tui-disasm: Fix window content buffer overrun

A user reported a GDB crash with TUI when trying to debug a function
with a long demangled C++ method name.  It turned out that the logic for
displaying the TUI disassembly window has a bug that can cause a buffer
overrun, possibly overwriting GDB-internal data structures.  In
particular, the logic performs an unguarded strcpy.

Another (harmless) bug in tui_alloc_source_buffer causes the buffer to
be two lines longer than needed.  This may have made the crash appear
less frequently.

gdb/ChangeLog:

	* tui/tui-disasm.c (tui_set_disassem_content): Fix line buffer
	overrun due to unchecked strcpy.

gdb/testsuite/ChangeLog:

	* gdb.base/tui-layout.c: New file.
	* gdb.base/tui-layout.exp: Use tui-layout.c, to ensure that the
	disassembly window contains very long lines.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2016-11-09  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
+	* tui/tui-disasm.c (tui_set_disassem_content): Fix line buffer
+	overrun due to unchecked strcpy.
+
 2016-11-09  Tristan Gingold  <gingold@adacore.com>
 
 	* darwin-nat.c (find_inferior_task_it): Fix indentation.

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2016-11-09  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
+	* gdb.base/tui-layout.c: New file.
+	* gdb.base/tui-layout.exp: Use tui-layout.c, to ensure that the
+	disassembly window contains very long lines.
+
 2016-11-08  Tom Tromey  <tom@tromey.com>
 
 	* gdb.python/py-value.exp (test_value_creation): Make "long" test

gdb/testsuite/gdb.base/tui-layout.c

@@ -0,0 +1,47 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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/>.  */
+
+#define LONGER_NAME(x) x ## x
+#define LONGER(x) LONGER_NAME(x)
+#define LONGNAME1 d_this_identifier_of_32_chars_an
+#define LONGNAME2 LONGER (LONGER (LONGER (LONGER (LONGER (LONGNAME1)))))
+
+/* Construct a long identifier name.  If SHORT_IDENTIFIERS is set, limit
+   it to 1024 chars.  */
+
+#ifdef SHORT_IDENTIFIERS
+#define LONGNAME3 LONGNAME2
+#else
+#define LONGNAME3 LONGER (LONGER (LONGER (LONGER (LONGER (LONGNAME2)))))
+#endif
+
+void LONGNAME3 (void);
+
+int
+main ()
+{
+  LONGNAME3 ();
+  return 0;
+}
+
+/* Function with a long name.  Placing it after main makes it more likely
+   to be shown in the disassembly window on startup.  */
+
+void
+LONGNAME3 (void)
+{
+}

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

@@ -13,12 +13,23 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-standard_testfile start.c
+standard_testfile
 
-if { [prepare_for_testing ${testfile}.exp ${testfile} $srcfile] } {
-    return -1
+set ccopts {debug quiet}
+if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "$binfile" \
+	  executable $ccopts] != "" } {
+    # Maybe the compiler can't handle arbitrarily long identfier names.
+    # Try with a shorter version.
+    lappend ccopts "additional_flags=-DSHORT_IDENTIFIERS"
+    if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "$binfile" \
+	      executable $ccopts] != "" } {
+	untested "compile"
+	return -1
+    }
 }
 
+clean_restart "$binfile"
+
 if {[skip_tui_tests]} {
     # TUI support is disabled.  Check for error message.
     gdb_test "layout asm" "Undefined command: \"layout\".  Try \"help\"."

gdb/tui/tui-disasm.c

@@ -172,7 +172,7 @@ tui_set_disassem_content (struct gdbarch *gdbarch, CORE_ADDR pc)
   enum tui_status ret = TUI_FAILURE;
   int i;
   int offset = TUI_DISASM_WIN->detail.source_info.horizontal_offset;
-  int max_lines;
+  int max_lines, line_width;
   CORE_ADDR cur_pc;
   struct tui_gen_win_info *locator = tui_locator_win_info_ptr ();
   int tab_len = tui_default_tab_len ();
@@ -193,8 +193,9 @@ tui_set_disassem_content (struct gdbarch *gdbarch, CORE_ADDR pc)
   TUI_DISASM_WIN->detail.source_info.start_line_or_addr.u.addr = pc;
   cur_pc = locator->content[0]->which_element.locator.addr;
 
-  max_lines = TUI_DISASM_WIN->generic.height - 2;	/* Account for
-							   hilite.  */
+  /* Window size, excluding highlight box.  */
+  max_lines = TUI_DISASM_WIN->generic.height - 2;
+  line_width = TUI_DISASM_WIN->generic.width - 2;
 
   /* Get temporary table that will hold all strings (addr & insn).  */
   asm_lines = XALLOCAVEC (struct tui_asm_line, max_lines);
@@ -233,20 +234,15 @@ tui_set_disassem_content (struct gdbarch *gdbarch, CORE_ADDR pc)
       src = &element->which_element.source;
       strcpy (line, asm_lines[i].addr_string);
       cur_len = strlen (line);
-
-      /* Add spaces to make the instructions start on the same
-	 column.  */
-      while (cur_len < insn_pos)
-        {
-          strcat (line, " ");
-          cur_len++;
-        }
-
-      strcat (line, asm_lines[i].insn);
+      memset (line + cur_len, ' ', insn_pos - cur_len);
+      strcpy (line + insn_pos, asm_lines[i].insn);
 
       /* Now copy the line taking the offset into account.  */
       if (strlen (line) > offset)
-        strcpy (src->line, &line[offset]);
+	{
+	  strncpy (src->line, &line[offset], line_width);
+	  src->line[line_width] = '\0';
+	}
       else
         src->line[0] = '\0';