DTrace fixes for node.js

[Fedor Indutny]

Hello Mark, DTrace people!

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.

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.

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
> >>>
>