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Re:


STAP runtime flag "-d MODULE" can potentially expose the external
symbols in the module. I have never tried to use it.

On Sun, Jul 30, 2017 at 10:26 AM, Arkady <arkady.miasnikov@gmail.com> wrote:
> See 6.3 in https://www.kernel.org/doc/Documentation/kbuild/modules.txt
>  for intricate details. The bottom line is that STAP builds modules in
> a specific environment which can not be easily (or at least I do not
> know how to) controlled.
>
> On Sun, Jul 30, 2017 at 10:17 AM, Arkady <arkady.miasnikov@gmail.com> wrote:
>> This link can be relevant
>> https://stackoverflow.com/questions/33718358/insmod-fails-with-unknown-symbol-in-module-for-a-symbol-defined-in-another-mod
>>
>> On Sun, Jul 30, 2017 at 10:09 AM, Arkady <arkady.miasnikov@gmail.com> wrote:
>>> Daniel,
>>>
>>> STAP attempts to compile the kernel module against the kernel source
>>> tree installed in the system. One way to resolve the issue is to
>>> update the kernel source tree installed in the system. Without
>>> updating the kernel sources the compilation will fail.
>>>
>>> On Sun, Jul 30, 2017 at 9:56 AM, Daniel Doron <danielmeirdoron@gmail.com> wrote:
>>>> Hi,
>>>>
>>>> How is systemtap's kernel module different from other modules?
>>>> Given module A which exports a function and module B using that exported
>>>> function and A is insmodded before B, I have not seen any problem. Why is
>>>> Systemtap's KO different? Is it not the kernel's job to resolve the exported
>>>> symbol?
>>>>
>>>>
>>>> Daniel.
>>>>
>>>> On Thu, 27 Jul 2017 at 19:29 Arkady <arkady.miasnikov@gmail.com> wrote:
>>>>>
>>>>> P.S.1 There is yet another way - very cool way - to to add a symbol to
>>>>> the stap script - via /sys/kernel/debug/systemtap/<module name>/.cmd
>>>>> (CTL_CHANNEL_NAME below)
>>>>>
>>>>> This is a Python sample
>>>>>
>>>>> def write_relocate_string(f, s, size):
>>>>>     f.write(s)
>>>>>     padding = size - len(s)
>>>>>     for _ in range(padding):
>>>>>         f.write('\x00')
>>>>>
>>>>> def write_relocate(module_name, symbol_name, address):
>>>>>     STP_MODULE_NAME_LEN = 128
>>>>>     STP_SYMBOL_NAME_LEN = 128
>>>>>
>>>>>     with open(CTL_CHANNEL_NAME, "wb") as f:
>>>>>     # STAP_RELOCATE (9)
>>>>>         f.write(struct.pack('<I', 9))
>>>>>         write_relocate_string(f, module_name, STP_MODULE_NAME_LEN)
>>>>>         write_relocate_string(f, symbol_name, STP_SYMBOL_NAME_LEN)
>>>>>         f.write(struct.pack('<Q', address))
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Jul 27, 2017 at 7:20 PM, Arkady <arkady.miasnikov@gmail.com>
>>>>> wrote:
>>>>> > P.S. Another idea is to use kernel IPC instead of function calls.
>>>>> > Files, named pipes, sockets, memory mapped files - just about anything
>>>>> > can do the trick.
>>>>> >
>>>>> > On Thu, Jul 27, 2017 at 7:03 PM, Arkady <arkady.miasnikov@gmail.com>
>>>>> > wrote:
>>>>> >> Eyal,
>>>>> >>
>>>>> >> Utility stap employs the kernel debug information installed in the
>>>>> >> system. When you load a module command insmod does not update the
>>>>> >> kernel debug info. There are simple two ways to resolve the issue
>>>>> >> *  Load the module, get the address of the function foo using
>>>>> >> /proc/kallsyms, provide the address of the foo as an argument to the
>>>>> >> STAP script.
>>>>> >> *  Link the module statically with the kernel and update the
>>>>> >> kernel-debuginfo
>>>>> >>
>>>>> >> Arkady
>>>>> >>
>>>>> >> On Thu, Jul 27, 2017 at 5:47 PM, Eyal Yehuda via systemtap
>>>>> >> <systemtap@sourceware.org> wrote:
>>>>> >>>
>>>>> >>>
>>>>> >>> hello
>>>>> >>>
>>>>> >>> The
>>>>> >>>  issue I am facing is of undefined symbols in system tap kernel module
>>>>> >>> when trying to link to another kernel module with exported symbol
>>>>> >>>
>>>>> >>> please note environment setup:
>>>>> >>> os:  debian 9 stretch 64bit
>>>>> >>> kernel version:  4.9.0-3-amd64
>>>>> >>>
>>>>> >>>
>>>>> >>>           I created the following simple systemtap script using guru
>>>>> >>> mode
>>>>> >>>
>>>>> >>>           system tap script:      temp.stp
>>>>> >>>
>>>>> >>>
>>>>> >>>          %{
>>>>> >>>                  extern int foo(void);
>>>>> >>>          %}
>>>>> >>>
>>>>> >>>           function call_foo:long() %{/* pure */
>>>>> >>>                   STAP_RETVALUE = foo();
>>>>> >>>          %}
>>>>> >>>
>>>>> >>>           probe syscall.open {
>>>>> >>>                  printf("foo() : %d\n",  call_foo())
>>>>> >>>           }
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>  In addition to that I created the following simple kernel module with
>>>>> >>> an exported symbol function to be used from inside system tap
>>>>> >>> script
>>>>> >>>
>>>>> >>>          kernel module:       xxx.c
>>>>> >>>
>>>>> >>>          #include <linux/kernel.h>
>>>>> >>>          #include <linux/module.h>
>>>>> >>>          #include <linux/printk.h>
>>>>> >>>
>>>>> >>>          static int foo(void){
>>>>> >>>                  pr_info("foo()\n"); return 0;
>>>>> >>>          }
>>>>> >>>          EXPORT_SYMBOL(foo);
>>>>> >>>
>>>>> >>>          static int __init xxx_init(void){
>>>>> >>>                 pr_info("xxx_init()\n");
>>>>> >>>            return 0;
>>>>> >>>          }
>>>>> >>>
>>>>> >>>          static void __exit xxx_exit(void){
>>>>> >>>                 pr_info("xxx_exit() \n");
>>>>> >>>          }
>>>>> >>>
>>>>> >>>          module_init(xxx_init);
>>>>> >>>          module_exit(xxx_exit);
>>>>> >>>          MODULE_LICENSE("GPL");
>>>>> >>>
>>>>> >>>
>>>>> >>>          After compiling the kernel module and insmoding it, I run the
>>>>> >>> command to compile systemtap script as follow:
>>>>> >>>          stap -gk -v temp.stp
>>>>> >>>
>>>>> >>>          the compilation command result with the following error:
>>>>> >>>
>>>>> >>>
>>>>> >>>  Pass 1: parsed user script and 465 library scripts using
>>>>> >>> 113912virt/46752res/6476shr/40564data kb, in 110usr/20sys/124real ms.
>>>>> >>>
>>>>> >>>  Pass 2: analyzed script: 2 probes, 2 functions, 99 embeds, 0 globals
>>>>> >>> using 165912virt/100212res/7716shr/92564data kb, in
>>>>> >>> 680usr/50sys/731real
>>>>> >>>  ms.
>>>>> >>>
>>>>> >>>  Pass 3: translated to C into "/tmp/stapzKUZ11/stap_1837_src.c" using
>>>>> >>> 165912virt/100404res/7908shr/92564data kb, in 10usr/10sys/9real ms.
>>>>> >>>          WARNING: "foo" [/tmp/stapzKUZ11/stap_1837.ko] undefined!
>>>>> >>>          Pass 4: compiled C into "stap_1837.ko" in
>>>>> >>> 1410usr/120sys/1963real ms.
>>>>> >>>          Pass 5: starting run.
>>>>> >>>          ERROR: Couldn't insert module '/tmp/stapzKUZ11/stap_1837.ko':
>>>>> >>> Invalid parameters
>>>>> >>>          WARNING: /usr/bin/staprun exited with status: 1
>>>>> >>>          Pass 5: run completed in 0usr/0sys/16real ms.
>>>>> >>>          Pass 5: run failed.  [man error::pass5]
>>>>> >>>          Tip: /usr/share/doc/systemtap/README.Debian should help you
>>>>> >>> get started.
>>>>> >>>          Keeping temporary directory "/tmp/stapzKUZ11"
>>>>> >>>
>>>>> >>>
>>>>> >>>          in dmesg I can see the following lines
>>>>> >>>
>>>>> >>>          Jul 27 03:56:14 debian9 kernel: [ 3938.166906] stap_2230: no
>>>>> >>> symbol version for foo
>>>>> >>>          Jul 27 03:56:14 debian9 kernel: [ 3938.166908] stap_2230:
>>>>> >>> Unknown symbol foo (err -22)
>>>>> >>>
>>>>> >>>
>>>>> >>>          I also checked /proc/kallsyms
>>>>> >>>
>>>>> >>>
>>>>> >>>          cat /proc/kallsyms | grep xxx
>>>>> >>>          ffffffffc0584000 T foo    [xxx]
>>>>> >>>          ffffffffc0584014 t xxx_exit    [xxx]
>>>>> >>>          ffffffffc0585030 r __ksymtab_foo    [xxx]
>>>>> >>>          ffffffffc058506e r __kstrtab_foo    [xxx]
>>>>> >>>          ffffffffc0585040 r __kcrctab_foo    [xxx]
>>>>> >>>          ffffffffc0586000 d __this_module    [xxx]
>>>>> >>>          ffffffffc0584014 t cleanup_module    [xxx]
>>>>> >>>
>>>>> >>>
>>>>> >>> Please advice
>>>>> >>> 1.
>>>>> >>>  what should i do in addition to solve this issue as I must create an
>>>>> >>> interaction between systemtap script and another kernel module
>>>>> >>> 2.
>>>>> >>>  In case this is not feasible can u please offer another alternative
>>>>> >>> to
>>>>> >>> make systemtap script use another kernel module services ?
>>>>> >>>
>>>>> >>> Thanks eyal yehuda
>>>>>
>>>>


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