Re: stap error: no match while resolving probe point kernel.function("do_mmap_pgoff@mm/mmap.c:901")

[Mark Wielaard <mjw at redhat dot com>]

Hi,

On Mon, 2010-02-22 at 11:27 +0800, a qi wrote:
>  ./t15.stp  --vp 01
> semantic error: libdw failure (dwarf_getsrc_file): no matching address range
> semantic error: no match while resolving probe point
> kernel.function("do_mmap_pgoff@mm/mmap.c:901")
> semantic error: no probes found
> [...]
> when I try to run  this simple stap script  which print the vaule of
> correct_wcount  ,
>
> # t15.stp
> probe kernel.function("do_mmap_pgoff@mm/mmap.c:901"){
>         printf("the correct_wcount is : %d\n ",$correct_wcount)
> }

Does it work when you don't put in a line number?
(my local kernel install doesn't have a correct_wcount variable)

If you need to try at a specific line, instead of at the function start,
then you might also try a kernel.statement probe instead of a
kernel.function probe.

> and here is the output of   'stap -l ' :
> stap -l 'kernel.function("do_mmap_pgoff@mm/mmap.c")'
> kernel.function("do_mmap_pgoff@mm/mmap.c:901")

Certainly odd. Locally I get:

$ stap -l 'kernel.function("do_mmap_pgoff@mm/mmap.c")'
kernel.function("do_mmap_pgoff@mm/mmap.c:928")

and probing at that explicit function/line does work:
$ stap -e 'probe kernel.function("do_mmap_pgoff@mm/mmap.c:928")
{ log(pp()); exit(); }'
kernel.function("do_mmap_pgoff@mm/mmap.c:928")

There was a fixlet in elfutils for dwarf_getsrc_file() some time back:

commit e23e9e7de7d070a47ef641abeaf272467a1cff4c
Author: Roland McGrath <roland@redhat.com>
Date:   Tue Jul 21 18:14:52 2009 -0700

    Fix dwarf_getsrc_file handling empty CUs.

But I don't know if that is related. You might want to check if using a
newer elfutils will help.

Cheers,

Mark