On Fri, Jun 11, 2010 at 02:09:33PM -0500, Quentin Neill wrote: > Currently GCC doesn't compute the current encoding offset (doesn't > know mnemonic/opcode lengths),
That's not true, gcc for i?86/x86_64 actually calculates the length and for most of the commonly used insns correctly, I've spent some time fixing various bugs in it a year ago, see http://gcc.gnu.org/ml/gcc-patches/2009-05/msg01808.html and the thread around it. Many of the remaining few issues (haven't tested bdver ISA additions for lengths) are fixable too, of course there is always inline asm where GCC can't know. Jakub