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From: "alexander.grund@tu-dresden.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/112301] New: Double destruction of returned object when
 exiting the scope causes an exception which gets rethrown
Date: Mon, 30 Oct 2023 16:14:40 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112301

            Bug ID: 112301
           Summary: Double destruction of returned object when exiting the
                    scope causes an exception which gets rethrown
           Product: gcc
           Version: 12.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alexander.grund@tu-dresden.de
  Target Milestone: ---

Created attachment 56476
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D56476&action=3Dedit
More complete example with logging pointers

I debugged a heap corruption I traced back to a use-after-free caused by an
extra destructor call.

I suspect the cause could be the fix for
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D33799 where a throwing destr=
uctor
led to a missing destructor call.
It could be similar to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D12751=
 which
also had an extra destructor call generated for an already destructed insta=
nce.

Minimized code sample:

#include <stdexcept>
#include <cassert>

int num =3D 0;
struct ptr{
    ptr(){
        ++num;
    }
    ptr(ptr&&){
        ++num;
    }
    ~ptr(){
        assert(num-- > 0);
    }
};

struct ThrowOnExit{
    ~ThrowOnExit() noexcept(false){
        throw std::runtime_error("");
    }
};

ptr foo(ptr x){
    try{
        ThrowOnExit _;
        return x;
    }catch (const std::exception&) {
        throw;
    }
}

void wrapper(){
    try{
        foo(ptr{});
    }catch(const std::exception&){}
}

int main(){
    wrapper();
}


The assertion fails, although it should not. Logging the constructions and
destructions and removing the assert gives me this:

construct 0x7ffd4538088e
move construct 0x7ffd4538088f
free 0x7ffd4538088f
free 0x7ffd4538088f
free 0x7ffd4538088e=