example.dasc

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
/* note - for windows this is different */
#include <sys/mman.h> 

#include "dynasm/dasm_proto.h"
#include "dynasm/dasm_x86.h"

// DynASM directives.
|.arch x64
|.actionlist actions
/* call a function (64 bit)
 * and yes, i did steal this from jitdemo :-) */
|.macro callp, addr
|  mov64  rdx, (uintptr_t)addr
|  call   rdx
|.endmacro



int main(int argc, char **argv) {
    dasm_State * state;
    char * hello = "hello, %s\n";
    char * world = "world";
    size_t codesize;
    char * memory;
    void (*fp)(void);
    /* initialize the assembler structure */
    dasm_init(&state, 1);
    dasm_setup(&state, actions);
    /* add some instructions */
#define Dst &state
    | mov64 rdi, (uintptr_t)hello
    | mov64 rsi, (uintptr_t)world
    | mov64 rax, (uint64_t)0
    | callp printf
    | ret
#undef Dst
    /* link the code and get its' final size */
    dasm_link(&state, &codesize);
    /* get r/w memory */
    memory = mmap(NULL, codesize, PROT_READ | PROT_WRITE,
                  MAP_ANON | MAP_PRIVATE, -1, 0);
    /* write the machine code */
    dasm_encode(&state, memory);
    /* clear up the assembler */
    dasm_free(&state);
    /* make the memory executable */
    mprotect(memory, codesize, PROT_EXEC | PROT_READ);
    /* cast to function */
    fp = (void(*)(void)) memory;
    /* call the function */
    fp();
    /* destroy the memory */
    munmap(memory, codesize);
    /* and leave */
    exit(0);
}