sample.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int allocate_struct(void    *pv,
                    size_t  s)
{
    struct generic *pgs;

    if ((pgs = malloc(s)) == NULL) {
        fputs("Error: malloc();\n", stderr);
        return -1;
    }
    
    memcpy(pv, &pgs, sizeof pgs);
    return 0;
}

int main(void)
{
    struct s1 { int i; } *s1;

    if (allocate_struct(&s1, sizeof *s1) != 0)
        return EXIT_FAILURE;

    s1->i = 123;
    
    free(s1);
    return EXIT_SUCCESS;
}