Consider this case:

#pragma pack(push, 1)
struct A {
   long long a;
   int b;
};
#pragma pack(pop)

struct B {
   struct A x[1];
};

In this case, jextract doesn't work as expected. The size of the struct A is 12 bytes, which is NOT a multiple of the struct alignment (8). As a result, when we try to create a sequence layout with A as element layout, we get an exception.