GCM (File format) - Revision history

Algoflash: /* File String Table */

2023-10-07T11:29:26Z

File String Table

← Older revision		Revision as of 13:29, 7 October 2023
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	The alignment is important when building boot.bin and FST and is generally aligned to 4. If adx/sfd or audio files are packed then it's often aligned to 0x800 bytes. When unaligned the game could crash or songs are not loaded correctly.		The alignment is important when building boot.bin and FST and is generally aligned to 4. If adx/sfd or audio files are packed then it's often aligned to 0x800 bytes. When unaligned the game could crash or songs are not loaded correctly.

	JAP mini DVD contains non utf-8 chars like JIS charsets in the name_block. If using the Virtual World RE tool [https://github.com/Virtual-World-RE/NeoGF/tree/main/gcmtool gcmtool.py] then you have to install this charsets in your OS. When Dolphin Emulator ~~extract~~ this JAP files it converts the original charset to utf-8.		JAP mini DVD contains non utf-8 chars like JIS charsets in the name_block. If using the Virtual World RE tool [https://github.com/Virtual-World-RE/NeoGF/tree/main/gcmtool gcmtool.py] then you have to install this charsets in your OS. When Dolphin Emulator extracts this JAP files it converts the original charset to utf-8.

	The sorting of files in the FST is often case insensitive and special chars are sorted before letters. However some FST are arbitrary sorted and we found sometimes duplicated files like the dol or even the apploader also packed in the user space.		The sorting of files in the FST is often case insensitive and special chars are sorted before letters. However some FST are arbitrary sorted and we found sometimes duplicated files like the dol or even the apploader also packed in the user space.

Algoflash: /* File String Table */

2023-10-07T11:28:18Z

File String Table

← Older revision		Revision as of 13:28, 7 October 2023
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	The root node is at the beginning of the FST and has the 3 bytes name_block name offset equal to 0x00 and the 4 bytes of the parent folder id also equal to 0x00. The index of the next file is equal to the total number of files and folders packed in the GCM/iso user space. We can find the name_block offset by multiplying this total by 12 and adding 12 to it (the root node length).		The root node is at the beginning of the FST and has the 3 bytes name_block name offset equal to 0x00 and the 4 bytes of the parent folder id also equal to 0x00. The index of the next file is equal to the total number of files and folders packed in the GCM/iso user space. We can find the name_block offset by multiplying this total by 12 and adding 12 to it (the root node length).

	The ~~align~~ is important when building boot.bin and FST and is ~~generaly~~ aligned to 4. If adx/sfd or audio files are packed then it's often aligned to 0x800 bytes. When unaligned the game could crash or ~~song~~ are not loaded correctly.		The alignment is important when building boot.bin and FST and is generally aligned to 4. If adx/sfd or audio files are packed then it's often aligned to 0x800 bytes. When unaligned the game could crash or songs are not loaded correctly.

	JAP mini DVD contains non utf-8 chars like JIS charsets in the name_block. If using the Virtual World RE tool [https://github.com/Virtual-World-RE/NeoGF/tree/main/gcmtool gcmtool.py] then you have to install this charsets in your OS. When Dolphin Emulator extract this JAP files it converts the original charset to utf-8.		JAP mini DVD contains non utf-8 chars like JIS charsets in the name_block. If using the Virtual World RE tool [https://github.com/Virtual-World-RE/NeoGF/tree/main/gcmtool gcmtool.py] then you have to install this charsets in your OS. When Dolphin Emulator extract this JAP files it converts the original charset to utf-8.

Algoflash: /* File String Table */

2023-10-07T11:24:55Z

File String Table

← Older revision		Revision as of 13:24, 7 October 2023
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	* The second one is the name_block which contains names of folders and files terminated by a NULL byte (0x00) in Little Endian.		* The second one is the name_block which contains names of folders and files terminated by a NULL byte (0x00) in Little Endian.

	In the first block we index ~~every folders~~ and ~~files~~ beginning with the index 1. ~~Every~~ folder or file is translated in a 12 bytes entry. The first entry is the root with index 0.		In the first block we index each folder and file beginning with the index 1. Each folder or file is translated into a 12 bytes entry. The first entry is the root with index 0.

	The 12 bytes for a folder entry:		The 12 bytes for a folder entry:

Algoflash: /* File String Table */

2023-10-07T11:21:37Z

File String Table

← Older revision		Revision as of 13:21, 7 October 2023
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	=== File String Table ===		=== File String Table ===
	The FST allow to pack the files and folders tree of the game and is divided in two blocks:		The FST allow to pack the files and folders tree of the game and is divided into two blocks:
	* The first one contains FST entries (folders and files) in Big Endian.		* The first one contains FST entries (folders and files) in Big Endian.
	* The second one is the name_block which contains names of folders and files terminated by a NULL byte (0x00) in Little Endian.		* The second one is the name_block which contains names of folders and files terminated by a NULL byte (0x00) in Little Endian.

Algoflash: /* boot.dol */

2023-10-07T11:19:20Z

boot.dol

← Older revision		Revision as of 13:19, 7 October 2023
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	=== boot.dol ===		=== boot.dol ===
	The [[DOL (File format)\|dol]] file format is an executable compiled for Gekko powerpc RISC architecture. It's [http://wiki.tockdom.com/wiki/DOL_(File_Format) header] has a length of 0x100 bytes and we calculate ~~it's~~ total length by summing the header length with all 18 sections in it. At offset 0x90 we found 18 uint of 4 bytes (big endian) containing the length of the 18 sections.		The [[DOL (File format)\|dol]] file format is an executable compiled for Gekko powerpc RISC architecture. It's [http://wiki.tockdom.com/wiki/DOL_(File_Format) header] has a length of 0x100 bytes and we calculate its total length by summing the header length with all 18 sections in it. At offset 0x90 we found 18 uint of 4 bytes (big endian) containing the length of the 18 sections.

	=== File String Table ===		=== File String Table ===

Algoflash: /* apploader.img */

2023-10-07T11:18:23Z

apploader.img

← Older revision		Revision as of 13:18, 7 October 2023
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	The [https://www.gc-forever.com/wiki/index.php?title=apploader apploader] is a file, loaded by the GameCube BIOS (also called the [https://wiki.dolphin-emu.org/index.php?title=GameCube_Main_Menu Initial Program Loader / IPL]), that creates virtual memory spaces and rebase the dol datas in those areas before starting it. Apploader is at offset 0x2440 just after the bi2.bin. The GCM/iso doesn't store any name of it so it's name depend to the software used to extract it: AppLoader.ldr / apploader.img (dolphin Emulator) and so on.		The [https://www.gc-forever.com/wiki/index.php?title=apploader apploader] is a file, loaded by the GameCube BIOS (also called the [https://wiki.dolphin-emu.org/index.php?title=GameCube_Main_Menu Initial Program Loader / IPL]), that creates virtual memory spaces and rebase the dol datas in those areas before starting it. Apploader is at offset 0x2440 just after the bi2.bin. The GCM/iso doesn't store any name of it so it's name depend to the software used to extract it: AppLoader.ldr / apploader.img (dolphin Emulator) and so on.

	The apploader length is calculated with ~~it's~~ header ~~informations~~:		The apploader length is calculated with its header information:
	* Header has a length of 0x20 bytes:		* Header has a length of 0x20 bytes:
	** 0 - 10 bytes - Version		** 0 - 10 bytes - Version

Algoflash: /* apploader.img */

2023-10-07T11:17:28Z

apploader.img

← Older revision		Revision as of 13:17, 7 October 2023
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	=== apploader.img ===		=== apploader.img ===
	The [https://www.gc-forever.com/wiki/index.php?title=apploader apploader] is a file, loaded by the GameCube BIOS (also called the [https://wiki.dolphin-emu.org/index.php?title=GameCube_Main_Menu Initial Program Loader / IPL]), that creates virtual memory spaces and rebase the dol datas in ~~this~~ areas before starting it. Apploader is at offset 0x2440 just after the bi2.bin. The GCM/iso doesn't store any name of it so it's name depend to the software used to extract it: AppLoader.ldr / apploader.img (dolphin Emulator) and so on.		The [https://www.gc-forever.com/wiki/index.php?title=apploader apploader] is a file, loaded by the GameCube BIOS (also called the [https://wiki.dolphin-emu.org/index.php?title=GameCube_Main_Menu Initial Program Loader / IPL]), that creates virtual memory spaces and rebase the dol datas in those areas before starting it. Apploader is at offset 0x2440 just after the bi2.bin. The GCM/iso doesn't store any name of it so it's name depend to the software used to extract it: AppLoader.ldr / apploader.img (dolphin Emulator) and so on.

	The apploader length is calculated with it's header informations:		The apploader length is calculated with it's header informations:

Algoflash: /* bi2.bin */

2023-10-07T11:15:24Z

bi2.bin

← Older revision		Revision as of 13:15, 7 October 2023
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	=== bi2.bin ===		=== bi2.bin ===
	{\| class="wikitable"		{\| class="wikitable"
	\|+ bi2.bin ~~files~~ has a length of 0x2000 bytes and reside just after boot.bin (offset 0x440 of the GCM). It contains locales informations and debug configurations.		\|+ bi2.bin file has a length of 0x2000 bytes and reside just after boot.bin (offset 0x440 of the GCM). It contains locales informations and debug configurations.
	! Offset (hex) !! Size (bytes) !! Description		! Offset (hex) !! Size (bytes) !! Description
	\|-		\|-

Algoflash at 11:13, 7 October 2023

2023-10-07T11:13:36Z

← Older revision		Revision as of 13:13, 7 October 2023
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	The file system is handled by the GameCube and we can see that files are loaded by names no matter in which order they have been stored (Dolphin Emulator).		The file system is handled by the GameCube and we can see that files are loaded by names no matter in which order they have been stored (Dolphin Emulator).

	The dol file and FST are stored after de apploader.img. The dol can be after or before FST. Most of the time dol is before FST. All GCM ROMs have a fixed length (mini DVD length): 1 459 978 240 bytes. Because of that there is often empty spaces between files in the game released containing junk datas or old values partially overridden by new ones during devs. This empty spaces contains unused information. It could be used for mini DVD cyphering hardening. The question could be "does this junks data are the sames in all released mini DVD of the game?" An ~~intersting~~ thing is that burning data at the out border of the DVD increases performances when hardware DVD read head access to it.		The dol file and FST are stored after de apploader.img. The dol can be after or before FST. Most of the time dol is before FST. All GCM ROMs have a fixed length (mini DVD length): 1 459 978 240 bytes. Because of that there is often empty spaces between files in the game released containing junk datas or old values partially overridden by new ones during devs. This empty spaces contains unused information. It could be used for mini DVD cyphering hardening. The question could be "does this junks data are the sames in all released mini DVD of the game?" An interesting thing is that burning data at the out border of the DVD increases performances when hardware DVD read head access to it.

	== GCM/ISO format Architecture ==		== GCM/ISO format Architecture ==

Algoflash: /* Extraction formats */

2023-10-07T11:11:20Z

Extraction formats

← Older revision		Revision as of 13:11, 7 October 2023
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	\|- boot.bin (Information de base du jeu)		\|- boot.bin (Information de base du jeu)
	\- bi2.bin (Information supplémentaires)		\- bi2.bin (Information supplémentaires)
	game.iso : Repack copy of original iso.		game.iso: Repack copy of original iso.

	We find many others formats.		We find many others formats.