Re: [PATCH] Fix packing issue of machine_mmap_entry

[Robert Millan <rmh@aybabtu.com>]

On Mon, Oct 22, 2007 at 11:00:11PM +0200, Christian Franke wrote:
> --- grub2.orig/include/grub/i386/pc/init.h	2007-07-22 01:32:23.000000000 +0200
> +++ grub2/include/grub/i386/pc/init.h	2007-10-13 21:25:24.000000000 +0200
> @@ -40,10 +40,14 @@ grub_uint32_t grub_get_eisa_mmap (void);
>  struct grub_machine_mmap_entry
>  {
>    grub_uint32_t size;
> -  grub_uint64_t addr;
> +  grub_uint64_t addr; /* must be at offset 4, see startup.S */ 
>    grub_uint64_t len;
>    grub_uint32_t type;
> -};
> +} __attribute__((packed));

Looks fine to me (I suppose we would have the same problem on x86_64).

> +/* Compile time assert to check packing */
> +typedef char ASSERT_sizeof_grub_machine_mmap_entry[
> +  sizeof (struct grub_machine_mmap_entry) == 4+8+8+4 ? 1 : -1];

Nice, I didn't know you could do compile time assertion in C.  But is it
really necessary to check for gcc bugs?  That __attribute__((packed)) can
only have the expected effect, right?  Besides, in this case maybe it'd
be better to use autoconf.

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What use is a phone call, if you are unable to speak?
(as seen on /.)