gdb: Avoid signed integer overflow when printing source lines

When printing source lines with calls to print_source_lines we need to
pass a start line number and an end line number.  The end line number
is calculated by calling get_lines_to_list and adding this value to
the start line number.  For example this code from list_command:

    print_source_lines (cursal.symtab, first,
                        first + get_lines_to_list (), 0);

The problem is that get_lines_to_list returns a value based on the
GDB setting `set listsize LISTSIZE`.  By default LISTSIZE is 10,
however, its also possible to set LISTSIZE to unlimited, in which
case get_lines_to_list will return INT_MAX.

As the parameter signature for print_source_lines is:

  void print_source_lines (struct symtab *, int, int,
                           print_source_lines_flags);

and `first` in the above code is an `int`, then when LISTSIZE is
`unlimited` the above code will result in signed integer overflow,
which is undefined.

The solution in this patch is a new class source_lines_range that can
be constructed from a single line number and a direction (forward or
backward).  The range is then constructed from the line number and the
value of get_lines_to_list.

gdb/ChangeLog:

	* cli/cli-cmds.c (list_command): Pass a source_lines_range to
	print_source_lines.
	* source.c (print_source_lines_base): Update line number check.
	(print_source_lines): New function.
	(source_lines_range::source_lines_range): New function.
	* source.h (class source_lines_range): New class.
	(print_source_lines): New declaration.

1 files changed, 48 insertions, 0 deletions

diff --git a/gdb/source.h b/gdb/source.h
index fcd83da..f1b5f6e 100644
--- a/gdb/source.h
+++ b/gdb/source.h
@@ -157,6 +157,54 @@ DEF_ENUM_FLAGS_TYPE (enum print_source_lines_flag, print_source_lines_flags);
 extern void print_source_lines (struct symtab *s, int line, int stopline,
 				print_source_lines_flags flags);
 
+/* Wrap up the logic to build a line number range for passing to
+   print_source_lines when using get_lines_to_list.  An instance of this
+   class can be built from a single line number and a direction (forward or
+   backward) the range is then computed using get_lines_to_list.  */
+class source_lines_range
+{
+public:
+  /* When constructing the range from a single line number, does the line
+     range extend forward, or backward.  */
+  enum direction
+  {
+   FORWARD,
+   BACKWARD
+  };
+
+  /* Construct a SOURCE_LINES_RANGE starting at STARTLINE and extending in
+   direction DIR.  The number of lines is from GET_LINES_TO_LIST.  If the
+   direction is backward then the start is actually (STARTLINE -
+   GET_LINES_TO_LIST).  There is also logic in place to ensure the start
+   is always 1 or more, and the end will be at most INT_MAX.  */
+  explicit source_lines_range (int startline, direction dir = FORWARD);
+
+  /* Construct a SOURCE_LINES_RANGE from STARTLINE to STOPLINE.  */
+  explicit source_lines_range (int startline, int stopline)
+    : m_startline (startline),
+      m_stopline (stopline)
+  { /* Nothing.  */ }
+
+  /* Return the line to start listing from.  */
+  int startline () const
+  { return m_startline; }
+
+  /* Return the line after the last line that should be listed.  */
+  int stopline () const
+  { return m_stopline; }
+
+private:
+
+  /* The start and end of the range.  */
+  int m_startline;
+  int m_stopline;
+};
+
+/* Variation of previous print_source_lines that takes a range instead of a
+   start and end line number.  */
+extern void print_source_lines (struct symtab *s, source_lines_range r,
+				print_source_lines_flags flags);
+
 /* Forget line positions and file names for the symtabs in a
    particular objfile.  */
 extern void forget_cached_source_info_for_objfile (struct objfile *);