[issue13405] Add DTrace probes

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

> So, yes. The code is intrusive. The code deals with a lot of internal
> machinery (PEP393 support in the ustack helper was quite difficult).
> It is going to break from time to time, sure. At the same time, I am
> committed to support it. And even if it is dropped in 3.4, no Python
> program will be affected.

To ease the concerns, I think you should make it so that dtrace-specific
code gets out of the way as much as possible.
I suggest you create a Python/ceval-dtrace.h header and put most
dtrace-specific code from ceval.c there. Its inclusion should be
conditional on WITH_DTRACE so that other core devs can ignore its
presence.

A couple other comments:
- in the makefile, DTRACEOBJS is inconsistent with DTRACE_STATIC and
LIBRARY_OBJS. You should make it DTRACE_OBJS.
- please add comments at the top of whatever header files you add, to
make it clear that they are dtrace-specific. Mentions of "ustack helper"
are a bit too specific to be helpful.
- some code lacks error checking, e.g. when calling PyUnicode_AsUTF8.
- is co_linenos ever freed or is it a memory leak?
- your indices and offsets should be Py_ssize_t, not int
- is an empty dtrace module really needed? a flag variable in the sys
module should be enough
- as you can see the Makefile uses "-rm -f", you should probably do the
same instead of "rm -f"
- you have a rather strange "if true" in your configure.in additions

Thanks in advance.

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