Fix crash when command arg is missing in faas/taas/tfaas commands.

GDB crashes when doing:
  (gdb) faas
  Aborted

Do the needed check to avoid crashing.

gdb/ChangeLog
2019-12-06  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
	* stack.c (faas_command): Check a command is provided.
	* thread.c (taas_command, tfaas_command): Likewise.

gdb/testsuite/ChangeLog
2019-12-06  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* gdb.threads/pthreads.exp: Test taas and tfaas without command.
	* gdb.base/frameapply.exp: Test faas without command.

gdb/ChangeLog

@@ -1,3 +1,7 @@
+2019-12-06  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
+	* stack.c (faas_command): Check a command is provided.
+	* thread.c (taas_command, tfaas_command): Likewise.
+
 2019-12-05  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
 	* inferior.c (prune_inferiors):  Only call delete_inferior,
 	Do not modify the inferior list.

gdb/stack.c

@@ -3281,6 +3281,8 @@ frame_apply_command (const char* cmd, int from_tty)
 static void
 faas_command (const char *cmd, int from_tty)
 {
+  if (cmd == NULL || *cmd == '\0')
+    error (_("Please specify a command to apply on all frames"));
   std::string expanded = std::string ("frame apply all -s ") + cmd;
   execute_command (expanded.c_str (), from_tty);
 }

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2019-12-06  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
+
+	* gdb.threads/pthreads.exp: Test taas and tfaas without command.
+	* gdb.base/frameapply.exp: Test faas without command.
+
 2019-12-04  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* lib/gdb.exp (gdb_compile): Add -J compiler option when building

gdb/testsuite/gdb.base/frameapply.exp

@@ -215,3 +215,5 @@ gdb_test "frame apply level 4-2 p 1" "inverted range" "inverted range"
 gdb_test "frame apply level 0-3" \
     "Please specify a command to apply on the selected frames" \
     "missing command"
+gdb_test "faas" "Please specify a command to apply on all frames" \
+    "missing command for faas"

gdb/testsuite/gdb.threads/pthreads.exp

@@ -334,10 +334,14 @@ proc check_qcs {} {
 	    ] \
 	"run a failing command except in one frame of thread 2,3, -s to silently continue.  Do not show thread and frame info"
 
-    # Check invalid flag combinations.
+    # Check invalid flag combinations and errors.
     gdb_test "thread apply all -c -s p 1" \
 	"thread apply all: -c and -s are mutually exclusive" \
 	"check -c and -s cannot be used simultaneously"
+    gdb_test "taas" "Please specify a command to apply on all threads" \
+	"missing command for taas"
+    gdb_test "tfaas" "Please specify a command to apply on all frames of all threads" \
+	"missing command for tfaas"
 
 }
 

gdb/thread.c

@@ -1818,6 +1818,8 @@ thread_apply_command (const char *tidlist, int from_tty)
 static void
 taas_command (const char *cmd, int from_tty)
 {
+  if (cmd == NULL || *cmd == '\0')
+    error (_("Please specify a command to apply on all threads"));
   std::string expanded = std::string ("thread apply all -s ") + cmd;
   execute_command (expanded.c_str (), from_tty);
 }
@@ -1827,6 +1829,8 @@ taas_command (const char *cmd, int from_tty)
 static void
 tfaas_command (const char *cmd, int from_tty)
 {
+  if (cmd == NULL || *cmd == '\0')
+    error (_("Please specify a command to apply on all frames of all threads"));
   std::string expanded
     = std::string ("thread apply all -s -- frame apply all -s ") + cmd;
   execute_command (expanded.c_str (), from_tty);