[Bug translator/17966] New: @defined always returns true in return probes

[Bug translator/17966] New: @defined always returns true in return probes

[aram.h at mgk dot ro]

https://sourceware.org/bugzilla/show_bug.cgi?id=17966

            Bug ID: 17966
           Summary: @defined always returns true in return probes
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
          Assignee: systemtap at sourceware dot org
          Reporter: aram.h at mgk dot ro
                CC: jistone at redhat dot com

@defined can't be used in return probes because it always returns 1.

stap -e 'probe process("bash").function("*").return {r0 = @defined($_r0) ? $_r0
: 0; printf ("r0: %d\n", r0); exit ()}'
WARNING: function _start return probe is blacklisted: keyword at <input>:1:1
 source: probe process("bash").function("*").return {r0 = @defined($_r0) ? $_r0
: 0; printf ("r0: %d\n", r0); exit ()}
         ^
semantic error: unresolved target-symbol expression: identifier '$_r0' at :1:67
        source: probe process("bash").function("*").return {r0 = @defined($_r0)
? $_r0 : 0; printf ("r0: %d\n", r0); exit ()}
                                                                               
  ^

Pass 2: analysis failed.  [man error::pass2]
: xgene:tmp;

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[Bug translator/17966] @defined always returns true in return probes

[aram.h at mgk dot ro]

https://sourceware.org/bugzilla/show_bug.cgi?id=17966

Aram Hăvărneanu <aram.h at mgk dot ro> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aram.h at mgk dot ro

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[Bug translator/17966] @defined always returns true in return probes

[jistone at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17966

Josh Stone <jistone at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|systemtap at sourceware dot org    |jistone at redhat dot com

--- Comment #1 from Josh Stone <jistone at redhat dot com> ---
I did suggest that's what going on, but it appears more subtle when I look
closer.

If I try process("bash").function("main").return, it gets this error.  I don't
have debuginfo installed for bash.

If I try process("stap").function("main").return, it works as expected.  I do
have debuginfo for my local stap.

In dwarf_var_expanding_visitor::visit_target_symbol, we have:

      // Everything else (pretty-printed vars, and context vars) require a
      // scope_die in which to search for them. If we don't have that, just
      // leave it unresolved; we'll produce an error later on.
      if (null_die(scope_die))
        {
          provide(e);
          return;
        }

The case without debuginfo will hit this and return without error, leaving
@defined undecided for the moment.  The case with debuginfo will get past this,
set an error on e directly, and cause @defined to be 0 right away, as desired.

So I need to figure out why the delayed case doesn't fix @defined later...

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