align-test.c

/* from include/my_compiler.h */

#if defined __GNUC__ || defined __SUNPRO_C || defined __SUNPRO_CC
/* Specifies the minimum alignment of a type. */
# define MY_ALIGNOF(type)   __alignof__(type)
/* Determine the alignment requirement of a type. */
# define MY_ALIGNED(n)      __attribute__((__aligned__((n))))
/* Microsoft Visual C++ */
#elif defined _MSC_VER
# define MY_ALIGNOF(type)   __alignof(type)
# define MY_ALIGNED(n)      __declspec(align(n))
#else /* Make sure they are defined for other compilers. */
# define MY_ALIGNOF(type)
# define MY_ALIGNED(size)
#endif

#ifndef CPU_LEVEL1_DCACHE_LINESIZE
  #if defined(__s390__)
    #define CPU_LEVEL1_DCACHE_LINESIZE 256
  #elif defined(__powerpc__) || defined(__aarch64__)
    #define CPU_LEVEL1_DCACHE_LINESIZE 128
  #else
    #define CPU_LEVEL1_DCACHE_LINESIZE 64
  #endif
#endif

struct s_one {
        char first[30] MY_ALIGNED(CPU_LEVEL1_DCACHE_LINESIZE);
};

struct s_multiple {
        char first[30] MY_ALIGNED(CPU_LEVEL1_DCACHE_LINESIZE);
        unsigned long two;
        char three[30];
        char four[40] MY_ALIGNED(CPU_LEVEL1_DCACHE_LINESIZE);
};

struct s_one one_arr[2];

struct s_multiple multiple_arr[2];

struct s_simple {
        char first[30];
};

struct s_simple simple_arr[2];

#include <stdio.h>
#include <stddef.h>

int main()
{
        printf("Alignment %x\n\n", CPU_LEVEL1_DCACHE_LINESIZE);

        printf("sizeof(one) %zx\n", sizeof(struct s_one));
        printf("one[0] %p\n", &one_arr[0].first);
        printf("one[1] %p\n", &one_arr[1].first);
        printf("one ptrdiff %tx\n", (ptrdiff_t) (&one_arr[1].first - &one_arr[0].first));

        printf("\nsizeof(multiple) %zx\n", sizeof(struct s_multiple));
        printf("multiple[0].first %p\n", &multiple_arr[0].first);
        printf("multiple[0].four %p\n",  &multiple_arr[0].four);
        printf("multiple[1].first %p\n", &multiple_arr[1].first);
        printf("multiple diff %tx\n", (ptrdiff_t) (&multiple_arr[1].first - &multiple_arr[0].first));

        printf("\nsimple diff %tx\n", (ptrdiff_t) (&simple_arr[1].first - &simple_arr[0].first));
}

X86_64
 uname -m ; gcc -o align-test align-test.c && ./align-test
x86_64
Alignment 40

sizeof(one) 40
one[0] 0x601240
one[1] 0x601280
one ptrdiff 2

sizeof(multiple) c0
multiple[0].first 0x6010c0
multiple[0].four 0x601140
multiple[1].first 0x601180
multiple diff 6

simple diff 1

Power:
uname -m ; gcc -o align-test align-test.c && ./align-test
ppc64le
Alignment 80

sizeof(one) 80
one[0] 0x10020480
one[1] 0x10020500
one ptrdiff 4

sizeof(multiple) 100
multiple[0].first 0x10020280
multiple[0].four 0x10020300
multiple[1].first 0x10020380
multiple diff 8

simple diff 1