illumos gate

Today libproc(3PROC) provides routines for getting at the registers of a given thread within a proccess, through routines like Plwp_getregs(), Plwp_getfpregs(), and Plwp_getxregs(). There are two caveats wit these as they stand right now:

• They require the entire process to be stopped before you can read from them. This is a larger requirement than /proc requires. It only needs an individual thread to be stopped.
• Internally, libproc caches the state of the lwpstatus file for individual threads that one has performed an Lgrab() for and for the corresponding representative lwp as part of the pr_lwp member of the status file. While the latter is kept up to date with writes that are done, the thread-specific handles are not. In particular a thread could have had outstanding changes to its general purpose registers as a result of someone calling Lputareg().

This change introduces analogues to the Plwp_getXXX and Plwp_setXXX functions in the form of LgetXXX and LsetXXX. It also ensures that the thread handles are updated to cover cache invalidations and that everything is synced out.