[Bug gdb/18149] New: The gdb cannot evaluate a C++ expression generated by the "-var-info-path-expression" for member of class.

[Bug gdb/18149] New: The gdb cannot evaluate a C++ expression generated by the "-var-info-path-expression" for member of class.

[mihail.nistor at freescale dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18149

            Bug ID: 18149
           Summary: The gdb cannot evaluate a C++ expression generated by
                    the "-var-info-path-expression" for member of class.
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: mihail.nistor at freescale dot com

Created attachment 8199
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8199&action=edit
an example, gdb and gcc information

The Eclipse CDT C++ uses the "-var-info-path-expression" command from “mi” to
obtain the expression for a certain variable. After that the expression is
evaluated by using the "-data-evaluate-expression" command from mi and finally
the result will be displayed in the detail panel from Variable/Expression View.

Let's have an example:

class A
{
public:
  A():_a(1) {}

private:
  int _a;
};

class B: public A
{
public:
  B(double b);

private:
  double _b;
};

B::B(double b):A()
{
  _b = b;  // line 23 in test.cpp is here !
}

The reproducible steps are below:
1) The command line to compile the test case
g++ -O0 -g -o test.elf test.cpp
2) Start the gdb
gdb test.elf
3) Set a break-point at line 23 in the test.cpp file
(gdb) b test.cpp:23
4) run
(gdb) run
5) Create a variable for "this" and explore the member of class;
   after that try to evaluate the expression obtained 
   from the "-var-info-path-expression" command
(gdb) interpreter-exec mi "-var-create --thread 1 --frame 0 - * this"
response from gdb == >
^done,name="var1",numchild="2",value="0x7fffffffe860",type="B *
const",thread-id="1",has_more="0"
(gdb) interpreter-exec mi "-var-list-children var1"
response from gdb == >
^done,numchild="2",children=[child={name="var1.A",exp="A",numchild="1",type="A",thread-id="1"},child={name="var1.private",exp="private",numchild="1",thread-id="1"}],has_more="0"
(gdb) interpreter-exec mi "-var-list-children var1.A"
response from gdb == >
^done,numchild="1",children=[child={name="var1.A.private",exp="private",numchild="1",thread-id="1"}],has_more="0"
(gdb) interpreter-exec mi "-var-info-path-expression var1.A"
response from gdb == > ^done,path_expr="(*(class A*) this)"
(gdb) print (*(class A*) this)
response from gdb == > This context has class, union or enum A, not a struct.
(gdb) print (*(struct A*) this)
response from gdb == > This context has class, union or enum A, not a struct.
(gdb) interpreter-exec mi '-data-evaluate-expression --thread 1 --frame 0
"(*(struct A*) this)"'
response from gdb == > ^error,msg="This context has class, union or enum A, not
a struct."
Here you can see the first type of C++ expression that cannot be evaluated!

(gdb) interpreter-exec mi "-var-list-children var1.A.private"
response from gdb == >
^done,numchild="1",children=[child={name="var1.A.private._a",exp="_a",numchild="0",type="int",thread-id="1"}],has_more="0"
(gdb) interpreter-exec mi "-var-list-children var1.A.private._a"
response from gdb == > ^done,numchild="0",has_more="0"
(gdb) interpreter-exec mi "-var-info-path-expression var1.A.private._a"
response from gdb == > ^done,path_expr="(((*(class A*) this))._a)"
(gdb) print (((*(class A*) this))._a)
response from gdb == > This context has class, union or enum A, not a struct.
(gdb) print (((*(struct A*) this))._a)
response from gdb == > This context has class, union or enum A, not a struct.
(gdb) interpreter-exec mi '-data-evaluate-expression --thread 1 --frame 0
"(((*(class A*) this))._a)"'
response from gdb == > ^error,msg="This context has class, union or enum A, not
a struct."
Here you can see the second type of C++ expression that cannot be evaluated!

-- 
You are receiving this mail because:
You are on the CC list for the bug.
>From gdb-prs-return-17707-listarch-gdb-prs=sources.redhat.com@sourceware.org Fri Mar 20 03:06:43 2015
Return-Path: <gdb-prs-return-17707-listarch-gdb-prs=sources.redhat.com@sourceware.org>
Delivered-To: listarch-gdb-prs@sources.redhat.com
Received: (qmail 102709 invoked by alias); 20 Mar 2015 03:06:42 -0000
Mailing-List: contact gdb-prs-help@sourceware.org; run by ezmlm
Precedence: bulk
List-Id: <gdb-prs.sourceware.org>
List-Subscribe: <mailto:gdb-prs-subscribe@sourceware.org>
List-Archive: <http://sourceware.org/ml/gdb-prs/>
List-Post: <mailto:gdb-prs@sourceware.org>
List-Help: <mailto:gdb-prs-help@sourceware.org>, <http://sourceware.org/lists.html#faqs>
Sender: gdb-prs-owner@sourceware.org
Delivered-To: mailing list gdb-prs@sourceware.org
Received: (qmail 102684 invoked by uid 48); 20 Mar 2015 03:06:41 -0000
From: "dje at google dot com" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug symtab/18150] New: Review testsuite results with removal of
 expansion of main's symtab
Date: Mon, 23 Mar 2015 04:59:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gdb
X-Bugzilla-Component: symtab
X-Bugzilla-Version: HEAD
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: dje at google dot com
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: unassigned at sourceware dot org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter
Message-ID: <bug-18150-4717@http.sourceware.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://sourceware.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-q1/txt/msg00472.txt.bz2
Content-length: 1249

https://sourceware.org/bugzilla/show_bug.cgi?id\x18150

            Bug ID: 18150
           Summary: Review testsuite results with removal of expansion of
                    main's symtab
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: dje at google dot com

As a followup to bug 18148, I see several testsuite regressions when I apply
the appended patch.  I haven't put any time into root causing them, some
mightn't be bugs at all. But I think it will be a useful exercise.

diff --git a/gdb/symfile.c b/gdb/symfile.c
index ba099d3..96baf21 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1693,7 +1693,7 @@ set_initial_language (void)
 {
   enum language lang = main_language ();

-  if (lang == language_unknown)
+  if (0 && lang == language_unknown)
     {
       char *name = main_name ();
       struct symbol *sym = lookup_symbol (name, NULL, VAR_DOMAIN, NULL);

The point of the patch is to stop the expansion of the symtab with main,
which for many tests is the only useful symtab.

--
You are receiving this mail because:
You are on the CC list for the bug.

[Bug gdb/18149] The gdb cannot evaluate a C++ expression generated by the "-var-info-path-expression" for member of class.

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18149

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at sourceware dot org
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |7.10

--- Comment #1 from Hannes Domani <ssbssa at sourceware dot org> ---
This is fixed since 7.10:

(gdb) interpreter-exec mi '-data-evaluate-expression --thread 1 --frame 0
"(*(struct A*) this)"'
^done,value="{_a = 1}"
(gdb) interpreter-exec mi '-data-evaluate-expression --thread 1 --frame 0
"(((*(class A*) this))._a)"'
^done,value="1"

-- 
You are receiving this mail because:
You are on the CC list for the bug.