Fix mutex pretty printer test and pretty printer output.

This fixes the mutex pretty printer so that, if the owner ID isn't recorded
(such as in the current lock elision implementation), "Owner ID" will be shown
as "Unknown" instead of 0. It also changes the mutex printer output so that it
says "Acquired" instead of "Locked". The mutex tests are updated accordingly.

In addition, this adds a paragraph to the "Known issues" section of the
printers README explaining that the printer output isn't guaranteed to cover
every detail.

2017-01-14  Martin Galvan  <martingalvan@sourceware.org>

        * README.pretty-printers (Known issues): Warn about printers not
        always covering everything.
        * nptl/nptl-printers.py (MutexPrinter): Change output.
        * nptl/test-mutex-printers.py: Fix test and adapt to changed output.

1 files changed, 6 insertions, 1 deletions

diff --git a/README.pretty-printers b/README.pretty-printers
index a2536cad80..2522cb858d 100644
--- a/README.pretty-printers
+++ b/README.pretty-printers
@@ -29,7 +29,7 @@ However, with a pretty printer gdb will output something like this:
 (gdb) print mutex
 $1 = pthread_mutex_t = {
   Type = Normal,
-  Status = Unlocked,
+  Status = Not acquired,
   Robust = No,
   Shared = No,
   Protocol = Priority protect,
@@ -145,6 +145,11 @@ any changes to the target code must also update the corresponding printers.
 On the plus side, the printer code itself may serve as a kind of documentation
 for the target code.
 
+* There's no guarantee that the information the pretty printers provide is
+complete, i.e. some details might be left off.  For example, the pthread_mutex_t
+printers won't report whether a thread is spin-waiting in an attempt to acquire
+the mutex.
+
 * Older versions of the gdb Python API have a bug where
 gdb.RegexpCollectionPrettyPrinter would not be able to get a value's real type
 if it was typedef'd.  This would cause gdb to ignore the pretty printers for