Bleh. This was a false path - it had nothing to do with romcc. The
issue was a #pragma pack(1) in one of the .h files. Please see my
subsequent commit for more information.
http://review.coreboot.org/#/c/2190/
Martin
On 01/21/2013 09:58 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;
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
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