[PATCH] [gdb/exp] Fix cast handling for indirection

[Tom de Vries]

Consider a test-case compiled without debug info, containing:
...
char a = 'a';

char *
a_loc (void)
{
  return &a;
}
...

We get:
...
(gdb) p (char)*a_loc ()
Cannot access memory at address 0x10
...

There's a bug in unop_ind_base_operation::evaluate that evaluates
"(char)*a_loc ()" the same as:
...
(gdb) p (char)*(char)a_loc ()
Cannot access memory at address 0x10
...

Fix this by instead evaluating it the same as:
...
(gdb) p (char)*(char *)a_loc ()
$1 = 97 'a'
...

Tested on x86_64-linux.

PR exp/31693
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31693
---
 gdb/expop.h                                 |  8 +++--
 gdb/testsuite/gdb.base/cast-indirection.c   | 31 ++++++++++++++++
 gdb/testsuite/gdb.base/cast-indirection.exp | 40 +++++++++++++++++++++
 3 files changed, 76 insertions(+), 3 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/cast-indirection.c
 create mode 100644 gdb/testsuite/gdb.base/cast-indirection.exp

diff --git a/gdb/expop.h b/gdb/expop.h
index b81e228c07e..1967d9779b7 100644
--- a/gdb/expop.h
+++ b/gdb/expop.h
@@ -1513,9 +1513,11 @@ class unop_ind_base_operation
 		   struct expression *exp,
 		   enum noside noside) override
   {
-    if (expect_type != nullptr && expect_type->code () == TYPE_CODE_PTR)
-      expect_type = check_typedef (expect_type)->target_type ();
-    value *val = std::get<0> (m_storage)->evaluate (expect_type, exp, noside);
+    struct type *pointer_to_expect_type = (expect_type != nullptr
+					   ? lookup_pointer_type (expect_type)
+					   : nullptr);
+    value *val
+      = std::get<0> (m_storage)->evaluate (pointer_to_expect_type, exp, noside);
     return eval_op_ind (expect_type, exp, noside, val);
   }
 
diff --git a/gdb/testsuite/gdb.base/cast-indirection.c b/gdb/testsuite/gdb.base/cast-indirection.c
new file mode 100644
index 00000000000..d59c66ead35
--- /dev/null
+++ b/gdb/testsuite/gdb.base/cast-indirection.c
@@ -0,0 +1,31 @@
+/* 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/>.  */
+
+char a = 'a';
+
+char *
+a_loc (void)
+{
+  return &a;
+}
+
+int
+main (void)
+{
+  int res = *a_loc () == 'a';
+  return !res;
+}
diff --git a/gdb/testsuite/gdb.base/cast-indirection.exp b/gdb/testsuite/gdb.base/cast-indirection.exp
new file mode 100644
index 00000000000..d2c6d58e3ca
--- /dev/null
+++ b/gdb/testsuite/gdb.base/cast-indirection.exp
@@ -0,0 +1,40 @@
+# Copyright (C) 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/>.
+
+# Check that "p (char)*a_loc ()" is handled as "p (char)*(char *)a_loc ()".
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
+	  {nodebug}] == -1} {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_test "p a_loc ()" \
+    "'a_loc' has unknown return type; cast the call to its declared return type"
+
+gdb_test "p *a_loc ()" \
+    "'a_loc' has unknown return type; cast the call to its declared return type"
+
+gdb_test "p *(char *)a_loc ()" " = 97 'a'"
+
+gdb_test "p (char)*(char *)a_loc ()" " = 97 'a'"
+
+# Regression test for PR31693.
+gdb_test "p (char)*a_loc ()" " = 97 'a'"

base-commit: 5ce0e02478cc79a260c7e29822450284a32b9b12
-- 
2.35.3