Re: Segmentation Fault: Task died at uprobe probepoint

[fche at redhat dot com (Frank Ch. Eigler)]

Gaurav Dhiman <dimanuec@gmail.com> writes:

> [...]
> The following commit is on the head of the git log I have (I don't
> know how to get the exact systemtap version):
>
> commit b275171e26c0cf9441858209ac62e70b8ddda71d
> [...]

That's perfectly specific, thanks.

> [...]
> Following are the logs from the Pass 5 of the run with stap -vvvt
> -DDEBUG_UPROBES:
>
> Pass 5: starting run.
> [...]
> stapio:stp_main_loop:571 probe_start() returned 0
> stap_uprobe_change_plus:67: +uprobe spec 0 idx 0 process uprobe-test[25763] addr 0000000000400517 pp process("/home/gdhiman/tests/uprobe-test").function("test_func@/home/gdhiman/tests/uprobe-test.c:4")
> test begin!!
> test_func called!
> i=0x5
> stap_uprobe_change_minus:220: -uprobe spec 0 idx 0 process uprobe-test[25763] reloc 0000000000400517 pp process("/home/gdhiman/tests/uprobe-test").function("test_func@/home/gdhiman/tests/uprobe-test.c:4")
>
> The program receives a SIGSEGV signal at this point.

OK, something is wrong here.  See that -uprobe line?  It means stap
has for some reason determined that it's time to remove the uprobe,
but that should not happen until either the script or the target
program exits.

This will make things more verbose, but could you try adding
-DDEBUG_TASK_FINDER and -DDEBUG_TASK_FINDER_VMA to the stap
command line? 


> By the probe target executable do you mean, the .ko file that is
> generated? The disassembled file of that is pretty big, close to 17000
> lines. Do you want that or something else?

I meant the uprobe-test binary, just to see what instructions were
in the vicinity of the test_func function.  Just that area.


- FChE