README.md

Just In Time NASM

Assemble your assemble listings and call it instantaneously within your program.

Build

To build jit-nasm, simply run the command

$ ./autogen.sh

$ ./configure

$ make

inside the code directory.

Install Library

To install the jit-nasm library, do the following after building

$ sudo make install PREFIX=/usr/local

to install libjitnasm in /usr/local/lib

Usage

To link your code with jit-nasm, use -ljitnasm $ gcc your_code.c -ljitnasm

Instantiate Library

To initialize library, first do the following

#include <jit-nasm.h>

jit_nasm_t jnasm = jit_nasm_create_instance(NULL, 0);   // interface: jit_nasm_create_instance(pointer to buffer, buffer size). These two parameters are used for external buffer. Default value is NULL, where jit-nasm will allocate the buffer used to assemble instructions internally.

Assemble Instructions

To assemble instructions, do the following after initialization

jit_nasm_t jnasm = jit_nasm_create_instance(NULL, 0);
jit_nasm_assemble(jnasm, "mov rdx, 0x14fff\n"
                         "mov rax, 4\n"
                         "cmp rax, 3\n"
                         "je label_1\n"
                         "add rax, 34\n"
                         "label_1: xor rax, rdx\n"
                         "imul rax, rax\n"
                         "idiv rdx\n"
                         "ret\n", 0, NULL);   // interface: jit_nasm(jit-nasm struct pointer, code to assemble, argc, argv). argc and argv are used by nasm for more advanced control over the program. Defaults to 0 and NULL.
                         

Getting Pointer to Assembled Code

After assembling your code, you can do the following to execute it.

jit_nasm_t jnasm = jit_nasm_create_instance(NULL, 0);
jit_nasm_assemble(jnasm, "mov rdx, 0x14fff\n"
                         "mov rax, 4\n"
                         "cmp rax, 3\n"
                         "je label_1\n"
                         "add rax, 34\n"
                         "label_1: xor rax, rdx\n"
                         "imul rax, rax\n"
                         "idiv rdx\n"
                         "ret\n", 0, NULL);  
void (*func)() = jit_nasm_get_code(jnasm);   // Cast value to a void function pointer
func();   // Call the code.

Hello World Example

Demo located in the demo/ folder

#include <stdint.h>
#include <stddef.h>

#include <jit-nasm.h>

int main() {
  const char* msg = "Hello World!\n";
  char* code = 
    "mov rdx, rsi\n"
    "mov rsi, rdi\n"
    "mov rax, 1\n"
    "mov rdi, 1\n"
    "syscall\n"
    "xor rax, rax\n"
    "ret\n";

  jit_nasm_t jnasm = jit_nasm_create_instance(NULL, 0);
  jit_nasm_assemble(jnasm, code, 0, NULL);

  void (*hello_world)(char*, int) = jit_nasm_get_code(jnasm);
  
  hello_world(msg, 13);

  jit_nasm_destroy_instance(jnasm);
}

outputs

Hello World!

Original NASM Readme Below

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NASM, the Netwide Assembler

Many many developers all over the net respect NASM for what it is: a widespread (thus netwide), portable (thus netwide!), very flexible and mature assembler tool with support for many output formats (thus netwide!!).

Now we have good news for you: NASM is licensed under the "simplified" (2-clause) BSD license. This means its development is open to even wider society of programmers wishing to improve their lovely assembler.

Visit our nasm.us website for more details.

With best regards, the NASM crew.