Re: [xml] Possible 64-bit issues in xml 2.9.2

On Tue, Nov 10, 2015 at 05:34:45PM -0800, Bruce Dawson wrote:
Sure. I'll do that.

  okay, thanks

On old architectures it would be easy enough to use a typedef to 'create'
intptr_t, so any compatibility problems that such a patch introduces will
be easily fixed.

  the problem is to know when that type is not defined, will require some magic I'm afraid


On Tue, Nov 10, 2015 at 5:32 PM, Daniel Veillard <veillard redhat com>

On Tue, Nov 10, 2015 at 01:04:51PM -0800, Bruce Dawson wrote:
Resending now that I've joined the mailing list...

While building 64-bit Chromium with VC++ 2015 Update 1 I noticed a
significant number of pointer truncation warnings in libxml, especially
xpath.c. A typical warning is:

warning C4311: 'type cast': pointer truncation from 'xmlChar *' to 'long'

which triggers on the last two lines of this block:

    if (node2->type == XML_ELEMENT_NODE) {
if ((0 > (long) node1->content) && /* TODO: Would a != 0 suffice here? */
    (0 > (long) node2->content) &&

The intent is not entirely clear but if these are supposed to be NULL
checks then they could easily give the wrong result. In the VC++ world
'long' is always a 32-bit type, so converting a pointer to a long both
throws away the top 32 bits and also makes it a signed type. That means
that pointers to the first 2 GB of address space will behave as expected,
and pointers beyond that will have a 50% chance of behaving incorrectly!

Another example is these two conversions. The code is apparently trying
sort by content address, but on 64-bit Windows builds it will just be
sorting by the bottom 32 bits of the content address.
l1 = -((long) node1->content);
l2 = -((long) node2->content);
if (l1 < l2)
if (l1 > l2)

This is not a problem with gcc or clang because their 64-bit builds have
64-bit long, but the C/C++ standard do not mandate and that is not the
with VC++.

I think that the correct type would be ptrdiff_t, or size_t, or intptr_t,
or uintptr_t. I've attached the full set of warnings in case that is of
assistance. Even though some of these warnings do not indicate actual
it would still be best to use the correct type in order to avoid
and warnings.

  Sounds like intptr_t would be the proper type to use for those, I just
wonder what kind of old arches will break if they don't have it.

Can you come up with a patch which just change the casts and possibly the
types ?


Daniel Veillard      | Open Source and Standards, Red Hat
veillard redhat com  | libxml Gnome XML XSLT toolkit | virtualization library

Bruce Dawson

Daniel Veillard      | Open Source and Standards, Red Hat
veillard redhat com  | libxml Gnome XML XSLT toolkit | virtualization library

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