[PATCH v2 3/4] gdb/cli: add '.' as an argument for 'list' command

[Bruno Larsen <blarsen@redhat.com>]

Currently, after the user has used the list command once, there is no
way to ask GDB to print the location where the inferior is stopped.
This commit adds a way to do that using '.' as a new argument for the
'list' command.  If the inferior isn't running, the command throws an
error.  The test gdb.base/list.exp was updated to test this new argument.

Because this necessitated having the inferior running and the test was
(seemingly unnecessarily) using printf in a non-essential way and it
would make the resulting log harder to read for no benefit, it was
replaced by a differen t statement.
---
 gdb/NEWS                        |  4 ++++
 gdb/cli/cli-cmds.c              | 26 ++++++++++++++++++++--
 gdb/doc/gdb.texinfo             |  6 ++++++
 gdb/testsuite/gdb.base/list.exp | 38 +++++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.base/list1.c  |  2 +-
 5 files changed, 73 insertions(+), 3 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index c5519e320e6..aa14e64e51c 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -85,6 +85,10 @@
   is either the last solitary line printed (if there was one) or around
   the main function.
 
+* The 'list' command now accepts '.' as an argument, which tells GDB to
+  print the location where the inferior is stopped.  If the inferior hasn't
+  started yet, the command will error out.
+
 * New commands
 
 maintenance print record-instruction [ N ]
diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index 5973aebfad3..a966142eaea 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -1232,14 +1232,14 @@ list_command (const char *arg, int from_tty)
   const char *p;
 
   /* Pull in the current default source line if necessary.  */
-  if (arg == NULL || ((arg[0] == '+' || arg[0] == '-') && arg[1] == '\0'))
+  if (arg == NULL || ((arg[0] == '+' || arg[0] == '-' || arg[0] == '.') && arg[1] == '\0'))
     {
       set_default_source_symtab_and_line ();
       symtab_and_line cursal = get_current_source_symtab_and_line ();
 
       /* If this is the first "list" since we've set the current
 	 source line, center the listing around that line.  */
-      if (get_first_line_listed () == 0)
+      if (get_first_line_listed () == 0 && (arg == nullptr || arg[0] != '.'))
 	{
 	  list_around_line (arg, cursal);
 	}
@@ -1293,6 +1293,27 @@ list_command (const char *arg, int from_tty)
 	  print_source_lines (cursal.symtab, range, 0);
 	}
 
+      /* "l *" lists the default location again.  */
+      else if (arg[0] == '.')
+	{
+	  try
+	    {
+	      /* Find the current line by getting the PC of the currently
+		 selected frame, and finding the line associated to it.  */
+	      frame_info_ptr frame = get_selected_frame (nullptr);
+	      CORE_ADDR curr_pc = get_frame_pc (frame);
+	      cursal = find_pc_line (curr_pc, 0);
+	    }
+	  catch (const gdb_exception &e)
+	    {
+	      /* If there was an exception above, it means the inferior
+		 is not running, so reset the current source location to
+		 the default.  */
+	      error (_("Inferior is not running. No current location."));
+	    }
+	  list_around_line (arg, cursal);
+	}
+
       return;
     }
 
@@ -2800,6 +2821,7 @@ and send its output to SHELL_COMMAND."));
     = add_com ("list", class_files, list_command, _("\
 List specified function or line.\n\
 With no argument, lists ten more lines after or around previous listing.\n\
+\"list .\" lists ten lines arond where the inferior is stopped.\n\
 \"list -\" lists the ten lines before a previous ten-line listing.\n\
 One argument specifies a line, and ten lines are listed around that line.\n\
 Two arguments with comma between specify starting and ending lines to list.\n\
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 9a2dff1b493..102c3f3e21e 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -9151,8 +9151,14 @@ it prints the lines around the function @code{main}.
 
 @item list -
 Print lines just before the lines last printed.
+
+@item list .
+Print the lines surrounding the location that is currently being
+examined by the user (that is, the lines around the last solitary
+line printed).
 @end table
 
+
 @cindex @code{list}, how many lines to display
 By default, @value{GDBN} prints ten source lines with any of these forms of
 the @code{list} command.  You can change this using @code{set listsize}:
diff --git a/gdb/testsuite/gdb.base/list.exp b/gdb/testsuite/gdb.base/list.exp
index 35e099ebaff..f853a9b814d 100644
--- a/gdb/testsuite/gdb.base/list.exp
+++ b/gdb/testsuite/gdb.base/list.exp
@@ -400,6 +400,41 @@ proc test_list_invalid_args {} {
 	"second use of \"list +INVALID\""
 }
 
+proc test_list_current_location {} {
+    global binfile
+    # If the first "list" command that GDB runs is "list ." GDB may be
+    # unable to recognize that the inferior isn't running, so we should
+    # reload the inferior to test that condition.
+    clean_restart
+    gdb_file_cmd ${binfile}
+
+    # Ensure that we are printing 10 lines
+    if {![set_listsize 10]} {
+	return
+    }
+
+    # First guarantee that GDB correctly identifies that the inferior
+    # isn't running.
+    gdb_test "list ." "Inferior is not running. No current location." \
+	"list . with inferior not running"
+
+    if {![runto_main]} {
+	warning "couldn't start inferior"
+	return
+    }
+
+    # Walk forward some lines
+    gdb_test "until 15" ".*15.*foo.*"
+
+    # Test that the correct location is printed and that
+    # using just "list" will print the following lines.
+    gdb_test "list ." ".*" "list current line after starting"
+    gdb_test "list" ".*" "confirm we are printing the following lines"
+
+    # Test that list . will reset to current location
+    gdb_test "list ." ".*" "list around current line again"
+}
+
 clean_restart
 gdb_file_cmd ${binfile}
 
@@ -519,4 +554,7 @@ test_list "list -" 10 2 "7-8" "5-6"
 # the current line.
 test_list "list -" 10 1 "7" "6"
 
+# Test printing the location where the inferior is stopped.
+test_list_current_location
+
 remote_exec build "rm -f list0.h"
diff --git a/gdb/testsuite/gdb.base/list1.c b/gdb/testsuite/gdb.base/list1.c
index d694495c3fb..9297f958f46 100644
--- a/gdb/testsuite/gdb.base/list1.c
+++ b/gdb/testsuite/gdb.base/list1.c
@@ -7,7 +7,7 @@ void bar (int x)
    -
    - */
 {
-    printf ("%d\n", x);
+    x++;
 
     long_line ();
 }
-- 
2.40.1