gdb/tui: Fix 'layout asm' before the inferior has started

Currently if a user starts the tui with 'layout asm' then they will be
presented with the 'src' layout.

What happens is:

  1. Layout command enables TUI, selecting the SRC layout by default.

  2. As part of tui_enable we call tui_display_main, which calls
     tui_get_begin_asm_address, which calls
     set_default_source_symtab_and_line.  This changes core GDBs
     current symtab and line, which triggers a call to the symtab
     changed hook tui_symtab_changed, which sets the flag
     from_source_symtab.

  3. Back in the layout command, the layout is changed from SRC to
     ASM.  After this the layout command completes and we return to
     core GDB which prints the prompt, however...

  4. The before prompt hook is called which sees the
     from_source_symtab flag is set and forces the SRC window to be
     displayed.  This switches us back to SRC view.

The solution I propose here is to delay installing the hooks into core
GDB until after we have finished setting up the tui and selecting the
default frame to view.  In this way we effectively ignore the first
symtab changed event triggered when making main the default symtab.

gdb/ChangeLog:

	* tui/tui.c (tui_enable): Register tui hooks after calling
	tui_display_main.

gdb/testsuite/ChangeLog:

	* gdb.tui/tui-layout-asm.exp: New file.

Change-Id: I858ab81a17ffb4aa72deb3f36c3755228a9c9d9a

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2020-01-09  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* tui/tui.c (tui_enable): Register tui hooks after calling
+	tui_display_main.
+
 2020-01-09  Christian Biesinger  <cbiesinger@google.com>
 
 	* gdbsupport/common-defs.h: Don't define _FORTIFY_SOURCE on MinGW.

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2020-01-09  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.tui/tui-layout-asm.exp: New file.
+
 2020-01-09  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* lib/tuiterm.exp (Term::check_box_contents): New proc.

gdb/testsuite/gdb.tui/tui-layout-asm.exp

@@ -0,0 +1,34 @@
+# Copyright 2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Ensure that 'layout asm' before starting the inferior puts us in the
+# asm layout and displays the disassembly for main.
+
+load_lib "tuiterm.exp"
+
+standard_testfile tui-layout.c
+
+if {[build_executable "failed to prepare" ${testfile} ${srcfile}] == -1} {
+    return -1
+}
+
+Term::clean_restart 24 80 $testfile
+if {![Term::prepare_for_tui]} {
+    unsupported "TUI not supported"
+}
+
+# This puts us into TUI mode, and should display the ASM window.
+Term::command "layout asm"
+Term::check_box_contents "check asm box contents" 0 0 80 15 "<main>"

gdb/tui/tui.c

@@ -489,10 +489,6 @@ tui_enable (void)
      clearok (stdscr, TRUE);
    }
 
-  /* Install the TUI specific hooks.  */
-  tui_install_hooks ();
-  rl_startup_hook = tui_rl_startup_hook;
-
   if (tui_update_variables ())
     tui_rehighlight_all ();
 
@@ -513,6 +509,12 @@ tui_enable (void)
   else
     tui_display_main ();
 
+  /* Install the TUI specific hooks.  This must be done after the call to
+     tui_display_main so that we don't detect the symtab changed event it
+     can cause.  */
+  tui_install_hooks ();
+  rl_startup_hook = tui_rl_startup_hook;
+
   /* Restore TUI keymap.  */
   tui_set_key_mode (tui_current_key_mode);