Re:

[Arkady <arkady dot miasnikov at gmail dot com>]

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