[SeaBIOS] [PATCH 2/2] accept MADT over fw_cfg

Kevin O'Connor kevin at koconnor.net
Tue Apr 23 02:42:18 CEST 2013


On Mon, Apr 22, 2013 at 08:23:39PM +0300, Michael S. Tsirkin wrote:
> > @@ -0,0 +1,28 @@
> > +#include "types.h" // u8
> > +#include "util.h" // romfile_s
> > +
> > +/* ROM file linker interface. Linker uses little endian format */
> > +struct linker_entry_s {
> > +    u8 size; /* size in bytes including the header */
> > +    u8 bytes; /* How many bytes to change. Can be 1,2,4 or 8. */
> > +    u8 type;
> > +    u8 format;
> > +    u32 reserved;
> > +    u64 src_offset; /* Offset in source. Little endian format. */
> 
> src_offset is not needed: host can pre-fill destination
> table with the offset value.
> Will probably drop it.
> 
> > +    u64 dst_offset; /* Offset in destination. Little endian format. */
> > +    /* Followed by source and destination
> 
> Add "file names"
> 
> >, optionally padded by
> > +     * 0, up to the total of entry_len - 4 bytes.
> > +     * Strings are 0-terminated. */
> > +    char src_dst[];
> > +} PACKED;
> > +
> > +enum linker_entry_type {
> 
> Documentation:
> 
> ADD: increment value in DST by the address of SRC
>      useful e.g. to fill in pointer values in ACPI tables
> SUB: decrement value in DST by the address of SRC
>      useful e.g. to fix up checksum values in ACPI tables

I don't see how one could implement a checksum with just a
subtraction.  If the table is at 0x12345678 the checksum isn't
(oldcksum-0x12345678), it's (oldcksum-0x12-0x34-0x56-0x78).

-Kevin



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