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@@ -10,9 +10,7 @@ used in a Multiboot2-kernel.
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It follows the Multiboot 2.0 specification at https://www.gnu.org/software/grub/manual/multiboot2/multiboot.html and the ELF 64 specification at http://www.uclibc.org/docs/elf-64-gen.pdf.
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-Below is the draft for a blog post about this. I don't plan to finish it but maybe it's helpful as documentation.
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-
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-## The Multiboot 2 Information Structure
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+## Background: The Multiboot 2 Information Structure
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The Multiboot information structure looks like this:
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Field | Type
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@@ -30,46 +28,7 @@ type | u32
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size | u32
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other fields | variable
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-All tags are 8-byte aligned. The last tag must be the _end tag_, which is a tag of type `0` and size `8`.
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-
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-## Tags
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-
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-We are interested in two tags, the _Elf-symbols_ tag and the _memory map_ tag. For a full list of possible tags see section 3.4 in the Multiboot 2 specification ([PDF][Multiboot 2]).
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-
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-[Multiboot 2]: http://nongnu.askapache.com/grub/phcoder/multiboot.pdf
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-
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-### The Elf-Symbols Tag
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-The Elf-symbols tag contains a list of all sections of the loaded [ELF] kernel. It has the following format:
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-
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-[ELF]: http://www.uclibc.org/docs/elf-64-gen.pdf
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-
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-Field | Type
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---------------------------- | -----------------
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-type = 9 | u32
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-size | u32
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-number of entries | u32
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-entry size | u32
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-string table | u32
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-section headers | variable
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-
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-Note that this format differs from the description in the Multiboot specification because it seems to be wrong for ELF 64 kernels: The `number of entries`, `entry size`, and `string table` fields seem to be `u32` instead of `u16`. The `multiboot2.h` file in the example section of the specification also specifies these fields as being `u32`, which suggests that the `u16` fields are an editing error. The GRUB2 bootloader [uses u32 fields](https://github.com/josefbacik/grub2/blob/96695ad84ce9c93f057ba53ae77d04d8561586e9/include/multiboot2.h#L298-L300), too.
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-
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-The section headers are just copied from the ELF file, so we need to look at the ELF specification to find the corresponding structure definition. Our kernel is a 64-bit ELF file, so we need to look at the ELF-64 specification ([PDF][ELF specification]). According to section 4 and figure 3, a section header has the following format:
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-
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-[ELF specification]: http://www.uclibc.org/docs/elf-64-gen.pdf
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-
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-Field | Type | Value
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---------------------------- | ---------------- | -----------
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-name | u32 | string table index
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-type | u32 | `0` (unused), `1` (section of program), `3` (string table), `8` (uninitialized section), etc.
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-flags | u64 | `0x1` (writable), `0x2` (loaded), `0x4` (executable), etc.
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-address | u64 | virtual start address of section (0 if not loaded)
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-file offset | u64 | offset (in bytes) of section contents in the file
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-size | u64 | size of the section in bytes
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-link | u32 | associated section (only for some section types)
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-info | u32 | extra information (only for some section types)
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-address align | u64 | required alignment of section (power of 2)
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-entry size | u64 | contains the entry size for table sections (e.g. string table)
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+All tags and the mbi itself are 8-byte aligned. The last tag must be the _end tag_, which is a tag of type `0` and size `8`.
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## License
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Philipp Schuster