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Add alignment requirements
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Vladimir 'phcoder' Serbinenko committed
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@@ -594,11 +594,12 @@ 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 consists of fixed part and a series of tags. Fixed part is as following:
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Boot information consists of fixed part and a series of tags. Its start is 8-bytes aligned. Fixed part is as following:
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@example
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@group
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+-------------------+
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0-3 | total_size |
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4-7 | reserved |
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+-------------------+
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@end group
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@end example
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@@ -606,6 +607,8 @@ Boot information consists of fixed part and a series of tags. Fixed part is as f
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@samp{total_size} contains the total size of boot information including
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this field and terminating tag in bytes
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@samp{reserved} is always set to zero and must be ignored by OS image
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Every tag begins with following fields:
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@example
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@@ -618,8 +621,8 @@ Every tag begins with following fields:
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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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@samp{size} contains the size of tag including header fields but not including padding.
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Tags follow one another padded when necessary in order for each tag to start at 8-bytes aligned address. Tags are terminated by a tag of type @samp{0} and size @samp{8}.
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@subsection Basic memory information
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@example
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@@ -695,8 +698,8 @@ partition on a disk partitioned in conventional DOS style, then
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@end group
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@end example
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@samp{string} contains command line. The command line is a normal C-styl
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zero-terminated UTF-8 string padded to have length divisible by 4.
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@samp{string} contains command line. The command line is a normal C-style
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zero-terminated UTF-8 string.
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@subsection Modules
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@example
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@@ -723,8 +726,6 @@ modules as executable programs), or a pathname (e.g. if the operating
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system treats boot modules as files in a file system), but its exact use
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is specific to the operating system.
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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. This tag type may appear multiple times.
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@subsection ELF-Symbols
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@@ -754,53 +755,46 @@ the sections are in memory (refer to the i386 @sc{elf} documentation for
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details as to how to read the section header(s)).
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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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the address, and @samp{mmap_length} is the total size of the buffer. The
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buffer consists of one or more of the following size/structure pairs
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(@samp{size} is really used for skipping to the next pair):
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@example
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@group
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+-------------------+
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-4 | size |
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+-------------------+
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0 | base_addr |
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8 | length |
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16 | type |
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+-------------------+
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@end group
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@end example
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This tag provides memory map.
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where @samp{size} is the size of the associated structure in bytes, which
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can be greater than the minimum of 20 bytes. @samp{base_addr} is the
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starting address. @samp{length} is the size of the memory region in bytes.
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@samp{type} is the variety of address range represented, where a
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value of 1 indicates available @sc{ram}, and all other values currently
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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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8 | entry_size |
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12 | entry_version |
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16-xx | entries |
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+-------------------+
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@end group
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@end example
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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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@samp{entry_size} contains the size of one entry so that in future new fields may be added to it. It's guaranteed to be a multiple of 8. @samp{entry_version} is currently set at @samp{0}. Future versions will increment this field. Future version are guranteed to be backward compatible with older format. Each entry has the following structure:
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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 | base_addr |
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8 | length |
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16 | type |
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20 | reserved |
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+-------------------+
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@end group
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@end example
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@samp{size} contains the size of current entry including this field itself. It may be bigger than 24 bytes in future versions but is guaranteed to be
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@samp{base_addr} is the starting physical address. @samp{length} is the size of the memory region in bytes.
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@samp{type} is the variety of address range represented, where a
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value of 1 indicates available @sc{ram}, and all other values currently
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indicated a reserved area.
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@samp{reserved} is set to @samp{0} by bootloader and must be ignored by the OS image.
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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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@subsection Boot loader name
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@example
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@group
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+-------------------+
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@@ -811,7 +805,9 @@ Corresponding tag is:
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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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@samp{string} contains the name of a boot
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loader booting the kernel. The name is a normal C-style UTF-8 zero-terminated
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string.
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@subsection APM table
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The tag type 10 contains @sc{apm} table
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@@ -819,7 +815,7 @@ The tag type 10 contains @sc{apm} table
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@group
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+----------------------+
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0 | type = 10 |
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4 | size |
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4 | size = 28 |
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8 | version |
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10 | cseg |
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12 | offset |
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@@ -889,17 +885,18 @@ yourself.
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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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30 | reserved |
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32 | color_info |
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+--------------------+
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@end group
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@end example
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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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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. @samp{reserved} always contains 0 in current version of specification and must be ignored by OS image. 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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@example
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@group
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+----------------------------------+
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30 | framebuffer_palette_num_colors |
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34-xx | framebuffer_palette |
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32 | framebuffer_palette_num_colors |
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36-xx | framebuffer_palette |
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+----------------------------------+
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@end group
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@end example
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@@ -920,12 +917,12 @@ Then color_type is defined as follows:
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@example
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@group
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+----------------------------------+
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30 | framebuffer_red_field_position |
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31 | framebuffer_red_mask_size |
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32 | framebuffer_green_field_position |
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33 | framebuffer_green_mask_size |
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34 | framebuffer_blue_field_position |
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35-35 | framebuffer_blue_mask_size |
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32 | framebuffer_red_field_position |
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33 | framebuffer_red_mask_size |
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34 | framebuffer_green_field_position |
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35 | framebuffer_green_mask_size |
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36 | framebuffer_blue_field_position |
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37-37 | framebuffer_blue_mask_size |
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+----------------------------------+
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@end group
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@end example
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