Previously test allocator only guaranteed alignment enough for a pointer.
On some platforms (e.g. SPARC) double has to be aligned to 8 bytes but pointers
can have a size of 4 bytes. This commit increases allocation header to fix that.
In practical terms the allocation header is now always 8 bytes.
This fixes tests in PUGIXML_NO_XPATH mode on SPARC64 (#48).
SPARC does not allow unaligned accesses - e.g. you can't read an unaligned int.
Normally pugixml does not perform unaligned integer/pointer accesses, but page
heap can allocate blocks that are not aligned so that we can detect a single-
byte read/write overrun.
Additionally, the hardcoded page size we're currently using is really system
specific - on SPARC the page size can be 8 Kb instead of 4 Kb so mprotect can
fail.
Address sanitizer can detect underflows so we don't really need the custom
allocator.
Additionally, custom allocator can return memory that is not pointer-aligned;
this causes undefined behavior sanitizer to complain.
Align allocations to right end of page boundary to catch buffer overruns,
instead of unmapping on deallocations mark the page as no-access to guarantee
a page fault on use-after-free.
This should never happen but can improve debugging experience for
work-in-progress changes since that avoids memcpy() into negative memory
space (debugger can't backtrace from failed memcpy since it does not set
up the stack frame).
git-svn-id: https://pugixml.googlecode.com/svn/trunk@1070 99668b35-9821-0410-8761-19e4c4f06640
