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From: "mcermak at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sourceware.org
Subject: [Bug translator/14924] warn on complex $ptr->foo expressions in .return probes
Date: Fri, 11 Nov 2016 12:17:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D14924

--- Comment #8 from Martin Cermak <mcermak at redhat dot com> ---
Created attachment 9622
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D9622&action=3Dedit
possible patch

(In reply to Frank Ch. Eigler from comment #7)
> IMHO, we should warn even for plain  .return {$var}  constructs

Attached patch does that. I've -p2'd all the return probes and it looks fine
except one problem: For example:

Probe signal.send.return is only defined in the tapset for systemtap_v <=3D
"2.1".  So, when a user runs modern stap without --compatible, and her scri=
pt
refers to probe signal.send.return, then this probe gets constructed using
probe signal.send, which actually is defined in the tapset. But since it is=
 an
"entry" probe used as a "return" probe, the translator shows misleading war=
ning
like this:

=3D=3D=3D=3D=3D=3D=3D
$ stap --poison-cache  -e "probe signal.send.return {exit()}"  -p2 >/dev/nu=
ll
WARNING: confusing usage, consider @entry($t) in .return probe: identifier =
'$t'
at /usr/local/share/systemtap/tapset/linux/signal.stp:76:28
 source:     task =3D @choose_defined($t, $p)
[ ... stuff deleted ... ]
=3D=3D=3D=3D=3D=3D=3D

Let's list the linux/signal.stp:76 neighbourhood:

=3D=3D=3D=3D=3D=3D=3D
  73 probe __signal.send.send_sigqueue =3D kernel.function("send_sigqueue")=
=20=20=20=20=20=20=20
  74 {=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20
  75     name =3D "send_sigqueue"=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20
  76     task =3D @choose_defined($t, $p)=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20
  77     sig =3D @choose_defined($q->info->si_signo, $sig)=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  78     sinfo =3D @choose_defined($q->info, 0)=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20
  79     shared =3D 0=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  80 %( systemtap_v <=3D "2.1" %?=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20
  81     send2queue =3D 1=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  82 %)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20
  83 }
=3D=3D=3D=3D=3D=3D=3D

So, that's misleading, since adding @entry() there would break the probe.

--=20
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