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

[Serguei Makarov <smakarov at redhat dot com>]

> 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.

Alright, that's more or less to be expected.

On Fedora and related systems, the "Pass 2: analysis failed" line would be followed by instructions to run a debuginfo-install for coreutils or somesuch package; depending on your distribution, there should be some other method of doing the same.

In any case, I should have picked a quick sanitycheck that doesn't depend on having a bunch of debuginfo installed, my apologies...

> 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 ?

Yes, exactly; when systemtap can't find debuginfo for one or more components examined by a probe, it issues the warning but proceeds to try to resolve the probe points anyways. Although, if it was an issue of building ./a.out without debug symbols, that warning should have been present in your original output, so there may be something else happening that I haven't put my finger on...

Anyhow, I'm glad to hear that uprobes seems to be functional on your machine. Now I'll just have to figure out how to fix the confusing error reporting so that other people don't trip over this in the future...

All the best,
     Serguei