gdb/dap: check values are available before converting to int

In VariableReference.to_object, we try to convert a gdb.Value to an
int without checking if the value is actually available.  This came to
light in PR gdb/33345, after the x86 CET shadow stack patches were
merged.

If the x86 CET shadow stack register is available on the machine,
but the shadow stack feature is not enabled at run time, then the
register will show as "<unavailable>".

As the register is of type 'void *', then in the DAP code we try to
add a 'memoryReference' attribute with the value of the register
formatted as hex.  This will fail if the register is unavailable.

To test this change you'll need:

  (a) a machine which support the shadow stack feature, and

  (b) to revert the changes from commit 63b862be762e1e6e7 in the file
      gdb.dap/scopes.exp.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33345
Reviewed-By: Christina Schimpe <christina.schimpe@intel.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/gdb/python/lib/gdb/dap/varref.py b/gdb/python/lib/gdb/dap/varref.py
index 1b54fe7..d18197b 100644
--- a/gdb/python/lib/gdb/dap/varref.py
+++ b/gdb/python/lib/gdb/dap/varref.py
@@ -246,7 +246,11 @@ class VariableReference(BaseReference):
             # changed DAP to allow memory references for any of the
             # variable response requests, and to lift the restriction
             # to pointer-to-function from Variable.
-            if self._value.type.strip_typedefs().code == gdb.TYPE_CODE_PTR:
+            if (
+                self._value.type.strip_typedefs().code == gdb.TYPE_CODE_PTR
+                and not self._value.is_optimized_out
+                and not self._value.is_unavailable
+            ):
                 result["memoryReference"] = hex(int(self._value))
         if client_bool_capability("supportsVariableType"):
             result["type"] = str(self._value.type)