DTrace fixes for node.js

[Fedor Indutny]

Mark,

Yes, 271413 is the one fixing PROGBITS. Anyway, my patch should
support both PROGBITS and DOFW_sun, making it quite universal.

Thank you for your time!

Fedor.

On Tue, Dec 2, 2014 at 12:54 AM, Mark Johnston <markj at freebsd.org> wrote:

> On Mon, Dec 01, 2014 at 04:59:02PM +0400, Fedor Indutny wrote:
> > Hello Mark, DTrace people!
> >
>
> Hi Fedor,
>
> > Hope you are doing well.
> >
> > Looks like FreeBSD 10.1 decided to play some not that funny games
> > with drti.c again :)
> >
> > I have submitted a [patch][0] as a problem report.
>
> Thank you. I'll test and commit it if I don't run into any problems.
>
> >
> > It fixes iteration over aligned DOFs, and accounts for a
> > non-master-branch FreeBSD stuff in:
> >
> > cddl/contrib/opensolaris/lib/libdtrace/common/dt_link.c
> >
> > Which is currently producing SHT_PROGBITS section instead of
> > expected SHT_SUNW_dof, thus confusing the drti.c file.
>
> Hm, are you referring to this change:
> https://svnweb.freebsd.org/base?view=revision&revision=271413
> ?
>
> I'm a bit confused, as it hasn't been merged to 10 yet: it exposed
> another dtrace bug that caused build failures in some USDT-enabled
> ports, so I'm waiting for the subsequent fixes to settle.
>
> -Mark
>
> >
> > Thank you,
> > Fedor.
> >
> > [0]: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=195555
> >
> >
> > On Thu, Feb 27, 2014 at 6:50 PM, Fedor Indutny <fedor at indutny.com>
> wrote:
> >
> > > Update sent, thank you!
> > >
> > > On Thu, Feb 27, 2014 at 6:39 PM, Mark Johnston <markj at freebsd.org>
> wrote:
> > > > On Thu, Feb 27, 2014 at 3:30 AM, Fedor Indutny <fedor at indutny.com>
> > > wrote:
> > > >> Mark,
> > > >>
> > > >> Thanks for looking into this. I just tried your patch and it (no
> > > >> surprise) builds fine. Node.js DOF symbols seems to be resolving
> > > >> properly too!
> > > >>
> > > >> Do you want me to squash this changes into my patch, and post them
> on
> > > >> that ticket?
> > > >>
> > > >
> > > > That would be good, thanks. When I have some time I'll do more
> testing
> > > > and commit the change.
> > > >
> > > > -Mark
> > > >
> > > >> On Thu, Feb 27, 2014 at 9:01 AM, Mark Johnston <markj at freebsd.org>
> > > wrote:
> > > >>> On Tue, Feb 25, 2014 at 06:16:15PM +0400, Fedor Indutny wrote:
> > > >>>> Hello devs!
> > > >>>>
> > > >>>> I have made some fixes to fix DTrace support for node.js in
> FreeBSD:
> > > >>>>
> > > >>>> * http://www.freebsd.org/cgi/query-pr.cgi?pr=186821
> > > >>>> * http://www.freebsd.org/cgi/query-pr.cgi?pr=187027
> > > >>>>
> > > >>>> Here is a blog post with a bit of explanation of why this is
> needed
> > > >>>> and what is fixed: https://blog.indutny.com/7.freebsd-dtrace
> > > >>>>
> > > >>>> Please let me know if I could be any help in reviewing it.
> > > >>>
> > > >>> Hi Fedor,
> > > >>>
> > > >>> The DOF limit change looks fine to me. I note that the illumos guys
> > > have
> > > >>> just pushed a change to illumos-gate which bumps
> dtrace_dof_maxsize,
> > > but
> > > >>> it's good to have the sysctl as well.
> > > >>>
> > > >>> The drti change looks mostly good to me. The real problem there is
> that
> > > >>> our linker doesn't know how to merge DOF, so it just concatenates
> the
> > > >>> tables into one SUNW_dof section. So we should really fix our
> linker,
> > > >>> but it doesn't hurt to also handle the problem in drti.o.
> > > >>>
> > > >>> There are a couple of bugs in the patch. First, the "break" added
> after
> > > >>> finding the DOF section causes problems if we haven't yet seen the
> > > >>> symbol table. Second, fixedprobes needs to be reset at the
> beginning of
> > > >>> each iteration of the while loop that you added, else we may not
> try
> > > >>> searching the dynamic symbol table when fixing the probe addresses.
> > > I've
> > > >>> pasted a patch below; could you test it and make sure things still
> work
> > > >>> properly with node?
> > > >>>
> > > >>> Thanks for the detailed blog post and problem description, they
> were
> > > >>> very helpful. :)
> > > >>>
> > > >>> -Mark
> > > >>>
> > > >>> diff --git a/cddl/contrib/opensolaris/lib/libdtrace/common/drti.c
> > > b/cddl/contrib/opensolaris/lib/libdtrace/common/drti.c
> > > >>> index e47cfb4d..bb02d8c 100644
> > > >>> --- a/cddl/contrib/opensolaris/lib/libdtrace/common/drti.c
> > > >>> +++ b/cddl/contrib/opensolaris/lib/libdtrace/common/drti.c
> > > >>> @@ -162,7 +162,7 @@ dtrace_dof_init(void)
> > > >>>         char *dofstrtabraw;
> > > >>>         size_t shstridx, symtabidx = 0, dynsymidx = 0;
> > > >>>         unsigned char *buf;
> > > >>> -       int fixedprobes = 0;
> > > >>> +       int fixedprobes;
> > > >>>  #endif
> > > >>>
> > > >>>         if (getenv("DTRACE_DOF_INIT_DISABLE") != NULL)
> > > >>> @@ -214,7 +214,6 @@ dtrace_dof_init(void)
> > > >>>                         if  (s && strcmp(s, ".SUNW_dof") == 0) {
> > > >>>                                 dofdata = elf_getdata(scn, NULL);
> > > >>>                                 dof = dofdata->d_buf;
> > > >>> -                               break;
> > > >>>                         }
> > > >>>                 }
> > > >>>         }
> > > >>> @@ -226,6 +225,7 @@ dtrace_dof_init(void)
> > > >>>         }
> > > >>>
> > > >>>         while ((char *) dof < (char *) dofdata->d_buf +
> > > dofdata->d_size) {
> > > >>> +               fixedprobes = 0;
> > > >>>                 dof_next = (void *) ((char *) dof +
> dof->dofh_filesz);
> > > >>>  #endif
> > > >>>
> > >
>