DTrace fixes for node.js

[Fedor Indutny]

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?

Cheers,
Fedor.

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
>