Re: [xml] Memory tag errors on xmlCleanupCharEncodingHandlers

[Daniel Veillard <veillard redhat com>]

On Sun, Aug 22, 2010 at 05:20:03PM -0400, Marco Rogers wrote:
> I believe I've found a bug, or at least annoying issue in libxml2.
>
> So I've got a library that is using libxml2 heavily. I had to turn on memory
> tracking in the so I can inspect the total memory allocated by libxml2.
>
> xmlMemSetup(xmlMemFree, xmlMemMalloc, xmlMemRealloc, xmlMemoryStrdup);
>
>   xmlInitMemory();
>
> // http://github.com/polotek/libxmljs/blob/master/src/libxmljs.cc#L160-161
>
> But now I get the Memory tag errors that occur when xml memory isn't
> allocated or freed properly.  I've studied this issue a lot because I
> thought it might be a problem of mine.  Here's an example thread below (not
> mine, just helped me understand the problem).
>
> http://mail.gnome.org/archives/xml/2010-April/msg00035.html
>
> I understand things now and I've been debugging to track down where this
> happens.  Despite what I might be doing in my library, I always get several
> memory errors.  I've traced the problem to the
> function xmlCleanupCharEncodingHandlers that gets called in
> xmlCleanupParser.
>
> The function calls xmlFree on all of the names of the handlers.  But the
> names were not created with xmlMalloc.  They are passed in as literal
> strings.  See ecoding.c around line 1351.

  Sounds wrong to me on 2 counts:
    1/ the handler name is up = xmlMemStrdup() line 1286, not the raw
       strring passed to the function call
    2/ libxml2 when compiled with memory debug use a memory wrapper
       which does an xmlMemSetup() equivalent and all functions go
       though that wrapped allocator. If the problem was present even
       the most trivial tests would fail in this mode.

The problem is likely to be somewhere else...

Daniel


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