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Date: Tue, 31 Jul 2007 08:56:41 +0200
From: Marco Spinetti <m.spinetti@pisa.iol.it>
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To: modules-dev@httpd.apache.org
Subject: Re: Strange segmentation fault
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Ralf Mattes ha scritto:
> On Mon, 2007-07-30 at 18:49 +0200, m.spinetti@pisa.iol.it wrote:
>   
>> I found that a similar problem was this:
>>
>> http://mail-archives.apache.org/mod_mbox/httpd-modules-dev/200703.mbox/%3c1173077706.5485.6.camel@test.asus%3e
>>     
>
> Similar? In what way? Abusing libxml2 interna? Are you doing this?
> Iff xmlFreeDoc triggers a segmentation violation than the most likely
> case is that you pass it a document pointer that's not (a valid
> libxml document any more). So what part of the module did invalidate
> that doc pointer? Is it more likely to be Apache or your module code? 
> BTW - one shure way to f^h^hk up you document is messing (i.e.
> releasing) nodes still refered to from the document. Does your module
> copy/move/delete nodes?
>   
The violation is inside my module,near the end. When I'm at the end of 
my module I reply to the client and I free the xml documents I used:

.....
ap_add_output_filter(SV_XSLT_FILTER_NAME, NULL, r, r->connection);
mod_transform_set_XSLT(r, xslfilename);

xmlDocDumpMemoryEnc(doc, &bufptr, &size, "UTF-8");
putXML(r, (char*)bufptr);

if (size > 0)
    xmlFree(bufptr);

if (docinter != NULL)
        xmlFreeDoc(docinter);
if (docs != NULL)
        xmlFreeDoc(docs);

xmlFreeDoc(doc);
xmlCleanupParser();
return OK;

where:

void putXML(request_rec *r, char* xml)
{
    ap_set_content_type(r, "text/xml");
    ap_rwrite(xml, strlen(xml), r);
    ap_rflush(r);
}

My final xml document is doc which is built in the module getting 
information from docinter and docs.
Yes my module copies some nodes from docs to doc with xmlCopyNode.
I think that my code is correct.
Am I doing some mistakes?
Best regards

Marco

>   
>> So it seems that it's possibile.
>> I don't understand how to solve it.
>> Could you give me some hints?
>>     
>
> Unless your module replaced libxml2's allocator the library uses
> malloc/free - you can use all the glorious GNU tools to debug. I guess
> you already set  MALLOC_CHECK_ to 1, did you?
>
>  HTH Ralf Mattes
>
>   
>> Best regards
>>
>> Marco
>>
>>     
>>> Sorry I don't understand the reply.
>>> You are telling me that it should be possibile or not?
>>> I always use r->pool to allocate memory in my module, but not for
>>> libxml2. It has it's memory allocation and looking at source it uses
>>> malloc and free.
>>> Best regards
>>>
>>> Marco
>>>
>>>
>>>       
>>>> On Mon, Jul 30, 2007 at 06:04:27PM +0200, m.spinetti@pisa.iol.it wrote:
>>>>         
>>>>> I isolated my problem.
>>>>> It seems that sometimes during xmlFreeDoc(doc) I get a Segmentation
>>>>>           
>>> fault.
>>>       
>>>>> xmlFreeDoc is a function of libxml2 which I use inside my module.
>>>>> I suppose that libxml2 uses malloc/free to alloc and free memory:
>>>>>           
>> is it
>>     
>>>>> possibile that there is some overlap of memory with apr poll
>>>>>           
>> (r->poll)?
>>     
>>>> Not an option. Unless you use somewhat pools to allocate memory for
>>>> libxml. If you do so, stop it. Either use apr pools or malloc/free.
>>>> Kind regards.
>>>>
>>>>         
>
>   

-- 
Software Engineer - Spinetti Marco
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