mirror of
https://git.savannah.gnu.org/git/grub.git
synced 2026-10-21 06:49:35 +00:00
Initial tag header
This commit is contained in:
Vladimir 'phcoder' Serbinenko committed
1 parent
165a055fb8
commit
7521ec5fef
1 file changed
+110
-71
+110
-71
@@ -344,8 +344,10 @@ executable header.
|
||||
@menu
|
||||
* Header layout:: The layout of Multiboot header
|
||||
* Header magic fields:: The magic fields of Multiboot header
|
||||
* Header address fields::
|
||||
* Header graphics fields::
|
||||
* Header tags::
|
||||
* Information request header tag::
|
||||
* Address header tag::
|
||||
* Graphics header tags::
|
||||
@end menu
|
||||
|
||||
|
||||
@@ -357,25 +359,15 @@ The layout of the Multiboot header must be as follows:
|
||||
@multitable @columnfractions .1 .1 .2 .5
|
||||
@item Offset @tab Type @tab Field Name @tab Note
|
||||
@item 0 @tab u32 @tab magic @tab required
|
||||
@item 4 @tab u32 @tab flags @tab required
|
||||
@item 4 @tab u32 @tab architecture @tab required
|
||||
@item 4 @tab u32 @tab header_length @tab required
|
||||
@item 8 @tab u32 @tab checksum @tab required
|
||||
@item 12 @tab u32 @tab header_addr @tab if flags[16] is set
|
||||
@item 16 @tab u32 @tab load_addr @tab if flags[16] is set
|
||||
@item 20 @tab u32 @tab load_end_addr @tab if flags[16] is set
|
||||
@item 24 @tab u32 @tab bss_end_addr @tab if flags[16] is set
|
||||
@item 28 @tab u32 @tab entry_addr @tab if flags[16] is set
|
||||
@item 32 @tab u32 @tab mode_type @tab if flags[2] is set
|
||||
@item 36 @tab u32 @tab width @tab if flags[2] is set
|
||||
@item 40 @tab u32 @tab height @tab if flags[2] is set
|
||||
@item 44 @tab u32 @tab depth @tab if flags[2] is set
|
||||
@item 12 @tab u32 @tab tags @tab required
|
||||
@end multitable
|
||||
|
||||
The fields @samp{magic}, @samp{flags} and @samp{checksum} are defined in
|
||||
@ref{Header magic fields}, the fields @samp{header_addr},
|
||||
@samp{load_addr}, @samp{load_end_addr}, @samp{bss_end_addr} and
|
||||
@samp{entry_addr} are defined in @ref{Header address fields}, and the
|
||||
fields @samp{mode_type}, @samp{width}, @samp{height} and @samp{depth} are
|
||||
defined in @ref{Header graphics fields}.
|
||||
The fields @samp{magic}, @samp{architecture}, @samp{header_length} and @samp{checksum} are defined in @ref{Header magic fields}, @samp{tags}
|
||||
are defined in @ref{Header tags}. All fields are in native endianness.
|
||||
On bi-endian platforms native-endianness means the endiannes OS image starts in.
|
||||
|
||||
|
||||
@node Header magic fields
|
||||
@@ -384,58 +376,82 @@ defined in @ref{Header graphics fields}.
|
||||
@table @samp
|
||||
@item magic
|
||||
The field @samp{magic} is the magic number identifying the header,
|
||||
which must be the hexadecimal value @code{0x1BADB002}.
|
||||
which must be the hexadecimal value @code{0xE85250D6}.
|
||||
|
||||
@item flags
|
||||
The field @samp{flags} specifies features that the OS image requests or
|
||||
requires of an boot loader. Bits 0-15 indicate requirements; if the
|
||||
boot loader sees any of these bits set but doesn't understand the flag
|
||||
or can't fulfill the requirements it indicates for some reason, it must
|
||||
notify the user and fail to load the OS image. Bits 16-31 indicate
|
||||
optional features; if any bits in this range are set but the boot loader
|
||||
doesn't understand them, it may simply ignore them and proceed as
|
||||
usual. Naturally, all as-yet-undefined bits in the @samp{flags} word
|
||||
must be set to zero in OS images. This way, the @samp{flags} fields
|
||||
serves for version control as well as simple feature selection.
|
||||
@item architecture
|
||||
The field @samp{architecture} specifies the Central Processing Unit
|
||||
Instruction Set Architecture. Since @samp{magic} isn't a palindrome
|
||||
it already specifies the endianness ISAs differing only in endianness
|
||||
recieve the same ID. @samp{0} means 32-bit (protected) mode of i386.
|
||||
|
||||
If bit 0 in the @samp{flags} word is set, then all boot modules loaded
|
||||
along with the operating system must be aligned on page (4KB)
|
||||
boundaries. Some operating systems expect to be able to map the pages
|
||||
containing boot modules directly into a paged address space during
|
||||
startup, and thus need the boot modules to be page-aligned.
|
||||
@item header_length
|
||||
The field @samp{header_length} specifies the Length of multiboot header
|
||||
in bytes including magic fields.
|
||||
|
||||
If bit 1 in the @samp{flags} word is set, then information on available
|
||||
memory via at least the @samp{mem_*} fields of the Multiboot information
|
||||
structure (@pxref{Boot information format}) must be included. If the
|
||||
boot loader is capable of passing a memory map (the @samp{mmap_*} fields)
|
||||
and one exists, then it may be included as well.
|
||||
|
||||
If bit 2 in the @samp{flags} word is set, information about the video
|
||||
mode table (@pxref{Boot information format}) must be available to the
|
||||
kernel.
|
||||
|
||||
If bit 16 in the @samp{flags} word is set, then the fields at offsets
|
||||
12-28 in the Multiboot header are valid, and the boot loader should use
|
||||
them instead of the fields in the actual executable header to calculate
|
||||
where to load the OS image. This information does not need to be
|
||||
provided if the kernel image is in @sc{elf} format, but it @emph{must}
|
||||
be provided if the images is in a.out format or in some other
|
||||
format. Compliant boot loaders must be able to load images that either
|
||||
are in @sc{elf} format or contain the load address information embedded
|
||||
in the Multiboot header; they may also directly support other executable
|
||||
formats, such as particular a.out variants, but are not required to.
|
||||
|
||||
@item checksum
|
||||
The field @samp{checksum} is a 32-bit unsigned value which, when added
|
||||
to the other magic fields (i.e. @samp{magic} and @samp{flags}), must
|
||||
have a 32-bit unsigned sum of zero.
|
||||
to the other magic fields (i.e. @samp{magic}, @samp{architecture}
|
||||
and @samp{header_length}), must have a 32-bit unsigned sum of zero.
|
||||
@end table
|
||||
|
||||
|
||||
@node Header address fields
|
||||
@subsection The address fields of Multiboot header
|
||||
@node Header tags
|
||||
@subsection General tag structure
|
||||
Tags constitutes a buffer of structures immediately following each other.
|
||||
Every structure has following format:
|
||||
|
||||
All of the address fields enabled by flag bit 16 are physical addresses.
|
||||
@example
|
||||
@group
|
||||
+-------------------+
|
||||
0 | type |
|
||||
4 | size |
|
||||
8-11 | optional |
|
||||
+-------------------+
|
||||
@end group
|
||||
@end example
|
||||
|
||||
@samp{type} contains an identifier of contents of the rest of the tag.
|
||||
@samp{size} contains the size of tag including header fields.
|
||||
@samp{optional} is set to 1 if bootloader may ignore this tag if it
|
||||
lacks relevant support.
|
||||
Tags are terminated by a tag of type @samp{0} and size @samp{12}.
|
||||
|
||||
@node Information request header tag
|
||||
@subsection Multiboot information request
|
||||
|
||||
@example
|
||||
@group
|
||||
+-------------------+
|
||||
0 | type = 1 |
|
||||
4 | size = 16 |
|
||||
8 | optional = 0 |
|
||||
12-15 | mbi_tag_type |
|
||||
+-------------------+
|
||||
@end group
|
||||
@end example
|
||||
|
||||
If this tag is present and @samp{optional} is set to @samp{0} at least
|
||||
one tag of type @samp{mbi_tag_type} must be present.
|
||||
|
||||
@node Address header tag
|
||||
@subsection The address tag of Multiboot header
|
||||
|
||||
@example
|
||||
@group
|
||||
+-------------------+
|
||||
0 | type = 2 |
|
||||
4 | size = 28 |
|
||||
8 | optional |
|
||||
12 | header_addr |
|
||||
16 | load_addr |
|
||||
20 | load_end_addr |
|
||||
24-27 | entry_addr |
|
||||
+-------------------+
|
||||
@end group
|
||||
@end example
|
||||
|
||||
All of the address fields in this tag are physical addresses.
|
||||
The meaning of each is as follows:
|
||||
|
||||
@table @code
|
||||
@@ -472,23 +488,32 @@ start running the operating system.
|
||||
@end table
|
||||
|
||||
|
||||
@node Header graphics fields
|
||||
@subsection The graphics fields of Multiboot header
|
||||
@node Graphics header tags
|
||||
@subsection The framebuffer tag of Multiboot header
|
||||
|
||||
All of the graphics fields are enabled by flag bit 2. They specify the
|
||||
preferred graphics mode. Note that that is only a @emph{recommended}
|
||||
|
||||
@example
|
||||
@group
|
||||
+-------------------+
|
||||
0 | type = 3 |
|
||||
4 | size = 24 |
|
||||
8 | optional = 1 |
|
||||
12 | width |
|
||||
16 | height |
|
||||
20-23 | depth |
|
||||
+-------------------+
|
||||
@end group
|
||||
@end example
|
||||
|
||||
|
||||
This tag specifies the preferred graphics mode. If this tag is present
|
||||
bootloader assumes that the payload has framebuffer support.
|
||||
Note that that is only a @emph{recommended}
|
||||
mode by the OS image. Boot loader may choose a different mode if it sees fit.
|
||||
|
||||
The meaning of each is as follows:
|
||||
|
||||
@table @code
|
||||
@item mode_type
|
||||
Contains @samp{0} for linear graphics mode or @samp{1} for
|
||||
EGA-standard text mode. Everything else is reserved for future
|
||||
expansion. Note that the boot loader may set a text mode even if this
|
||||
field contains @samp{0}, or set a video mode even if this field contains
|
||||
@samp{1}.
|
||||
|
||||
@item width
|
||||
Contains the number of the columns. This is specified in pixels in a
|
||||
graphics mode, and in characters in a text mode. The value zero
|
||||
@@ -505,6 +530,20 @@ a text mode. The value zero indicates that the OS image has no
|
||||
preference.
|
||||
@end table
|
||||
|
||||
@subsection The EGA text tag of Multiboot header
|
||||
|
||||
@example
|
||||
@group
|
||||
+-------------------+
|
||||
0 | type = 4 |
|
||||
4 | size = 12 |
|
||||
8-11 | optional = 1 |
|
||||
+-------------------+
|
||||
@end group
|
||||
@end example
|
||||
|
||||
This tag indicates that the OS image has EGA text support.
|
||||
|
||||
|
||||
@node Machine state
|
||||
@section Machine state
|
||||
|
||||
Reference in new issue
Block a user