DynASM Features

LuaJIT

# DynASM Features

## DynASM Toolchain Features

- DynASM is a pre-processing assembler.
- DynASM converts mixed C/Assembler source to plain C code.
- The primary knowledge about instruction names, operand modes, registers, opcodes and how to encode them is only needed in the pre-processor.
- The generated C code is extremely small and fast.
- A tiny embeddable C library helps with the process of dynamically assembling, relocating and linking machine code.
- There are no outside dependencies on other tools (such as stand-alone assemblers or linkers).
- Internal consistency checks catch runtime errors (e.g. undefined labels).
- The toolchain is split into a portable subset and CPU-specific modules.
- DynASM itself (the pre-processor) is written in Lua.
- There is no machine-dependency for the pre-processor itself. It should work everywhere you can get Lua 5.1 up and running (i.e. Linux, *BSD, Solaris, Windows, ... you name it).

## DynASM Assembler Features

- C code and assembler code can be freely mixed. Readable, too.
- All the usual syntax for instructions and operand modes you come to expect from a standard assembler.
- Access to C variables and CPP defines in assembler statements.
- Access to C structures and unions via type mapping.
- Convenient shortcuts for accessing C structures.
- Local and global labels.
- Numbered labels (e.g. for mapping bytecode instruction numbers).
- Multiple code sections (e.g. for tailcode).
- Defines/substitutions (inline and from command line).
- Conditionals (translation time) with proper nesting.
- Macros with parameters.
- Macros can mix assembler statements and C code.
- Captures (output diversion for code reordering).
- Simple and extensible template system for instruction definitions.

## Restrictions

Currently only a subset of x86 (i386+) instructions is supported. Unsupported instructions are either not usable in user-mode or are slow on modern CPUs (i.e. not suited for a code generator). SSE, SSE2, SSE3 and SSSE3 are fully supported. MMX is not supported.

The whole toolchain has been designed to support multiple CPU architectures. As LuaJIT gets support for more architectures, DynASM will be extended with new CPU-specific modules.

The assembler itself will be extended with more features on an as-needed basis. E.g. I'm thinking about vararg macros.

Note that runtime conditionals are not really needed, since you can just use plain C code for that (and LuaJIT does this a lot). It's not going to be more (time-) efficient if conditionals are done by the embedded C library (maybe a bit more space-efficient).

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