[Bug c++/11836] New: gdb cannot access variables that are subject to return value optimization

[Bug c++/11836] New: gdb cannot access variables that are subject to return value optimization

[andre dot poenitz at nokia dot com]

#include <string>

std::string foo()
{
    std::string s;
    s = "hello";
    s += "world";
    return s;
}

std::string bar()
{
    std::string s;
    s = "hello";
    s += "world";
    return "something else";
}

int main()
{
    int a = foo().size();
    int b = bar().size();
    return a + b;
}

/*

Gcc seems to apply return value optimization (even at -O0) but there is
some problem with either the generated debug information or the way
gdb handles it. 

To reproduce it, save this file here as rvo.cpp and run

    g++ -g -O0 rvo.cpp -o rvo 

    gdb -ex 'set confirm off' -ex 'file ./rvo' \
        -ex 'b rvo.cpp:8' -ex 'b rvo.cpp:16' \
        -ex 'run' -ex 'print s'  \
        -ex 'cont' -ex 'print s' \
        -ex 'quit'


The result will look like:

    Breakpoint 1, foo () at rvo.cpp:8
    8           s += "world";
    $1 = {static npos = <optimized out>, 
      _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>>
    = {<No daa fields>}, <No data fields>}, _M_p = 0x1 <Address 0x1 out of
    bounds>}}

    Breakpoint 2, bar () at rvo.cpp:16
    16          s += "world";
    $2 = {static npos = <optimized out>, 
      _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>>
    = {<No data fields>}, <No data fields>}, _M_p = 0x804b014 "hello"}}

    Program exited with code 030.

RVO seems to be applied in the first case with "dangling" debug information.
If no RVO is used (second case), all is fine.


*/

-- 
           Summary: gdb cannot access variables that are subject to return
                    value optimization
           Product: gdb
           Version: 7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at sourceware dot org
        ReportedBy: andre dot poenitz at nokia dot com
                CC: gdb-prs at sourceware dot org
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://sourceware.org/bugzilla/show_bug.cgi?id=11836

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[andre dot poenitz at nokia dot com]

------- Additional Comments From andre dot poenitz at nokia dot com  2010-07-23 10:48 -------
Created an attachment (id=4882)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=4882&action=view)
Test code and build instructions


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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[swagiaal at redhat dot com]

------- Additional Comments From swagiaal at redhat dot com  2010-07-23 14:54 -------
Andre,

Thanks for the nice test case. 's' seems to have a location in the debug info
but it is either wrong or gdb is reading it wrong. I'll take a look at this when
I get a chance. If anyone else is interested, in the mean while, go for it :)

Sami

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |swagiaal at redhat dot com
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1


http://sourceware.org/bugzilla/show_bug.cgi?id=11836

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[andre dot poenitz at nokia dot com]

------- Additional Comments From andre dot poenitz at nokia dot com  2010-07-23 16:43 -------

It turns out it is known on the gcc side: 

  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44731

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[tromey at redhat dot com]

------- Additional Comments From tromey at redhat dot com  2010-07-23 16:46 -------
Possibly this gcc bug:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44731

-- 
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----------------------------------------------------------------------------
                 CC|                            |tromey at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=11836

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[schwab at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=11836

Andreas Schwab <schwab at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|jackie.rosen at hushmail dot com   |

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[jackie.rosen at hushmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=11836

Jackie Rosen <jackie.rosen at hushmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jackie.rosen at hushmail dot com

--- Comment #11 from Jackie Rosen <jackie.rosen at hushmail dot com> ---
*** Bug 260998 has been marked as a duplicate of this bug. ***
Seen from the domain http://volichat.com
Page where seen: http://volichat.com/adult-chat-rooms
Marked for reference. Resolved as fixed @bugzilla.

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=11836

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|                            |INVALID

--- Comment #10 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-02-17 17:28:43 UTC ---
So let's say it has never been a GDB bug.

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[rdengler at arcor dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=11836

--- Comment #9 from rdengler at arcor dot de 2011-02-17 17:14:59 UTC ---
Hi Jan,

thanks for the information.
Sorry I couldn't test it yet, there only is g++ 4.4.3
on my system.
I suppose the confusing behaviour will have gone,
the test code is simple enough.

Regards
Richard



jan.kratochvil at redhat dot com schrieb:

>http://sourceware.org/bugzilla/show_bug.cgi?id=11836
>
>Jan Kratochvil <jan.kratochvil at redhat dot com> changed:
>
>           What    |Removed                     |Added
>----------------------------------------------------------------------------
>             Status|NEW                         |WAITING
>                 CC|                            |jan.kratochvil at redhat
>                   |                            |dot com
>
>--- Comment #8 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-02-14 12:34:01 UTC ---
>http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44367
>
>Breakpoint 1, foo () at rvo.C:8
>8        return s;
>$1 = "helloworld"
>
>Breakpoint 2, bar () at rvo.C:16
>16        return "something else";
>$2 = "helloworld"
>
>with /r:
>
>Breakpoint 1, foo () at rvo.C:8
>8        return s;
>$1 = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>>
>= {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
>    _M_p = 0x601058 "helloworld"}}
>
>Breakpoint 2, bar () at rvo.C:16
>16        return "something else";
>$2 = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>>
>= {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
>    _M_p = 0x601028 "helloworld"}}
>
>This should be a GCC-only bug which is already fixed:
>FAIL g++ (GCC) 4.4.6 20110124 (prerelease)
>PASS g++ (GCC) 4.5.3 20110124 (prerelease)
>PASS g++ (GCC) 4.6.0 20110212 (experimental)
>PASS gcc-c++-4.6.0-0.6.fc15.x86_64
>
>Behaves the same with both:
>GNU gdb (GDB) 7.2.50.20110213-cvs
>gdb-7.2.50.20110206-18.fc15.x86_64
>
>Is the bug still reproducible with recent GCC?
>
>  
>

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=11836

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING
                 CC|                            |jan.kratochvil at redhat
                   |                            |dot com

--- Comment #8 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-02-14 12:34:01 UTC ---
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44367

Breakpoint 1, foo () at rvo.C:8
8        return s;
$1 = "helloworld"

Breakpoint 2, bar () at rvo.C:16
16        return "something else";
$2 = "helloworld"

with /r:

Breakpoint 1, foo () at rvo.C:8
8        return s;
$1 = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>>
= {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
    _M_p = 0x601058 "helloworld"}}

Breakpoint 2, bar () at rvo.C:16
16        return "something else";
$2 = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>>
= {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
    _M_p = 0x601028 "helloworld"}}

This should be a GCC-only bug which is already fixed:
FAIL g++ (GCC) 4.4.6 20110124 (prerelease)
PASS g++ (GCC) 4.5.3 20110124 (prerelease)
PASS g++ (GCC) 4.6.0 20110212 (experimental)
PASS gcc-c++-4.6.0-0.6.fc15.x86_64

Behaves the same with both:
GNU gdb (GDB) 7.2.50.20110213-cvs
gdb-7.2.50.20110206-18.fc15.x86_64

Is the bug still reproducible with recent GCC?

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[safinaskar at mail dot ru]

http://sourceware.org/bugzilla/show_bug.cgi?id=11836

Askar Safin <safinaskar at mail dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|safinaskar at mail dot ru   |

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[tromey at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=11836

Tom Tromey <tromey at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |cmayer at xp8 dot de

--- Comment #7 from Tom Tromey <tromey at redhat dot com> 2010-10-11 22:13:52 UTC ---
*** Bug 9607 has been marked as a duplicate of this bug. ***

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[tromey at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=11836

Tom Tromey <tromey at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rdengler at arcor dot de

--- Comment #6 from Tom Tromey <tromey at redhat dot com> 2010-10-11 22:13:08 UTC ---
*** Bug 9640 has been marked as a duplicate of this bug. ***

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[Bug c++/11836] gdb cannot access variables that are subject to return value optimization

[tromey at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=11836

Tom Tromey <tromey at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |safinaskar at mail dot ru

--- Comment #5 from Tom Tromey <tromey at redhat dot com> 2010-10-11 22:09:20 UTC ---
*** Bug 12106 has been marked as a duplicate of this bug. ***

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