doc/man/tracef-tracelog-limitations.txt

   1 The +{macro-name}()+ and +v{macro-name}()+ utility macros were
   2 developed to make user space tracing super simple, albeit with notable
   3 disadvantages compared to custom, full-fledged tracepoint providers:
   4
   5   * All generated events have the same provider/event names.
   6   * There's no static type checking.
   7   * The only event field with user data you actually get, named `msg`,
   8     is a string potentially containing the values you passed to the
   9     macro using your own format. This also means that you cannot use
  10     filtering using a custom expression at run time because there are no
  11     isolated fields.
  12   * Since +{macro-name}()+ and +v{macro-name}()+ use C standard
  13     library's man:vasprintf(3) function in the background to format the
  14     strings at run time, their expected performance is lower than using
  15     custom tracepoint providers with typed fields, which do not require
  16     a conversion to a string.
  17   * Generally, a string containing the textual representation of the
  18     user data fields is not as compact as binary fields in the resulting
  19     trace.
  20
  21 Thus, +{macro-name}()+/+v{macro-name}()+ are useful for quick
  22 prototyping and debugging, but should not be considered for any
  23 permanent/serious application instrumentation.
  24
  25 +v{macro-name}()+ does not have a `STAP_PROBEV()` call, because
  26 `STAP_PROBEV()` does not support `va_list`. If you need it, you should
  27 emit this call yourself.
  28
  29 See man:lttng-ust(3) to learn more about custom tracepoint providers.