scc

simple c99 compiler
git clone git://git.simple-cc.org/scc
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commit c8c1fe6c1f71c4be3205e9b6299f7747b0ebd2be
parent 6032058285a26fb41080c6989049a5b3bcffd841
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Fri,  2 Feb 2018 20:55:20 +0100

[doc] Add documentation about myro

Diffstat:
Adoc/myro.txt | 179+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 179 insertions(+), 0 deletions(-)

diff --git a/doc/myro.txt b/doc/myro.txt @@ -0,0 +1,179 @@ +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 bit + +----------------+ + | format str | 32 bit + | | + +----------------+ + | entrypoint | 64 bit + | | + +----------------+ + | stringtab size | 64 bit + | | + +----------------+ + | section size | 64 bit + | | + +----------------+ + | symtab size | 64 bit + | | + +----------------+ + | reloctab size | 64 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 of 32 bits into the string table. If it is needed +to indicate a "no string" then the value 0FFFFFFFFH 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 | 64 bit + +----------------+ + | len | 64 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 bit + +----------------+ + | str type | 32 bit + +----------------+ + | section id | 8 bit + +----------------+ + | flags | 8 bit + +----------------+ + | offset | 64 bit + | | + +----------------+ + | len | 64 bit + | | + +----------------+ + +A symbol is 24 bytes in size. + +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 bit + | 1 | section id | + +----------------+ + | flags | 8 bit + +----------------+ + | rel size | 8 bit + +----------------+ + | mask size | 8 bit + +----------------+ + | mask shift | 8 bit + +----------------+ + | offset | 64 bit + | | + +----------------+ + +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?