Re:

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

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
>>
>