[Bug libc/206] malloc does not align memory correctly for sse capable systems

["bangerth at dealii dot org" <sourceware-bugzilla at sources dot redhat dot com>]

------- Additional Comments From bangerth at dealii dot org  2004-06-06 18:27 -------
For a history of this bug: this used to be PR 15795 in gcc's bugzilla, see  
  http://gcc.gnu.org/ml/gcc-bugs/2004-06/msg00552.html  
  
As for the implications: the C standard says that the pointer returned by  
malloc needs to be sufficiently aligned for _all_ data types. This alignment  
is specified in the ABI of a system, and for systems that allow the creation  
of SSE data types, this means that malloc needs to return 16-byte aligned  
pointers. I know that this is unfortunate, but there really is no other  
way of fixing malloc; for example, consider a program that uses  
  std::vector<__m128> x(13);  
Here, std::vector has to call 'operator new' which itself has to call  
malloc(). If malloc doesn't return sufficiently aligned pointers, the  
resulting std::vector is unusable. Note that here the memory allocation  
has to happen inside gcc's libstdc++, and is this out of user's control  
-- so one can't use posix_memalign here.  
  
W.  

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org


http://sources.redhat.com/bugzilla/show_bug.cgi?id=206

------- You are receiving this mail because: -------
You are on the CC list for the bug, or are watching someone who is.