On Tue, 28 Jul 2009, Jan Dubois wrote:
> On Mon, 27 Jul 2009, Elliot Shank wrote:
> > Using Strawberry Perl 5.10.0.4, t/50-errno.t crashes perl during test
> > 8. I tracked it down to r834, it works in r833 and crashes up through
> > the current r847.
>
> I can reproduce the problem too (with MSC instead of GCC). It seems to happen
> in the SvOK() test in this part of the code:
>
> /* Should we calculate the caller or can we reuse the caller_subr_entry?
> * Sometimes we'll have a caller_subr_entry but it won't have the name
> yet.
> * For example if the caller is an xsub that's callback into perl.
> */
> if (profile_findcaller /* user wants us to calculate each
> time */
> || !caller_subr_entry /* we don't have a caller
> struct */
> || !caller_subr_entry->called_subpkg_pv /* we don't have caller details
> */
> || !SvOK(caller_subr_entry->called_subnam_sv)
>
> The stack trace is:
>
> subr_entry_setup(interpreter * 0x015d3fc4, cop * 0x01b806d8, subr_entry_st
> * 0x00000000) line 2433 + 26 bytes
> pp_subcall_profiler(interpreter * 0x015d3fc4, int 0x00000000) line 2556 +
> 15 bytes
> pp_entersub_profiler(interpreter * 0x015d3fc4) line 2488 + 13 bytes
>
> caller_subr_entry->called_subnam_sv doesn't look like a valid SV*, but
> I can access all the fields from the debugger, so I'm not sure why
> this is generating an access violation. Or maybe I'm reading the
> disassembled code incorrectly; I didn't disable -O2 yet. I can have
> another look tomorrow, but I thought maybe the exact location gives
> you enough hints to understand what might be going wrong.
Ok, I was confused. caller_subr_entry->called_subnam_sv is actually
NULL, explaining the access violation. I was looking at
caller_subr_entry->caller_subnam_sv, which seemed to contain invalid
data, but at least pointed to readable memory.
I added a checl to the condition above for
|| !caller_subr_entry->called_subnam_sv
before testing for SvOK(), but then the crash happened again and
caller_subr_entry->called_subnam_sv turned out to be 1.
I don't quite understand how this can happen; any ideas what I should be
looking at?
Cheers,
-Jan
PS: Any reason why called_subname_pv isnt't called called_subnam_pv
for consistency? I also find that I'm easily getting confused
between caller_subnam_sv and called_subnam_sv. It would be
nice to have more than a single character difference in these
names. Unfortunately I can't come up with good alternatives.
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