Listing probe alias resolution failures

[patm@pdx.edu]

Quoting David Smith <dsmith@redhat.com>:

> patm@pdx.edu wrote:
>> Quoting David Smith <dsmith@redhat.com>:
>>> The only thing that doesn't work is:
>>>
>>> # stap -p2 -u -e 'probe syscall.compat_getitimer {}'
>>>
>>> So, the only error I get is when I explicitly list the system call that
>>> doesn't exist on my current arch and kernel.  I could see where if you
>>> were writing a script targeting either multiple architectures or
>>> multiple kernel versions that might bother you.  However, the solution
>>> is easy - make that probe optional:
>>>
>>> # stap -p2 -u -e 'probe syscall.compat_getitimer ? { }'
>>
>> Very nice, I had no idea that you could do this to a probe alias.   
>> But, and I don't know if this is intended or not, it still fails on  
>>  certain errors:
>>
>> $ stap -p2 -u -e 'probe vm.mmap ? { }'
>> semantic error: failed to retrieve location attribute for local   
>> 'addr' (dieoffset: 0xb84881): identifier '$addr' at
>
> Hmm.
>
> Here I've got good news and bad news.  The good news is that if you
> take away the '-u', then your example works (since the optimizer
> removes references to the variables that aren't read).
>
> The bad news is that if you reference the local variable version of the
> function's parameters in your optional probe, it errors out, like this:
>
> # stap -p2 -e 'probe vm.mmap ? { printf("%p %d\n", address, length) }'
> semantic error: failed to retrieve location attribute for local 'addr'
> (dieoffset: 0xbf6524): identifier '$addr' at
> /usr/local/share/systemtap/tapset/memory.stp:118:15
> ...
>
> Here it seems like we should be able to discard the probe before trying
> to look up its parameters.
>
> Could you file a bugzilla on this so we don't forget to look at this?

I'll file a bug later today. Also, I have found some probes that don't  
seem to behave correctly when used with that conditional (?) :

$ stap -p2 -u -e 'probe syscall.compat_sys_times {}'
...mismatch...cannot resolve probe point syscall.compat_sys_times

$ stap -p2 -u -e 'probe syscall.compat_sys_times? {}'
...mismatch...cannot resolve probe point syscall.compat_sys_times

Mostly syscall probes, especially syscall.compat_* , and  
signal.handle_stop is another example.