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DynASM is a Dynamic Assembler for code generation engines. DynASM has been developed primarily as a tool for LuaJIT, but might be useful for other projects, too.

If you are writing a just-in-time compiler or need to generate code on the fly (e.g. for high-performance graphics or other CPU-intensive computations), DynASM might be just what you are looking for.

DynASM is Copyright © 2005-2013 Mike Pall. DynASM is free software, released under the MIT license.


DynASM is a very well-designed tool that provides a very useful framework for generating dynamic code during program execution. One of DynASM's strengths is that it allows intermixing C and assembly code in the same source file in a natural and free-form manner. Unfortunately, DynASM is rather weak in the documentation department. Figuring out feature use often requires "reverse-engineering" its usage example from the LuaJIT source, which seriously hinders DynASM's accessibility to potential new users.

This wiki entry is here to change that by providing a central repository for the community to help document DynASM's features along with simple example usage.

External resources

Workflow Integration

DynASM proto API Functions

dasm_init(Dst_DECL, int maxsection)

Initialize and free DynASM state

DASM_FDEF void dasm_init(Dst_DECL, int maxsection);
DASM_FDEF void dasm_free(Dst_DECL);

dasm_setupglobal(Dst_DECL, void **gl, unsigned int maxgl)

Setup global array. Must be called before dasm_setup()

DASM_FDEF void dasm_setupglobal(Dst_DECL, void **gl, unsigned int maxgl);

dasm_growpc(Dst_DECL, unsigned int maxpc)

Grow PC label array. Can be called after dasm_setup()

DASM_FDEF void dasm_growpc(Dst_DECL, unsigned int maxpc);

dasm_setup(Dst_DECL, const void *actionlist)

Setup encoder

DASM_FDEF void dasm_setup(Dst_DECL, const void *actionlist);

dasm_put(Dst_DECL, int start, ...)

Feed encoder with actions. Calls are generated by pre-processor

DASM_FDEF void dasm_put(Dst_DECL, int start, ...);

dasm_link(Dst_DECL, size_t *szp)

Link sections and return the resulting size

DASM_FDEF int dasm_link(Dst_DECL, size_t *szp);

dasm_encode(Dst_DECL, void *buffer)

Encode sections into buffer

DASM_FDEF int dasm_encode(Dst_DECL, void *buffer);

dasm_getpclabel(Dst_DECL, unsigned int pc)

Get PC label offset

DASM_FDEF int dasm_getpclabel(Dst_DECL, unsigned int pc);

Label types