alignment bug?

Gagan Arneja gaagaan@gmail.com
Sun Apr 20 12:45:00 GMT 2008


What am I doing wrong? Why is "bar" getting truncated down to 128?

 > gcc -v
gcc version 4.1.1 20070105 (Red Hat 4.1.1-51)



#include <stdio.h>

#define ALIGNED(n) __attribute__((__aligned__(n)))

typedef struct Bar {
    char c[200];
} Bar ALIGNED(128);

typedef struct Foo {
   Bar bar[4];
} Foo;

Foo foo[4];

main()
{
    int i;
    Foo *foop = &foo[0];

    printf("sizeof(Bar) = %d\n", sizeof(Bar));
    printf("sizeof(Foo) = %d\n", sizeof(Foo));

    for (i=0; i < 4; i++) {
       Bar *bar = &foop->bar[i];
       printf("&bar[%d]=%p, addr%128=0x%lx\n",
              i, bar, ((unsigned long)bar) % 128);
    }

}

 > ./a.out
sizeof(Bar) = 200
sizeof(Foo) = 896
&bar[0]=0x8049180, addr%128=0x0
&bar[1]=0x8049200, addr%128=0x0
&bar[2]=0x8049280, addr%128=0x0
&bar[3]=0x8049300, addr%128=0x0



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