[gdb/testsuite] Remove dependence on tcl_unknown

In gdb_init we install a local version of ::unknown, which relies on
::tcl_unknown, which is defined by dejagnu.

This proc may be moved into a namespace, or disappear altogether, as
indicated by dejagnu maintainers, so we can't rely on it.

Fix this by recreating tcl's version of unknown, and using that instead.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-06-17  Tom de Vries  <tdevries@suse.de>

	* lib/gdb.exp (gdb_tcl_unknown): New proc.
	(gdb_init): Use gdb_tcl_unknown for ::unknown override.  Make override
	conditional on presence of gdb_tcl_unknown.
	(gdb_finish): Make override undo conditional on presence of
	gdb_tcl_unknown.

2 files changed, 34 insertions, 11 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 97fecf6..d010125 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2020-06-17  Tom de Vries  <tdevries@suse.de>
+
+	* lib/gdb.exp (gdb_tcl_unknown): New proc.
+	(gdb_init): Use gdb_tcl_unknown for ::unknown override.  Make override
+	conditional on presence of gdb_tcl_unknown.
+	(gdb_finish): Make override undo conditional on presence of
+	gdb_tcl_unknown.
+
 2020-06-16  Tom Tromey  <tom@tromey.com>
 
 	* gdb.python/tui-window.py (failwin): New function.  Register it
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index f502eb1..02867fb 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5177,6 +5177,17 @@ proc gdb_cleanup_globals {} {
     }
 }
 
+# Create gdb_tcl_unknown, a copy tcl's ::unknown, provided it's present as a
+# proc.
+set temp [interp create]
+if { [interp eval $temp "info procs ::unknown"] != "" } {
+    set old_args [interp eval $temp "info args ::unknown"]
+    set old_body [interp eval $temp "info body ::unknown"]
+    eval proc gdb_tcl_unknown {$old_args} {$old_body}
+}
+interp delete $temp
+unset temp
+
 proc gdb_init { test_file_name } {
     # Reset the timeout value to the default.  This way, any testcase
     # that changes the timeout value without resetting it cannot affect
@@ -5283,14 +5294,16 @@ proc gdb_init { test_file_name } {
 
     gdb_setup_known_globals
 
-    # Dejagnu overrides proc unknown.  The dejagnu version may trigger in a
-    # test-case but abort the entire test run.  To fix this, we install a
-    # local version here, which reverts dejagnu's override, and restore
-    # dejagnu's version in gdb_finish.
-    rename ::unknown ::dejagnu_unknown
-    proc unknown { args } {
-	# Dejagnu saves the original version in ::tcl_unknown, use it.
-	return [uplevel 1 ::tcl_unknown $args]
+    if { [info procs ::gdb_tcl_unknown] != "" } {
+	# Dejagnu overrides proc unknown.  The dejagnu version may trigger in a
+	# test-case but abort the entire test run.  To fix this, we install a
+	# local version here, which reverts dejagnu's override, and restore
+	# dejagnu's version in gdb_finish.
+	rename ::unknown ::dejagnu_unknown
+	proc unknown { args } {
+	    # Use tcl's unknown.
+	    return [uplevel 1 ::gdb_tcl_unknown $args]
+	}
     }
 
     return $res
@@ -5302,9 +5315,11 @@ proc gdb_finish { } {
     global cleanfiles
     global known_globals
 
-    # Restore dejagnu's version of proc unknown.
-    rename ::unknown ""
-    rename ::dejagnu_unknown ::unknown
+    if { [info procs ::gdb_tcl_unknown] != "" } {
+	# Restore dejagnu's version of proc unknown.
+	rename ::unknown ""
+	rename ::dejagnu_unknown ::unknown
+    }
 
     # Exit first, so that the files are no longer in use.
     gdb_exit