[Bug c++/55922] New: brace initializing parent cause bogus virtual base constructor calls

[Bug c++/55922] New: brace initializing parent cause bogus virtual base constructor calls

[nicolas.cavallari at lri dot fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55922

             Bug #: 55922
           Summary: brace initializing parent cause bogus virtual base
                    constructor calls
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: nicolas.cavallari@lri.fr
              Host: x86_64-unknown-linux-gnu
            Target: x86_64-unknown-linux-gnu


Created attachment 29128
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29128
minimal program which does not work.

The attached minimal c++11 source compiles with g++ -std=c++11 minimal.c++, but
the program does not run as expected (indicated by a non-zero exit value).
Using clang works.

The same source with debug outputs shows that the virtual base constructor is
called more than once upon initialization with bogus 'this' pointers. Not all
classes agree on the offset to the virtual base. This causes silent member
corruption (and ultimately crashes if some of the members are pointers).

Replacing brace initializers for B1 and A2 with C++03 parentheses initializers
makes the problem go away.

Bug is also reproducible on trunk@195009 configured with ./configure
--enable-languages=c,c++ --prefix=...

[Bug c++/55922] brace initializing parent cause bogus virtual base constructor calls

[nicolas.cavallari at lri dot fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55922

--- Comment #1 from nicolas.cavallari at lri dot fr 2013-01-09 17:42:47 UTC ---
Created attachment 29129
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29129
same source with more outputs.

Example output of what i have on my system with this attachment :

Base ctor is called at 0x7fffb7eeb474
Base ctor is called at 0x7fffb7eeb468
A1::Base is at 0x7fffb7eeb468
B1::Base is at 0x7fffb7eeb468
Base ctor is called at 0x7fffb7eeb470
A2::Base is at 0x7fffb7eeb470
C::Base is at 0x7fffb7eeb474
2 2 3


Standard output should read "1 2 3".

[Bug c++/55922] brace initializing parent cause bogus virtual base constructor calls

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55922

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
bool called = false;

struct Base {
  Base() { if (called) throw 1; called = true; }
};

struct B1 : virtual Base {
  B1() { }
};

struct C : B1, virtual Base {
  C() :
#ifdef FIX
    B1()
#else
    B1{}
#endif
  { }
};

int main() {
  C c;
}

[Bug c++/55922] brace initializing parent cause bogus virtual base constructor calls

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55922

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |7.0
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #16 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed so closing.