Bug#731806: debian-installer: FTBFS on sparc: genisoimage errors

[Patrick Baggett <baggett.patrick@gmail.com>]

On Mon, Apr 28, 2014 at 1:20 PM, Thomas Schmitt <scdbackup@gmx.net> wrote:

Hi,

> I really need a disassembly and to be able to probe the runtime

It's the job of a C union to provide a common hull around objects
of different size. One may dispute whether using union is a good
idea (like overloading in the OO paradigm). But unions are part of C
since K&R and they are supposed to be safe.
  http://www.gnu.org/software/gnu-c-manual/gnu-c-manual.html#Size-of-Unions

No, it's plain wrong. Unions are fine, if used properly. You aren't using them properly. Let me show you how by a more extreme example:

#include <stdlib.h>

struct small {

   int a;

};

struct big {

   int b[1024*1024];

};

union both {

   struct small imSmall;

   struct big imBig;

};

void copy(union both* b, void* data) {

    *b = *(union both*)data; //copies 4MB of data.

}

void main() {

    struct small smallThing;

    union both* bothThings = malloc(sizeof(union both));

    copy(bothThings, &smallThing); // NOT OK. struct small cannot NOT be converted to union both.

}

figgles@ghost:~$ ./big

Segmentation fault

----

The problem is that union can convert to a member (by accessing the field), but a member CANNOT convert to a union. add_worker() takes a member and tries to convert it to a union. This is WRONG. Period.