CODEWITHSUNDEEP
c++gccc++17memory-alignment
Marek R
Marek R

Reputation: 38092

Gcc custom operator new[] and delete[] is buggy for aligned class - address sanitizer reprots buffer overflow

Basically when class has alignment requirement and custom operators new[] and delete[], then on gcc bad things happen and address sanitizer reports buffer overflow:

MCVE:

#include <iostream>
#include <memory>

class EndlineOnDone {
    std::ostream& out;
public:
    EndlineOnDone(std::ostream& out) : out{out} {}
    ~EndlineOnDone()
    {
        out << std::endl;
    }
    std::ostream& stream() { return out; }
};

#define VAR(x) " " #x "=[" << x << "]" 
#define LOG EndlineOnDone(std::cout).stream() << __PRETTY_FUNCTION__

std::ostream& operator<<(std::ostream& out, std::align_val_t a)
{
    return out << static_cast<size_t>(a);
}

class alignas(32) Foo
{
public :
    double x, y, z;

    void * operator new (size_t s, std::align_val_t a)
    {
        auto p = aligned_alloc(static_cast<size_t>(a), s);
        LOG << VAR(p) << VAR(s) << VAR(a);
        return p;
    }

    void operator delete (void * p, size_t s, std::align_val_t a)
    {
        LOG << VAR(p) << VAR(s) << VAR(a);
        if (p) free(p);
    }

#if 1
    void * operator new[ ] (size_t s, std::align_val_t a)
    {
        auto p = aligned_alloc(static_cast<size_t>(a), s);
        LOG << VAR(p) << VAR(s) << VAR(a);
        return p;
    }

    void operator delete[ ] (void *p, size_t s, std::align_val_t a)
    {
        LOG << VAR(p) << VAR(s) << VAR(a);
        if (p) free(p);
    }
#endif
};

int main()
{
    {
        LOG << " std::make_unique<Foo>";
        auto p = std::make_unique<Foo>();
    }

    {
        LOG << " std::make_unique<Foo[]>";
        auto p = std::make_unique<Foo[]>(3);
    }
}

https://godbolt.org/z/7xd8YM

gcc logs (no address sanitizer):

int main() std::make_unique<Foo>
static void* Foo::operator new(size_t, std::align_val_t) p=[0x21d6ec0] s=[32] a=[32]
static void Foo::operator delete(void*, size_t, std::align_val_t) p=[0x21d6ec0] s=[32] a=[32]
int main() std::make_unique<Foo[]>
static void* Foo::operator new [](size_t, std::align_val_t) p=[0x21d6f40] s=[96] a=[32]
static void Foo::operator delete [](void*, size_t, std::align_val_t) p=[0x21d6f40] s=[3616] a=[32]

Note that s value for Foo[] doesn't match for new[] and delete[] operations.

Address sanitizer reports buffer overflow.

clang is fine

Question

Its there a way to fix this problem? For example add some compiler flag (there is see edit section below).

Is this a known issue? I do not know how to find respective bug report for that (IMO it is gcc bug).

Edit/Clue

Ok I have a workaround. Adding explicit destructor ~Foo() {} fixes this issue: https://godbolt.org/z/WoM91Y (use of ~Foo() = default; doesn't fix it).

Upvotes: 4

Views: 360

Answers (1)

alagner
alagner

Reputation: 4062

Interestingly enough, adding default non-inline destructor (Foo::~Foo()=default;) fixes the problem too.

Upvotes: 1

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