Question

struct Test
{
    int a;
    char b;
    int c;
} __attribute__((packed, aligned( 128 )))test;

sizeof( test ) returns 128 .

Why is the size not 9 ?

Is it that memory is rounded of to multiple of 128 ?

For example:

struct Test
{
 int b;
 char c;
} test;

sizeof( test ) returns 8 ( rounded of to multiple of 8 )

Answer 1

If you were to create an array of struct Test then each element would need to be 128 byte aligned, therefore each instance of the struct needs to be padded to a multiple of 128 bytes to maintain this. Hence sizeof(struct Test) = 128.