Support $pdir and $sdir in libthread-db-search-path.

	* NEWS: Mention $sdir,$pdir.
	* gdb_thread_db.h (LIBTHREAD_DB_SEARCH_PATH): Add $sdir:$pdir.
	* linux-thread-db.c (try_thread_db_load_from_pdir): New function.
	(try_thread_db_load_from_sdir): New function.
	(try_thread_db_load_from_dir): New function.
	(thread_db_load_search): Handle $pdir, $sdir.  Remove trying of
	system directories if search of libthread-db-search-path fails,
	that is now done via $sdir.
	(has_libpthread): New function.
	(thread_db_load): Remove search for libthread_db in directory of
	libpthread, that is now done via $pdir.

	gdbserver/
	* thread-db.c (try_thread_db_load_from_sdir): New function.
	(try_thread_db_load_from_dir): New function.
	(thread_db_load_search): Handle $sdir, ignore $pdir.
	Remove trying of system directories if search of
	libthread-db-search-path fails,	that is now done via $sdir.

	doc/
	* gdb.texinfo (Threads): Document $sdir,$pdir.
	(Server): Document $pdir exception.

2 files changed, 16 insertions, 4 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 15d203e..f145574 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,5 +1,8 @@
 2011-05-13  Doug Evans  <dje@google.com>
 
+	* gdb.texinfo (Threads): Document $sdir,$pdir.
+	(Server): Document $pdir exception.
+
 	* gdb.texinfo (Auto-loading): Document "info auto-load-scripts".
 
 	* gdb.texinfo (Threads): Clarify default value for
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index ae87528..08ee158 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -2858,16 +2858,22 @@ watchpoints in programs with multiple threads.
 If this variable is set, @var{path} is a colon-separated list of
 directories @value{GDBN} will use to search for @code{libthread_db}.
 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
-its default value (an empty list on @sc{gnu}/Linux and Solaris systems).
+its default value (@code{$sdir:$pdir} on @sc{gnu}/Linux and Solaris systems).
 Internally, the default value comes from the @code{LIBTHREAD_DB_SEARCH_PATH}
 macro.
 
 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
 @code{libthread_db} library to obtain information about threads in the
 inferior process.  @value{GDBN} will use @samp{libthread-db-search-path}
-to find @code{libthread_db}.  If that fails, @value{GDBN} will continue
-with default system shared library directories, and finally the directory
-from which @code{libpthread} was loaded in the inferior process.
+to find @code{libthread_db}.
+
+A special entry @samp{$sdir} for @samp{libthread-db-search-path}
+refers to the default system directories that are
+normally searched for loading shared libraries.
+
+A special entry @samp{$pdir} for @samp{libthread-db-search-path}
+refers to the directory from which @code{libpthread}
+was loaded in the inferior process.
 
 For any @code{libthread_db} library @value{GDBN} finds in above directories,
 @value{GDBN} attempts to initialize it with the current inferior process.
@@ -16382,6 +16388,9 @@ directories to search for @code{libthread_db} (@pxref{Threads,,set
 libthread-db-search-path}).  If you omit @var{path},
 @samp{libthread-db-search-path} will be reset to its default value.
 
+The special entry @samp{$pdir} for @samp{libthread-db-search-path} is
+not supported in @code{gdbserver}.
+
 @item monitor exit
 Tell gdbserver to exit immediately.  This command should be followed by
 @code{disconnect} to close the debugging session.  @code{gdbserver} will