[gdb] Further fix "value is not available" with debug frame

In commit 2aaba744467 ("[gdb] Fix "value is not available" with debug frame")
I fixed a case in frame_unwind_register_value where using "set debug frame on"
caused an "info frame" command to abort, reporting a "value is not available"
error, due to the tpidruro register being unavailable.

Subsequently, commit bbb12eb9c84 ("gdb/arm: Remove tpidruro register from
non-FreeBSD target descriptions") removed the unavailable register, which
caused a progression on test-case gdb.base/inline-frame-cycle-unwind.exp.

While investigating the progression (see PR python/31437), I found that the
"debug frame" output of the test-case (when reverting commit bbb12eb9c84)
showed a smilar problem:
...
Python Exception <class 'gdb.error'>: value is not available^M
...
that was absent without "debug frame".

Fix this likewise in fetch_lazy_register, and update the test-case to check
for the exception.

Furthermore, I realized that there's both value::entirely_available and
value::entirely_unavailable, and that commit 2aaba744467 handled the case
of !entirely_available by printing unavailable.

Instead, print:
- "unavailable" for entirely_unavailable, and
- "partly unavailable" for !entirely_unavailable && !entirely_available.

Tested on x86_64-linux and arm-linux.

3 files changed, 26 insertions, 12 deletions

diff --git a/gdb/frame.c b/gdb/frame.c
index d3c4c96..f1f9704 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -1315,9 +1315,7 @@ 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
+	  else if (value->entirely_available ())
 	    {
 	      int i;
 	      gdb::array_view<const gdb_byte> buf = value->contents ();
@@ -1328,6 +1326,10 @@ frame_unwind_register_value (const frame_info_ptr &next_frame, int regnum)
 		gdb_printf (&debug_file, "%02x", buf[i]);
 	      gdb_printf (&debug_file, "]");
 	    }
+	  else if (value->entirely_unavailable ())
+	    gdb_printf (&debug_file, " unavailable");
+	  else
+	    gdb_printf (&debug_file, " partly unavailable");
 	}
 
       frame_debug_printf ("%s", debug_file.c_str ());
diff --git a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
index 8263275..85e3cc3 100644
--- a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
+++ b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
@@ -131,9 +131,14 @@ with_test_prefix "cycle at level 1" {
 gdb_test "maint flush register-cache" \
     "Register cache flushed\\." ""
 gdb_test_no_output "set debug frame 1"
+set ok 1
 gdb_test_multiple "bt" "backtrace with debugging on" {
     -re "^$gdb_prompt $" {
-	pass $gdb_test_name
+	gdb_assert { $ok } $gdb_test_name
+    }
+    -re "Python Exception <class 'gdb.error'>: \[^\r\n\]*\r\n" {
+	set ok 0
+	exp_continue
     }
     -re "\[^\r\n\]+\r\n" {
 	exp_continue
diff --git a/gdb/value.c b/gdb/value.c
index a2b2721..7ddfeb7 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -4014,9 +4014,6 @@ value::fetch_lazy_register ()
 	}
       else
 	{
-	  int i;
-	  gdb::array_view<const gdb_byte> buf = new_val->contents ();
-
 	  if (new_val->lval () == lval_register)
 	    gdb_printf (&debug_file, " register=%d", new_val->regnum ());
 	  else if (new_val->lval () == lval_memory)
@@ -4026,11 +4023,21 @@ value::fetch_lazy_register ()
 	  else
 	    gdb_printf (&debug_file, " computed");
 
-	  gdb_printf (&debug_file, " bytes=");
-	  gdb_printf (&debug_file, "[");
-	  for (i = 0; i < register_size (gdbarch, regnum); i++)
-	    gdb_printf (&debug_file, "%02x", buf[i]);
-	  gdb_printf (&debug_file, "]");
+	  if (new_val->entirely_available ())
+	    {
+	      int i;
+	      gdb::array_view<const gdb_byte> buf = new_val->contents ();
+
+	      gdb_printf (&debug_file, " bytes=");
+	      gdb_printf (&debug_file, "[");
+	      for (i = 0; i < register_size (gdbarch, regnum); i++)
+		gdb_printf (&debug_file, "%02x", buf[i]);
+	      gdb_printf (&debug_file, "]");
+	    }
+	  else if (new_val->entirely_unavailable ())
+	    gdb_printf (&debug_file, " unavailable");
+	  else
+	    gdb_printf (&debug_file, " partly unavailable");
 	}
 
       frame_debug_printf ("%s", debug_file.c_str ());