Re: How to use systemtap with linux 3.5 userspace probes ?

[David Cournapeau <cournape at gmail dot com>]

On Wed, Aug 22, 2012 at 3:32 PM, Serguei Makarov <smakarov@redhat.com> wrote:
> Hello David,
>
>>> I was expecting to be able to use the same dysp probes as with the
>>> utrace patches, but trying a simple stap scripts such as:
>>>
>>> probe process("./a.out").function("foo")
>>> { printf("hello\n"); }
>>> fails to run:
>>>
>>> semantic error: while resolving probe point [...]
>
> Thanks for pointing this out -- this is evidently a new problem since 1.8.
>
> I found myself getting the same error, which makes it less likely that the issue is configuration-dependent. Two questions to verify:
>
> - have you tried running
>
> # stap -e 'probe process("/bin/ls").function("main") { printf("hello\n"); }'
>
> to see if that fails as well? (If it fails, you have a different issue from what I think you have...)

Yes, I get this message:

WARNING: cannot find module /bin/ls debuginfo: No DWARF information found
semantic error: while resolving probe point: identifier 'process' at <input>:1:7
        source: probe process("/bin/ls").function("main") { printf("hello\n"); }
                      ^

semantic error: no match
Pass 2: analysis failed.  Try again with another '--vp 01' option.

>
> - basically, does the process ./a.out in question actually have a function foo() defined?

So following your remark and the previous error, I rebuild my small
program with debug symbols, and it worked ! Could the error with ls be
due to the lack of debugging info causing systemtap to generate the
same kind of errors as a missing function ?

David