DTrace fixes for node.js

[Mark Johnston]

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
>>