(Ada) fix handling of minimal symbols (UNOP_CAST and UNOP_ADDR)

Consider a program which provides a symbol without debugging
information. For instance, compiling the following code without -g:

    Some_Minimal_Symbol : Integer := 1234;
    pragma Export (C, Some_Minimal_Symbol, "some_minsym");

Trying to print this variable with GDB now causes an error, which
is now expected:

    (gdb) p some_minsym
    'some_minsym' has unknown type; cast it to its declared type

However, trying to cast this symbol, or to take its address
does not work:

    (gdb) p integer(some_minsym)
    'some_minsym' has unknown type; cast it to its declared type
    (gdb) p &some_minsym
    'some_minsym' has unknown type; cast it to its declared type

Another manisfestation of this issue can be seen when trying to
insert an Ada exception catchpoint for a specific standard exception
(this only occurs if the Ada runtime is built without debugging
information, which is the default).  For instance:

    $ (gdb) catch exception constraint_error
    warning: failed to reevaluate internal exception condition for catchpoint 0: 'constraint_error' has unknown type; cast it to its declared type

This is because, internally, the cachtpoint uses a condition referencing
a minimal symbol, more precisely:

   long_integer (e) = long_integer (&constraint_error)

This patch fixes all issues listed above:

  1. resolve_subexp: Special-case the handling of OP_VAR_MSYM_VALUE
     expression elements, where there are no ambiguities to be resolved
     in that situation;

  2. ada_evaluate_subexp: Enhance the handling of the UNOP_CAST
     handling so as to process the case where the target of
     the cast is a minimal symbol (as well as a symbol with debugging
     information). This mimics what's done in C.

gdb/ChangeLog:

        * ada-lang.c (resolve_subexp): Add handling of OP_VAR_MSYM_VALUE.
        (ada_evaluate_subexp_for_cast): New function.
        (ada_evaluate_subexp) <UNOP_CAST>: Replace code by call to
        ada_evaluate_subexp_for_cast.
        (ada_evaluate_subexp) <nosideret>: Replace code by call to
        eval_skip_value.
        * eval.c (evaluate_var_value): Make non-static.
        (evaluate_var_msym_value, eval_skip_value): Likewise.
        * value.h (evaluate_var_value, evaluate_var_msym_value)
        (eval_skip_value): Declare.

gdb/testsuite/ChangeLog:

        * gdb.ada/minsyms: New testcase.

Tested on x86_64-linux. No regression. Fixes the following failures:

    catch_ex.exp: continuing to Program_Error exception
    catch_ex.exp: continuing to failed assertion
    catch_ex.exp: continuing to unhandled exception
    catch_ex.exp: continuing to program completion
    complete.exp: p <Exported_Capitalized>
    complete.exp: p Exported_Capitalized
    complete.exp: p exported_capitalized
    mi_catch_ex.exp: catch Program_Error (unexpected output)
    mi_catch_ex.exp: continue to exception catchpoint hit (unknown output after running)
    mi_catch_ex.exp: continue to assert failure catchpoint hit (unknown output after running)
    mi_catch_ex.exp: continue to unhandled exception catchpoint hit (unknown output after running)
    mi_ex_cond.exp: catch C_E if i = 2 (unexpected output)

4 files changed, 103 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.ada/minsyms.exp b/gdb/testsuite/gdb.ada/minsyms.exp
new file mode 100644
index 0000000000..2c91125899
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/minsyms.exp
@@ -0,0 +1,41 @@
+# Copyright 2017 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 "ada.exp"
+
+standard_ada_testfile foo_qb07_057
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable ""] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+if ![runto "_ada_foo_qb07_057" ] then {
+  perror "Couldn't run ${testfile}"
+  return
+}
+
+gdb_test "print some_minsym" \
+         "'some_minsym' has unknown type; cast it to its declared type"
+
+gdb_test "print integer(some_minsym)" \
+         " = 1234"
+
+gdb_test "print &some_minsym" \
+         " = \\(access <data variable, no debug info>\\) 0x62c2f8 <some_minsym>"
+
+gdb_test "print /x integer(&some_minsym)" \
+         " = $hex"
diff --git a/gdb/testsuite/gdb.ada/minsyms/foo_qb07_057.adb b/gdb/testsuite/gdb.ada/minsyms/foo_qb07_057.adb
new file mode 100644
index 0000000000..5a081dc18a
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/minsyms/foo_qb07_057.adb
@@ -0,0 +1,20 @@
+--  Copyright 2017 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/>.
+
+with Pck; use Pck;
+procedure Foo_QB07_057 is
+begin
+   Increment (Some_Minimal_Symbol);
+end Foo_QB07_057;
diff --git a/gdb/testsuite/gdb.ada/minsyms/pck.adb b/gdb/testsuite/gdb.ada/minsyms/pck.adb
new file mode 100644
index 0000000000..10e8c9bd31
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/minsyms/pck.adb
@@ -0,0 +1,21 @@
+--  Copyright 2017 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/>.
+
+package body Pck is
+   procedure Increment (I: in out Integer) is
+   begin
+      I := I + 1;
+   end Increment;
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/minsyms/pck.ads b/gdb/testsuite/gdb.ada/minsyms/pck.ads
new file mode 100644
index 0000000000..4ad4c07837
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/minsyms/pck.ads
@@ -0,0 +1,21 @@
+--  Copyright 2017 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/>.
+
+package Pck is
+   Some_Minimal_Symbol : Integer := 1234;
+   pragma Export (C, Some_Minimal_Symbol, "some_minsym");
+
+   procedure Increment (I: in out Integer);
+end Pck;