3832shr/36156data kb, in
20usr/60sys/114real ms.
Pass 3: translated to C into
"/tmp/stap2MezRE/stap_6395070fd6c3c139709af3ecba82092d_2576_src.c"
using 221360virt/40108res/4196shr/36168data kb, in 10usr/50sys/66real
ms.
Pass 4: compiled C into
"stap_6395070fd6c3c139709af3ecba82092d_2576.ko" in
2280usr/540sys/5099real ms.
Pass 5: starting run.
WARNING: no or bad debug frame hdr
WARNING: No binary search table for debug frame, doing slow linear
search for /root/kernel/105.ops/kex.ko
 0xffffffffa0037000 : kex_init+0x0/0x0 [kex]
 0xffffffff810020e8 (inexact)
 0xffffffff810ed4ae (inexact)
 0xffffffff81316880 (inexact)
 0xffffffff810e9743 (inexact)
 0xffffffff810ede66 (inexact)
 0xffffffff81645909 (inexact)

 0xffffffffa03d70c4 : kex_cleanup+0x0/0x0 [kex]
 0xffffffff810eb23b (inexact)
 0xffffffff81641113 (inexact)
 0xffffffff81014b12 (inexact)
 0xffffffff81645909 (inexact)

Thanks!
Best Regards
Nan Xiao


On Fri, Dec 4, 2015 at 8:15 PM, David Smith <dsmith@redhat.com> wrote:
> On 12/04/2015 03:56 AM, Nan Xiao wrote:
>> Hi Dave,
>>
>>> It looks like you've got a couple of options:
>>
>>> 1) Copy your module into the kernel module tree (located at
>>> /lib/modules/`uname -r`/kernel) to use systemtap on it.
>>
>> I copy "kex.ko" into /lib/modules/`uname -r`/kernel, and it always
>> executes error:
>>
>> # cd /lib/modules/`uname -r`/kernel
>> # pwd
>> /lib/modules/3.10.0-123.el7.x86_64.debug/kernel
>> # ls
>> arch  crypto  drivers  fs  kernel  kex.ko  lib  mm  net  sound
>>
>> # stap -v -e 'probe
>> module("/lib/modules/3.10.0-123.el7.x86_64.debug/kernel/kex.ko").function("*")
>> { printf("%s\n", ppfunc()) }'
>> Pass 1: parsed user script and 103 library script(s) using
>> 214092virt/31440res/3036shr/29032data kb, in 160usr/60sys/226real ms.
>> semantic error: while resolving probe point: identifier 'module' at <input>:1:7
>>         source: probe
>> module("/lib/modules/3.10.0-123.el7.x86_64.debug/kernel/kex.ko").function("*")
>> { printf("%s\n", ppfunc()) }
>>                       ^
>>
>> semantic error: no match
>> Pass 2: analyzed script: 0 probe(s), 0 function(s), 0 embed(s), 0
>> global(s) using 372028virt/33024res/3412shr/30124data kb, in
>> 20usr/770sys/804real ms.
>> Pass 2: analysis failed.  [man error::pass2]
>>
>> # stap -v -e 'probe module("kex.ko").function("*") { printf("%s\n",
>> ppfunc()) }'                                    Pass 1: parsed user
>> script and 103 library script(s) using
>> 214096virt/31432res/3036shr/29036data kb, in 140usr/60sys/209real ms.
>> semantic error: while resolving probe point: identifier 'module' at <input>:1:7
>>         source: probe module("kex.ko").function("*") { printf("%s\n",
>> ppfunc()) }
>>                       ^
>>
>> semantic error: no match
>> Pass 2: analyzed script: 0 probe(s), 0 function(s), 0 embed(s), 0
>> global(s) using 372032virt/33016res/3412shr/30128data kb, in
>> 40usr/880sys/929real ms.
>> Pass 2: analysis failed.  [man error::pass2]
>
> I see I didn't explain well here. Once you copied your module to the
> kernel's module directory, systemtap no longer would need a full path to
> the module name - just "kex" should have worked.
>
>>> 2) Upgrade systemtap to at least 2.6. (I ran systemtap 2.6 on a RHEL 7.1
>>> system, and the modules_out_of_tree.exp test case passed there.)
>>
>> I install the RHEL 7.2, and it really works! But it can't print actual
>> stack traces:
>>
>> # stap -e 'probe module("/root/kernel/105.ops/kex.ko").function("*") {
>> print_backtrace() }'
>> WARNING: no or bad debug frame hdr
>> WARNING: No binary search table for debug frame, doing slow linear
>> search for /root/kernel/105.ops/kex.ko
>>  0xffffffffa006b000 : kex_init+0x0/0x0 [kex]
>>  0xffffffff810020e8 (inexact)
>>  0xffffffff810ed4ae (inexact)
>>  0xffffffff81316880 (inexact)
>>  0xffffffff810e9743 (inexact)
>>  0xffffffff810ede66 (inexact)
>>  0xffffffff81645909 (inexact)
>>  0xffffffffa02600c4 : kex_cleanup+0x0/0x0 [kex]
>>  0xffffffff810eb23b (inexact)
>>  0xffffffff81641113 (inexact)
>>  0xffffffff81014b12 (inexact)
>>  0xffffffff81645909 (inexact)
>>
>> So it means the module isn't built with debuginfo, right?
>
> Hmm, it could mean that we just need to make sure that the debuginfo is
> loaded. Try adding the '-d  /root/kernel/105.ops/kex.ko' option to the
> stap command line. (The '-d' option asks stap to load the symbol/unwind
> information for a module even if stap doesn't think it needs it.)
>
> --
> David Smith
> dsmith@redhat.com
> Red Hat
> http://www.redhat.com
> 256.217.0141 (direct)
> 256.837.0057 (fax)


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