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Diffstat (limited to 'Documentation/x86')
| -rw-r--r-- | Documentation/x86/boot.rst | 43 |
1 files changed, 42 insertions, 1 deletions
diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst index 6cdd767c3835..90bb8f5ab384 100644 --- a/Documentation/x86/boot.rst +++ b/Documentation/x86/boot.rst @@ -827,6 +827,47 @@ Protocol: 2.09+ sure to consider the case where the linked list already contains entries. + The setup_data is a bit awkward to use for extremely large data objects, + both because the setup_data header has to be adjacent to the data object + and because it has a 32-bit length field. However, it is important that + intermediate stages of the boot process have a way to identify which + chunks of memory are occupied by kernel data. + + Thus setup_indirect struct and SETUP_INDIRECT type were introduced in + protocol 2.15. + + struct setup_indirect { + __u32 type; + __u32 reserved; /* Reserved, must be set to zero. */ + __u64 len; + __u64 addr; + }; + + The type member is a SETUP_INDIRECT | SETUP_* type. However, it cannot be + SETUP_INDIRECT itself since making the setup_indirect a tree structure + could require a lot of stack space in something that needs to parse it + and stack space can be limited in boot contexts. + + Let's give an example how to point to SETUP_E820_EXT data using setup_indirect. + In this case setup_data and setup_indirect will look like this: + + struct setup_data { + __u64 next = 0 or <addr_of_next_setup_data_struct>; + __u32 type = SETUP_INDIRECT; + __u32 len = sizeof(setup_data); + __u8 data[sizeof(setup_indirect)] = struct setup_indirect { + __u32 type = SETUP_INDIRECT | SETUP_E820_EXT; + __u32 reserved = 0; + __u64 len = <len_of_SETUP_E820_EXT_data>; + __u64 addr = <addr_of_SETUP_E820_EXT_data>; + } + } + +.. note:: + SETUP_INDIRECT | SETUP_NONE objects cannot be properly distinguished + from SETUP_INDIRECT itself. So, this kind of objects cannot be provided + by the bootloaders. + ============ ============ Field name: pref_address Type: read (reloc) @@ -986,7 +1027,7 @@ Field name: setup_type_max Offset/size: 0x000c/4 ============ ============== - This field contains maximal allowed type for setup_data. + This field contains maximal allowed type for setup_data and setup_indirect structs. The Image Checksum |