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[PATCH] Do not consider reference types as dynamic


Hello,

I'm working on a GCC patch that fixes the type of Ada functions that return their result by reference: the debugging information currently says they return a pointer to the result and my patch turns these into references. The intent is that when evaluating a call to such functions from debuggers, the returned value is automatically dereferenced:

   # Currently we have:
   (gdb) print my_function("foo")
   $1 = (access ...) 0x...

   # We would like to have instead:
   (gdb) print my_function("foo")
   $1 = <referenced object>

Doing so in GDB is currently not possible when the referenced object type is dynamic. Indeed, the return value for such calls is not in memory and GDB considers reference types as dynamic iff the referenced type is dynamic. As a consequence, the type resolving process ends up trying to read memory at address 0x0, fails to do so and aborts printing the final value:

    # With my locally patched GCC, I have:
    (gdb) print my_function("foo")
    $1 = Cannot access memory at address 0x0

The attached patch fixes GDB so that the above works. It just makes GDB never consider reference types as dynamic (which makes sense per se IMHO) so this memory problem does not occurs.

I tested this patch on x86_64-linux with C, C++, Ada, Fortran and Java compilers: it triggers no regression. Note that the testcase it adds (gdb.ada/funcall_ref.exp) cannot pass without my local GCC patch and relies on my previous submitted patch (https://www.sourceware.org/ml/gdb-patches/2015-03/msg00241.html).

Ok to push?
Thank you in advance!

    gdb/ChangeLog:
    2015-03-10  Pierre-Marie de Rodat  <derodat@adacore.com>

        * gdbtypes.c (is_dynamic_type_internal): Remove special handling
        of TYPE_CODE_REF types so that they are not considered as
        dynamic depending on the referenced type.

    gdb/testsuite/ChangeLog:
    2015-03-10  Pierre-Marie de Rodat  <derodat@adacore.com>

        * gdb.ada/funcall_ref.exp: New file.
        * gdb.ada/funcall_ref/foo.adb: New file.

--
Pierre-Marie de Rodat
>From fbd03f077be85a8c455aa82cf247cc12cc9dea5f Mon Sep 17 00:00:00 2001
From: Pierre-Marie de Rodat <derodat@adacore.com>
Date: Tue, 10 Mar 2015 09:18:45 +0100
Subject: [PATCH] Do not consider reference types as dynamic

Even when referenced types are dynamic, the corresponding referencing
type should not be considered as dynamic: it's only a pointer.  This
prevents reference type for values not in memory to be resolved.

gdb/ChangeLog:
2015-03-10  Pierre-Marie de Rodat  <derodat@adacore.com>

	* gdbtypes.c (is_dynamic_type_internal): Remove special handling
	of TYPE_CODE_REF types so that they are not considered as
	dynamic depending on the referenced type.

gdb/testsuite/ChangeLog:
2015-03-10  Pierre-Marie de Rodat  <derodat@adacore.com>

	* gdb.ada/funcall_ref.exp: New file.
	* gdb.ada/funcall_ref/foo.adb: New file.
---
 gdb/gdbtypes.c                            |  4 ---
 gdb/testsuite/gdb.ada/funcall_ref.exp     | 42 +++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.ada/funcall_ref/foo.adb | 19 ++++++++++++++
 3 files changed, 61 insertions(+), 4 deletions(-)
 create mode 100644 gdb/testsuite/gdb.ada/funcall_ref.exp
 create mode 100644 gdb/testsuite/gdb.ada/funcall_ref/foo.adb

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index a80151c..f75eac5 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1748,10 +1748,6 @@ is_dynamic_type_internal (struct type *type, int top_level)
 {
   type = check_typedef (type);
 
-  /* We only want to recognize references at the outermost level.  */
-  if (top_level && TYPE_CODE (type) == TYPE_CODE_REF)
-    type = check_typedef (TYPE_TARGET_TYPE (type));
-
   /* Types that have a dynamic TYPE_DATA_LOCATION are considered
      dynamic, even if the type itself is statically defined.
      From a user's point of view, this may appear counter-intuitive;
diff --git a/gdb/testsuite/gdb.ada/funcall_ref.exp b/gdb/testsuite/gdb.ada/funcall_ref.exp
new file mode 100644
index 0000000..b754e59
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/funcall_ref.exp
@@ -0,0 +1,42 @@
+# Copyright 2008-2015 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
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable \
+                     [list debug]] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "STOP" ${testdir}/foo.adb]
+runto "foo.adb:$bp_location"
+
+# Test printing and type-printing of a discriminated record that a function
+# returns by reference.
+
+gdb_test "p get (\"Hello world!\")" \
+         "= \\(n => 12, s => \"Hello world!\"\\)" \
+         "p get (\"Hello world!\")"
+
+gdb_test "ptype get (\"Hello world!\")" \
+         [multi_line "type = <ref> record" \
+                     "    n: natural;" \
+                     "    s: access array \\(1 \\.\\. n\\) of character;" \
+                     "end record"] \
+         "ptype get (\"Hello world!\")"
diff --git a/gdb/testsuite/gdb.ada/funcall_ref/foo.adb b/gdb/testsuite/gdb.ada/funcall_ref/foo.adb
new file mode 100644
index 0000000..17d7641
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/funcall_ref/foo.adb
@@ -0,0 +1,19 @@
+procedure Foo is
+   type Bar (N : Natural) is record
+      S : String (1 .. N);
+   end record;
+
+   function Get (S : String) return Bar is
+   begin
+      return (N => S'Length, S => S);
+   end Get;
+
+   procedure Do_Nothing (B : Bar) is
+   begin
+      null;
+   end Do_Nothing;
+
+   B : Bar := Get ("Foo");
+begin
+   Do_Nothing (B); --  STOP
+end Foo;
-- 
2.3.1


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