multiboot2: Add description of support for relocatable images

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

doc/multiboot.texi

@@ -353,6 +353,7 @@ executable header.
 * Console header tags::
 * Module alignment tag::
 * EFI boot services tag::
+* Relocatable header tag::
 
 @end menu
 
@@ -679,6 +680,47 @@ u32     | size = 8          |
 This tag indicates that payload supports starting without
 terminating boot services.
 
+@node Relocatable header tag
+@subsection Relocatable header tag
+
+@example
+@group
+        +-------------------+
+u16     | type = 10         |
+u16     | flags             |
+u32     | size = 24         |
+u32     | min_addr          |
+u32     | max_addr          |
+u32     | align             |
+u32     | preference        |
+        +-------------------+
+@end group
+@end example
+
+This tag indicates that image is relocatable.
+
+The meaning of each field is as follows:
+
+@table @code
+@item min_addr
+Lowest possible physical address at which image should be loaded.
+The bootloader cannot load any part of image below this address.
+
+@item max_addr
+Highest possible physical address at which loaded image should end.
+The bootloader cannot load any part of image above this address.
+
+@item align
+Image alignment in memory, e.g. 4096.
+
+@item preference
+It contains load address placement suggestion for boot loader.
+Boot loader should follow it. @samp{0} means none, @samp{1} means
+load image at lowest possible address but not lower than min_addr
+and @samp{2} means load image at highest possible address but not
+higher than max_addr.
+@end table
+
 @node Machine state
 @section MIPS machine state
 
@@ -1323,6 +1365,20 @@ u64     | pointer           |
 This tag contains pointer to EFI amd64 image handle.
 Usually it is boot loader image handle.
 
+@subsection Image load base physical address
+@example
+@group
+        +-------------------+
+u32     | type = 21         |
+u32     | size = 12         |
+u32     | load_base_addr    |
+        +-------------------+
+@end group
+@end example
+
+This tag contains image load base physical address. It is
+provided only if image has relocatable header tag.
+
 @node Examples
 @chapter Examples
 

doc/multiboot2.h

@@ -62,6 +62,7 @@
 #define MULTIBOOT_TAG_TYPE_EFI_BS            18
 #define MULTIBOOT_TAG_TYPE_EFI32_IH          19
 #define MULTIBOOT_TAG_TYPE_EFI64_IH          20
+#define MULTIBOOT_TAG_TYPE_LOAD_BASE_ADDR    21
 
 #define MULTIBOOT_HEADER_TAG_END  0
 #define MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST  1
@@ -73,11 +74,16 @@
 #define MULTIBOOT_HEADER_TAG_EFI_BS        7
 #define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI32  8
 #define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI64  9
+#define MULTIBOOT_HEADER_TAG_RELOCATABLE  10
 
 #define MULTIBOOT_ARCHITECTURE_I386  0
 #define MULTIBOOT_ARCHITECTURE_MIPS32  4
 #define MULTIBOOT_HEADER_TAG_OPTIONAL 1
 
+#define MULTIBOOT_LOAD_PREFERENCE_NONE 0
+#define MULTIBOOT_LOAD_PREFERENCE_LOW 1
+#define MULTIBOOT_LOAD_PREFERENCE_HIGH 2
+
 #define MULTIBOOT_CONSOLE_FLAGS_CONSOLE_REQUIRED 1
 #define MULTIBOOT_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED 2
 
@@ -162,6 +168,17 @@ struct multiboot_header_tag_module_align
   multiboot_uint32_t size;
 };
 
+struct multiboot_header_tag_relocatable
+{
+  multiboot_uint16_t type;
+  multiboot_uint16_t flags;
+  multiboot_uint32_t size;
+  multiboot_uint32_t min_addr;
+  multiboot_uint32_t max_addr;
+  multiboot_uint32_t align;
+  multiboot_uint32_t preference;
+};
+
 struct multiboot_color
 {
   multiboot_uint8_t red;
@@ -388,6 +405,13 @@ struct multiboot_tag_efi64_ih
   multiboot_uint64_t pointer;
 };
 
+struct multiboot_tag_load_base_addr
+{
+  multiboot_uint32_t type;
+  multiboot_uint32_t size;
+  multiboot_uint32_t load_base_addr;
+};
+
 #endif /* ! ASM_FILE */
 
 #endif /* ! MULTIBOOT_HEADER */