[gdb/symtab] Fix handling of DW_TAG_unspecified_type

Currently, the test-case contained in this patch fails:
...
(gdb) p (int) foo ()^M
Invalid cast.^M
(gdb) FAIL: gdb.dwarf2/dw2-unspecified-type.exp: p (int) foo ()
...
because DW_TAG_unspecified_type is translated as void.

There's some code in read_unspecified_type that marks the type as stub, but
that's only active for ada:
...
  if (cu->lang () == language_ada)
    type->set_is_stub (true);
...

Fix this by:
- marking the type as a stub for all languages, and
- handling the stub return type case in call_function_by_hand_dummy.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29558

3 files changed, 119 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type-foo.c b/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type-foo.c
new file mode 100644
index 0000000..b1e3a8b
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type-foo.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2022 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/>.  */
+
+int
+foo (void)
+{
+  asm ("foo_label: .globl foo_label");
+}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type.c b/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type.c
new file mode 100644
index 0000000..e321820
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type.c
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2022 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 int foo (void);
+
+int
+main (void)
+{
+  int res = foo ();
+  return res;
+}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type.exp b/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type.exp
new file mode 100644
index 0000000..20c31dc
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-unspecified-type.exp
@@ -0,0 +1,72 @@
+# Copyright 2022 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/>.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile .c -foo.c dwz.S
+
+set foo_res \
+    [function_range foo \
+	 [list ${srcdir}/${subdir}/$srcfile ${srcdir}/${subdir}/$srcfile2]]
+lassign $foo_res \
+    foo_start foo_len
+set foo_end "$foo_start + $foo_len"
+
+# Create the DWARF.
+set asm_file [standard_output_file $srcfile3]
+Dwarf::assemble $asm_file {
+    global foo_start foo_end
+    declare_labels unspecified_type_label
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_Mips_Assembler}
+	} {
+	    unspecified_type_label: unspecified_type {}
+
+	    DW_TAG_subprogram {
+		{name foo}
+		{low_pc $foo_start addr}
+		{high_pc $foo_end addr}
+		{type :$unspecified_type_label}
+	    }
+
+	}
+    }
+}
+
+if [prepare_for_testing "failed to prepare" $testfile \
+	"${asm_file} ${srcfile} ${srcfile2}" {}] {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# Print the function type.  Return type should be stub type, which is printed
+# as void.
+gdb_test "ptype foo" "type = void \\(void\\)"
+
+# Call the function, casting the function to the correct function type.
+gdb_test "p ((int (*) ()) foo) ()" " = 0"
+
+# Call the function, casting the function result to the correct type.
+gdb_test "p (int) foo ()" " = 0"