ref: 4eaac6bfb11cc84259e8b418d4babffdf1c637eb
dir: /doc/myro.txt/
Object File Format ------------------ The object file format is designed to be the simplest format that covers all the needs of many modern programming languages, with sufficient support for hand written assembly. All the types are little endian. File Format ----------- +== Header ======+ | signature | 32 bits +----------------+ | format str | MyroN bit | | +----------------+ | entrypoint | MyroN bit | | +----------------+ | stringtab size | MyroN bit | | +----------------+ | section size | MyroN bit | | +----------------+ | symtab size | MyroN bit | | +----------------+ | reloctab size | MyroN bit | | +== Metadata ====+ | strings... | | .... | +----------------+ | sections... | | ... | |----------------+ | symbols.... | | ... | +----------------+ | relocations... | | ... | +== Data ========+ | data... | | ... | +================+ The file is composed of three components: The header, the metadata, and the data. The header begins with a signature, containing the four bytes "uobj", identifying this file as a unified object. It is followed by a string offste with a format description (it may be used to indicate file format version, architecture, abi, ...) .This is followed by the size of the string table, the size of the section table, the size of the symbol table, and the size of the relocation table. Metadata: Strings ----------------- The string table directly follows the header. It contains an array of strings. Each string is a sequence of bytes terminated by a zero byte. A string may contain any characters other than the zero byte. Any reference to a string is done using an offset into the string table. If it is needed to indicate a "no string" then the value -1 may be used. Metadata: Sections ------------------ The section table follows the string table. The section table defines where data in a program goes. +== Sect ========+ | str | 32 bit +----------------+ | flags | 16 bit +----------------+ | fill value | 8 bit +----------------+ | aligment | 8 bit +----------------+ | offset | MyroN bit +----------------+ | len | MyroN bit +----------------+ All the files must defined at least 5 sections, numbered 1 through 5, which are implcitly included in every binary: .text SprotRread | SprotWrite | Sload | Sfile | SprotExec .data SprotRread | SprotWrite | Sload | Sfile .bss SprotRread | SprotWrite | Sload .rodata SprotRread | Sload | Sfile .blob Sblod | Sfile A program may have at most 65,535 sections. Sections have the followign flags; SprotRead = 1 << 0 SprotWrite = 1 << 1 SprotExec = 1 << 2 Sload = 1 << 3 Sfile = 1 << 4 Sabsolute = 1 << 5 Sblob = 1 << 6 Blob section. This is not loaded into the program memory. It may be used for debug info, tagging the binary, and other similar uses. Metadata: Symbols ----------------- The symbol table follows the string table. The symbol table contains an array of symbol defs. Each symbol has the following structure: +== Sym =========+ | str name | 32 bits +----------------+ | str type | 32 bits +----------------+ | section id | 8 bits +----------------+ | flags | 8 bits +----------------+ | offset | MyroN bits | | +----------------+ | len | MyroN bits | | +----------------+ The string is an offset into the string table, pointing to the start of the string. The kind describes where in the output the data goes and what its role is. The offset describes where, relative to the start of the data, the symbol begins. The length describes how many bytes it is. Currently, there's one flag supported: 1 << 1: Deduplicate the symbol. 1 << 2: Common storage for the symbol. 1 << 3: external symbol 1 << 4: undefined symbol Metadata: Relocations ---------------------- The relocations follow the symbol table. Each relocation has the following structure: +== Reloc =======+ | 0 | symbol id | 32 bits | 1 | section id | +----------------+ | flags | 8 bits +----------------+ | rel size | 8 bits +----------------+ | mask size | 8 bits +----------------+ | mask shift | 8 bits +----------------+ | offset | MyroN bits | | +----------------+ Relocations write the appropriate value into the offset requested. The offset is relative to the base of the section where the symbol is defined. The flags may be: Rabsolute = 1 << 0 Roverflow = 1 << 1 Data ---- It's just data. What do you want?