linux: Add maintenance commands to test libthread_db

This commit adds two new commands which may be used to test thread
debugging libraries used by GDB:

  * "maint check libthread-db" tests the thread debugging library GDB
     is using for the current inferior.

  * "maint set/show check-libthread-db" selects whether libthread_db
     tests should be run automatically as libthread_db is auto-loaded.
     The default is to not run tests automatically.

The test itself is a basic integrity check exercising all libthread_db
functions used by GDB on GNU/Linux systems.  By extension this also
exercises the proc_service functions provided by GDB that libthread_db
uses.

This functionality is useful for NPTL developers and libthread_db
developers.  It could also prove useful investigating bugs reported
against GDB where the thread debugging library or GDB's proc_service
layer is suspect.

gdb/ChangeLog:

	* linux-thread-db.c (valprint.h): New include.
	(struct check_thread_db_info): New structure.
	(check_thread_db_on_load, tdb_testinfo): New static globals.
	(check_thread_db, check_thread_db_callback): New functions.
	(try_thread_db_load_1): Run integrity checks if requested.
	(maintenance_check_libthread_db): New function.
	(_initialize_thread_db): Register "maint check libthread-db"
	and "maint set/show check-libthread-db".
	* NEWS: Mention the above new commands.

gdb/doc/ChangeLog:

	* gdb.texinfo (Maintenance Commands): Document "maint check
	libthread-db" and "maint set/show check-libthread-db".

gdb/testsuite/ChangeLog:

	* gdb.threads/check-libthread-db.exp: New file.
	* gdb.threads/check-libthread-db.c: Likewise.

2 files changed, 25 insertions, 0 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 6191e84..d36affe 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-08  Gary Benson <gbenson@redhat.com>
+
+	* gdb.texinfo (Maintenance Commands): Document "maint check
+	libthread-db" and "maint set/show check-libthread-db".
+
 2018-06-05  Tom Tromey	<tom@tromey.com>
 
 	PR cli/12326:
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4968b37..2c0ac33 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -35547,6 +35547,15 @@ modify XML target descriptions.
 Check that the target descriptions dynamically created by @value{GDBN}
 equal the descriptions created from XML files found in @var{dir}.
 
+@kindex maint check libthread-db
+@item maint check libthread-db
+Run integrity checks on the current inferior's thread debugging
+library.  This exercises all @code{libthread_db} functionality used by
+@value{GDBN} on GNU/Linux systems, and by extension also exercises the
+@code{proc_service} functions provided by @value{GDBN} that
+@code{libthread_db} uses.  Note that parts of the test may be skipped
+on some platforms when debugging core files.
+
 @kindex maint print dummy-frames
 @item maint print dummy-frames
 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
@@ -35854,6 +35863,17 @@ number of blocks in the blockvector
 @end enumerate
 @end table
 
+@kindex maint set check-libthread-db
+@kindex maint show check-libthread-db
+@item maint set check-libthread-db [on|off]
+@itemx maint show check-libthread-db
+Control whether @value{GDBN} should run integrity checks on inferior
+specific thread debugging libraries as they are loaded.  The default
+is not to perform such checks.  If any check fails @value{GDBN} will
+unload the library and continue searching for a suitable candidate as
+described in @ref{set libthread-db-search-path}.  For more information
+about the tests, see @ref{maint check libthread-db}.
+
 @kindex maint space
 @cindex memory used by commands
 @item maint space @var{value}