[Xcb] [PATCH libxcb 1/1] Fix handling of align-pads in end-iterators

[Christian Linhart]

If a list is preceded by an align-pad, then
accessor for the end-iterator returned a wrong
value.

Reason: the length of the align-iterator was added
to a pointer of list-member type. Therefore, the length
was multiplied by the size of the list-member type,
due to C pointer arithmetic rules.

This has looked like the following, e.g., in
xcb_randr_get_crtc_transform_pending_params_end:

i.data = ((xcb_render_fixed_t *) prev.data) + ((-prev.index) & (4 - 1)) + (R->pending_nparams);

This bug was introduced with the following commit:
http://cgit.freedesktop.org/xcb/libxcb/commit/?id=4033d39d4da21842bb1396a419dfc299591c3b1f

The fix handles this by casting to char* before adding the align,
and then casting the result to the member type.

Signed-off-by: Christian Linhart <chris at demorecorder.com>
---
 src/c_client.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/c_client.py b/src/c_client.py
index c38b434..5d01289 100644
--- a/src/c_client.py
+++ b/src/c_client.py
@@ -1942,16 +1942,17 @@ def _c_accessors_list(self, field):
 
             if align_pad is None:
                 align_pad = ('XCB_TYPE_PAD(%s, prev.index)' %
                     type_pad_type(field.first_field_after_varsized.type.c_type))
 
             _c('    xcb_generic_iterator_t prev = %s;',
                 _c_iterator_get_end(prev_varsized_field, 'R'))
-            _c('    i.data = ((%s *) prev.data) + %s + (%s);', field.type.c_wiretype,
-                align_pad, _c_accessor_get_expr(field.type.expr, fields))
+            _c('    i.data = ((%s *) ((char*) prev.data + %s)) + (%s);',
+                field.type.c_wiretype, align_pad,
+                _c_accessor_get_expr(field.type.expr, fields))
 
         _c('    i.rem = 0;')
         _c('    i.index = (char *) i.data - (char *) %s;', param)
         _c('    return i;')
         _c('}')
 
     else:
-- 
2.1.4