Unused const object of class with virtual desctructor causes segmentation fault

Question

I was struggling with segmentation fault after returning from main in C++0x code compiled under GCC with MinGW, and have narrowed it to simple case:

class A {
public:
    virtual ~A();
};

A::~A() {
}

const A a;

int main() {
    return 0;
}

The reason is correlated with:

const qualifier before object, removing it stops seg fault,
Lack of constructor in class A - adding empty one stops seg fault.
Version of compialtor - newer TDM MinGW with gcc 4.8.1 does not build code causing seg fault.

Am I triggering some undefined behavior, or really compiler bug is reason of such behavior?

Affected compiler:

gcc --version gcc.exe (tdm-1) 4.7.1

g++ --version g++.exe (tdm-1) 4.7.1

ld --version GNU ld (GNU Binutils) 2.22

see [this](http://stackoverflow.com/questions/7411515/why-does-c-require-a-user-provided-default-constructor-to-default-construct-a). — yngccc, Jul 16 '14 at 00:04
http://stackoverflow.com/questions/7411515/why-does-c-require-a-user-provided-default-constructor-to-default-construct-a — Jimmy Thompson, Jul 16 '14 at 00:05
@yngum: Was that restriction scrapped post-11? Or where is it in the newest draft? — Deduplicator, Jul 16 '14 at 00:32
@yngum: You mean 8.5§6? Because there's no 8.5.6... Still, 8.5§6 in n3797 does not seem to handle that either... — Deduplicator, Jul 16 '14 at 01:02

score 2 · Accepted Answer · answered Jul 16 '14 at 00:09

2

This appears to be gcc bug 55893 that was fixed in 4.7.3. The attached testcase is very similar to yours:

struct foo
{
  virtual ~foo () { }
};

int main ()
{
  static const foo tmp;
}

The error occurs because gcc places the const object in read-only memory, because it is trivially constructible, without checking that the object has a non-trivial destructor. The destructor, being virtual, attempts to update the vtable pointer, leading to the segfault.

answered Jul 16 '14 at 00:09

Praetorian

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Which naturally raises the question of why the destructor call is not simply optimized out ... – Deduplicator Jul 16 '14 at 00:23

Unused const object of class with virtual desctructor causes segmentation fault

1 Answers1