[Bug tree-optimization/105078] Maybe wrong *** buffer overflow detected ***: terminated with -D_FORTIFY_SOURCE

[marxin at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105078

--- Comment #4 from Martin Liška <marxin at gcc dot gnu.org> ---
Note the libQt6 version of the function looking approximately like this:

#include <cstdlib>
#include <cstdint>
#include <unistd.h>

struct QArrayData { 
        int size; 

        __attribute__((malloc))
        static void *allocate(QArrayData **pdata, size_t size, size_t
alignment) { 
                size_t headerSize = sizeof(QArrayData); 
                headerSize += (alignment - alignof(QArrayData)); 
                *pdata = static_cast<QArrayData *>(::malloc(headerSize +
size)); 
                (*pdata)->size = size; 
                return reinterpret_cast<void *>(uintptr_t(*pdata) +
headerSize); 
        } 
}; 

template <class T> 
struct QTypedArrayData : QArrayData { 
        class AlignmentDummy { QArrayData header; T data; }; 

        static QTypedArrayData *allocate(size_t size) { 
                QArrayData *d; 
                QArrayData::allocate(&d, size, alignof(AlignmentDummy)); 
                return static_cast<QTypedArrayData *>(d); 
        } 

        static T *dataStart(QArrayData *data, size_t alignment) { 
                void *start = reinterpret_cast<void *>((uintptr_t(data) +
sizeof(QArrayData) + alignment - 1) & ~(alignment - 1)); 
                return static_cast<T *>(start); 
        } 
}; 

int main() 
{ 
        int size = 256; 
        auto *data = QTypedArrayData<char>::allocate(size); 
        return readlink("asdf", data->dataStart(data,
alignof(QTypedArrayData<char>::AlignmentDummy)), data->size - 1); 
}