[gdb] Fix "value is not available" with debug frame

On arm-linux, with a started hello world, running "info frame" works fine, but
when I set debug frame to on, I run into:
...
(gdb) info frame
  ...
[frame] frame_unwind_register_value: exit
value is not available
(gdb)
...

The problem is here in frame_unwind_register_value:
...
          if (value->lazy ())
            gdb_printf (&debug_file, " lazy");
          else
            {
              int i;
              gdb::array_view<const gdb_byte> buf = value->contents ();
...
where we call value->contents () while !value->entirely_available ().

Fix this by checking value->entirely_available () and printing:
...
    [frame] frame_unwind_register_value:   -> register=91 unavailable
...

Tested on arm-linux.

PR gdb/31369
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31369

4 files changed, 106 insertions, 0 deletions

diff --git a/gdb/frame.c b/gdb/frame.c
index 9c3f0df..5c7aae9 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -1315,6 +1315,8 @@ frame_unwind_register_value (const frame_info_ptr &next_frame, int regnum)
 
 	  if (value->lazy ())
 	    gdb_printf (&debug_file, " lazy");
+	  else if (!value->entirely_available ())
+	    gdb_printf (&debug_file, " unavailable");
 	  else
 	    {
 	      int i;
diff --git a/gdb/testsuite/gdb.base/debug-frame-2.c b/gdb/testsuite/gdb.base/debug-frame-2.c
new file mode 100644
index 0000000..571b140
--- /dev/null
+++ b/gdb/testsuite/gdb.base/debug-frame-2.c
@@ -0,0 +1,22 @@
+/* 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/>.  */
+
+void
+foo (void)
+{
+
+}
diff --git a/gdb/testsuite/gdb.base/debug-frame.c b/gdb/testsuite/gdb.base/debug-frame.c
new file mode 100644
index 0000000..629c309
--- /dev/null
+++ b/gdb/testsuite/gdb.base/debug-frame.c
@@ -0,0 +1,25 @@
+/* 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 (void);
+
+int
+main (void)
+{
+  foo ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/debug-frame.exp b/gdb/testsuite/gdb.base/debug-frame.exp
new file mode 100644
index 0000000..f928f19
--- /dev/null
+++ b/gdb/testsuite/gdb.base/debug-frame.exp
@@ -0,0 +1,57 @@
+# 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/>.
+
+# Test relies on checking gdb debug output. Do not run if gdb debug is
+# enabled as any debug will be redirected to the log.
+require !gdb_debug_enabled
+
+standard_testfile .c -2.c
+set srcfiles [list $srcfile $srcfile2]
+if {[prepare_for_testing "failed to prepare" $testfile $srcfiles]} {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# Redirect debug output to file.
+set logfile [host_standard_output_file gdb.txt]
+gdb_test_no_output "set logging file $logfile" \
+    "set logging file [file tail $logfile]"
+gdb_test_no_output "set logging debugredirect on"
+gdb_test "set logging enabled on"
+
+# Enable debug frame.
+gdb_test "set debug frame 1"
+
+# Check that calling info frame doesn't trigger an exception that escapes to
+# the CLI.
+set re_locals " Locals at \[^\r\n\]*"
+set re_regs1 " Saved registers:"
+set re_reg "\[^ \]+ at $hex"
+set re_regs2 "  $re_reg,( $re_reg,)*"
+set re_regs3 "  ${re_reg}(, $re_reg)*"
+
+set re1 $re_locals
+set re2 \
+    [multi_line \
+	 $re_locals\
+	 $re_regs1 \
+	 ($re_regs2\r\n)*$re_regs3]
+gdb_test "info frame" "\r\n($re1|$re2)"
+
+gdb_test_no_output "set debug frame 0"
+gdb_test "set logging enabled off"