[Bug c/59259] New: [x32] Incorrect packing and/or alignment when using a 64 bit type as array of zero length in a structure

[cjanderson at yandex dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59259

            Bug ID: 59259
           Summary: [x32] Incorrect packing and/or alignment when using a
                    64 bit type as array of zero length in a structure
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cjanderson at yandex dot com

I believe that x32 has 32 bit pointers. I hope that I am not barking up the
wrong tree, but I have a problem with gcc versions 4.7.2 4.8.3 and the current
head on git with the following:

struct blah {
        long long a,b;
};
struct ipt_get_entries {
        unsigned int size;
        struct blah entrytable[0];
};

int x = sizeof(struct ipt_get_entries);

which produces the following when compiled with the -mx32 flag. ie. cc1 -mx32
produces:
    .file    "1.c"
    .globl    x
    .data
    .align 4
    .type    x, @object
    .size    x, 4
x:
    .long    8
    .ident    "GCC: (GNU) 4.9.0 20131120 (experimental)"
    .section    .note.GNU-stack,"",@progbits

When compiled with the -m32 flag the size is 4 and with the -m64 flag the size
is 8.

However, if you change the blah struct to a 32 bit value, ie 

struct blah {
        long long a,b;
};
...

The result for x is 4.

Also, when using -fpack-struct=4 the value of 4 is given, for all of -mx32 -m32
and -m64. 

The behaviour here seems to be that x32 is doing the same as for 64 bit. Is
this  correct.