[PATCH v2] gdb: Change "list ." command's error when no debuginfo is available

[Guinevere Larsen <blarsen@redhat.com>]

From: Simon Marchi <simark@simark.ca>

Currently, when a user tries to list the current location, there are 2
different error messages that can happen, either:

    (gdb) list .
    No symbol table is loaded.  Use the "file" command.
or
    (gdb) list .
    No debug information available to print source lines.

The difference here is if gdb can find any symtabs at all or not, which
is not something too important for end-users - and isn't informative at
all. This commit changes it so that the error always says that there
isn't debug information available, with these two variants:

    (gdb) list .
    No debug information available to print source lines at current PC (0x55555555511d).
or
    (gdb) list .
    No debug information available to print source lines at default location.

The difference now is if the inferior has started already, which is
controlled by the user and may be useful.

Unfortunately, it isn't as easy to differentiate if the symtab found for
other list parameters is correct, so other invocations, such as "list +"
still retain their original error message.

Co-Authored-By: Simon Marchi <simark@simark.ca>
---

Changes for v2:
  Added NEWS entry, should have done that from the start oops.
  Added test. This test aims to roughly recreate a situation where the
    current function is in a spot with no debuginfo, and being called
    from somewhere that has debuginfo.

---
 gdb/NEWS                                      |  6 ++
 gdb/cli/cli-cmds.c                            | 47 +++++++++----
 .../gdb.base/list-dot-nodebug-extra.c         | 24 +++++++
 gdb/testsuite/gdb.base/list-dot-nodebug.c     | 34 ++++++++++
 gdb/testsuite/gdb.base/list-dot-nodebug.exp   | 67 +++++++++++++++++++
 5 files changed, 164 insertions(+), 14 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/list-dot-nodebug-extra.c
 create mode 100644 gdb/testsuite/gdb.base/list-dot-nodebug.c
 create mode 100644 gdb/testsuite/gdb.base/list-dot-nodebug.exp

diff --git a/gdb/NEWS b/gdb/NEWS
index feb3a37393a..99909414796 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -36,6 +36,12 @@ set unwindonsignal on|off
 show unwindonsignal
   These commands are now aliases for the new set/show unwind-on-signal.
 
+list .
+  When using the command "list ." in a location that has no debug information
+  or no file loaded, GDB now says that there is no debug information to print
+  lines.  This makes it more obvious that there is no information, as opposed
+  to implying there is no inferior loaded.
+
 * New commands
 
 info missing-debug-handler
diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index 3afe2178199..a537a370cc2 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -1235,37 +1235,39 @@ list_command (const char *arg, int from_tty)
   /* Pull in the current default source line if necessary.  */
   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 && (arg == nullptr || arg[0] != '.'))
 	{
-	  list_around_line (arg, cursal);
+	  set_default_source_symtab_and_line ();
+	  list_around_line (arg, get_current_source_symtab_and_line ());
 	}
 
       /* "l" and "l +" lists the next few lines, unless we're listing past
 	 the end of the file.  */
       else if (arg == nullptr || arg[0] == '+')
 	{
+	  set_default_source_symtab_and_line ();
+	  const symtab_and_line cursal = get_current_source_symtab_and_line ();
 	  if (last_symtab_line (cursal.symtab) >= cursal.line)
 	    print_source_lines (cursal.symtab,
 				source_lines_range (cursal.line), 0);
 	  else
-	    {
-	      error (_("End of the file was already reached, use \"list .\" to"
-		       " list the current location again"));
-	    }
+	    error (_("End of the file was already reached, use \"list .\" to"
+		     " list the current location again"));
 	}
 
       /* "l -" lists previous ten lines, the ones before the ten just
 	 listed.  */
       else if (arg[0] == '-')
 	{
+	  set_default_source_symtab_and_line ();
+	  const symtab_and_line cursal = get_current_source_symtab_and_line ();
+
 	  if (get_first_line_listed () == 1)
 	    error (_("Already at the start of %s."),
 		   symtab_to_filename_for_display (cursal.symtab));
+
 	  source_lines_range range (get_first_line_listed (),
 				    source_lines_range::BACKWARD);
 	  print_source_lines (cursal.symtab, range, 0);
@@ -1274,25 +1276,42 @@ list_command (const char *arg, int from_tty)
       /* "list ." lists the default location again.  */
       else if (arg[0] == '.')
 	{
+	  std::optional<const symtab_and_line> cursal;
 	  if (target_has_stack ())
 	    {
 	      /* 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);
+	      cursal.emplace (find_pc_line (curr_pc, 0));
+
+	      if (cursal->symtab == nullptr)
+		error
+		  (_("No debug information available to print source lines at "
+		     "current PC (%s)."), paddress (get_frame_arch (frame),
+						    curr_pc));
 	    }
 	  else
 	    {
 	      /* The inferior is not running, so reset the current source
 		 location to the default (usually the main function).  */
 	      clear_current_source_symtab_and_line ();
-	      set_default_source_symtab_and_line ();
-	      cursal = get_current_source_symtab_and_line ();
+	      try
+		{
+		  set_default_source_symtab_and_line ();
+		}
+	      catch (const gdb_exception &e)
+		{
+		  error (_("No debug information available to print source "
+			   "lines at default location"));
+		}
+	      cursal.emplace (get_current_source_symtab_and_line ());
+
+	      gdb_assert (cursal->symtab != nullptr);
 	    }
-	  if (cursal.symtab == nullptr)
-	    error (_("No debug information available to print source lines."));
-	  list_around_line (arg, cursal);
+
+	  list_around_line (arg, *cursal);
+
 	  /* Set the repeat args so just pressing "enter" after using "list ."
 	     will print the following lines instead of the same lines again. */
 	  if (from_tty)
diff --git a/gdb/testsuite/gdb.base/list-dot-nodebug-extra.c b/gdb/testsuite/gdb.base/list-dot-nodebug-extra.c
new file mode 100644
index 00000000000..c3d2416e70d
--- /dev/null
+++ b/gdb/testsuite/gdb.base/list-dot-nodebug-extra.c
@@ -0,0 +1,24 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2024 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/>.  */
+
+extern void bar(int *);
+
+void
+foo (int *x)
+{
+  bar (x);
+}
diff --git a/gdb/testsuite/gdb.base/list-dot-nodebug.c b/gdb/testsuite/gdb.base/list-dot-nodebug.c
new file mode 100644
index 00000000000..5e1a09fa645
--- /dev/null
+++ b/gdb/testsuite/gdb.base/list-dot-nodebug.c
@@ -0,0 +1,34 @@
+/* main */
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2024 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/>.  */
+
+extern void foo (int *x);
+
+int x;
+
+void
+bar (int *p)
+{
+  *p++;
+}
+
+int
+main ()
+{
+  foo (&x);
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/list-dot-nodebug.exp b/gdb/testsuite/gdb.base/list-dot-nodebug.exp
new file mode 100644
index 00000000000..7c4144da8ab
--- /dev/null
+++ b/gdb/testsuite/gdb.base/list-dot-nodebug.exp
@@ -0,0 +1,67 @@
+# Copyright 2005-2024 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/>.
+
+# This test is here to confirm that the command "list ." will print the
+# same message if GDB detects no debug information at all, or detects some
+# but nothing for the current objfile.
+
+require !use_gdb_stub
+
+set linkflags [list additional_flags="-static"]
+
+if { ![gdb_can_simple_compile static-libc \
+	   {
+	       void main (void) { return 0; }
+	   } \
+	   executable $linkflags] } {
+    untested "Can't statically link"
+    return -1
+}
+
+standard_testfile .c -extra.c
+set objmainfile [standard_output_file ${testfile}-main.o]
+set objextrafile [standard_output_file ${testfile}-extra.o]
+
+if {[gdb_compile "$srcdir/$subdir/$srcfile" $objmainfile object {nodebug}] != "" } {
+    untested "couldn't compile main file into object"
+    return -1
+}
+
+foreach_with_prefix debug {"none" "some"} {
+
+    set flags "nodebug"
+    if {$debug == "some"} {
+	set flags "debug"
+    }
+
+    if {[prepare_for_testing_full "failed to prepare" \
+	    [list ${testfile}-${debug} $linkflags \
+		$srcfile [list nodebug] \
+		$srcfile2 [list $debug]]]} {
+	return -1
+    }
+
+    gdb_test "list ." \
+	"No debug information available to print source lines.*" \
+	"print before start"
+
+    if { ![runto bar] } {
+	return -1
+    }
+
+    gdb_test "list ." \
+	"No debug information available to print source lines at current PC.*" \
+	"print after start"
+}
-- 
2.44.0