[Bug c++/28907] New: Wrong pointer cast with multiple inheritance

[Bug c++/28907] New: Wrong pointer cast with multiple inheritance

[simark at simark dot ca]

https://sourceware.org/bugzilla/show_bug.cgi?id=28907

            Bug ID: 28907
           Summary: Wrong pointer cast with multiple inheritance
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: c++
          Assignee: unassigned at sourceware dot org
          Reporter: simark at simark dot ca
  Target Milestone: ---

$ cat test.cpp                                                       
struct Base1 {
  int b1 = 0x1111;
};

struct Base2 {
  int b2 = 0x2222;
};

struct Derived : public Base1, Base2 {
  int d = 0x3333;
};

int main() {
  Derived d;
  return 0;
}
$ g++ test.cpp -g3 -O0                                               
$ DEBUGINFOD_URLS= ./gdb -nx -q --data-directory=data-directory a.out -ex "b
15" -ex r
Reading symbols from a.out...
Breakpoint 1 at 0x1165: file test.cpp, line 15.
Starting program: /home/simark/build/binutils-gdb/gdb/a.out 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/../lib/libthread_db.so.1".

Breakpoint 1, main () at test.cpp:15
15        return 0;
(gdb) p &d
$1 = (Derived *) 0x7fffffffdcfc
(gdb) p (Base2 *) &d
$2 = (Base2 *) 0x7fffffffdd00
(gdb) p (Derived *) (Base2 *) &d
$3 = (Derived *) 0x7fffffffdcf8


Pretty sure that $1 and $3 should be equal.

Might be related to https://sourceware.org/bugzilla/show_bug.cgi?id=20285.  Not
quite the same, but it might be the same root cause.

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

[Bug c++/28907] Wrong pointer cast with multiple inheritance

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28907

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at sourceware dot org

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

[Bug c++/28907] Wrong pointer cast with multiple inheritance

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28907

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
Sending a patch.

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

[Bug c++/28907] Wrong pointer cast with multiple inheritance

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28907

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom Tromey <tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=2390419d1cb72882110538e01e5586372df19657

commit 2390419d1cb72882110538e01e5586372df19657
Author: Tom Tromey <tom@tromey.com>
Date:   Sat Apr 2 09:54:40 2022 -0600

    Fix C++ cast of derived class to base class

    PR c++/28907 points out that casting from a derived class to a base
    class fails in some situations.  The problem turned out to be a
    missing use of value_embedded_offset.  One peculiarity here is that,
    if you managed to construct a pointer-to-derived with an embedded
    offset of 0, the cast would work -- for example, one of the two new
    tests here passes without the patch.

    This embedded offset stuff is an endless source of bugs.  I wonder if
    it's possible to get rid of it somehow.

    Regression tested on x86-64 Fedora 34.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28907

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

[Bug c++/28907] Wrong pointer cast with multiple inheritance

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28907

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.1
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
Fixed.

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