Manual stack canary

canary.cpp

namespace {

class Canary {
public:

    static constexpr size_t kSize = 1024;

    explicit Canary(volatile unsigned char* const t) noexcept : _t(t) {
        ::memset(const_cast<unsigned char*>(_t), kBits, kSize);
        _verify();
    }

    ~Canary() {
        _verify();
    }

private:
    static constexpr uint8_t kBits = 0xCD;
    static constexpr size_t kChecksum = kSize * size_t(kBits);

    void _verify() const noexcept {
        invariant(std::accumulate(&_t[0], &_t[kSize], 0UL) == kChecksum);
    }

    const volatile unsigned char* const _t;
};

}  // namespace

 Status ... {

    volatile unsigned char* const cookie = static_cast<unsigned char *>(alloca(Canary::kSize));
    const Canary c(cookie);