drutil_expand_rep_string's jecxz has a short reach

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on June 16, 2014 17:18:37_

The jecxz used by drutil_expand_rep_string() is marked meta (by drmgr: xref issue #676 ) so DR does not mangle it into a long jump. Currently (ok, soon) we
document this:
- WARNING: The added instructions include a jecxz instruction which
- will not be transformed into a 32-bit-reach instruction: thus,
- excessive added instrumentation may result in a reachability problem.

This issue covers trying to get it mangled.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1461_

Start by reading drutil_expand_rep_string() and the drmgr handling referenced by xref issue #676. Determine how the meta jecxz can be mangled into a 32-bit-reach instruction, then verify that excessive added instrumentation no longer creates a reachability problem and that the warning remains accurate.

Written by the indexing model from the issue text.