[Bug tapsets/23738] New: c++ string access tapset

[Bug tapsets/23738] New: c++ string access tapset

[wcohen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23738

            Bug ID: 23738
           Summary: c++ string access tapset
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tapsets
          Assignee: systemtap at sourceware dot org
          Reporter: wcohen at redhat dot com
  Target Milestone: ---

The systemtap example script stap_time.stp needed to access C++ strings
provided inside the session variable to get the script name.

$ stap -L "stap.pass*"
stap.pass0 session:long $arg1:long
stap.pass1a session:long $arg1:long
stap.pass1b session:long $arg1:long
stap.pass2 session:long $arg1:long
stap.pass3 session:long $arg1:long
stap.pass4 session:long $arg1:long
stap.pass5 session:long $arg1:long
stap.pass6 session:long $arg1:long

Ended up with some ugly code like the following snippet to implement this:

    len = @cast(session, "struct
systemtap_session")->script_file->_M_string_length
    if (len <= 15) {
      script_file = @cast(session, "struct
systemtap_session")->script_file->_M_local_buf
    } else {
      script_file = @cast(session, "struct
systemtap_session")->script_file->_M_dataplus->_M_p
    }

There should be c++ string tapset like the existing access to traditional C
strings user_string() et al.

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[Bug tapsets/23738] c++ string access tapset

[wcohen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23738

--- Comment #1 from William Cohen <wcohen at redhat dot com> ---
There are differences between f28 and rhel7, so needed something like the
following on rhel7 for the code to work.

  // Dig through C++ string private fields to find the systemtap script name
  cmdline_script = @cast(session, "struct
systemtap_session")->cmdline_script->_M_dataplus->_M_p
  if (strlen(user_string2(cmdline_script, "<unavailable>"))){
    script = "<cmdline_script>"
  } else {
    script_file = @cast(session, "struct
systemtap_session")->script_file->_M_dataplus->_M_p
    script = user_string2(script_file, "<unavailable>")
  }

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[Bug tapsets/23738] c++ string access tapset

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23738

Frank Ch. Eigler <fche at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fche at redhat dot com
           Assignee|systemtap at sourceware dot org    |wcohen at redhat dot com

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