Re: Access violation in SV.C new_body_inline()

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.

-John
[email protected]
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