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

[Martin Roth]

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;
    unsigned int    reserved : 29;
    struct pci_irq_info pci_irq_info[4];
    u8 command;
    u8 res_1;
    u8 res_2;
    u8 res_3;
..
    ROMSTAGE_CONST void *chip_info;


This gives me the correct disassembly:  mov esi,DWORD PTR [eax+0x8c]
and I pick up the pointer to chip_info correctly.  Note that with these 
changes, the structure in memory doesn't change at all.

TLDR: Structure is getting set up as dword aligned, but accessed by 
romcc as if it were packed.


Martin

--
coreboot mailing list: coreboot@coreboot.org
http://www.coreboot.org/mailman/listinfo/coreboot