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Tagged mbi
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Vladimir 'phcoder' Serbinenko committed
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+173
-7
@@ -414,6 +414,9 @@ If bit 2 in the @samp{flags} word is set, information about the video
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mode table (@pxref{Boot information format}) must be available to the
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kernel.
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If bit 3 in the @samp{flags} word is set, the multiboot information
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must be in tagged format.
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If bit 16 in the @samp{flags} word is set, then the fields at offsets
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12-28 in the Multiboot header are valid, and the boot loader should use
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them instead of the fields in the actual executable header to calculate
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@@ -515,7 +518,7 @@ must have the following state:
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@table @samp
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@item EAX
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Must contain the magic value @samp{0x2BADB002}; the presence of this
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Must contain the magic value @samp{0x2BADB002} if Boot info is non-tagged and @samp{0x3BADB002} otherwise; the presence of this
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value indicates to the operating system that it was loaded by a
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Multiboot-compliant boot loader (e.g. as opposed to another type of
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boot loader that the operating system can also be loaded from).
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@@ -578,9 +581,8 @@ changed them during the switch to 32-bit mode.
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@node Boot information format
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@section Boot information format
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FIXME: Split this chapter like the chapter ``OS image format''.
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@section Boot information
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@subsection Boot information format
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Upon entry to the operating system, the @code{EBX} register contains the
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physical address of a @dfn{Multiboot information} data structure,
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@@ -595,6 +597,25 @@ memory reserved for the kernel and boot modules, of course). It is the
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operating system's responsibility to avoid overwriting this memory until
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it is done using it.
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@subsection Basic tags structure
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Boot information can be passed in one of two formats: pointer-based
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or tag-based. Tag-based format must be used if and only it was requested
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in multiboot header. Every tag begins with following fields:
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@example
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@group
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+-------------------+
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0 | type |
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4-7 | size |
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+-------------------+
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@end group
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@end example
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@samp{type} contains an identifier of contents of the rest of the tag.
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@samp{size} contains the size of tag including header fields.
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Tags follow one another without any gaps. Tags are terminated by a tag of type @samp{0} and size @samp{8}.
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@subsection Basic non-tagged structure
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The format of the Multiboot information structure (as defined so far)
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follows:
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@@ -655,6 +676,7 @@ field also functions as a version indicator, allowing the Multiboot
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information structure to be expanded in the future without breaking
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anything.
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@subsection Basic memory information
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If bit 0 in the @samp{flags} word is set, then the @samp{mem_*} fields
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are valid. @samp{mem_lower} and @samp{mem_upper} indicate the amount of
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lower and upper memory, respectively, in kilobytes. Lower memory starts
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@@ -663,6 +685,20 @@ possible value for lower memory is 640 kilobytes. The value returned for
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upper memory is maximally the address of the first upper memory hole
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minus 1 megabyte. It is not guaranteed to be this value.
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Corresponding tag is:
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@example
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@group
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+-------------------+
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0 | type = 4 |
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4 | size = 16 |
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8 | mem_lower |
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12-15 | mem_upper |
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+-------------------+
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@end group
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@end example
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@subsection BIOS Boot device
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If bit 1 in the @samp{flags} word is set, then the @samp{boot_device}
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field is valid, and indicates which @sc{bios} disk device the boot
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loader loaded the OS image from. If the OS image was not loaded from a
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@@ -705,11 +741,39 @@ partition on a disk partitioned in conventional DOS style, then
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@samp{part1} will be 5, and @samp{part2} and @samp{part3} will both be
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0xFF.
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Corresponding tag is:
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@example
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@group
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+-------------------+
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0 | type = 5 |
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4 | size = 20 |
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8 | biosdev |
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12 | partition |
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16-19 | sub-parition |
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+-------------------+
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@end group
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@end example
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@subsection Boot command line
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If bit 2 of the @samp{flags} longword is set, the @samp{cmdline} field
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is valid, and contains the physical address of the command line to
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be passed to the kernel. The command line is a normal C-style
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zero-terminated string.
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UTF-8 zero-terminated string.
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Corresponding tag is:
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@example
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@group
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+-------------------+
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0 | type = 1 |
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4 | size |
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8-xx | string |
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+-------------------+
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@end group
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@end example
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@samp{string} contains zero-terminated UTF-8 string padded to have length divisible by 4.
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@subsection Modules
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If bit 3 of the @samp{flags} is set, then the @samp{mods} fields
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indicate to the kernel what boot modules were loaded along with the
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kernel image, and where they can be found. @samp{mods_count} contains
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@@ -734,7 +798,7 @@ set. Each module structure is formatted as follows:
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The first two fields contain the start and end addresses of the boot
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module itself. The @samp{string} field provides an arbitrary string to
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be associated with that particular boot module; it is a zero-terminated
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ASCII string, just like the kernel command line. The @samp{string} field
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UTF-8 string, just like the kernel command line. The @samp{string} field
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may be 0 if there is no string associated with the module. Typically the
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string might be a command line (e.g. if the operating system treats boot
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modules as executable programs), or a pathname (e.g. if the operating
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@@ -742,6 +806,25 @@ system treats boot modules as files in a file system), but its exact use
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is specific to the operating system. The @samp{reserved} field must be
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set to 0 by the boot loader and ignored by the operating system.
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Corresponding tag is:
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@example
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@group
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+-------------------+
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0 | type = 3 |
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4 | size |
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8 | mod_start |
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12 | mod_end |
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16-xx | string |
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+-------------------+
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@end group
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@end example
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Tag is padded in the way to have size divisible by 4.
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One tag appears per module.
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@subsection Symbols
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@strong{Caution:} Bits 4 & 5 are mutually exclusive.
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If bit 4 in the @samp{flags} word is set, then the following fields in
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@@ -795,6 +878,7 @@ details as to how to read the section header(s)). Note that
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@samp{shdr_num} may be 0, indicating no symbols, even if bit 5 in the
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@samp{flags} word is set.
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@subsection Memory map
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If bit 6 in the @samp{flags} word is set, then the @samp{mmap_*} fields
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are valid, and indicate the address and length of a buffer containing a
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memory map of the machine provided by the @sc{bios}. @samp{mmap_addr} is
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@@ -824,6 +908,18 @@ indicated a reserved area.
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The map provided is guaranteed to list all standard @sc{ram} that should
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be available for normal use.
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The corresponding tag is
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@example
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@group
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+-------------------+
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0 | type = 6 |
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4 | size |
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8-xx | entries |
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+-------------------+
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@end group
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@end example
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@subsection Drives table
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If bit 7 in the @samp{flags} is set, then the @samp{drives_*} fields
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are valid, and indicate the address of the physical address of the first
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drive structure and the size of drive structures. @samp{drives_addr}
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@@ -878,16 +974,32 @@ unsigned two-bytes integers, and is terminated with zero. Note that the
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array may contain any number of I/O ports that are not related to the
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drive actually (such as @sc{dma} controller's ports).
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@subsection Configuration table
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If bit 8 in the @samp{flags} is set, then the @samp{config_table} field
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is valid, and indicates the address of the @sc{rom} configuration table
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returned by the @dfn{GET CONFIGURATION} @sc{bios} call. If the @sc{bios}
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call fails, then the size of the table must be @emph{zero}.
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@subsection Boot loader name
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If bit 9 in the @samp{flags} is set, the @samp{boot_loader_name} field
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is valid, and contains the physical address of the name of a boot
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loader booting the kernel. The name is a normal C-style zero-terminated
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string.
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Corresponding tag is:
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@example
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@group
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+-------------------+
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0 | type = 2 |
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4 | size |
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8-xx | string |
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+-------------------+
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@end group
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@end example
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@samp{string} contains zero-terminated UTF-8 string padded to have length divisible by 4.
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@subsection APM table
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If bit 10 in the @samp{flags} is set, the @samp{apm_table} field is
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valid, and contains the physical address of an @sc{apm} table defined as
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below:
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@@ -920,6 +1032,7 @@ bytes, and the others are 2 bytes. See
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@uref{http://www.microsoft.com/hwdev/busbios/amp_12.htm, Advanced Power
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Management (APM) BIOS Interface Specification}, for more information.
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@subsection VBE info
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If bit 11 in the @samp{flags} is set, the @sc{vbe} table is available.
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The fields @samp{vbe_control_info} and @samp{vbe_mode_info} contain
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@@ -942,6 +1055,25 @@ The fields for the graphics table are designed for @sc{vbe}, but
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Multiboot boot loaders may simulate @sc{vbe} on non-@sc{vbe} modes, as
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if they were @sc{vbe} modes.
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Corresponding tag is:
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@example
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@group
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+-------------------+
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0 | type = 7 |
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4 | size = 784 |
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8 | vbe_mode |
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10 | vbe_interface_seg |
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12 | vbe_interface_off |
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14 | vbe_interface_len |
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16 | vbe_control_info |
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528-783 | vbe_mode_info |
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+-------------------+
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@end group
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@end example
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Notice that the tag contains VBE control and mode information structures directly rather than a pointer to them
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@subsection Framebuffer info
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If bit 12 in the @samp{flags} is set, the @sc{Framebuffer} table is available.
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The field @samp{framebuffer_addr} contains framebuffer physical address. This field is 64-bit wide but bootloader @dfn{should} set it under 4GiB if possible for compatibility with payloads which aren't aware of PAE or amd64. The field @samp{framebuffer_pitch} contains pitch in bytes. The fields @samp{framebuffer_width}, @samp{framebuffer_height} contain framebuffer dimensions in pixels. The field @samp{framebuffer_bpp} contains number of bits per pixel. If @samp{framebuffer_type} is set to 0 it means indexed color. In this case color_info is defined as follows:
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@@ -959,7 +1091,7 @@ The field @samp{framebuffer_addr} contains framebuffer physical address. This fi
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+-------------+
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0 | red_value |
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1 | green_value |
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2 | blue_value |
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2-2 | blue_value |
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+-------------+
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@end group
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@end example
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@@ -981,6 +1113,40 @@ If @samp{framebuffer_type} is set to 1 it means direct RGB color. Then color_typ
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If @samp{framebuffer_type} is set to 2 it means EGA text. In this case @samp{framebuffer_width} and @samp{framebuffer_height} are expressed in characters and not in pixels. @samp{framebuffer_bpp} is equal 16 (16 bits per character) and @samp{framebuffer_pitch} is expressed in bytes per text line.
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All further values of @samp{framebuffer_type} are reserved for future expansion
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Corresponding tag is:
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@example
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@group
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+--------------------+
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0 | type = 8 |
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4 | size |
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8 | framebuffer_addr |
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16 | framebuffer_pitch |
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20 | framebuffer_width |
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24 | framebuffer_height |
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28 | framebuffer_bpp |
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29 | framebuffer_type |
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30 | color_info |
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+--------------------+
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@end group
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@end example
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If @samp{framebuffer_type} is @samp{0} color_info has the following format:
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@example
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@group
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+---------------------------------+
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0 | framebuffer_palette_num_colors |
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4-xx | framebuffer_palette |
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+---------------------------------+
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@end group
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@end example
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With @samp{framebuffer_palette_num_colors} and @samp{framebuffer_palette} having the same format as in non-tagged version
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Note: @samp{framebuffer_palette} contains the palette and not its address.
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If @samp{framebuffer_type} is @samp{1} or @samp{2} color_info has the same format as non-tagged version.
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@node Examples
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@chapter Examples
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