REL (File Format)

REL is a executable file format containing relocatable objects. It is similar to RSO, however, RSO files are relocated using symbol names while REL files are relocated using static memory addresses.

File Format

Header

The file starts with the following structure:

Offset	Type	Description
0x00	UInt32	Module ID. Must be a unique non-zero integer amongst all loaded REL files.
0x04	UInt32	Next module pointer. Always 0, filled at runtime.
0x08	UInt32	Previous module pointer. Always 0, filled at runtime.
0x0C	UInt32	Number of sections stored in the file.
0x10	UInt32	'Section info table offset.
0x14	UInt32	Name offset.
0x18	UInt32	Name size.
0x1C	UInt32	Version number of the REL format.
0x20	UInt32	.bss size in bytes.
0x24	UInt32	Relocation table offset.
0x28	UInt32	Import table offset.
0x2C	UInt32	Import table size in bytes.
0x30	Byte	Prolog section index.
0x31	Byte	Epilog section index.
0x32	Byte	Unresolved section index.
0x33	Byte	.bss section index. Always 0, filled at runtime.
0x34	UInt32	Prolog offset into the section specified above.
0x38	UInt32	Epilog offset into the section specified above.
0x3C	UInt32	Unresolved offset into the section specified above.
If version ≥ 2
0x40	UInt32	REL load alignment constraint, as a power of 2.
0x44	UInt32	.bss section alignment constraint, as a power of 2.
If version ≥ 3
0x48	UInt32	Fix size. If a REL is linked with OSLinkFixed, the space after this address can be used for other purposes such as .bss.

Section Info Table

The section info table points to the data for each section. The header specifies the number of sections. Each section has the following structure:

Offset	Type	Description
0x00	UInt32	Section data offset, relative to the start of the file. If the offset is zero, the section is allocated and initialized at runtime (like .bss). The least significant bit specifies whether the section is executable (1) or just data (0).
0x04	UInt32	Section data size in bytes.

Relocation Table

The relocation table is used to relocate section data to a different memory address. Each relocation entry has the following structure:

Offset	Type	Description
0x00	UInt16	Data offset, relative to the previous relocation table entry. For the first relocation entry this is relative to the section start.
0x02	Byte	Relocation type.
0x03	Byte	Section index.
0x04	Byte	Add end. Offset in bytes of the symbol to relocate against, relative to the start of its section. For relocations against main.dol, this is instead a virtual memory address.

Import Table

The import table specify information used for relocation. It specifies relocation data for each module. Each entry has the following structure:

Offset	Type	Description
0x00	UInt32	Module number which the relocation refers to. 0 means the relocations are for main.dol.
0x04	UInt32	Relocation table offset, relative to the start of the file.

Tools

The following tools can handle REL files:

• BrawlBox, by Kryal and BlackJax96