From: Vladimir 'phcoder' Serbinenko Date: Wed, 20 Jan 2010 23:20:37 +0000 (+0100) Subject: Initial tag header X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7521ec5fef0959af3d7769239e29510187cf16fc;p=thirdparty%2Fgrub.git Initial tag header --- diff --git a/doc/multiboot.texi b/doc/multiboot.texi index 5fbff712b..3b5506200 100644 --- a/doc/multiboot.texi +++ b/doc/multiboot.texi @@ -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 @@ -355,27 +357,17 @@ executable header. 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 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 Offset @tab Type @tab Field Name @tab Note +@item 0 @tab u32 @tab magic @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 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}. - -@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. - -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. - -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. +which must be the hexadecimal value @code{0xE85250D6}. + +@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. + +@item header_length +The field @samp{header_length} specifies the Length of multiboot header +in bytes including magic fields. + @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: + +@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 -All of the address fields enabled by flag bit 16 are physical addresses. +@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 + + +@example +@group + +-------------------+ +0 | type = 3 | +4 | size = 24 | +8 | optional = 1 | +12 | width | +16 | height | +20-23 | depth | + +-------------------+ +@end group +@end example -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} + +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