On 10/08/12 16:18, Ulrich Weigand wrote: > Richard Earnshaw wrote: >> On 10/08/12 14:44, Ulrich Weigand wrote: >>> Would the following htdocs patch be OK with you? Feel free to suggest >>> a more appropriate wording ... >> >> I think we need to make it clear that this also fixes a bug in the >> compiler that could lead to a run-time error. Otherwise, people will be >> asking why an abi-breaking change was made mid-cycle. > > Something along the following lines? > > <p>The default alignment of vector types on ARM EABI targets has been changed > to 8 bytes (for types larger than 8 bytes in size). This change was necessary > in order to fix a bug that could lead to generation of wrong code in certain > cases. It also brings the ABI as implemented by GCC back in compliance with > the AAPCS. This is an ABI change that affects e.g. layout of structures > having > a member of vector type. Code using such types may be incompatible with > binary > objects built with older versions of GCC.</p> > > Bye, > Ulrich >
How about: <p>On ARM, a bug has been fixed in GCC's implementation of the AAPCS rules for the layout of vectors that could lead to wrong code being generated. Vectors larger than 8 bytes in size are now by default aligned to an 8-byte boundary. This is an ABI change: code that makes explicit use of vector types may be incompatible with binary objects built with older versions of GCC. Auto-vectorized code is not affected by this change.</p> R.
