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ModFormat.md

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Orka Module Descriptor Format

This specification describes the binary format used by the module system of orka to describe, in a platform-independant manner, the module, and properties of the module.

This format is based upon LCS 4 and uses the definitions provided there. The file is written in Little Endian Byte Order Mode.

This format shall use the extension .mia

The type empty used in this document shall be a type that has an empty byte representation.

Base Structure

struct OKM{
    u8 magic[4];
    version ver;
    ConstantTable constants;
    u16 mod_name;
    u16 mod_version;
    DependencyTable requires;
    ExportTable exports;
    TypesTable types;
    InitTable init;
};

magic MUST be the bytes [EE 4D 49 41]. version MUST be a version supported by the implementation. The currently specified version is 1.0, encoded as [00 00]. constants is the constant pool of the file, mod_name is the name of the file and shall be an index into the Constant Pool which is a Const_Utf8. mod_version is the version of the module, and shall be an index into the constant pool which is a Const_Version, which MUST be an exact version specifier, and not a version range specifier.

Constant Pool

struct ConstantTable{
   u16 nconsts;
   Constant consts[nconsts];
};


struct Constant{
   u8 tag;
   union{
       string Const_Utf8;
       i32 Const_i32;
       i64 Const_i64;
       u32 Const_u32;
       u64 Const_u64;
       u16 Const_Type;
       u16 Const_Version;
   } payload;
};

tag shall be one of Const_Utf8 (0), Const_i32 (1), Const_i64 (2), Const_u64 (3), Const_Type (4), Const_Version (5).

For Const_Version, the payload shall be an index into the constant pool which is a Const_Utf8, and the the form of a semantic versioning requirement string (either an exact version, or a version range), or a wildcard version string "*".

For Const_Type, the payload shall be an index into the constant pool which is Const_Utf8, in the form of an itanium mangled typename.

Dependencies

struct DependencyTable{
  u16 len;
  struct{
      u16 module;
      u16 version;
      u8 order;
  } dependencies[len];
};

Each module in dependencies shall be an index into the constant pool which is a Const_Utf8, and is the name of the module. Each version shall be a Const_Version, and the version requirement for the dependency. Each order shall be either REQUIRED AFTER (0), OPTIONAL AFTER (1), OPTIONAL BEFORE (2), OPTIONAL UNORDERED (3), REQUIRED BEFORE (4), REQUIRED UNORDERED (5), INIT (6), or INTERCEPT (7).

Attributes and Items

struct Attribute{
    u16 attr;
    u16 payload_len;
    u8 payload[payload_len];
};

attr shall be an index into the constant pool which is a Const_Utf8. The interpretation of payload depends on attr.

struct Item{
    u8 kind;
    u16 name;
    u16 type;
    u16 value;
    u16 nattrs;
    Attribute attrs[nattrs];
};

kind shall either be Field (0), Function (1), Interface (2), or Type (3). name shall be an index into the constant pool which is the Const_Utf8. type shall be an index into the constant pool which is a Const_Type. For Field or Function, value shall be an index into the constant pool which is a Const_Utf8. Otherwise value MUST be 0.

Exports and Types

struct ExportsTable{
    u16 len;
    Item exports[len];
};

struct TypesTable{
    u16 len;
    struct{
        u8 kind;
        u16 name;
        union{
            u16 by;
            struct{
                u16 nitems;
                Item items[nitems];
            };
        }
        u16 nattrs;
        Attribute attrs[nattrs];
    } types[len];
};

kind shall be either Struct (0), Class (1), Interface (2) (which all use the variant items), or ProvidedInterface (3) (which uses the variant by) If kind is ProvidedInterface, then by shall be an index into the Constant Pool which is a Const_Utf8, which names a type exported by this module. For this kind, name is the name of the interface which is provided by this entry.

No item may be an Interface or Type.

If kind is Class or ProvidedInterface then at least one Attribute MUST be a vtable attribute.

struct Attribute_VTable{
    u16 attr;
    u8 length;
    u16 vtable;
};

attr shall be a Const_Utf8 which is exactly the text "vtable". length shall be 2.

vtable shall be either an entry into the constant pool which is a Const_Utf8 and does not have index 0, where the vtable represents a symbol in the module dso, or it shall be the value 0, in which case, it represents a null pointer.

A ProvidedInterface type item shall not contain a null pointer for a vtable.

This attribute MUST only be present on a type. A given item may have at most one vtable attribute.

Initialization

struct InitTable{
    u16 load;
    u16 init;
    u16 main;
    u16 unload;
    u16 exit;
    u16 interceptLoad;
};

All fields in the InitTable shall be indices into the constant pool which are Const_Utf8 and do not have index 0, where the item represents a symbol in the module dso, or shall be the value 0, in which case it is a null pointer.