Documentation is now handled by the same processes we use for code: Add something to the Documentation/ directory in the coreboot repo, and it will be rendered to https://doc.coreboot.org/. Contributions welcome!
coreboot provides a couple of means to pass information on to the OS and payloads.
coreboot passes control to a payload or OS in form of a self contained ELF binary.
The one central data structure in coreboot is the coreboot table. It is an extensible data structure providing the information gathered by coreboot to payloads and operating systems.
The table usually sits in memory around address 0x500. FIXME: describe how to search for the table correctly.
The table header looks like this:
<source lang="C"> struct lb_header {
uint8_t signature[4]; /* LBIO */
uint32_t header_bytes;
uint32_t header_checksum;
uint32_t table_bytes;
uint32_t table_checksum;
uint32_t table_entries;
}; </source>
Every entry in the boot enviroment list will correspond to a boot info record. Encoding both type and size. The type is obviously so you can tell what it is. The size allows you to skip that boot enviroment record if you don't know what it is. This allows forward compatibility with records not yet defined.
<source lang="C"> struct lb_record {
uint32_t tag; /* tag ID */
uint32_t size; /* size of record (in bytes) */
}; </source>
Entry Types:
<source lang="C">
// 0x000e is used by device tree entry?
</source>