[PATCH 4/6] Fix PR gdb/15294: list with unlimited listsize broken

[Pedro Alves <palves at redhat dot com>]

Currently, "set listsize -1" is supposed to mean "unlimited" source
lines, but, alas, it doesn't actually work:

 (gdb) set listsize -1
 (gdb) show listsize
 Number of source lines gdb will list by default is unlimited.
 (gdb) list 1
 (gdb) list 1
 (gdb) list 1
 (gdb) set listsize 10
 (gdb) list 1
 1       /* Main function for CLI gdb.
 2          Copyright (C) 2002-2013 Free Software Foundation, Inc.
 3
 4          This file is part of GDB.
 5
 6          This program is free software; you can redistribute it and/or modify
 7          it under the terms of the GNU General Public License as published by
 8          the Free Software Foundation; either version 3 of the License, or
 9          (at your option) any later version.
 10

Before this patch

     http://sourceware.org/ml/gdb-patches/2012-08/msg00021.html

the "set listsize" command was a var_integer command, and "unlimited"
was set with 0.  Internally, var_integer maps 0 to INT_MAX

   case var_integer:
      {
      ...
	if (val == 0 && c->var_type == var_integer)
	  val = INT_MAX;

The change to zuinteger_unlimited command, meant that -1 is left as -1
in the command's control variable (lines_to_list), and the code in
source.c isn't expecting that -- it only expects positive numbers.  I
find that the simplest and clearest to handle this is the approach of
this patch.  Keep the command as zuinteger_unlimited and have source.c
itself map -1 to a largest source line number GDB could handle, which
is the same as "unlimited" in practice, which is what also was done
(albeit not explicitly) when the command was var_integer.

This results in actually passing the old "set listsize -1; list 1"
test:

 -XFAIL: gdb.base/list.exp: list line 1 with unlimited listsize
 +XPASS: gdb.base/list.exp: list line 1 with unlimited listsize

gdb/
2013-03-21  Pedro Alves  <palves@redhat.com>

	PR gdb/15294

	* source.c (lines_to_list): Rename to ...
	(setshow_listsize_var): ... this.  Update comment.
	(get_lines_to_list): Update comment.  Return INT_MAX when "set
	listsize" is -1.
	(select_source_symtab, forward_search_command)
	(reverse_search_command): Use get_lines_to_list instead of the
	command variable directly.
	(_initialize_source): Adjust to command variable rename.
---
 gdb/source.c |   36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/gdb/source.c b/gdb/source.c
index 2d9410e..108c2ee 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -92,13 +92,15 @@ static int current_source_line;
 
 static struct program_space *current_source_pspace;
 
-/* Default number of lines to print with commands like "list".
-   This is based on guessing how many long (i.e. more than chars_per_line
-   characters) lines there will be.  To be completely correct, "list"
-   and friends should be rewritten to count characters and see where
-   things are wrapping, but that would be a fair amount of work.  */
+/* The variable registered in the "set listsize" command, which
+   controls the default number of lines to print with commands like
+   "list".  Don't read the value of this variable directly -- use
+   get_lines_to_list instead.  */
+
+static int setshow_listsize_var = 10;
+
+/* "Show" hook for "set listsize".  */
 
-int lines_to_list = 10;
 static void
 show_lines_to_list (struct ui_file *file, int from_tty,
 		    struct cmd_list_element *c, const char *value)
@@ -156,14 +158,20 @@ get_first_line_listed (void)
 }
 
 /* Return the default number of lines to print with commands like the
-   cli "list".  The caller of print_source_lines must use this to
-   calculate the end line and use it in the call to print_source_lines
-   as it does not automatically use this value.  */
+   cli "list".  This is based on guessing how many long (i.e. more
+   than chars_per_line characters) lines there will be.  To be
+   completely correct, "list" and friends should be rewritten to count
+   characters and see where things are wrapping, but that would be a
+   fair amount of work.  The caller of print_source_lines must use
+   this to calculate the end line and use it in the call to
+   print_source_lines as it does not automatically use this value.  */
 
 int
 get_lines_to_list (void)
 {
-  return lines_to_list;
+  /* In the user command, -1 means unlimited.  In practice, we just
+     handle that as a very large number.  */
+  return (setshow_listsize_var < 0 ? INT_MAX : setshow_listsize_var);
 }
 
 /* Return the current source file for listing and next line to list.
@@ -270,7 +278,7 @@ select_source_symtab (struct symtab *s)
       xfree (sals.sals);
       current_source_pspace = sal.pspace;
       current_source_symtab = sal.symtab;
-      current_source_line = max (sal.line - (lines_to_list - 1), 1);
+      current_source_line = max (sal.line - (get_lines_to_list () - 1), 1);
       if (current_source_symtab)
 	return;
     }
@@ -1644,7 +1652,7 @@ forward_search_command (char *regex, int from_tty)
 	  do_cleanups (cleanups);
 	  print_source_lines (current_source_symtab, line, line + 1, 0);
 	  set_internalvar_integer (lookup_internalvar ("_"), line);
-	  current_source_line = max (line - lines_to_list / 2, 1);
+	  current_source_line = max (line - get_lines_to_list () / 2, 1);
 	  return;
 	}
       line++;
@@ -1722,7 +1730,7 @@ reverse_search_command (char *regex, int from_tty)
 	  do_cleanups (cleanups);
 	  print_source_lines (current_source_symtab, line, line + 1, 0);
 	  set_internalvar_integer (lookup_internalvar ("_"), line);
-	  current_source_line = max (line - lines_to_list / 2, 1);
+	  current_source_line = max (line - get_lines_to_list () / 2, 1);
 	  return;
 	}
       line--;
@@ -2045,7 +2053,7 @@ The matching line number is also stored as the value of \"$_\"."));
     }
 
   add_setshow_zuinteger_unlimited_cmd ("listsize", class_support,
-				       &lines_to_list, _("\
+				       &setshow_listsize_var, _("\
 Set number of source lines gdb will list by default."), _("\
 Show number of source lines gdb will list by default."), NULL,
 				       NULL, show_lines_to_list,