Re: Access violation in SV.C new_body_inline()

John E. Malmberg wrote:
> John E. Malmberg wrote:
>> Nicholas Clark wrote:
>>> On Mon, Apr 27, 2009 at 12:27:02AM -0500, John E. Malmberg wrote:
>>>> I just started looking into a failure of 19_CPANPLUS-Dist.  I have 
>>>> not determined what exactly is wrong, and am out of time for the 
>>>> moment.
>>>>
>>>> I will try to get some more information later.
>>>>
>>>> It is failing from an access violation in SV.C.
>>>>
>>>> ok 57 -    Perl version not high enough
>>>> %SYSTEM-F-ACCVIO, access violation, reason mask=00, virtual 
>>>> address=000000000000002C, PC=00000000000F9AB8, PS=0000001B
>>>> %TRACE-F-TRACEBACK, symbolic stack dump follows
>>>>   image    module    routine             line      rel PC
>>>> abs PC
>>>>  DBGPERLSHR  SV  Perl_sv_upgrade        73671 0000000000001F58 
> 
>>> #define new_body_inline(xpv, sv_type) \
>>>     STMT_START { \
>>>     void ** const r3wt = &PL_body_roots[sv_type]; \
>>>     xpv = (PTR_TBL_ENT_t*) (*((void **)(r3wt))      \
>>>       ? *((void **)(r3wt)) : more_bodies(sv_type)); \
>>>     *(r3wt) = *(void**)(xpv); \
>>>     } STMT_END
>>>
>>> I'm curious what the value of sv_type is. It's the second (real) 
>>> parameter:
>>>
>>> void
>>> Perl_sv_upgrade(pTHX_ register SV *const sv, svtype new_type)
>>
>> case SVt_PVMG:
>>      ...
>>     new_body_inline(new_body, new_type);
>>
>> new_type = SVt_PVMG,
>> SVt_PVMG has a value of 7.
>>
>> new_body = 44.
>>
>> PL_Body_roots[sv_type] = 44.
>>
>>  From the code, it looks like this was expected to contain a valid 
>> pointer.
> 
>  From looking at the source code, it appears that the linked list of 
> bodies is corrupted.  my_perl->Ibodyroots[7] has 44.
> 
> I have been looking at the S_more_bodies routine.  Would it be practical 
> to put an assert on for a pointer being added to the linked list with a 
> value above 512?  On VMS, the first page of memory is protected no access.

I put a modified test script at 
http://eisner.encompasserve.org/~malmberg/perl/19_CPANPLUS-DIST.TXT

I commented out as much as I could and still reproduce the access violation.

-John
[email protected]
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