Re: [coreboot] romcc issue with bitfields and chars in static.c

[ron minnich]

On Mon, Jan 21, 2013 at 8:58 PM, Martin Roth  wrote:
> I've run into what looks like an issue with how romcc handles bitfields and
> chars vs how the structure in static.c is created.
> When I'm accessing a member of a structure that comes after a bitfield or a
> single char  between dwords or pointers, the code is grabbing data from a
> different address than the actual location of the data.  I've found that if
> I add extra "reserved" bits to the bitfield to fill it up to a dword, and
> extra chars to do the same, everything works as expected.
>
> I'm currently running into this trying to access data from the 'device'
> structure from static.c in romstage.  If I don't add any changes, I'm
> getting a null pointer returned because I'm trying to access my data 6 bytes
> too early: mov esi,DWORD PTR [eax+0x86]
>
> Here's what the structure currently looks like:
> unsigned int    enabled : 1;    /* set if we should enable the device */
> unsigned int    initialized : 1; /* set if we have initialized the
>
> device */
>     unsigned int    on_mainboard : 1;
>     struct pci_irq_info pci_irq_info[4];
>     u8 command;
> ...
>     ROMSTAGE_CONST void *chip_info;
>
> Here's how I need to fix it to access chip_info correctly:
>     unsigned int    enabled : 1;    /* set if we should enable the device */
>     unsigned int    initialized : 1; /* set if we have initialized the
> device */
>     unsigned int    on_mainboard : 1;

Actually the :1 stuff is old-school for "bool". Bit-fields were
proclaimed a botch by their creator; here is another examply why. I
would feel better if we just got rid of
the :1 completely and kept it simple. I doubt the storage we save is
worth the effort.

ron